The anatomy of the ear can be a little confusing, especially since the ear is responsible not only for hearing, but also for balance.
There are three components to the ear: the outer ear, the middle ear and the inner ear. All three are involved in hearing but only the inner ear is responsible for balance.
The outer ear is composed of the pinna, or ear lobe, and the external auditory canal. Both structures funnel sound waves towards the ear drum or tympanic membrane allowing it to vibrate. The pinna is also responsible for protecting the ear drum from damage. Modified sweat glands in the ear canal form ear wax.
The middle ear is an air filled space located in the temporal bone of the skull. Air pressure is equalized in this space via the Eustachian tube which drains into the nasopharynx or the back of the throat and nose. There are three small bones, or ossicles, that are located adjacent to the tympanic membrane. The malleus, incus, and stapes are attached like a chain to the tympanic membrane and convert sound waves that vibrate the membrane into mechanical vibrations of the three bones. The stapes fills the oval window which is the connection to the inner ear.
The bony labyrinth itself has three sections. 1) The cochlea is responsible for hearing, 2) the semicircular canals have function associated with balance, and 3) the vestibule which connects the two and contains two more balance and equilibrium related structures, the saccule and utricle.
The final structures of the inner ear are the round window and the eighth cranial nerve (cranial nerve VIII) which is composed of the vestibular nerve (balance) and the cochlear (hearing) nerve.
Hearing
We hear by funneling sound from the environment into the outer ear and causing the tympanic membrane to vibrate. Those sound waves vibrations are transferred into mechanical vibrations of the ossicles. Those mechanical vibrations cause the oval window to move back and forth causing the perilymph of the inner ear to begin wave-like motions. The perilymph fluid motion is transferred to the endolymph and the wave motion is transformed into electrical impulses picked up by the hairy cells of Corti and sent to the brain via the cochlear nerve. The round window is responsible for absorbing the fluid wave vibrations and releasing any increased pressure in the inner ear caused by the wave motion.
Balance
Balance is a choreographed arrangement that takes sensory information from a variety of organs and integrates it to tell the body where it is in related to gravity and the earth.
Information from the vestibular system of the inner ear (semicircular canals, the saccule and the utricle) is sent to the brainstem, cerebellum, and spinal cord. Potential balance abnormalities do not require conscious input from the cerebrum of the brain. Abnormal vestibular signals cause the body to try to compensate by making adjustments in posture of the trunk and limbs as well as making changes in eye movement to adjust sight input into the brain.
There are three semicircular canals in the inner ear positioned at right angles to each other like a gyroscope. They are able to sense changes in movement of the body. With such changes, endolymph waves within the canals cause hair cells located within their base to move. Position of the head is sensed by hair cells of the utricle and saccule which is stimulated when the head moves and the relationship to gravity changes.
Ear: Anatomy of Hearing and Balance (cont.)
There is a small dense area of nerve fibers called the macule located in each of the saccule and utricle. The macule of the saccule is oriented vertically while the utricle macule is horizontal. Each macule consists of fine hair bundles which are covered by an otolithic membrane that is jelly-like and covered by a blanket of calcium crystals.
The calcium crystals are the structures that ultimately stimulate the position hairs and provoke nerve impulses created by the position changes and transmit that information to the brain stem and cerebellum.
Abnormalities of the vestibular system may cause:
• vertigo (the sensation that the room is spinning);
• benign paroxysmal positional vertigo;
• labyrinthitis, and
• Meniere's Disease.
Some examples of common diseases and conditions involving the ear include:
• swimmer's ear,
• ear wax
• cauliflower ear,
• Eustachian tube problems,
• otitis media (middle ear infection), and
• tinnitus (ringing in the ear).
Ear
• Overview of the ear
• Anatomy of the ear
o Outer ear
Pinna
Ear canal
o Middle ear
Tympanic membrane (eardrum)
Auditory ossicles and muscles
Converting sound wave vibrations into inner ear fluid movement
o Inner ear
Cochlear
Chambers of the cochlear
Organ of Corti
• Physiology of the middle ear
o Concentration of energy
o Protection of inner ear
o Coordinating speech with hearing
• Physiology of the inner ear
o Cochlear hair cells
o Role of inner hair cells
o Role of outer hair cells
o Other components of cochlear physiology
o Sound transduction
o Sensory coding
• Equilibrium - Coordination and Balance
o Saccule and Utricle
o The Semicircular Canals - Detecting rotational acceleration
• Dysfunctions of the ear
o Deafness
o Neural prebycusis
o Vertigo
o Meniere's Syndrome
• Treatments for hearing loss
o Hearing aids
o Cochlear implants
Overview of the ear
The ear is the sense organ that enables us to hear. Hearing can be defined as the perception of sound energy via the brain and central nervous system. Hearing consists of two components: identification of sounds (what the sound is) and localisation of those sounds (where the sounds are coming from). The ear is divided into three main parts - the outer ear, the middle ear, and the inner ear. The inner ear is filled with fluid. The inner ear also contains the receptors for sound which convert fluid motion into electrical signals known as action potentials that are sent to the brain to enable sound perception. The airborne sound waves must therefore be channelled toward and transferred into the inner ear for hearing to occur. The role of the outer and middle ear is to transmit sound to the inner ear. They also help compensate for the loss in sound energy that naturally occurs when the sound waves pass from air into water by amplifying the sound energy during the process of sound transmission. In addition to converting sound waves into nerve action potentials, the inner ear is also responsible for the sense of equilibrium, which relates to our general abilities for balance and coordination.
Anatomy of the ear
Outer ear
The outer ear acts as a funnel to conduct air vibrations through to the eardrum. It also has the function of sound localisation. Sound localisation for sounds approaching from the left or the right is determined in two ways. Firstly, the sound wave reaches the ear closer to the sound slightly earlier than it reaches the other ear. Secondly, the sound is less intense when it reaches the second ear, because the head acts as a sound barrier, partially disrupting the spreading of the sound waves. All these cues are integrated by the brain to determine the location of the source of the sound. It is therefore difficult to localise sound with only one ear. The outer ear consists of the pinna and the ear canal.
Pinna
The pinna is a prominent skin-covered flap located on the side of the head, and is the visible part of the ear externally. It is shaped and supported by cartilage except for the earlobe. It collects sound waves and channels them down the external ear canal through patterns formed on the pinna known as whorls and recesses. Its shape also partially shields sound waves that approach the ear from the rear, therefore enabling a person to tell whether a sound is coming directly from the front or the back.
Ear canal
The ear canal is roughly 3cm long in adults and slightly S-shaped. It is supported by cartilage at its opening, and by bone for the rest of its length. Skin lines the canal, and contains glands that produce secretions that mix with dead skin cells to produce cerumen (earwax). Cerumen, along with the fine hairs that guard the entrance to the ear canal, helps prevent airborne particles from reaching the inner portions of the ear canal, where they could accumulate or injure the eardrum and interfere with hearing. Cerumen usually dries up and falls out of the canal. However, it can sometimes become impact and disrupt hearing.
Middle ear
The middle ear is located between the external and inner ear. It is separated from the ear canal of the outer ear by the tympanic membrane (the eardrum). The middle ear functions to transfer the vibrations of the eardrum to the inner ear fluid. This transfer of sound vibrations is possible through a chain of movable small bones, called ossicles, which extend across the middle ear, and their corresponding small muscles.
Tympanic membrane (eardrum)
The tympanic membrane is commonly known as the eardrum, and separates the ear canal from the middle ear. It is about 1cm in diameter and slightly concave (curving inward) on its outer surface. It vibrates freely in response to sound. The membrane is highly innervated, making it highly sensitive to pain. For the membrane to move freely when air strikes it, the resting air pressure on both sides of the tympanic membrane must be equal. The outside of the membrane is exposed to atmospheric pressure (pressure of the environment in which we find ourselves) through the auditory tube, so that the cavity in which it is located, called the tympanic cavity, is continuous with the cells in the jaw and thorat area. Normally, the auditory tube is flattered and closed, but swallowing, yawning and chewing pull the tube open, allowing air to enter or leave the tympanic cavity. This opening of the auditory tube allows air pressure in the middle ear to equilibrate with atmospheric pressure, so that the pressures on both sides of the tympanic membrane become equal to each other. Excessive pressure on either side of the tympanic membrane dampens the sense of the hearing because the tympanic membrane cannot vibrate freely. When external pressure changes rapidly, for example during air flight, the eardrum can bulge painfully because as the pressure outside the ear changes, the pressure in the middle ear remains unchanged. Yawning or swallowing in this instance opens up the auditory tube, allowing the pressure on both sides of the tympanic membrane to equalise, relieving the pressure distortion as the eardrum "pops" back into place. Since the auditory tube connects the jaw/throat areas to the ear, it allows throat infections to spread relatively easily to the middle ear. Middle ear infection is common in children because their auditory tubes are relatively short, compared to adults. This leads to fluid accumulation in the middle ear, which is not only painful but also disrupts the transference of sound across the middle ear. If the infection is left untreated, it can spread from the cells near the jaw, causing meningitis (inflammation of the brain lining). Middle ear infection can also cause the fusion of the ear ossicles, resulting in hearing loss.
Auditory ossicles and muscles
The tympanic cavity contains the body's three smallest bones and two smallest muscles. The bones are also referred to as auditory ossicles, and connect the eardrum to the inner ear. From the outermost to innermost, the bones are called the malleus, incus and stapes.
