THE EAR - HEARING AND BALANCE Flashcards
describe the ear?
- contains the two sense organs for hearing and balance, but their receptors respond differently to stimuli and are activated independently of eachother
- hearing apparatus helps us hear a range of sound
- equilibrium receptors keel the nervous system continuously up to date on position and movement of the head
state the 3 major areas of the ear?
- the external or outer ear (hearing only)
- the middle ear (hearing only)
- the internal or inner ear (both equilibrium and hearing)
describe the structure and function of the external/ outer ear?
*the pinna = the shell shaped structure surrounding the auditory canal opening
—in many animals it collects and directs sound waves into the auditory canal (not in humans)
*external acoustic meatus (auditory canal) = short/narrow chamber carved in temporal bone (skull)
—1 inch long by 1/4 inch wide
*skin lined walls = ceruminous glands that secrete cerumen (earwax)
—provides sticky trap for foreign bodies, protects tympanic membrane (eardrum), repels insects
*tympanic membrane = eardrum that vibrates when sound waves enter the auditory canal
—the end of the outer ear, which separates the external from the middle ear
decried the structure and function of the middle ear?
*tympanic cavity (middle ear cavity) = small air filled cavity within temporal bone
—flanked laterally by eardrum and medially by bony wall with two openings: the oval window and the inferior membrane covered round window
—spanned by the 3 smallest bones in the body (ossicles) which transmit vibratory motion of the eardrum to the fluids in the inner ear
*auditory (eustachian) tube = runs downward to link middle ear cavity with throat
—mucous lining of them is continuous
describe how pressure is equalised in the middle ear?
*usually auditory tube closed but in sneezing yawning etc can open to equalise pressure in middle ear cavity with atmospheric pressure
—equalisation of pressure key as eardrum won’t vibrate freely in its absence
*when pressures unequal, eardrum bulges, causing hearing difficulty or earache
—the ear popping sensation when flying
name and describe the role of the 3 bones which make up the ossicles in the middle ear?
- the hammer (malleus)
- the anvil (incus)
- the stirrup (stapes)
-when the eardrum vibrates, the hammer moves and transfers vibration to the anvil
-the anvil passes the vibration onto the stirrup, which presses on the oval window of the inner ear
-the movement of the oval window sets the fluids in the inner ear to motion
—this eventually excites the hearing receptors
describe the structure of the inner/ internal ear?
*a maze of bony chambers called the bony labyrinth / osseous labyrinth
—located deep within the temporal bone, behind the eye socket
name the 3 subdivisions of the bony labyrinth in the inner ear?
*the cochlea
*the vestibule
*the semi-circular canals
—cavities hollowed out of the bone and lined with periosteum
describe the differences between the bony labyrinth and the membranous labyrinth of the inner ear?
- bony labyrinth = filled with plasma like fluid called perilymph and suspended in it is a membranous labyrinth that largely follows the shape of the bony labyrinth
- membraneous labyrinth contains a thicker fluid called endolymph
describe the process of hearing?
*the organ of corti contains hearing receptors or hair cells
—it is found in the endolymph containing membranous labyrinth of the cochlea
*sound waves transmitted by the ossicles from eardrum to oval window, set the cochlear fluids into motion
*the receptor cells in the organ of corti are stimulated by the vibrating movement
—the hairs bend and once stimulated they transmit nervous impulses along the cochlear nerve to the auditory cortex in the temporal lobe, where interpretation of the sound of heart occurs
explain the difference between processing high pitch and low pitch sounds?
- high pitch = disturb the shorter, stiffer hairs nearer to the oval window
- low pitch = affect the longer hair cells further along the cochlea
define deafness as a hearing and equilibrium deficit?
hearing loss of any degree, from a slight loss to a total inability to hear sound
explain conduction deafness as a hearing and equilibrium deficit?
conduction deafness = something interferes with the conduction of sound vibrations to the fluids
—hearing aids that use skull bones to conduct sound vibrations typically help
*earwax build up
*ostoclerosis - fusion or congenital absence of the ossicles
*a ruptured eardrum
*otitis media (inflammation or infection in the middle ear)
*fluid accumulation in the middle ear (glue ear)
—treated using a gromet (tube)
explain sensorineural deafness as a hearing and equilibrium deficit?
sensorineural deafness = degeneration or damage to receptor cells in organ of corti, cochlear nerve or to neurones in the auditory cortex
—hearing aids which use skull bones to conduct sound vibrations are usually unhelpful
name and describe 9 equilibrium deficits?
*nausea
*dizziness
*problems in maintaining balance = particularly when impulses from the vestibular apparatus disagree with visual input
*Ménière’s disease = long term progressive condition affecting balance + hearing parts of inner ear
—lead to acute attacks of vertigo, fluctuating tinnitus, increasing deafness, pressure in the ear
*tinnitus = sensation of hearing a sound in the absence of any external sound
—symptoms - ringing, humming or buzzing
—suspected causes - arteriosclerosis, degeneration cranial nerve 8, increased fluid pressure
—treatment - anti emetics e.g. perphenazine, chlorpromazine etc
*labyrinthis = inner ear disorder, dizziness, nausea, hearing loss
—caused by inflammation of accessory nerve which moves the face (cranial nerve 11)
