3.5

Question 1

Surface anatomy of the ear

Answer 1

Question 2

External ear

Answer 2

External structures and external auditory canal

Question 3

Middle ear

Answer 3

Tympanic cavity containing ossicles which vibrate in response to sound waves

Question 4

Inner ear

Answer 4

Bony labyrinth: hollow space with petrous part of temporal bone
Membranous labyrinth: membranous sacs/ducts inside bony labyrinth
Cochlea: hearing
Vestibule and semicircular canals: balance

Question 5

Muscles of middle ear

Answer 5

Tensor tympani
- tenses the tympanic membrane and reduces the amplitude of its oscillations
- prevents damage to the internal ear during loud sounds
- innervated by CN V3 (mandibular branch of trigeminal nerve)

Stapedius
- inserts into the neck of the stapes
- reduces oscillatory range of tympanic membrane
- stapedius reflex: protects from loud noises
- innervated by CN VIII (facial)

Question 6

Chorda tympani

Answer 6

Contains gustatory fibers to anterior 2/3 of tongue
Passes through middle ear and has no function
Can be injured in ear infections
Branch of CN VII (facial)

Question 7

Pathway of sound

Answer 7

Sound waves create oscillations
1. external auditory canal
2. tympanic membrane
3. ossicles vibrate, pushing on the oval window of the cochlea, setting the fluid of the cochlea in motion
4. oval window
5. scala vestibuli (in)
6. scala tympani (out)
7. round window

Question 8

Cochlea

Answer 8

The waves generated by the ossicle on the oval window travel into the cochlea through the scala vestibuli to the center, then the wave continues on through the scala tympani.
The cochlear duct is between the scala vestibuli and the scala tympani.
It contains receptors for transducing fluid waves into electrical signal at organ of Corti

Question 9

The generation of an auditory signal

Answer 9

The signal travels from neurons synapsed at the basilar membrane to CN VIII

Question 10

Ascending auditory pathway

Answer 10

The auditory pathway travels along CN VIII to immediately become a bilateral signal which goes to the thalamus, then the auditory cortical areas.
- primary auditory cortex: transverse temporal gyri
- secondary auditory cortex: surround PAC
- higher order cortical areas: multiple areas integrate sound

Question 11

Primary auditory cortex

Answer 11

Receives sound from the thalamus
Sends projection to the other hemisphere
Function: conscious perception of sound and sound localization

Question 12

Secondary auditory cotrex

Answer 12

Surrounds primary auditory cortex, poorly defined
Reciprocal projections fro primary auditory cortex
Interpret sound, including language

Question 13

Higher auditory cortical areas

Answer 13

Two main pathways:
- sound localization: where
- sounds and language: what

Question 14

The sense of balance

Answer 14

Conscious proprioception: muscle spindles, GTO, free nerve endings of joints –> DCML
Unconscious proprioception: same receptors –> cerebellar pathway

Question 15

The vestibular system

Answer 15

The inner ear is embedded in the temporal bone
The bony labyrinth contains the organs of the vestibular system
- semicircular canals
- otolith organs

Question 16

Semicircular canals

Answer 16

Respond to rotational movement and angular acceleration
Anterior: nod yes
Posterior: head to shoulder
Horizontal: shake no
As head moves, the fluid inside the canals moves, pushing on the ampulla of the canal
The hair cells are bent, causing a change in the neuron rate of firing.
- either stimulatory or inhibitory
- allows detection of the direction of movement as the pairs of SSC work together
* right anterior with left posterior
* right horizontal with left horizontal

Question 17

Otolith organs

Answer 17

In the vestibule:
- saccule: detect vertical forces
- utricle: detect horizontal forces
Respond to linear movement

Question 18

Receptors of the otolith organs

Answer 18

Hair cells are embedded in a gelatinous membrane. Movement causes hair cells to bend, depolarizing sensory neurons.
Otoliths sit on top of the membrane, causing the membrane to move in response to gravity.

Question 19

Sensory neurons of the vestibular organs

Answer 19

Travel from each sensory structure to become the vestibular portion of CN VIII.

Question 20

Vestibular nerve

Answer 20

Travels to the brainstem pons/medulla and synapses on the vestibular nuclear complex and travels directly to the cerebellum

Question 21

Vestibular nuclear complex

Answer 21

Afferent projections to the vestibular nuclear complex
1. vestibular nerve
2. cerebellar nuclei
3. contralateral vestibular nucleus
4. spinal cord (spinovestibular fibers)
5. pretectal nuclei (eye movement coordination)

Question 22

Vestibular projections

Answer 22

1. motor nuclei of CN III, IV, VI: extraocular movements and eye reflexes
2. cerebellum: integrates sensory movement and coordinates movement
3. reticular formatioin: reflex motor activity
4. spinal cord: postural adjustments
5. vestibular labyrinth: modulate the afferent signals

Question 23

Brany chair

Answer 23

Rotation test
Expect nystagmus in the direction of spin until stopped, then postrotary nystagmus is in the opposite direction
Lean or fall in same direction as rotation
Vertigo opposite of rotation
Past pointing

Question 24

Caloric testing

Answer 24

Warm or cold water in ear

Question 25

How does the shape of the ear assist in sound localization?

Answer 25

Cartilaginous auricles (pinna) and the external auditory meatus (canal), facilitate the reception of sound waves conducted by the air by funneling them towards the tympanic membrane (eardrum) at the internal extent of the meatus.
○ The contour of the helical-shaped auricle alters the frequency spectrum of sound depending on the position of the listener in reference to the location of the sound source.
○ The tympanic membrane resembles a resilient trampoline that oscillates in response to incoming sound waves.
■ Forms a partition and seals off the external auditory meatus from the middle ear cavity.

Question 26

Functions of the tympanic membrane and ossicles

Answer 26

The middle ear functions in the transmission and transduc­tion of tympanic membrane vibrations to the inner ear (from an air to a fluid medium).
Ossicles are linked in series by synovial joints and are suspended within the tympanic cavity. They conduct oscillations from the tympanic membrane to the membrane of the oval window.

Question 27

The signals from one ear go to which thalamus?

Answer 27

The auditory pathway travels along CN VIII to immediately become a bilateral signal which goes to the thalamus then the auditory cortical areas.

Question 28

Which canals function as a pair?

Answer 28

● The anterior canal of each side is posi­tioned anterolateral to the median plane. It is oriented parallel to the posterior canal, on the contralateral side, which is positioned posterolateral to the median plane and function as a pair.
● Two lateral canals of right and left sides are on same horizontal plane and function as a pair.

Question 29

The signals from the auditory cortex