chapter 15 Flashcards
3 parts of the ear
- external
- middle
- inner
external ear
- auricle/pinna
- shape serves to funnel sound waves into external auditory canal which terminates at the TM
external auditory canal lined with glands that secrete
cerumen, a yellow, waxy material that lubricates and protects the ear.
-wax forms sticky barrier that helps keep foreign bodies from entering and reaching the TM
how does cerumen exit the meatus
movements of chewing and talking
TM characteristics
- translucent with pearly gray color
- prominent cone of line in the anteroinferior quadrant
- drum is oval and slightly concave pulled at the center by malleus
parts of malleus
umbo, manubrium, short process
small slack superior section of the TM
pars flaccida
remainder of the drum (thicker and more taut)
pars tensa
outer fibrous rim of the drum
annulus
where lymphatic drainage of the external ear flows
parotid, mastoid, and superficial cervical nodes
middle ear auditory ossicles
malleus, incus, stapes
eustachian tube
connects middle ear with the nasopharynx and allows passage of air
-normally closed but opens with swallowing/yawning
middle ear functions (3)
- conducts sound vibrations from outer eat to the central hearing apparatus in the inner ear
- protects the inner ear by reducing amplitude of loud sounds
- eustachian tube allows equalization of air pressure on each side of the TM to prevent rupture
inner ear embedded in
bone
inner ear contains
bony labyrinth which holds the sensory organs for equilibrium and hearing
vestibule and semicircular canals compose the
vestibular apparatus
cochlea
snail shaped
central hearing appartus
can the inner ear be accessible to direct examination
no but can assess functions
function of hearing involves auditory system at 3 levels
- peripheral
- brainstem
- cerebral cortex
peripheral level
ear transmits sound and converts its vibrations into electrical impulses
amplitude
how loud
frequency
pitch
how sound travels
- sound waves produce vibrations on TM
- vibrations carried out by middle ear ossicles to oval window
- sound waves travel through cochlea and dissipated against round window
- basilar membrane vibrates at specific point to the frequency
- hair cells of organ of corti bend and mediate vibrations into electric impulses
- electrical impulses conducted by CN VIII to the brainstem
- CN VIII from each ear sends signals to both sides of brainstem
- cortex interprets meaning of the sound and begin the appropriate response
sensory organ of hearing
organ of corti
brainstem level
binaural interaction permits locating the direction of a sound in space and identifying the sound
- CN VIII from each ear sends signals to both sides of the brainstem
- -brainstem sensitive to differences in intensity and timing of the messages from the two ears depending on the way the head is turned
cortex
interprets the meaning of sound and begin the appropriate response
normal pathway of hearing
air conduction
most efficient
bone conduction
bones of the skull vibrate
-vibrations transmitted directly to the inner ear and to CN VIII
hearing loss
anything that obstructs the transmission of sound impairs hearing
conductive hearing loss
mechanical dysfunction of the external or middle ear
- partial loss because person is able to hear if sound amplitude is increased enough
- may be caused b y impacted cerumen, foreign bodies, perforated TM, pus or serum in the middle ear, and otosclerosis
sensorineural loss
pathology of the inner ear, CN VIII, or auditory areas of the cerebral cortex
-may be caused by presbycusis or ototoxic drugs
presbycusis
gradual nerve degeneration that occurs with aging
mixed loss
combo of conductive and sensorineural
equilibrium
3 semicircular canals/labryinth in inner ear feed info to brain about the position of body in space
-if labyrinth becomes inflames, feeds the wrong info to the brain creating a staggering gait and strong spinning/whirling sensation (vertigo)
infant’s eustachian tube
shorter and wider, more horizontal
- easier for pathogens to enter nasopharynx to migrate through to the middle ear
- lumen easily occluded
- greater risk for ear infections
otosclerosis
gradual bone formation that causes the footplate of the stapes to become fixed in the oval window, impeding the transmission of sound and causing progressive deafness
aging adult’s cilia
become coarse and stiff
- cause cerumen to accumulate and oxidize
- cerumen itself is drier because of atrophy of apocrine glands
aging adult’s hearing
presbycusis is a gradual sensorineural loss
-first notice high-frequency tone loss; harder to hear consonants than vowels
otitis media
aka middle ear infection
- occurs because of obstruction of the eustsachian tube or passage of nasopharyngeal secretions into middle ear
- -creates ripe environment for bacteria to grow
risk factors predispose to acute OM
- absence of breastfeeding in the first 3 months
- exposure to SHS
- daycare attendance
- male sex
- seasonality
- bottle feeding in the supine position
genetic variation of cerumen
either dry or wet
dry cerumen
gray and flaky
wet cerumen
honey brwon to dark brown and moist
chromosome responsible for determining wet or dry cerumen phenotype
chromosome 16