• Malleus
The malleus is attached to the eardrum. It has a handle that attaches to the inner surface of the eardrum, and a head that is suspended from the wall of the tympanic cavity.
• Incus
The incus is connected to the malleus on the side closer to the eardrum, and to the stapes on the side closer to the inner ear.
• Stapes
The stapes has an arch and a footplate. This footplate is held by a ringlike piece of tissue in an opening called the oval window, which is the entrance into the inner ear.
• Stapedius and Tensor tympani
The stapedius is the muscle of the inner ear that inserts on the stapes. The tensor tympani is the inner ear muscle that insert on the malleus.
Converting sound wave vibrations into inner ear fluid movement
As the eardrum vibrates in response to air waves, the chain of inner ear bones are set into motion at the same frequency. The frequency of movement is transmitted across from the eardrum to the oval window (another structure in the ear), resulting in a pressure being exerted on the oval window with each vibration. This produces wavelike movements of the inner ear fluid at the same frequency as the original sound wave. However, in order to set the fluid into motion, greater pressure is required, so that the pressure must be amplified. This amplification of the pressure of the airborne sound wave to set up fluid vibrations in the cochlear is related to two mechanisms. Firstly, the surface area of the tympanic membrane is much large than that of the oval window. In addition, the lever action of the ossicles greatly increases the force exerted on the oval window. The extra pressure generated through these mechanisms is sufficient to set the cochlear fluid in motion.
Inner ear
The inner ear is the deepest part of the whole ear, and is located in a place known as the bony labyrinth, which is a maze of bone passageways lined by a network of fleshy tubes known as the membranous labyrinth. A cushion of fluid, called perilymph, lies between the bony and membranous labyrinth, while a fluid called endolymph is found within the membranous labyrinth itself. Within the inner ear is a chamber called the vestibule, which plays a major role in the sense of balance. Balance is further discussed later in this article. (Equilibrium - Coordination and Balance)
Cochlear
Arising from the vestibule is the cochlear, which is sometimes referred to as the organ of hearing, as it is the part of the whole ear that actually converts sound vibrations to the perception of hearing. The cochlear is in the form of a snail-like spiral, so that a longer cochlear is able to fit inside an enclosed space. It is about 9mm wide at the base and 5mm high, and winds around a section of spongy bone called the modiolus. The modiolus is shaped like a screw whose threads form a spiral platform that support the cochlear, which is fleshy and unable to support itself.
Chambers of the cochlear
The cochlear contains three fluid-filled chambers separated by membranes. The upper chamber, scala vestibule, and the bottom chamber, scala tympani, are filled with perilymph. The scala tympani is covered by a secondary tympanic membrane. The middle chamber is the scala media, or the cochlear duct. It is filled with endolymph, instead of perilymph.
Organ of Corti
The organ of corti is supported by a membrane called the basilar membrane. It about the size of a pea, and acts as a transducer, converting vibration into nerve impulses. It has hair cells and supporting cells. Hair cells have long stiff microvilli called stereocilia on their apical surfaces. Microvilli are fine hair-like structures on cells that help to increase cell surface area. On top of these stereocilia is a jelly-like membrane called the tectorial membrane. Four rows of hair cells spiral along the length of the organ of Corti. Of these, there are about 3500 inner hair cells (IHCs), each with a cluster of 50-60 stereocilia graded from short to tall. There are another 20 000 outer hair cells (OHCs) that are arranged in three rows opposite the IHCs. Each OHC has about 100 stereocilia with their tips embedded in the tectorial membrane above them. These outer hair cells adjust the response of the cochlear to different sound frequencies so as to enable the inner hair cells to function more accurately. The physiological mechanisms, by which hair cells within the cochlear act to produce hearing, are discussed in more detail below. (Physiology of the inner ear)
Physiology of the middle ear
Concentration of energy
The function of the auditory ossicles in the middle ear is to concentrate the energy of the vibrating eardrum so as to create a greater force per unit area at the oval window, as previously described.
Protection of inner ear
In addition to this, the ossicles and their adjacent muscles also serve a protective function. In response to a loud noise, the tensor tympani pulls the eardrum inward and tenses it. At the same time, the stapedius reduces movement of the stapes. These actions of the muscles are known collectively as the tympanic reflex. This reflex muffles the transfer of vibrations from the eardrum to the oval window. It is thought that the tympanic reflex is an evolutionary adaptation for protection against loud but slowly building noises such as thunder. However, because it has a time delay of about 40 ms, it is not quick enough to protect the inner ear from sudden loud noises such as gunshots. It also does not adequately protect the ears from sustained loud noises such as factory noises or loud music. These noises can irreversibly damage the stereocilia of the hair cells in the inner ear, leading to hearing loss.
Coordinating speech with hearing
The muscles of the middle ear also assist in coordinating speech with hearing, so that the sound of our own speech is not so loud as to damage our inner ear and drown out soft or high-pitched sounds from other sources. Just as we are about to speak, the brain signals the middle ear muscles to contract, dampening the sense of hearing in coordination with the sound of our own voice. This makes it possible to hear other people while we are speaking ourselves.
Physiology of the inner ear
Cochlear hair cells
As previously mentioned, the cochlear is the organ that enables sound perception. The physiology of the cochlear revolves around the functioning of the inner and outer cochlear hair cells. In addition to the cells themselves, there are several other components of the cochlear that contribute to the ability to hear.
Role of inner hair cells
The inner hair cells transform the mechanical force of sound (cochlear fluid vibration) into the electrical impulses of hearing (action potentials sending auditory messages to the brain). They communicate with nerve fibres that make up the auditory nerve leading to the brain. When the rate of neurotransmitter (chemicals released by cells in response to stimuli) release from these hair cells is increased, the rate of firing in the nerve fibres is also increased. This occurs when the voltage of the hair cells becomes more positive. Conversely, when the voltage of the hair cells becomes more negative, the hair cells release less neurotransmitter and the firing rate in nerve fibres decreases.
Role of outer hair cells
Unlike the inner hair cells, the outer hair cells do not signal the brain about incoming sounds. They instead actively and rapidly elongate in response to changes in the voltages of the cell membrane. This behaviour is known as electromotility. When the outer hair cells elongate, the motion of the basilar membrane is amplified. This modification of the basilar membrane is believed to improve and tune the stimulation of the inner hair cells. The outer hair cells therefore enhance the receptors of the inner hair cells, increasing their sensitivity to sound intensity and rendering them highly discriminatory between various pitches of sound.
Other components of cochlear physiology
The activity of the inner and outer hair cells is possible through various other components within the cochlear. They key components are listed as follows:
Basilar Membrane
The vibration of the auditory ossicles, as previously described, eventually leads to the vibration of the basilar membrane on which the hair cells rest through sequence of chain reactions. During the vibration of the auditory ossicles, the stapes vibrates rapidly in and out, leading to the basilar membrane vibrating down and up, and the secondary tympanic membrane vibrating out and in. This can occur as often as 20 000 times per second.
Endolymph
In order for inner hair cells to function properly, the tips of their stereocilia must be bathed in endolymph, which has an exceptionally high potassium ion (K+) concentration, creating a strong electrochemical gradient (large difference in voltage) from the tip to base of a hair cell. This electrochemical gradient provides the energy that allows the hair cell to function. The interaction between stereocilia and endolymph is further discussed below. (Stereocilia)
Tectorial membrane
The stereocilia of the outer hair cells have their tips embedded in the tectorial membrane, while the stereocilia of the inner hair cells come very close to the membrane. The tectorial membrane is anchored to a structure called the modiolus, which holds it relatively still as the basilar membrane and hair cells vibrate. Vibration of the basilar membrane therefore causes shearing of the hair cells against the tectorial membrane, bending the hair cell stereocilia back and forth.
Stereocilia
A protein functions as a mechanically gated ion channel on the top of each stereocilia of the inner hair cells. In addition, there is a fine stretchy protein filament known as a tip link that extends like a spring from the ion channel of one stereocilium to the side of the streocilium next to it. On each inner hair cell, the stereocilia progressively increase in height, so that all but the tallest ones have tip links leading to taller stereocilia beside them. When a taller stereocilium bends away from a shorter one, it pulls on the tip link, so that the ion channel of the short stereocilium is opened. The endolymph bathing the stereocilia has a very high concentration of K+ ions, so that when the channel is pulled open, there is a rapid flow of K+ into each hair cell. This makes the voltage of the hair cell become positive when the channel is open. When the stereocilium is bent the other way, the channel closes and the cell voltage becomes negative. When the cell voltage is positive, the inner hair cells release a neurotransmitter that stimulates the sensory nerves at the base of the hair cell. This leads to the generation of action potentials in the cochlear nerve.
Sound transduction
The conversion of sound energy into a neural signal that is interpreted by the brain as sound perception, as described above, is known as sound transduction. The following diagram summarises this process:
Sensory coding
Loud vs Soft sounds
The organ of Corti allows us to discriminate between different sound intensities. Loud sounds produce more vigorous vibrations of the organ of Corti, thereby exciting a greater number of hair cells over a greater area of basilar membrane. This leads to a high frequency of action potentials being initiated in the cochlear nerve. Intense activity in the cochlear nerve fibres from a broad region of the organ of Corti is therefore detected by the brain and interpreted as a loud sound. The reverse applies to detect soft sounds.
