Anatomy And Physiology Of The Ear

Anatomy and Physiology of the Ear

The ear is the organ of hearing. Hearing starts with the outer ear. When a sound is made outside the outer ear, the sound waves, or vibrations, travel down the external ear canal and strike the eardrum (tympanic membrane). The eardrum vibrates. The vibrations are then passed to the three tiny bones in the middle ear called the ossicles. The ossicles amplify the sound and send the sound waves to the inner ear and into the fluid-filled hearing organ (cochlea). The parts of the ear include:

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external or outer ear, consisting of: o pinna or auricle - the outside part of the ear. o external auditory canal or tube - the tube that connects the outer ear to the inside or middle ear. tympanic membrane - also called the eardrum. The tympanic membrane divides the external ear from the middle ear. middle ear (tympanic cavity), consisting of: o ossicles - three small bones that are connected and transmit the sound waves to the inner ear. The bones are called:  malleus  incus  stapes o eustachian tube - a canal that links the middle ear with the throat area. The eustachian tube helps to equalize the pressure between the outer ear and the middle ear. Having the same pressure allows for the proper transfer of sound waves. The eustachian tube is lined with mucous, just like the inside of the nose and throat. inner ear, consisting of: o cochlea (contains the nerves for hearing) o vestibule (contains receptors for balance) o semicircular canals (contain receptors for balance)

Ear Disorders Deafness and Hearing Loss Hearing loss falls into two categories: conductive, which involves sound transmission abnormalities in the middle and outer ear, and sensorineural, which involves the inner ear. Conductive loss can usually be corrected; sensorineural is much more difficult to treat.

Conductive hearing loss might result, for example, when impacted earwax prevents sounds from reaching the inner ear, where sounds are translated into electric nerve impulses that are transmitted to the brain. Other causes of conductive loss might be an injury to the eardrum or a middle-ear infection. In sensorineural loss, there is nerve failure. Thus, even though sound vibrations reach the inner ear, they don't get sent on as impulses to the brain. This type of hearing loss results from nerve damage, which can be caused by old age, viral infection, loud noises, or the side effects of medication, to name just a few.Deafness, or the total absence of hearing, can result from either conductive or sensorineural loss, or a mix of the two types. Whenever you suspect hearing loss, you need to see an ear specialist who can identify the root cause or causes. The best way to deal with hearing loss is to do all you can to prevent it in the first place. But if you already have hearing loss, a hearing aid may help. Today's hearing aids have gone high-tech; they're much sleeker, smaller, and more effective than the devices of yesteryear. There are three main types: behind the ear, in the ear, and in the canal, each having particular advantages and disadvantages. The canal version is smallest and, therefore, least visible, but because of its limited size it can't hold as much circuitry and isn't as versatile in its functions. It amplifies all sounds equally, rather than being programmable to amplify sounds selectively. The effectiveness of hearing aids comes down to a few key factors. First, the doctor must prescribe the type of hearing aid that's right for the individual. The wearer also has to use the device properly and communicate their needs clearly to the doctor. Just as important, the user must have realistic expectations about what the hearing aid can do.

Earache When you have an earache, suddenly your ears seem bigger than life. The pain distracts every thought and absorbs every ounce of your attention. And you just want it to end. Earaches can be caused by a blocked eustachian tube -- the thin tube that connects the inside back portion of the nose with the middle ear. The air in the middle ear is constantly being absorbed by its membranous lining, but the air is never depleted as long as the eustachian tube remains open and able to resupply air during the process of swallowing. In this manner, the air pressure on both sides of the eardrum stays about equal. But when the eustachian tube is blocked, the pressure in the middle ear can't be equalized. The air that's already there is absorbed and, without an incoming supply, a vacuum occurs in the middle ear, sucking the eardrum inward and stretching it painfully taut.

Air travel is a common cause of ear aches This type of earache is particularly common in people who travel by air, especially when they have a cold or stuffy nose. The air pressure in the middle ear doesn't equalize on takeoff and landing as it would if the eustachian tube were unblocked. Another leading cause of earache is ear infection. Infections of the middle ear are extremely common in children. This sort of infection develops when bacteria or viruses--usually from colds or sore throats--make their way up the eustachian tube. As a result of the infection, the eardrum can become swollen and inflamed. Because an untreated ear infection can lead to permanent hearing loss, and because ear pain can sometimes reflect a problem in another part of the body, it's important to have an earache checked by a doctor. Labyrinthitis Severe dizziness or vertigo -- a sensation that the room is spinning -- is scary and can stir worries that something is dreadfully wrong. If it happens to you, you should see a doctor immediately. It's possible that the root of your problem is labyrinthitis, an infection of the labyrinth -- a group of fluidfilled chambers in the inner ear. The labyrinth controls balance. Even though the vertigo will make it extremely difficult for you to function, the infection itself is not dangerous. Bed rest is usually the main treatment. Your doctor may give you medications to combat the dizziness, as well as the nausea and vomiting you may also experience. In most cases, symptoms clear up within one to three weeks. Recurrent episodes of vertigo should be investigated by a physician as they can represent some other underlying condition.

