Hearing and the structure of the ear

Hearing may be defined as the reception of sound vibra­tion by the ear. This is the main function of this organ. Another function of the ear is that of providing sense of balance (equilibrium). It is the ear that detects and analyzes noises by conversion of sound waves, into electromechanical impulses. The following succession represents the pathway of sound waves, and vibrations through the ear: auricle (pinna); external auditory canal (meatus); eardrum (tympar nic membrane); malleus (hammer); incus (anvil); stapes (stirrup); oval window; cochlea; auditory liquids and recep­tors in the organ of Corti; auditory nerve fibers; cerebral cortex (brain).

Auditory sensory system is the second in significance for I he normal life of man. The acoustic receptors are found in I he cochlea of the internal ear located in the pyramid of the temporal bone. Sound vibrations are transmitted to them I h rough a whole system of special formations. By such for­mations as the external auditory meatus (pinna or the au­ricle), eardrum, ossicles-(malleus, incus, stapes), labyrinthine lluid and basilar membrane of the cochlea the auditory analyzer performs consecutive transmission of signals to the cerebral cortex.

Usually the auditory system is subdivided into three parts:

I he outer ear, the middle ear, and the inner ear. The outer ear consists of the auricle. It is the projecting visible flap of the car composed of folds of skin, and cartilage. The auditory canal leads from the auricle. It is closed at its inner end by the eardrum. There are many tiny glands in the skin that covers cartilage of the canal. They produce and secrete yello­wish brown substance called cerumen (wax). Cerumen lu­bricates the ear, traps dust, small foreign particles and in such a way protects the ear.

The eardrum is between the outer and middle ear. It is a I liin fibrous membrane covered with a thin layer of skin. As

1. lie eardrum vibrates under the influence of sound Waves, it makes the three ossicles move. They Conduct Sound to the inner ear. As the last of the three osssicles, the stapes, moves

2. touches an oval window in the bony wall on the opposite Inner side of the middle-ear cavity.

Although the middle ear is cut off from the outside by the eardrum the balance of the atmospheric pressure and that in the middle ear is regulated by a ventilation passage, called t he Eustachian tube. Inequality of the air pressure on the inside and outside of the eardrum makes the eardrum bulge outward and if the outer pressure is hazardous the tympanic membrane can burst. Normally the Eustachian tube is closed but swallowing, and yawning will open it and the pressures of air are balanced.

Sound vibrations reach the inner ear via the fluctuations of the oval window- The inner ear is an extremely intricate series of structures contained deep within the bones of the skull. It is also called the labyrinth because of its circular, mazelike structure. The front part, the cochlea, is a bony, snail-shaped structure that contains special auditory liquids through which vibrations travel. A sensitive auditory receptor called the organ of Corti is provided in the cochlea for receiving vibrations from the auditory liquids via tiny cells (cilia) and relaying the sound waves to auditory nerve fibers and then conveying message to the cerebral cortex.The rear part of labyrinth is concerned with balance. Three organs (semicircular canals, utricle, and saccule) contain haircells bathed in the fluid (endolymph). These cells fluctuate in response to the movements of the head in rather an intricate manner. The impulses obtained from this fluctuation get to nerve fibers and in such a manner any information concern­ing positions, movements, posture or directions is obtained and messages are then sent to muscles in all parts of the body to assure the balance of the body.

Task 12. Study some additional definitions of terms to the unit and use them in your English language commu­nication practice;

ampulla ['aempjuda] the dilatation containing a patch of sensory epithelium at one end of each semicircular canal of the ear

basilar ['baszila] membrane — a membrane that extends from the margin of the bony part of the cochlea to the outer wall and that supports the organ of Corti cilia ['sihaj —; minute hairlike processes on cells cochlear ['kokliaj duct — the spirally arranged canal in the bony canal of the cochlea that contains the organ of Corti. It is triangular in cross section, and is bounded by the vestibular membrane above, by the periosteum-lined wall of the cochlea laterally, and by the basilar membrane below (called also sea I a media, cochlear canal) crista ['kristaj — one of the areas of specialized sensory epithelium in the ampullae of the semicircular canals of the ear serving as end organs for the labyrinthine sense graft |gra:ft] a piece of transplanted organ or living tissue as a substitute or replacement for a damaged or missing part

helicotrema [,helikou'tri:ni3] (of cochlea) — the minute opening by which the scala tympani and scala vestibuli communicate at the top of the cochlea of the ear labyrinthine fluid — special auditory liquids called perilymph(a) and endolymph(a). The former is the wa­tery fluid in the membranous labyrinth of the ear and the latter is the fluid between the membranous and bony laby­rinths of the ear

lobule rio:bju:l] — a small lobe of the ear organ of Corti — it is a complex epithelial structure spiral in shape that is found in the cochlea of the inner ear purulent ['pju:9rulent] — suppurative; pus; pus-forming;

consisting of pus tragus ['treigss] — a small projection in front of the exter­nal opening of the ear tinnitus [ti'naitas] (ringing, buzzing) — noises heard in the ear in the absence of matching noises in the surrounding environment

vestibular apparatus — the vestibule of the inner ear to­gether with the end organs and nerve fibers that function in mediating in labyrinthine sense

Task 13. Try to use the following phrases while making