High-pitched vs Low-pitched sounds
The basilar membrane enables us to differentiate between high and low pitched sounds. The membrane is spanned by short stiff fibres of various lengths. At its lower end, the basilar membrane is attached, narrow and stiff. At the top end, however, it is unattached, wider and more flexible. The vibration of one region of the basilar membrane causes a wave of vibration to travel down its length and back again. This is referred to as a standing wave, and is akin to plucking a string at one end, causing a wave vibration (like on a guitar). The peak amplitude of the standing wave is near the top end during low-frequency sounds and near the bottom end during higher-frequency sounds. When the brain receives signals mainly from inner hair cells at the top end, it interprets this sound as being low-pitched. Likewise, when the brain receives signals mainly from inner hair cells at the bottom end, the sound is interpreted as being high-pitched. In the reality of everyday life, speech, music and other everyday sounds are not pure tones. Instead, they create complex patterns of vibration in the basilar membrane that have to be decoded and interpreted by the brain.
Equilibrium - Coordination and Balance
Although we think of the ear as the sense organ for hearing, it did not evolve originally for this purpose. It was instead originally an adaptation for coordination and balance, collectively known as the sense of equilibrium. Vertebrates only evolved the cochlear, middle ear structures and consequent auditory function of the ear later on. In humans, the parts of the ear that allow for the sense of equilibrium are the vestibular apparatus (or the vestibule). These consist of the three semicircular canals, and the two chambers - the saccule and the utricle. There are two components of the sense of equilibrium. One is static equilibrium, referring to the ability to detect the direction of the head when the body is not moving. The second is dynamic equilibrium, referring to the perception of motion or acceleration. Acceleration can in turn be divided into linear acceleration, which is a change in velocity (rapidity) in a straight line, and angular acceleration, which is a change in the rate of rotation of the head. The saccule and utricle detect static equilibrium and linear acceleration, while the semicircular canals only detect angular acceleration.
Saccule and Utricle
Both the saccule and the utricle contain a small patch of hair cells and their supporting cells, which collectively are known as a macula. The macula lying vertically on the wall of the saccule is called the macula sacculi, while the macula lying horizontally on the floor of the utricle is called the macula utriculi. Each hair cell of a macula has about 40-70 stereocilia (structures on the hair cells that sense mechanical stimuli), as well as one true cilium (a tail-like cell projection) called a kinocilium. The tips of the stereocilia and the kinocilium are embedded in a jelly-like membrane called the otholithic membrane. This membrane is weighed down by granules which are referred to as otoliths. The otoliths add to the density and inertia of the membrane, aiding in sensing gravity and motion.
Detecting tilt of the head
Horizontal tilt of the head is detected by the macula utriculi, while vertical tilt of the head is detected by the macula sacculi. When the head is upright, the otolithic membrane weighs down directly on the hair cells, keeping stimulation to a minimum. However, when the head is tilted, the weight of the membrane bends the stereocilia, stimulating the hair cells. Any orientation of the head causes a combination of stimulation to the utricles and saccules of both ears. The overall orientation of the head is interpreted by the brain by comparing the inputs from both organs to each other, and to other input from the eyes and stretch receptors in the neck.
Detecting linear acceleration
When we begin to move forward after being stationary, the heavy otolithic membrane of the macula utriculi briefly lags behind the rest of the tissues. When we stops moving, the macula stops as well, but the otolithic membrane keeps moving for a moment, bending the stereocilia forward. The hair cells covert this pattern of stimulation into nerve signals which are relayed to the brain to be interpreted. This results in the brain interpreting changes in linear velocity (ie. detecting linear acceleration). If we begin to move upwards after being stationary (for example, going upwards in an elevator), the otolithic membrane of the vertical macula sacculi lags briefly behind and pulls down on the hair cells. When we stop moving, the otolithic membrane keeps moving for a moment, bending the hair cells upward. The brain therefore receives signals from the macula sacculi, enabling it to interpret vertical acceleration.
The Semicircular Canals - Detecting rotational acceleration
Each of the three semicircular canals houses a semicircular duct. Collectively, they detect rotational acceleration. Two ducts are positioned vertically at right angles to each other. The third duct lies at an angle of approximately 30 degrees from the horizontal plane. The different orientations of the three ducts cause different ducts to be stimulated, depending on what plane the head is rotating in. The head can be turned from side to side (eg. Gesturing "no"), up and down (eg. Gesturing "yes"), or tilted from side to side (eg. Touching to ears to each of your shoulders, one at a time). All the semicircular ducts are filled with a fluid called endolymph. Each duct opens into the utricle and has a dilated sac at one end called an ampulla. Inside the ampulla are hair cells and their supporting cells. These are referred to as the crista ampullaris. A jelly-like membrane called the cupula extends from the crista ampullaris to the roof of the ampulla. The stereocilia of the hair cells are embedded in the cupula. As the head turns, the duct rotates, but the endolymph in it lags behind. The endolymph thus pushes against the cupula, causing the stereocilia to bend, stimulating the hair cells. However, after 25-30 seconds of continual rotation, the endolymph catches up with the movement of the duct and stimulation of the hair cell ceases.
Dysfunctions of the ear
Deafness
Deafness refers to a loss of hearing, which may be temporary or permanent, partial or complete.
Conductive deafness
Conductive deafness occurs when sound waves are not properly conducted through the external and middle portions of the ear to set the fluid in the inner ear in motion. Possible causes include:
• Physical blockage of the ear canal with earwax
• Eardrum rupture
• Middle ear infection with accompanying fluid accumulation
• Restriction of the movement of the ossicles, due to bony adhesions between the stapes and oval window
Sensorineural deafness
In sensorineural deafness, the sound waves are transmitted to the inner ear, but they are not converted into nerve signals that are interpreted by the brain as sounds. The defect can lie in the organ of Corti or the auditory nerves, or rarely, in some pathways and parts of the brain.
Neural prebycusis
Neural prebycusis is one of the most common causes of partial hearing loss. It is a progressive age-related process that occurs over time as the hair cells "wear out" with use. Even exposure to ordinary modern-day sounds can eventually damage hair cells over long periods of time. An adult loses on average more than 40% of their cochlear hair cells by the age of 65. Those hair cells that process high-frequency sounds are the most vulnerable to destruction.
Vertigo
Vertigo refers to the sensation of rotation in the absence of equilibrium - in other words, dizziness. Vertigo can be caused by viral infections, certain drugs, and tumours such as acoustic neuroma. Vertigo can also produced normally in individuals through excessive stimulation of the semicircular ducts. In some individuals, excessive stimulation of the utricle can also produce motion sickness (carsickness, airsickness, seasickness).
Meniere's Syndrome
Meniere's Syndrome is a disease of the internal ear affecting both hearing and equilibrium. Patients initially experience episodes of dizziness and tinnitus (ringing noise in the ears), and later develop a low-frequency hearing loss. The causes relate to the blockage of a duct in the cochlear which drains excess endolymph away. Blockage of the duct causes an increase in endolymphatic pressure and swelling of the membranous labyrinth in which the inner ear hair cells are located.
Treatments for hearing loss
Hearing aids
Hearing aids can be useful in treating conductive deafness but are less beneficial for sensorineural deafness. They increase the intensity of airborne sounds and may modify the sound spectrum to suit the patient's particular pattern of hearing loss at higher or lower frequencies. However, the receptor cell-neural pathway system must still be intact and functioning for the sound to be perceived, so hearing aids are useless in sensorineural deafness.
Cochlear implants
Recently, cochlear implants have become available. The implants are electronic devices which are surgically implanted. They convert sound signals into electrical signals that can directly stimulate the auditory nerve, so as to bypass a defective cochlear system. Cochlear implants cannot restore normal hearing but they permit recipients to recognise sounds. Success can range from an ability to hear a phone ringing, to being able to carry on a conversation over the telephone.
Thursday, April 29, 2010
The Ear (Hearing and Balance)
auditory system, involved in the detection of sound,
the vestibular system, involved with maintaining body balance/ equilibrium.
• In auditory system - perception of sound
• In vestibular system - maintenance of balance.
The external ear (or pinna, the part you can see) serves to protect the tympanic membrane (eardrum), as well to collect and direct sound waves through the ear canal to the eardrum. About 1¼ inches long, the canal contains modified sweat glands that secrete cerumen, or earwax. Too much cerumen can block sound transmission.
AURICLE (PINNA)
Location: oval-shaped appendage on the lateral surface of the head.
Function: sound localization and amplification.
Composition: thin skin with hair follicles, sweat glands, and sebaceous glands covers supporting structure of elastic cartilage
EXTERAL AUDITORY MEATUS (CANAL)
Location: between the auricle and tympanic membrane
Composition: skin that contains hair follicles, ceruminous - modified sweat glands, and sebaceous glands covers supporting structure of elastic cartilage (lateral one-third) or bone (medial two-thirds)
TYMPANIC MEMBRANE (EARDRUM)
Location: separates the external auditory canal from the middle ear
Function: sound in the form of airwaves causes the membrane to vibrate, and these vibrations are transmitted to the attached auditory ossicles
Composition: the layers from outside to inside
• The epidermis of skin
• Radially and circularly arranged collagen fibers
• Mucous membrane covered by simple squamous epithelium
AUDITORY OSSICLES
Location: cross the space of middle ear in series and connect the tympanic membrane to the oval window
Function: help to convert sound waves (vibrations in air) to mechanical (hydraulic) vibrations in tissues and fluid-filled chambers
Composition: movable joints connect the bones:
• Malleus (hammer), attached to the tympanic membrane
• Stapes (stirrup), whose footplate fits into the oval window
• Incus (anvil), linking the malleus to the stapes
AUDITORY (EUSTACHIAN) TUBE
Location: connects the middle ear to the nasopharynx
Function: allow pressure in the middle ear to equilibrate with atmospheric pressure.
