HEARING LOSS Flashcards
(145 cards)
Structure and function of external auditory meatus?
From outside of ear to TM. Contains ceruminous glands which secrete cerumen and small hairs
Guides sound waves to TM and traps FBs
Structure and function of tympanic membrane?
A thin connective tissue membrane covered by skin externally and a mucous membrane internally
This separates the external and middle ear
It vibrates when hit by sound waves which vibrates the ossicles
What are the 3 auditory ossicles?
Malleus (“hammer”)
Incus (“anvil”)
Stapes (“stirrup”)
What does the malleus connect?
Tympanic membrane and incus
What does the incus connect?
Malleus and stapes
What does the stapes connect?
The incus and oval window
What are the 2 skeletal muscles that attach to the auditory ossicles? What are their functions?
Stapedius and tensor tympani
Protect ears from prolonged, loud noises
What is the oval window?
A membrane-covered opening connecting the middle and inner ear
It transforms vibrations into fluid waves
What is the round window?
A membrane-covered opening that relieves pressure created by fluid waves
What is the pharyngotympanic tube?
This is the Eustachian tube
A canal linking the middle ear and nasopharynx
Swallowing/yawning opens the tube to equalise middle ear cavity and atmospheric air pressure
What is the bony labyrinth?
A system of channels that house the memabrnous labyrinth and is fluid-filled
Pathway of sound waves?
Sound waves travel through the external ear canal and vibrate the TM. This vibrates the ossicles which amplify the sound. The stales vibrates the oval window. Perilymph in scala vestibuli moves causing pressure waves which travel through the perilymph towards helicotrema, the cochlear duct and vibrates the basilar membrane
Hair cells bend by shearing force and cilia push against the tectorial membrane. When cilia bend in 1 direction there is an increase in potassium conduction which causes depolarisation. The opposite hyppens when cilia bend the other way. This generates an action potential within the cochlear nerve which sends signals to the brain = hearing
What is the cochlea?
A spiral bony chamber which coils around a central axis
This contains the organ of corti which is the site of auditory transduction
This has 2 receptors: inner and outer hair cells
What is the basilar membrane?
A membrane which is narrow and thick near the oval window/base and wide and thin near the cochlea
Function is for sound reception
What are the 3 chambers of the ear?
Scala vestibuli
Scala media
Scala tympani
What is the scala vestibuli?
The superior chamber filled with perilymph and conducts sound vibrations for hearing and proprioception
Connected to the middle ear through the oval window
What is the scala media?
The middle chamber of the ear
Filled with endoymph
Contains the cochlear duct
What is the scala tympani?
The inferior chambe filled with perilymph
Connected to the middle ear via the round window
Outline the tonotopic map?
This is the idea that sound frequencies displace the basilar membrane at different locations
At the base the fibres are short and stiff and 20,000Hz are needed to displace this. At the apex the fibres are long and floppy so only 20Hz is needed to displace this and therefore it responds best to low frequencies
What comprises the vestibular system?
3 semicircular canals
Otolith organs: utricle and saccule
Function of the semicircular ducts?
Rotational acceleration to maintain balance
Structure of the semicircular ducts?
3 canals at right angles to one another in each plane of space
Filled with endolymph
Has an ampulla which is a dilated portion at 1 end containing hair cells which protrude into a gelatinous substance
Outline how semicircular ducts work?
Head rotation means that endolymph deflects hair cells in certain directions within the semicircular canals. This changes from the baseline electrical firing rate which causes propagation down the vestibular nerve to the brain stem
What are the 2 otolith organs?
The utricle and saccule