Week 6 - Lecture 2b - alterations in hearing and balance Flashcards Preview

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Flashcards in Week 6 - Lecture 2b - alterations in hearing and balance Deck (20):

three major areas of the ear

external (outer) ear - hearing only
middle ear (tympanic cavity) - hearing only
internal ear (inner) - hearing and equilibrium

receptors for hearing and balance respond to separate stimuli

are activated independently


External ear is composed of

auricle (pinna)
external acoustic meatus (auditory canal)
tympanic membrane
(eardrum )


auricle (pinna) is composed of

helix (rim); lobule (ear lobe)
funnels sound waves into auditory canal


external acoustic meatus (auditory canal) is composed of

short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands (secrete wax, cerumen)
transmits sound waves to eardrum
protect against foreign bodies and environmental debris


Tympanic membrane is

boundary between external and middle ears
connective tissue membrane that vibrates in response to sound
transfers sound energy to bones of middle ear


Middle ear is referred to as the

tympanic cavity


middle ear is

a small, air filled, mucosa-lined cavity in temporal bone


The three small bones in the tympanic cavity are

(stapes footprint pushes into the oval window)


what is the mastoid Antrum
(located in the middle ear)

canal for communication with mastoid air cells -- mastoiditis


What is the Eustachian tube
(part of the middle ear)

it connects the middle ear to the nasopharynx

also known as the pharyngotympanic (auditory) tube
equalises pressure in the middle ear cavity with external air pressure

in children : shorter, more horizontal tubes -- otitis media


What does the inner ear compose of

outer bony labyrinth

inner membraneous labyrinth


outer bony labyrinth



inner membranous labyrinth


1. vestibule
2. semicircular canals
3. cochlea


sounds waves heard

sound waves vibrate tympanic membrane
ossicles vibrate and amplify pressure at oval window

cochlea fluid set into wave motion

pressure waves move through perilymph of Scala vestibuli

pg. 6



a spiral, conical, bony chamber
- size of a split pea
- extends from vestibule, coils around a bony pillar

cavity of cochlea divided into three chambers
1. scala vestibuli
next to the oval window, contains perilymph
2. scala media (cochlear duct)
contains endolymph
3. Scala tympani
terminates at round window; contains perilymph

scala tympani and vestibuli are continuous with each other at helicotrama (apex)

the cochlear duct houses the spiral organ (organ of corti)

The cochlear branch of CN VIII runs from spiral organ to the brain


hair cells in the spiral organ

cells or the spiral organ (hair cells) contain hairs that protrude into the endolymph (stereo cilia)

stereo cilia - longest hair is enmeshed in gel-like tectorial membrane
opens mechanical gated ion channels
inward K+ and Ca2+ current causes graded potential and release of neurotransmitter glutamate
cochlear fibres transmit impulses to brain


Equilibrium and orientation

vestibule (vestibular apparatus)

responsible for equilibrium
1. vestibular receptors : monitor static equilibrium
2. semicircular canal receptors : monitor dynamic equilibrium

vestibular receptors : macula
located in the saccule and utricle wall
- monitor the position of head in space
-- necessary for control of head in space
-respond to linear acceleration forces
- - not rotation
contain hair cells

stereo cilia are embedded in the otolith membrane studded with otoliths (CaCO3 stones)



maculae in utricle : respond to horizontal movements and tilting head side to side

maculae in saccule : respond to vertical movements

hair cells release neurotransmitter continuously - movement modifies amount they release


semicircular canals

three canals (anterior, lateral, posterior) that each define 2/3 circle
- lie in three planes of space

membranous semicircular ducts line each canal and communicate with utricle

ampulla of each canal houses an equilibrium receptor region called the crista ampullaris (crista)
--receptors respond to angular (rotational) movements of the head

sensory receptor for rotational acceleration
-one in ampulla of each semicircular canal
- major stimuli are rotational movements


The crista ampullares (crista)

each crista has supporting cells and hair cells that extend into gel-like mass called ampullary cupula

dendrites of vestibular nerve fibres encircle base of hair cells

cristae respond to changes in velocity of rotational movements of the head

1. bending of hairs in cristae causes depolarisation of nerve fibres

2. bending of hairs in the opposite direction causes hyperpolarisation

thus brain informed of rotational movements of head