Composition: lined with ciliated pseudostratified columnar epithelium with small mass of lymphatic tissue
CRISTAE AMPULLARIS
Location: three sensory regions of the semicircular ducts in the ampullae of the semicircular canals
Function: sensors of angular movement
Composition: the ridge of epithelium that is oriented perpendicular to the long axis of the semicircular canal
Cells:
• Hair cells - nonneuronal mechnoreceptors with 50-100 stereocilia (sensory hairs) - modified microvilli. They are associated with both afferent and efferent nerve endings
o Type I hair cells - piriform in shape with a rounded base
o Type II hair cells - cylindrical in shape
• Supporting epithelial cells
• Cupula - gelatinous structure projects into the lumen and is surrounded by endolymph.
MACULAE
Location: saccule and utricle of the vestibule
Function: sensors of gravity and liner movement
Composition: the innervated sensory thickenings of the epithelium facing the endolymph
Cells:
• {#hair} Hair cells - nonneuronal mechanoreceptors with 50-100 stereocilia (sensory hairs) - modified microvilli and single true cilium - kinocilium. They are associated with both afferent and efferent nerve endings
o Type I hair cells - piriform in shape with a rounded base
o Type II hair cells - cylindrical in shape
• Supporting epithelial cells
• Otolithic membrane - gelatinous material with otoliths - 3-5mkm crystalline particles of calcium carbonate and protein
SCALA MEDIA (COCHLEA DUCT)
Location: the middle compartment in the cochlear canal
Composition: appears in transverse section as a triangular space.
• The most acute angle is attached to a bony extension of the modiolus
• The upper wall is the vestibular (Reissner's) membrane -two layers of squamous epithelial cells
• The lateral or outer wall is the stria vascularis - thick pseudostratified epithelium rich in blood vessels, the site of synthesis of endolymph
• The lower wall or floor is the basilar membrane - a dense mat of collagenic and some elastic fibers on which organ of Corti rests
ORGAN OF CORTI
Location: on the floor of scala media
Function: sound perception
Composition: complex epithelial layer
Cells:
• Inner (close to the stria vascularis) hair cells with 50-100 stereocilia and outer hair cells with 100-300 stereocilia are arranged in the rows of cells
• Inner (close to the stria vascularis) and outer phalangeal (supporting) cells - completely surround the basal portions of sensory cells, preventing them from touching the basilar membrane
• Pillar cells - form a triangular-shaped tunnel of Corti with cortilymph
• Tectorial membrane extends over the hair cells and attaches to the stereocilia. It consists of ground substance and collagen fibers
eardrum, is an air-filled cavity (tympanic cavity)
carved out of the temporal bone. It connects to the throat/nasopharynx via the Eustachian tube.
This ear-throat connection makes the ear susceptible to infection (otitis media).
The eustachian tube functions to equalize air pressure on both sides of the eardrum.
The inner ear consists of a maze of fluid-filled tubes, running through the temporal bone of the skull. The bony tubes, the bony labyrinth, are filled with a fluid called perilymph. Within this bony labyrinth is a second series of delicate cellular tubes, called the membranous labyrinth, filled with the fluid called endolymph. This membranous labyrinth contains the actual hearing cells, the hair cells of the organ of Corti. There are three major sections of the bony labyrinth:
1. The front portion is the snail-shaped cochlea, which functions in hearing.
2. The rear part, the semicircular canals, helps maintain balance.
3. Interconnecting the cochlea and the semicircular canals is the vestibule, containing the sense organs responsible for balance, the utricle and saccule.
The round window serves as a pressure valve, bulging outward as fluid pressure rises in the inner ear. Nerve impulses generated in the inner ear travel along the vestibulocochlear nerve (cranial nerve VIII), which leads to the brain. This is actually two nerves, somewhat joined together, the cochlear nerve for hearing and the vestibular nerve for equilibrium.
The base of the stapes rocks in and out against the oval window - this is the entrance for the vibrations.
The round window dissipates the pressure generated by the fluid vibrations, thus serves as the release valve: It can push out or expand as needed. The nerve impulses travel over the cochlear nerve to the auditory cortex of the brain, which interprets the impulses as sound.
The semicircular canals and vestibule function to sense movement (acceleration and deceleration) and static position.
Hearing
The most basic function of the ear is hearing. The following is the short description of the hearing process:
The first step is when the pinna collects external sounds that enter through the meatus or ear canal as sound waves. The ear drum begins to vibrate as these sound waves strikes. These vibrations pass through to the three ossicles of the middle ear (hammer, anvil and stapes) where they are amplified. As the transmission proceeds, the vibrations first hit the hammer, then the hammer pushes the anvil, and the anvil hits the stapes.
The vibrations are finally interpreted as sound in the brain after being transmitted and transformed into nerve signals by the cochlea (snail shaped component of the inner ear). This is due to the connectivity of the oval window of the inner ear to the edge of the stapes. When the stapes vibrates, they always transmit the sound vibrations to the inner ear.
Balance
The other important function of the ear is to help maintain balance. Oriented at the right angles to each other are three semicircular canals of the inner ear. Whenever the head is turned or change position, the resulting movement of fluids within these canals help the brain to identify or detect the extent of movement and positioning of the head.
In response to gravity, another part of the inner ear sends information to the brain when the head is held still in a stagnant position.
• Otitis media – also known as middle ear infection
• Otitis externa – also known as a swimmer's ear
There are other several ear disorders that we will soon have a look at. These include the following:
• Tinnitus – ringing of ear
• Vertigo – nahihilo
• Meniere's disease – nagkatubig ang tenga
• Hyperacusis – echoing of ear
• neural prebycusis – Alzheimer’s
• otitis - tuga
the vestibular system, involved with maintaining body balance/ equilibrium.
• In auditory system - perception of sound
• In vestibular system - maintenance of balance.
The external ear (or pinna, the part you can see) serves to protect the tympanic membrane (eardrum), as well to collect and direct sound waves through the ear canal to the eardrum. About 1¼ inches long, the canal contains modified sweat glands that secrete cerumen, or earwax. Too much cerumen can block sound transmission.
AURICLE (PINNA)
Location: oval-shaped appendage on the lateral surface of the head.
Function: sound localization and amplification.
Composition: thin skin with hair follicles, sweat glands, and sebaceous glands covers supporting structure of elastic cartilage
EXTERAL AUDITORY MEATUS (CANAL)
Location: between the auricle and tympanic membrane
Composition: skin that contains hair follicles, ceruminous - modified sweat glands, and sebaceous glands covers supporting structure of elastic cartilage (lateral one-third) or bone (medial two-thirds)
TYMPANIC MEMBRANE (EARDRUM)
Location: separates the external auditory canal from the middle ear
Function: sound in the form of airwaves causes the membrane to vibrate, and these vibrations are transmitted to the attached auditory ossicles
Composition: the layers from outside to inside
• The epidermis of skin
• Radially and circularly arranged collagen fibers
• Mucous membrane covered by simple squamous epithelium
AUDITORY OSSICLES
Location: cross the space of middle ear in series and connect the tympanic membrane to the oval window
Function: help to convert sound waves (vibrations in air) to mechanical (hydraulic) vibrations in tissues and fluid-filled chambers
Composition: movable joints connect the bones:
• Malleus (hammer), attached to the tympanic membrane
• Stapes (stirrup), whose footplate fits into the oval window
• Incus (anvil), linking the malleus to the stapes
AUDITORY (EUSTACHIAN) TUBE
Location: connects the middle ear to the nasopharynx
Function: allow pressure in the middle ear to equilibrate with atmospheric pressure.
Composition: lined with ciliated pseudostratified columnar epithelium with small mass of lymphatic tissue
CRISTAE AMPULLARIS
Location: three sensory regions of the semicircular ducts in the ampullae of the semicircular canals
Function: sensors of angular movement
Composition: the ridge of epithelium that is oriented perpendicular to the long axis of the semicircular canal
Cells:
• Hair cells - nonneuronal mechnoreceptors with 50-100 stereocilia (sensory hairs) - modified microvilli. They are associated with both afferent and efferent nerve endings
o Type I hair cells - piriform in shape with a rounded base
o Type II hair cells - cylindrical in shape
• Supporting epithelial cells
• Cupula - gelatinous structure projects into the lumen and is surrounded by endolymph.
MACULAE
Location: saccule and utricle of the vestibule
Function: sensors of gravity and liner movement
Composition: the innervated sensory thickenings of the epithelium facing the endolymph
Cells:
• {#hair} Hair cells - nonneuronal mechanoreceptors with 50-100 stereocilia (sensory hairs) - modified microvilli and single true cilium - kinocilium. They are associated with both afferent and efferent nerve endings
o Type I hair cells - piriform in shape with a rounded base
o Type II hair cells - cylindrical in shape
• Supporting epithelial cells
• Otolithic membrane - gelatinous material with otoliths - 3-5mkm crystalline particles of calcium carbonate and protein
SCALA MEDIA (COCHLEA DUCT)
Location: the middle compartment in the cochlear canal
Composition: appears in transverse section as a triangular space.