Tinnitus Everyone gets a little ringing in their ears at times. But when it goes on incessantly, it can drive you nuts. The medical name for this ringing-in-the-ear sensation is tinnitus. It is the result of damage to the tiny hair cells in the inner ear. These hair cells pick up sound vibrations and send electrical impulses through the auditory nerve to the brain. In tinnitus, the hair cells are "on" all the time, making the brain think that sound vibrations are entering the ear nonstop. Possible causes of tinnitus include acoustical trauma (loud noise), earwax, infection, the side effect of certain medications (more than 200 medications can case tinnitus), a perforated eardrum, fluid accumulation, high blood pressure, a tumor, diabetes, and aging. To stop the buzz, try the following:  

Stop the loud noise, or wear ear protection. Keep your blood pressure down.

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Cut down on salt, which may sometimes be a problem for tinnitus sufferers.

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Limit aspirin; chronic intake (or even frequent use over one or two days) can cause tinnitus.

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Avoid caffeine, tobacco, and addictive substances, which can also trigger tinnitus.

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Work it out; if poor circulation is the cause of ringing in your ears, exercise will help.

 Be sure you're getting enough rest

Anatomy and Physiology of the Eye

The protective outer layer of the eye, sometimes referred to as the “white of the eye” is called the sclera and it maintains the shape of the eye. The front portion of the sclera, called the cornea, is transparent and allows light to enter the eye. The cornea is a powerful refracting surface, providing much of the eye's focusing power (Cassin and Solomon, 1997). Attached to the sclera are six extraocular muscles responsible for movement of the eyes (Bianco, 2002). The choroid is the second layer of the eye and lies between the sclera and the retina. It contains the blood vessels that provide nourishment to the outer layers of the retina (Cassin and Solomon, 1997). The iris is the part of the eye that gives it color. It consists of muscular tissue that responds to surrounding light, making the pupil, or circular opening in the center of the iris, larger or smaller depending on the brightness of the light (Pachler and Rizun, n.d.). Light entering the pupil falls onto the lens of the eye where it is altered before passing through to the retina. The lens is a transparent, biconvex structure, encased in a thin transparent covering. The function of the lens is to refract and focus incoming light onto the retina for processing (Moorfields Eye Hospital, 2002). The retina is the innermost layer in the eye. It converts images into electrical impulses that are sent along the optic nerve to the brain where the images are interpreted. The retina can be compared to the film of a camera. It is composed of light sensitive cells known as rods and cones interconnected by a complex mesh of neurons that provide early stage visual processing. Rod cells are primarily in the outer retina, do not discriminate colors, have low spatial resolution, support vision in low light (“night vision”), are sensitive to object movement and provide peripheral vision. Cone cells are densely packed within the central visual field, function best in bright light, process acute images and discriminate colors (Montgomery, 2002). The macula is located in the back of the eye, in the center of the retina. Within the macula is an area called the fovea centralis. This area contains the highest concentration of cones, produces the sharpest vision, and is used to see details clearly (Moorfields Eye Hospital, 2002).

The inside of the eyeball is divided by the lens into two fluid-filled sections. The larger section at the back of the eye is filled with a colorless gelatinous mass called the vitreous humor. The smaller section in the front contains a clear, water-like material called aqueous humor (Discovery Fund for Eye Research, 1999). A circular canal, called the Canal of Schlemm provides a drainage system for the aqueous humor from the eye into the bloodstream. Blockages in the Canal of Schlemm are believed to be contributing factors in the development of glaucoma (Bianco, 2002). The conjunctiva is a mucous membrane that begins at the edge of the cornea and lines the inside surface of the eyelids and sclera, which serves to lubricate the eye. Inflammation of this membrane results in conjunctivitis, commonly known as pink eye (Bianco, 2002; Cassin and Solomon, 1997).