MNSR 28 - Structure of the ear Flashcards
what does the outer ear consist of?
the pinna
function of pinna
collects the sound and amplifies sound into the auditory canal
links the outer and middle ear
transmits sound waves into the skull
tympanic membrane/ear drums
thin connective tissue converts sound waves into physical vibrations in the membrane
what does the middle ear consist of?
tympanic membrane tympanic cavity ossicles (malleus, incus, stapes) oval window round window auditory tube stabilizing ligaments eustachian tube
function of stabilizing ligaments
hold ossicles in place
smallest bone in the human body
stapes
functions of eustachian tube
connects middle ear and back of nasal pharynx cavity
help w/ secretions of middle ear to be released through nasal pharynx
equalise pressure
function of ossicles
transmit vibrations from the ear drum to the inner ear
translates the low-pressure movement of the large eardrum into high-pressure movement of the small oval window
purpose of malleus/hammer ossicle in particular
connects to the eardrum on one side and the incus bone on the other
takes the vibrational energy of the eardrum and transfers it to the incus.
function of incus
transfers the energy to the stapes
features of inner ear
semi circular canals
cochlea
how are parts of the semi circular canal and cochlea divided
outer - bony labyrinth
inner - membranous labyrinth
bony labyrinth function
provides bony covering for membranous fluid
membranous labyrinth description
A system of fluid-filled chambers and channels
function of perilymph fluid
separates and covers the membranous and bony labyrinth
2 systems in the inner ear
vestibular system
cochlea system
function of vestibular system
provides us with our sense of balance and spatial awareness.
which structure transmits sound waves from the outer ear to the middle ear?
tympanic membrane
pinna - collect and amplify sound in canal
and transmit sound wave to skull
what does vestibular system consist of and their purpose?
semi circular canals - detect rotation
otholith organs - detect linear acceleration
what does each canal in the semi circular canal contain?
each canal is filled w/ endolymph fluid
has a sac - osseous ampulla at one end
base of sac crista ampullaris
three planes for semi circular canal
roll - x axis (front and back)
pitch - y axis (lean from side to side)
yaw - z axis (left to right)
how do canals detect movement and know movement of head
move head - endolymph fluid move crista ampullaris is activated stimulates pull on crista ampullaris
sends impulse to vestibular nerve then to brain
nerve impulse from brain allows us to regain our balance
function of crista ampullaris
translates flow of endolymph to nerve signals
what does crista ampullaris consist of?
cupula - a gelatinous structure with hair cells at the base
describe direction of cupula and endolymph as the body is moving
endolymph and cupula move in opposite direction of the body
how does cupula help transmit signal to vestibular nerve
movement of cupula in opposite direction of body triggers membrane depolarisation of hair cells and transmit signals through nerves
name the 2 otolith organs
utricle
smaller - saccule
both filled with endolymph
function of 2 otolith organs
detect linear acceleration
what type of movement does the utricle detect
horizontal movement
what type of movement does saccule detect
vertical acceleration
otoliths
crystals / ear stones on top of gel layer which has hair cells embedded in gel like substance which trigger nerve cells when the body moves
3 canals of cochlea
scala vestibuli
scala tympana
scala media
what is the scala vestibuli connected to?
connected to the oval window and thus the stapes
what is the scala tympana connected to?
connected to round window
what is helicotrema connected to?
connects scala tympani and scala vestibuli at the apex
what do both scala tympani and scala vestibuli both contain
perilymph fluid
what is the scala media (canal between scala vestibuli and scala tympana) connected to?
connected to saccule and contains endolymph
what separates scala media from scala vestibuli
vestibular membrane
what separates scala media from scala tympani
basilar membrane
how is sound waves interpreted as sound
sound vibrations from oval window set up pressure waves in scala vestibuli and scala media
sound waves - waves in fluid cause basilar membrane to move up and down
central structure - organ of corti
basilar membrane bouncers off tectorial membrane over organ of corti and triggers hair cells in organ of corti
open K and Ca channels to enter cell
triggers release of glutamate
activate postsynaptic cochlear nerves
how do basilar fibres change towards helicotrema and why
fibres become taller and thinner towards the helicotrema allows cochlea to pick up sound waves of different pitches and frequencies
where will cochlea pick up high freq.
mid freg.
low freq.
high freq. - near base
mid freq - in middle
low freq - near apex