• The most acute angle is attached to a bony extension of the modiolus
• The upper wall is the vestibular (Reissner's) membrane -two layers of squamous epithelial cells
• The lateral or outer wall is the stria vascularis - thick pseudostratified epithelium rich in blood vessels, the site of synthesis of endolymph
• The lower wall or floor is the basilar membrane - a dense mat of collagenic and some elastic fibers on which organ of Corti rests
ORGAN OF CORTI
Location: on the floor of scala media
Function: sound perception
Composition: complex epithelial layer
Cells:
• Inner (close to the stria vascularis) hair cells with 50-100 stereocilia and outer hair cells with 100-300 stereocilia are arranged in the rows of cells
• Inner (close to the stria vascularis) and outer phalangeal (supporting) cells - completely surround the basal portions of sensory cells, preventing them from touching the basilar membrane
• Pillar cells - form a triangular-shaped tunnel of Corti with cortilymph
• Tectorial membrane extends over the hair cells and attaches to the stereocilia. It consists of ground substance and collagen fibers
eardrum, is an air-filled cavity (tympanic cavity)
carved out of the temporal bone. It connects to the throat/nasopharynx via the Eustachian tube.
This ear-throat connection makes the ear susceptible to infection (otitis media).
The eustachian tube functions to equalize air pressure on both sides of the eardrum.
The inner ear consists of a maze of fluid-filled tubes, running through the temporal bone of the skull. The bony tubes, the bony labyrinth, are filled with a fluid called perilymph. Within this bony labyrinth is a second series of delicate cellular tubes, called the membranous labyrinth, filled with the fluid called endolymph. This membranous labyrinth contains the actual hearing cells, the hair cells of the organ of Corti. There are three major sections of the bony labyrinth:
1. The front portion is the snail-shaped cochlea, which functions in hearing.
2. The rear part, the semicircular canals, helps maintain balance.
3. Interconnecting the cochlea and the semicircular canals is the vestibule, containing the sense organs responsible for balance, the utricle and saccule.
The round window serves as a pressure valve, bulging outward as fluid pressure rises in the inner ear. Nerve impulses generated in the inner ear travel along the vestibulocochlear nerve (cranial nerve VIII), which leads to the brain. This is actually two nerves, somewhat joined together, the cochlear nerve for hearing and the vestibular nerve for equilibrium.
The base of the stapes rocks in and out against the oval window - this is the entrance for the vibrations.
The round window dissipates the pressure generated by the fluid vibrations, thus serves as the release valve: It can push out or expand as needed. The nerve impulses travel over the cochlear nerve to the auditory cortex of the brain, which interprets the impulses as sound.
The semicircular canals and vestibule function to sense movement (acceleration and deceleration) and static position.
Hearing
The most basic function of the ear is hearing. The following is the short description of the hearing process:
The first step is when the pinna collects external sounds that enter through the meatus or ear canal as sound waves. The ear drum begins to vibrate as these sound waves strikes. These vibrations pass through to the three ossicles of the middle ear (hammer, anvil and stapes) where they are amplified. As the transmission proceeds, the vibrations first hit the hammer, then the hammer pushes the anvil, and the anvil hits the stapes.
The vibrations are finally interpreted as sound in the brain after being transmitted and transformed into nerve signals by the cochlea (snail shaped component of the inner ear). This is due to the connectivity of the oval window of the inner ear to the edge of the stapes. When the stapes vibrates, they always transmit the sound vibrations to the inner ear.
Balance
The other important function of the ear is to help maintain balance. Oriented at the right angles to each other are three semicircular canals of the inner ear. Whenever the head is turned or change position, the resulting movement of fluids within these canals help the brain to identify or detect the extent of movement and positioning of the head.
In response to gravity, another part of the inner ear sends information to the brain when the head is held still in a stagnant position.
• Otitis media – also known as middle ear infection
• Otitis externa – also known as a swimmer's ear
There are other several ear disorders that we will soon have a look at. These include the following:
• Tinnitus – ringing of ear
• Vertigo – nahihilo
• Meniere's disease – nagkatubig ang tenga
• Hyperacusis – echoing of ear
• neural prebycusis – Alzheimer’s
• otitis - tuga
Enzymes
Enzymes
Enzyme: A protein (or protein-based molecule) that speeds up a chemical reaction in a living organism. An enzyme acts as catalyst for specific chemical reactions, converting a specific set of reactants (called substrates) into specific products. Without enzymes, life as we know it would not exist.
Enzymes are nonetheless subject to error. In 1902 Sir Archibald Garrod was the first to attribute a disease to an enzyme defect, to what Garrod called an "inborn error of metabolism." Today, newborns are routinely screened for certain enzyme defects such as PKU (phenylketonuria) and galactosemia, an error in the handling (metabolism) of the sugar galactose.
Enzymes are biological catalysts. They speed up reactions by lowering the activation energy (the energy required for a reaction to begin). This is accomplished by increasing the local concentration of reactants (the compounds used in the reaction) and bringing the reactants into proper orientation for the reaction to begin. All enzymes are made of protein and their production is controlled by DNA. Enzymes can be reused many times. The standard suffix for enzymes is "ase."
Practically all of the numerous and complex biochemical reactions that take place in animals, plants, and microorganisms are regulated by enzymes. These catalytic proteins are efficient and specific—that is, they accelerate the rate of one kind of chemical reaction of one type of compound, and they do so in a far more efficient manner than man-made catalysts. They are controlled by activators and inhibitors that initiate or block reactions. All cells contain enzymes, which usually vary in number and composition, depending on the cell type; an average mammalian cell,
Classification of enzyme
Enzymes are classified according to the reactions they catalyze. In some cases, the terms used are fairly clear; in others, less so. Examples:
Oxidoreductases:
These are enzymes which catalyze the reduction or oxidation of a molecule. Remember that oxidation is the reverse of reduction and that an enzyme has to catalyze the forward and reverse reactions to the same degree. Any enzyme which catalyzes a reduction has to also catalyze the reverse (oxidation) reaction, thus the double-barreled name "oxidoreductase."
Transferases:
These enzymes catalyze the transfer of a group of atoms from one molecule to another. A common example involves transfer of a phosphate between ATP and a sugar molecule.
Hydrolases:
As the name suggests, these enzymes catalyze hydrolysis reactions (and their reverse reactions). The hydrolysis of an ester would be an example of such a reaction.
Isomerases:
These enzymes catalyze the conversion of a molecule into an isomer. The cis-trans interconversion of maleate and fumarate is an example.
Lyases:
Reactions which add a small molecule such as water or ammonia to a double bond (and the reverse, elimination, reactions) are catalyzed by lyases.
Ligases:
These enzymes catalyze reactions which make bonds to join together (ligate) smaller molecules to make larger ones.
Activity of Enzyme
Enzymes serve a wide variety of functions inside living organisms. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases.[68] They also generate movement, with myosin hydrolysing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton.[69] Other ATPases in the cell membrane are ion pumps involved in active transport. Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies.[70] Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.
An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines. Starch molecules,
Several enzymes can work together in a specific order, creating metabolic pathways.
Enzymes determine what steps occur in these pathways. Without enzymes, metabolism would neither progress through the same steps, nor be fast enough to serve the needs of the cell.
Enzyme activity
Enzyme activity = moles of substrate converted per unit time = rate × reaction volume. Enzyme activity is a measure of the quantity of active enzyme present and is thus dependent on conditions, which should be specified. The SI unit is the katal, 1 katal = 1 mol s-1, but this is an excessively large unit. A more practical and commonly-used value is 1 enzyme unit (U) = 1 μmol min-1. 1 U corresponds to 16.67 nanokatals.[1]
Specific activity
The specific activity of an enzyme is another common unit. This is the activity of an enzyme per milligram of total protein (expressed in μmol min-1mg-1). Specific activity gives a measurement of the purity of the enzyme. It is the amount of product formed by an enzyme in a given amount of time under given conditions per milligram of enzyme. Specific activity is equal to the rate of reaction multiplied by the volume of reaction divided by the mass of enzyme. The SI unit is katal kg-1, but a more practical unit is μmol mg-1 min-1. Specific activity is a measure of enzyme processivity, usually constant for a pure enzyme.
Enzyme: A protein (or protein-based molecule) that speeds up a chemical reaction in a living organism. An enzyme acts as catalyst for specific chemical reactions, converting a specific set of reactants (called substrates) into specific products. Without enzymes, life as we know it would not exist.
Enzymes are nonetheless subject to error. In 1902 Sir Archibald Garrod was the first to attribute a disease to an enzyme defect, to what Garrod called an "inborn error of metabolism." Today, newborns are routinely screened for certain enzyme defects such as PKU (phenylketonuria) and galactosemia, an error in the handling (metabolism) of the sugar galactose.
Enzymes are biological catalysts. They speed up reactions by lowering the activation energy (the energy required for a reaction to begin). This is accomplished by increasing the local concentration of reactants (the compounds used in the reaction) and bringing the reactants into proper orientation for the reaction to begin. All enzymes are made of protein and their production is controlled by DNA. Enzymes can be reused many times. The standard suffix for enzymes is "ase."
