Anatomy & Physiology of Hearing Flashcards
Parts of the outer ear
- auricle/ pinna
- external auditory canal
auricle/pinna
- the outer most part of the ear made up of mostly cartilage
- funnels sound into ear to help localize sound
External Auditory Canal
- aka external auditory meatus
- muscular tube made up of mostly cartilage
- resonates sounds that enter- frequency 2500 Hz
- contains the cells that produce cerumen that lubricates and cleans canal
Parts of the middle ear
- TM- tympanic membrane
- Ossicular chain
- Eustachian tube
Middle Ear
T-Air filled cavity separated from the outer ear by the TM
Tympanic Membrane
- elastic, thin, cone shaped
- vibrates in response to sound pressure
- whole thing responds to low freqs but only a certain portion responds to high freq
- EASILY DAMAGED, may repair spontaneously but repeated damage will decrease mobility
Ossicular Chain
- Suspended in the air by muscles
- smallest bones in the body
- malleus, incus, stapes
- transmits sound with no distortion
- amplifies sound by approx 30 dB before transmitting it into the inner ear fluid
Malleus
- largest of 3 ear bones
- first in the chain
- attached to the TM and vibrations are transmitted to malleus from TM
Incus
second bone in the ossicular chain
Stapes
last bone if the ossicular chain that is attached to the oval window
Muscles of the Acoustic Reflex
Tensor Tympani and Stapedius
Tensor Tympani
- innervated by cranial nerve V (trigeminal)
- tenses the TM to reduce vibrations (sound intensity)
Stapedius
- innervated by the cranial nerve VII (facial)
- smallest muscle in the body
- stiffens the ossicular chain to reduce vibrations (sound intensity)
Eustachian Tube
- connect the middle ear with the nasopharynx. Goes from anterior middle ear to the posterior wall of the nasopharynx
Function of Eustachian Tube
- helps to maintain equal air pressure within and outside the middle ear
- yawning or swallowing can open the nasopharyngeal side by letting in fresh air this ventilates the middle ear
Eustachian tube opening
the tensor veli palatini and the levator veli palatini
Eustachian tube and PEDS population
- eustachian tube is flatter in infants so ir allows fluid to spread into the middle ear from the nasoparynx
- infants with cleft palate frequesntly have eustachian tube dysfunction which makes them vulnerable to eharing loss
Inner ear
- most complex part of the ear
- begins at the oval window (on the other side of the stapes footplate)
- The oval window is a small hole in the temporal bone- the stapes footplate moves in and out of the oval window to to send mechanical vibrations of sound
Labyrinths
Interconnecting tunnels filled with perilymph
Two major structures of the inner ear
- vestibular system with 3 semi-circular canals responsible for equilibrium
- cochlea the snail shaped coiled tunnel- filled with endolymph
Basilar membrane
the floor of the cochlear duct which contains the organ or corti
Organ of Corti
- bathed in endolymph snd contains many thousand (approx. 15,000 per ear) hair cells (cilia)
- hair cells on the OOC respond to the vibrations and cause a shearing action
- turns mechanical energy is changed to electrical energy which communicates with the nerve endings
- this is important because nerve endings will not understand mechanical vibrations
Reissner’s membrane
transmits movements to the endolymph from the perilymph and the stapes footplate
Basilar membrane
- movement transmitted here from the endolymph
-organized by frequency:
~low frequency sounds stimulate the apex
~high frequency sounds stimulate the base - that stimulation sets off waves in the fluid that moves the membrane
Cranial Nerve VIII
Acoustic Nerve (aka vestibulocochlear nerve)- picks up the neural impulses created by the movement of the hair cells in the cochlea (cilia on the organ of Corti) -bundle of neurons with two branches: vestibular and auditory/acoustic
CN-VIII vestibular
concerned with body equilibrium and balance
CN-VII auditory/acoustic
concerned supplies many hair cells of the cochlea & conducts electrical sound impulses from the cochlea to the brain
Internal Auditory Meatus
-where the auditory nerve exits the inner ear
Cerebellopontine Angle
- space filled with spinal fluid
- where the suditory nerve exits the temporal bone through the EAM
Sound localization
- at the brainstem level most of the auditory nerve fibers from one ear decussate (cross over) the the other side (contralateral pathways)
- some continue of the same side forming ipsilateral pathways which helps with sound localization
Parts of the brain
From the brainstem–> acoustic nerve fibers project sound to the temporal lobe–> temporal lobe contains the primary auditory area (responsible for receiving and interpreting sound stimuli)
