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

Question 1

three major areas of the ear

Answer 1

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

Question 2

External ear is composed of

Answer 2

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

Question 3

auricle (pinna) is composed of

Answer 3

helix (rim); lobule (ear lobe)

funnels sound waves into auditory canal

Question 4

external acoustic meatus (auditory canal) is composed of

Answer 4

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

Question 5

Tympanic membrane is

Answer 5

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

Question 6

Middle ear is referred to as the

Answer 6

tympanic cavity

Question 7

middle ear is

Answer 7

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

Question 8

The three small bones in the tympanic cavity are

Answer 8

malleus
stapes
incus
(stapes footprint pushes into the oval window)

Question 9

what is the mastoid Antrum

located in the middle ear

Answer 9

canal for communication with mastoid air cells – mastoiditis

Question 10

What is the Eustachian tube

part of the middle ear

Answer 10

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

Question 11

What does the inner ear compose of

Answer 11

outer bony labyrinth

inner membraneous labyrinth

Question 12

outer bony labyrinth

Answer 12

perilymph

Question 13

inner membranous labyrinth

Answer 13

endolymph

1. vestibule
2. semicircular canals
3. cochlea

Question 14

sounds waves heard

Answer 14

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

Question 15

Cochlea

Answer 15

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

Question 16

hair cells in the spiral organ

Answer 16

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

Question 17

Equilibrium and orientation

Answer 17

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)

Question 18

maculae

Answer 18

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

Question 19

semicircular canals

Answer 19

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

Question 20

The crista ampullares (crista)

Answer 20

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