Practically all of the numerous and complex biochemical reactions that take place in animals, plants, and microorganisms are regulated by enzymes. These catalytic proteins are efficient and specific—that is, they accelerate the rate of one kind of chemical reaction of one type of compound, and they do so in a far more efficient manner than man-made catalysts. They are controlled by activators and inhibitors that initiate or block reactions. All cells contain enzymes, which usually vary in number and composition, depending on the cell type; an average mammalian cell,
Classification of enzyme
Enzymes are classified according to the reactions they catalyze. In some cases, the terms used are fairly clear; in others, less so. Examples:
Oxidoreductases:
These are enzymes which catalyze the reduction or oxidation of a molecule. Remember that oxidation is the reverse of reduction and that an enzyme has to catalyze the forward and reverse reactions to the same degree. Any enzyme which catalyzes a reduction has to also catalyze the reverse (oxidation) reaction, thus the double-barreled name "oxidoreductase."
Transferases:
These enzymes catalyze the transfer of a group of atoms from one molecule to another. A common example involves transfer of a phosphate between ATP and a sugar molecule.
Hydrolases:
As the name suggests, these enzymes catalyze hydrolysis reactions (and their reverse reactions). The hydrolysis of an ester would be an example of such a reaction.
Isomerases:
These enzymes catalyze the conversion of a molecule into an isomer. The cis-trans interconversion of maleate and fumarate is an example.
Lyases:
Reactions which add a small molecule such as water or ammonia to a double bond (and the reverse, elimination, reactions) are catalyzed by lyases.
Ligases:
These enzymes catalyze reactions which make bonds to join together (ligate) smaller molecules to make larger ones.
Activity of Enzyme
Enzymes serve a wide variety of functions inside living organisms. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases.[68] They also generate movement, with myosin hydrolysing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton.[69] Other ATPases in the cell membrane are ion pumps involved in active transport. Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies.[70] Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.
An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines. Starch molecules,
Several enzymes can work together in a specific order, creating metabolic pathways.
Enzymes determine what steps occur in these pathways. Without enzymes, metabolism would neither progress through the same steps, nor be fast enough to serve the needs of the cell.
Enzyme activity
Enzyme activity = moles of substrate converted per unit time = rate × reaction volume. Enzyme activity is a measure of the quantity of active enzyme present and is thus dependent on conditions, which should be specified. The SI unit is the katal, 1 katal = 1 mol s-1, but this is an excessively large unit. A more practical and commonly-used value is 1 enzyme unit (U) = 1 μmol min-1. 1 U corresponds to 16.67 nanokatals.[1]
Specific activity
The specific activity of an enzyme is another common unit. This is the activity of an enzyme per milligram of total protein (expressed in μmol min-1mg-1). Specific activity gives a measurement of the purity of the enzyme. It is the amount of product formed by an enzyme in a given amount of time under given conditions per milligram of enzyme. Specific activity is equal to the rate of reaction multiplied by the volume of reaction divided by the mass of enzyme. The SI unit is katal kg-1, but a more practical unit is μmol mg-1 min-1. Specific activity is a measure of enzyme processivity, usually constant for a pure enzyme.
LOGIC abd Critical Thinking
Proposition - an expression in language or signs of something that can be believed, doubted, or denied or is either true or false
~a proposition is identified ontologically as an idea, concept, or abstraction whose token instances are patterns of symbols, marks, sounds, or strings of words.
Inference - the act of passing from one proposition, statement, or judgment considered as true to another whose truth is believed to follow from that of the former.
~is the process of drawing a conclusion by applying clues (of logic, statistics etc.) to observations or hypotheses; or by interpolating the next logical step in an intuited pattern. The conclusion drawn is also called an inference.
Premise - In logic, an argument is a set of one or more declarative sentences (or "propositions") known as the premises along with another declarative sentence (or "proposition") known as the conclusion.
Antecedent is the first half of a hypothetical proposition.
Ex.
• If P, then Q.
This is a nonlogical formulation of a hypothetical proposition. In this case, the antecedent is P, and the consequent is Q.
• If X is a man, then X is mortal.
"X is a man" is the antecedent for this proposition.
• If men have walked on the moon, then I am the king of France.
Here, "men have walked on the moon" is the antecedent.
Consequent is the second half of a hypothetical proposition. In the standard form of such a proposition, it is the part that follows "then".
Ex.
• If P, then Q.
Q is the consequent of this hypothetical proposition.
• If X is a mammal, then X is an animal.
Here, "X is an animal" is the consequent.
• If computers can think, then they are alive.
"They are alive" is the consequent.
The consequent in a hypothetical proposition is not necessarily a consequence of the antecedent.
• If monkeys are purple, then fish speak Klingon.
"Fish speak Klingon" is the consequent here, but clearly is not a consequence of (nor has anything to do with) the claim made in the antecedent that "monkeys are purple".
Inductive reasoning, also known as induction or inductive logic, is a type of reasoning that involves moving from a set of specific facts to a general conclusion. It uses premises from objects that have been examined to establish a conclusion about an object that has not been examined. It can also be seen as a form of theory-building, in which specific facts are used to create a theory that explains relationships between the facts and allows prediction of future knowledge. The premises of an inductive logical argument indicate some degree of support (inductive probability) for the conclusion but do not entail it; i.e. they do not ensure its truth. Induction is used to ascribe properties or relations to types based on an observation instance (i.e., on a number of observations or experiences); or to formulate laws based on limited observations of recurring phenomenal patterns. Induction is employed, for example, in using specific propositions such as:
This ice is cold. (Or: All ice I have ever touched has been cold.)
This billiard ball moves when struck with a cue. (Or: Of one hundred billiard balls struck with a cue, all of them moved.)
...to infer general propositions such as:
All ice is cold.
All billiard balls move when struck with a cue.
Another example would be:
3+5=8 and eight is an even number. Therefore, an odd number added to another odd number will result in an even number.
Deductive Inferences
When an argument claims that the truth of its premises guarantees the truth of its conclusion, it is said to involve a deductive inference. Deductive reasoning holds to a very high standard of correctness. A deductive inference succeeds only if its premises provide such absolute and complete support for its conclusion that it would be utterly inconsistent to suppose that the premises are true but the conclusion false.
Notice that each argument either meets this standard or else it does not; there is no middle ground. Some deductive arguments are perfect, and if their premises are in fact true, then it follows that their conclusions must also be true, no matter what else may happen to be the case. All other deductive arguments are no good at all—their conclusions may be false even if their premises are true, and no amount of additional information can help them in the least.
This is an example of a valid argument. The first premise is false, yet the conclusion is still true.
1. Everyone who eats steak is a quarterback.
2. John eats steak.
3. [Therefore,] John is a quarterback.
Inductive Inferences
When an argument claims merely that the truth of its premises make it likely or probable that its conclusion is also true, it is said to involve an inductive inference. The standard of correctness for inductive reasoning is much more flexible than that for deduction. An inductive argument succeeds whenever its premises provide some legitimate evidence or support for the truth of its conclusion. Although it is therefore reasonable to accept the truth of that conclusion on these grounds, it would not be completely inconsistent to withhold judgment or even to deny it outright.
Inductive arguments, then, may meet their standard to a greater or to a lesser degree, depending upon the amount of support they supply. No inductive argument is either absolutely perfect or entirely useless, although one may be said to be relatively better or worse than another in the sense that it recommends its conclusion with a higher or lower degree of probability. In such cases, relevant additional information often affects the reliability of an inductive argument by providing other evidence that changes our estimation of the likelihood of the conclusion.
It should be possible to differentiate arguments of these two sorts with some accuracy already. Remember that deductive arguments claim to guarantee their conclusions, while inductive arguments merely recommend theirs. Or ask yourself whether the introduction of any additional information—short of changing or denying any of the premises—could make the conclusion seem more or less likely; if so, the pattern of reasoning is inductive.
An inductive inference apparatus comprises an input section for inputting a proposition, conditions for the proposition, and the tendency of each condition, a storage section for storing the proposition, and necessary and sufficient conditions of the proposition, a condition detecting section for forming the necessary and sufficient conditions for the truth or falsity of the proposition in accordance with the input proposition, the input conditions, and the input tendency of each condition, a judging section for, with respect to an example in which the truth or falsity of the proposition is unknown, judging the truth or falsity of the proposition using already stored necesary and sufficient conditions, and a control section for, when the truth or falsity of the proposition in a new example input to the input section is known, supplying the conditions of the proposition and the tendency of each condition to the condition detecting section to store the necessary and sufficient conditions formed by the condition detecting section in the storage section, and for, when the truth or falsity of the proposition in the example is unknown, supplying the conditions of the proposition to the judging section.
Truth and Validity
Since deductive reasoning requires such a strong relationship between premises and conclusion, we will spend the majority of this survey studying various patterns of deductive inference. It is therefore worthwhile to consider the standard of correctness for deductive arguments in some detail.
A deductive argument is said to be valid when the inference from premises to conclusion is perfect. Here are two equivalent ways of stating that standard:
• If the premises of a valid argument are true, then its conclusion must also be true.
• It is impossible for the conclusion of a valid argument to be false while its premises are true.
(Considering the premises as a set of propositions, we will say that the premises are true only on those occasions when each and every one of those propositions is true.) Any deductive argument that is not valid is invalid: it is possible for its conclusion to be false while its premises are true, so even if the premises are true, the conclusion may turn out to be either true or false.
Notice that the validity of the inference of a deductive argument is independent of the truth of its premises; both conditions must be met in order to be sure of the truth of the conclusion. Of the eight distinct possible combinations of truth and validity, only one is ruled out completely:
~a proposition is identified ontologically as an idea, concept, or abstraction whose token instances are patterns of symbols, marks, sounds, or strings of words.
Inference - the act of passing from one proposition, statement, or judgment considered as true to another whose truth is believed to follow from that of the former.
~is the process of drawing a conclusion by applying clues (of logic, statistics etc.) to observations or hypotheses; or by interpolating the next logical step in an intuited pattern. The conclusion drawn is also called an inference.
Premise - In logic, an argument is a set of one or more declarative sentences (or "propositions") known as the premises along with another declarative sentence (or "proposition") known as the conclusion.
Antecedent is the first half of a hypothetical proposition.
Ex.
• If P, then Q.
This is a nonlogical formulation of a hypothetical proposition. In this case, the antecedent is P, and the consequent is Q.
• If X is a man, then X is mortal.
"X is a man" is the antecedent for this proposition.
• If men have walked on the moon, then I am the king of France.
Here, "men have walked on the moon" is the antecedent.
Consequent is the second half of a hypothetical proposition. In the standard form of such a proposition, it is the part that follows "then".
Ex.
• If P, then Q.
Q is the consequent of this hypothetical proposition.
• If X is a mammal, then X is an animal.
Here, "X is an animal" is the consequent.
• If computers can think, then they are alive.
"They are alive" is the consequent.
The consequent in a hypothetical proposition is not necessarily a consequence of the antecedent.
• If monkeys are purple, then fish speak Klingon.
"Fish speak Klingon" is the consequent here, but clearly is not a consequence of (nor has anything to do with) the claim made in the antecedent that "monkeys are purple".
Inductive reasoning, also known as induction or inductive logic, is a type of reasoning that involves moving from a set of specific facts to a general conclusion. It uses premises from objects that have been examined to establish a conclusion about an object that has not been examined. It can also be seen as a form of theory-building, in which specific facts are used to create a theory that explains relationships between the facts and allows prediction of future knowledge. The premises of an inductive logical argument indicate some degree of support (inductive probability) for the conclusion but do not entail it; i.e. they do not ensure its truth. Induction is used to ascribe properties or relations to types based on an observation instance (i.e., on a number of observations or experiences); or to formulate laws based on limited observations of recurring phenomenal patterns. Induction is employed, for example, in using specific propositions such as:
This ice is cold. (Or: All ice I have ever touched has been cold.)
This billiard ball moves when struck with a cue. (Or: Of one hundred billiard balls struck with a cue, all of them moved.)
...to infer general propositions such as:
All ice is cold.
All billiard balls move when struck with a cue.
Another example would be:
3+5=8 and eight is an even number. Therefore, an odd number added to another odd number will result in an even number.
Deductive Inferences
When an argument claims that the truth of its premises guarantees the truth of its conclusion, it is said to involve a deductive inference. Deductive reasoning holds to a very high standard of correctness. A deductive inference succeeds only if its premises provide such absolute and complete support for its conclusion that it would be utterly inconsistent to suppose that the premises are true but the conclusion false.
Notice that each argument either meets this standard or else it does not; there is no middle ground. Some deductive arguments are perfect, and if their premises are in fact true, then it follows that their conclusions must also be true, no matter what else may happen to be the case. All other deductive arguments are no good at all—their conclusions may be false even if their premises are true, and no amount of additional information can help them in the least.
This is an example of a valid argument. The first premise is false, yet the conclusion is still true.
1. Everyone who eats steak is a quarterback.
2. John eats steak.
3. [Therefore,] John is a quarterback.
Inductive Inferences
When an argument claims merely that the truth of its premises make it likely or probable that its conclusion is also true, it is said to involve an inductive inference. The standard of correctness for inductive reasoning is much more flexible than that for deduction. An inductive argument succeeds whenever its premises provide some legitimate evidence or support for the truth of its conclusion. Although it is therefore reasonable to accept the truth of that conclusion on these grounds, it would not be completely inconsistent to withhold judgment or even to deny it outright.
Inductive arguments, then, may meet their standard to a greater or to a lesser degree, depending upon the amount of support they supply. No inductive argument is either absolutely perfect or entirely useless, although one may be said to be relatively better or worse than another in the sense that it recommends its conclusion with a higher or lower degree of probability. In such cases, relevant additional information often affects the reliability of an inductive argument by providing other evidence that changes our estimation of the likelihood of the conclusion.
It should be possible to differentiate arguments of these two sorts with some accuracy already. Remember that deductive arguments claim to guarantee their conclusions, while inductive arguments merely recommend theirs. Or ask yourself whether the introduction of any additional information—short of changing or denying any of the premises—could make the conclusion seem more or less likely; if so, the pattern of reasoning is inductive.
An inductive inference apparatus comprises an input section for inputting a proposition, conditions for the proposition, and the tendency of each condition, a storage section for storing the proposition, and necessary and sufficient conditions of the proposition, a condition detecting section for forming the necessary and sufficient conditions for the truth or falsity of the proposition in accordance with the input proposition, the input conditions, and the input tendency of each condition, a judging section for, with respect to an example in which the truth or falsity of the proposition is unknown, judging the truth or falsity of the proposition using already stored necesary and sufficient conditions, and a control section for, when the truth or falsity of the proposition in a new example input to the input section is known, supplying the conditions of the proposition and the tendency of each condition to the condition detecting section to store the necessary and sufficient conditions formed by the condition detecting section in the storage section, and for, when the truth or falsity of the proposition in the example is unknown, supplying the conditions of the proposition to the judging section.
Truth and Validity
Since deductive reasoning requires such a strong relationship between premises and conclusion, we will spend the majority of this survey studying various patterns of deductive inference. It is therefore worthwhile to consider the standard of correctness for deductive arguments in some detail.
A deductive argument is said to be valid when the inference from premises to conclusion is perfect. Here are two equivalent ways of stating that standard:
• If the premises of a valid argument are true, then its conclusion must also be true.
• It is impossible for the conclusion of a valid argument to be false while its premises are true.
(Considering the premises as a set of propositions, we will say that the premises are true only on those occasions when each and every one of those propositions is true.) Any deductive argument that is not valid is invalid: it is possible for its conclusion to be false while its premises are true, so even if the premises are true, the conclusion may turn out to be either true or false.
Notice that the validity of the inference of a deductive argument is independent of the truth of its premises; both conditions must be met in order to be sure of the truth of the conclusion. Of the eight distinct possible combinations of truth and validity, only one is ruled out completely:
Tagalog Physics Jinggles
The 12 days of Physics
On the first day of physics
my teacher gave to me
A formula for relativity
(second day) two carts colliding
(third day) three vectors adding
(fourth day) four questions puzzling
(fifth day) five ticker-tapes
(sixth day) six curves a-graphing
(seventh day) seven labs disgusting
(eight day) eight worksheets solving
(ninth day) nine bricks-a-falling
(tenth day) ten books-a-stacking
(eleventh day) eleven tests a-writing
(twelfth day) twelve pendulums swinging
Lab Reports (sung to Jingle Bells)
Dashing through the lab
Streaming ticker tape
Taking all those tests
And laughing all the way
Bells for fire bells ring
Making spirits bright
What fun it is to laugh and sing
A physics song tonight.
Oh lab reports, lab reports
Graphing all the way
Oh what fun it is to study
For a physics test today HEY
Physics test, physics test
Isn’t it a blast!
Oh what fun it is to take
A physics test and pass!
Oh come Albert Einstein
Oh come Albert Einstein
And Sir Isaac Newton
Oh come yea, oh come yea
To our physics class.
Come and help clarify
Help us with your theories
And then we will rejoice here
And then we will rejoice here
And then we will rejoice here
In our physics class
CHALLENGES
Suggested tune: Pagsubok by Orient Pearl
I. Isip mo'y litong-lito
Sa mga equation sa Physics
Kaya naman nahihilo
Dahil sa hirap ng equations
Ang Physics ay sadyang ganyan
Equation ay di maiwasan
Itanim mo lang sa iyong utak
Kaya mo yan....
* Mga equations at questions
Gumugulo sa isipan
Mga pagsubok lamang yan
Huwag mong itigil ang pagsolve
Huwag kang sumuko at pag-aralan....
II. Huwag mong isiping ikaw lamang
Ang nahihirapan sa lessons
Ika'y hindi pababayaan ng ating guro sa Physics
Hindi lang ikaw ang nagdurusa at 'di lang ikaw ang naghihrap
Pasakit mo'y may katapusan kaya mo 'yan...
Repeat *
On the first day of physics
my teacher gave to me
A formula for relativity
(second day) two carts colliding
(third day) three vectors adding
(fourth day) four questions puzzling
(fifth day) five ticker-tapes
(sixth day) six curves a-graphing
(seventh day) seven labs disgusting
(eight day) eight worksheets solving
(ninth day) nine bricks-a-falling
(tenth day) ten books-a-stacking
(eleventh day) eleven tests a-writing
(twelfth day) twelve pendulums swinging
Lab Reports (sung to Jingle Bells)
Dashing through the lab
Streaming ticker tape
Taking all those tests
And laughing all the way
Bells for fire bells ring
Making spirits bright
What fun it is to laugh and sing
A physics song tonight.
Oh lab reports, lab reports
Graphing all the way
Oh what fun it is to study
For a physics test today HEY
Physics test, physics test
Isn’t it a blast!
Oh what fun it is to take
A physics test and pass!
Oh come Albert Einstein
Oh come Albert Einstein
And Sir Isaac Newton
Oh come yea, oh come yea
To our physics class.
Come and help clarify
Help us with your theories
And then we will rejoice here
And then we will rejoice here
And then we will rejoice here
In our physics class
CHALLENGES
Suggested tune: Pagsubok by Orient Pearl
I. Isip mo'y litong-lito
Sa mga equation sa Physics
Kaya naman nahihilo
Dahil sa hirap ng equations
Ang Physics ay sadyang ganyan
Equation ay di maiwasan
Itanim mo lang sa iyong utak
Kaya mo yan....
* Mga equations at questions
Gumugulo sa isipan
Mga pagsubok lamang yan
Huwag mong itigil ang pagsolve
Huwag kang sumuko at pag-aralan....
II. Huwag mong isiping ikaw lamang
Ang nahihirapan sa lessons
Ika'y hindi pababayaan ng ating guro sa Physics
Hindi lang ikaw ang nagdurusa at 'di lang ikaw ang naghihrap
Pasakit mo'y may katapusan kaya mo 'yan...
Repeat *
Definition of Logic
Logic-The science or art of exact reasoning, or of pure and formal thought, or of the laws according to which the processes of pure thinking should be conducted; the science of the formation and application of general notions; the science of generalization, judgment, classification, reasoning, and systematic arrangement; correct reasoning.
L01.1 A preliminary definition
The term "logic" came from the Greek word logos, which is sometimes translated as "sentence", "discourse", "reason", "rule", and "ratio". Of course, these translations are not enough to help us understand the more specialized meaning of "logic" as it is used today.
So what is logic? Briefly speaking, we might define logic as the study of the principles of correct reasoning. This is a rough definition, because how logic should be properly defined is actually quite a controversial matter. However, for the purpose of this tour, we thought it would be useful to give you at least some rough idea as to the subject matter that you will be studying. So this is what we shall try to do on this page.
L01.3 The principles of logic
So what are these principles of reasoning that are part of logic? There are many such principles, but the main (not the only) thing that we study in logic are principles governing the validity of arguments - whether certain conclusions follow from some given assumptions. For example, consider the following three arguments :
If Tom is a philosopher, then Tom is poor.
Tom is a philosopher.
Therefore, Tom is poor.
If K>10, then K>2.
K>10.
Therefore, K>2.
If Tarragona is in Europe, then Tarragona is not in China.
Tarragona is in Europe.
Therefore, Tarragona is not in China.
These three arguments here are obviously good arguments in the sense that their conclusions follow from the assumptions. If the assumptions of the argument are true, the conclusion of the argument must also be true. A logician will tell us that they are all cases of a particular form of argument known as "modus ponens" :
L01.5 Necessity in logic
A second feature of the principles of logic is that they are non-contingent, in the sense that they do not depend on any particular accidental features of the world. Physics and the other empirical sciences investigate the way the world actually is. Physicists might tell us that no signal can travel faster than the speed of light, but if the laws of physics have been different, then perhaps this would not have been true. Similarly, biologists might study how dolphins communicate with each other, but if the course of evolution had been different, then perhaps dolphins might not have existed. So the theories in the empirical sciences are contingent in the sense that they could have been otherwise. The principles of logic, on the other hand, are derived using reasoning only, and their validity does not depend on any contingent features of the world.
For example, logic tells us that any statement of the form "If P then P." is necessarily true. This is a principle of the second kind that logician study. This principle tells us that a statement such as "if it is raining, then it is raining" must be true. We can easily see that this is indeed the case, whether or not it is actually raining. Furthermore, even if the laws of physics or weather patterns were to change, this statement will remain true. Thus we say that scientific truths (mathematics aside) are contingent whereas logical truths are necessary. Again this shows how logic is different from the empirical sciences like physics, chemistry or biology.
Sometimes a distinction is made between informal logic and formal logic. The term "informal logic" is often used to mean the same thing as critical thinking. Sometimes it is used to refer to the study of reasoning and fallacies in the context of everyday life. "Formal logic" is mainly concerned with formal systems of logic. These are specially constructed systems for carrying out proofs, where the languages and rules of reasoning are precisely and carefully defined. Sentential logic (also known as "Propositional logic") and Predicate Logic are both examples of formal systems of logic.
There are many reasons for studying formal logic. One is that formal logic helps us identify patterns of good reasoning and patterns of bad reasoning, so we know which to follow and which to avoid. This is why studying basic formal logic can help improve critical thinking. Formal systems of logic are also used by linguists to study natural languages. Computer scientists also employ formal systems of logic in research relating to Aritificial Intelligence. Finally, many philosophers also like to use formal logic when dealing with complicated philosophical problems, in order to make their reasoning more explicit and precise.
L01.1 A preliminary definition
The term "logic" came from the Greek word logos, which is sometimes translated as "sentence", "discourse", "reason", "rule", and "ratio". Of course, these translations are not enough to help us understand the more specialized meaning of "logic" as it is used today.
So what is logic? Briefly speaking, we might define logic as the study of the principles of correct reasoning. This is a rough definition, because how logic should be properly defined is actually quite a controversial matter. However, for the purpose of this tour, we thought it would be useful to give you at least some rough idea as to the subject matter that you will be studying. So this is what we shall try to do on this page.
L01.3 The principles of logic
So what are these principles of reasoning that are part of logic? There are many such principles, but the main (not the only) thing that we study in logic are principles governing the validity of arguments - whether certain conclusions follow from some given assumptions. For example, consider the following three arguments :
If Tom is a philosopher, then Tom is poor.
Tom is a philosopher.
Therefore, Tom is poor.
If K>10, then K>2.
K>10.
Therefore, K>2.
If Tarragona is in Europe, then Tarragona is not in China.
Tarragona is in Europe.
Therefore, Tarragona is not in China.
These three arguments here are obviously good arguments in the sense that their conclusions follow from the assumptions. If the assumptions of the argument are true, the conclusion of the argument must also be true. A logician will tell us that they are all cases of a particular form of argument known as "modus ponens" :
L01.5 Necessity in logic
A second feature of the principles of logic is that they are non-contingent, in the sense that they do not depend on any particular accidental features of the world. Physics and the other empirical sciences investigate the way the world actually is. Physicists might tell us that no signal can travel faster than the speed of light, but if the laws of physics have been different, then perhaps this would not have been true. Similarly, biologists might study how dolphins communicate with each other, but if the course of evolution had been different, then perhaps dolphins might not have existed. So the theories in the empirical sciences are contingent in the sense that they could have been otherwise. The principles of logic, on the other hand, are derived using reasoning only, and their validity does not depend on any contingent features of the world.
For example, logic tells us that any statement of the form "If P then P." is necessarily true. This is a principle of the second kind that logician study. This principle tells us that a statement such as "if it is raining, then it is raining" must be true. We can easily see that this is indeed the case, whether or not it is actually raining. Furthermore, even if the laws of physics or weather patterns were to change, this statement will remain true. Thus we say that scientific truths (mathematics aside) are contingent whereas logical truths are necessary. Again this shows how logic is different from the empirical sciences like physics, chemistry or biology.
L01.6 Formal and informal logic
Sometimes a distinction is made between informal logic and formal logic. The term "informal logic" is often used to mean the same thing as critical thinking. Sometimes it is used to refer to the study of reasoning and fallacies in the context of everyday life. "Formal logic" is mainly concerned with formal systems of logic. These are specially constructed systems for carrying out proofs, where the languages and rules of reasoning are precisely and carefully defined. Sentential logic (also known as "Propositional logic") and Predicate Logic are both examples of formal systems of logic.
There are many reasons for studying formal logic. One is that formal logic helps us identify patterns of good reasoning and patterns of bad reasoning, so we know which to follow and which to avoid. This is why studying basic formal logic can help improve critical thinking. Formal systems of logic are also used by linguists to study natural languages. Computer scientists also employ formal systems of logic in research relating to Aritificial Intelligence. Finally, many philosophers also like to use formal logic when dealing with complicated philosophical problems, in order to make their reasoning more explicit and precise.
Great Physicist
Name Living time Contribution
Aristotle BC384-322
Physicae Auscultationes
Archimedes BC287-212
On Floating Bodies
Ptolemaeus AD90-168
Almagest, Geography, Apotelesmatika
Copernicus 1473–1543 1543
On the Revolutions of the Celestial Spheres
Galilei 1564–1642 1632
Dialogue Concerning the Two Chief World Systems
Descartes 1596–1650 1641
Meditations on First Philosophy
Newton 1643–1727 1687
Mathematical Principles of Natural Philosophy
Faraday 1791–1867 1839, 1844,
Experimental Researches in Electricity, vols. i. and ii.
Maxwell 1831–1879 1873
Treatise on Electricity and Magnetism
Einstein 1879–1955 1905
On the Electrodynamics of Moving Bodies
Aristotle BC384-322
Physicae Auscultationes
Archimedes BC287-212
On Floating Bodies
Ptolemaeus AD90-168
Almagest, Geography, Apotelesmatika
Copernicus 1473–1543 1543
On the Revolutions of the Celestial Spheres
Galilei 1564–1642 1632
Dialogue Concerning the Two Chief World Systems
Descartes 1596–1650 1641
Meditations on First Philosophy
Newton 1643–1727 1687
Mathematical Principles of Natural Philosophy
Faraday 1791–1867 1839, 1844,
Experimental Researches in Electricity, vols. i. and ii.
Maxwell 1831–1879 1873
Treatise on Electricity and Magnetism
Einstein 1879–1955 1905
On the Electrodynamics of Moving Bodies
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