Lecture 10 The Ear & Hearing

Question 1

Basic structure of outer ear (2)

Answer 1

• Pinna
• Auditory canal

Question 2

Basic structure of middle ear (5)

Answer 2

• Tympanic membrane (ear drum)
• Auditory ossicles: malleus, incus & stapes
• oval window (stapes is connected to/in round window)
• round window
• auditory/Eustachian tube

Question 3

Basic structure of inner ear

Answer 3

• semicircular canals: anterior, posterior, lateral
• bony labyrinth (contains perilymph)
• membranous labyrinth (contains endolymph)
• cochlea
• utricle
• saccule

Question 4

Cross-section through 1 turn of cochlea (6)

Answer 4

1. Vestibular canal = scala vestibuli
2. Cochlear duct = scala media
3. Tympanic canal = scala tympani
4. Perilymph= fluid in vestibular & tympanic canals
5. Endolymph= fluid in cochlear duct (more K+ than perilymph)
6. Organ of corti which rests on basilar membrane in cochlear duct

Question 5

Fibres of the Basilar membrane and location

Answer 5

1. Short Stiff fibres are near the oval window and detect high frequency at the base end
2. Long floppy fibres are near the apex point and resonate with low frequencies

Question 6

Describe structure of organ of corti (3)

Answer 6

• 3 rows of outer hair cells
• 1 row of inner hair cells
• 40-80 stereo cilia on apical surface of each hair cell which project tectorial membrane

Question 7

Describe the steps involved in the conversion of mechanical stimulation to electrical signals (6)

Answer 7

1. Basilar membrane vibration
2. Stereocilia detect movement
3. Depolarisation of hair cell
4. Neurotransmitter released
5. Activation of sensory neurones
6. Messages conveyed to brain via cochlear branch of vestíbulo-cochlear nerve

Question 8

Physiology of balance ?

Answer 8

Vestibular apparatus =
Semicircular ducts/canals
Utricle
Saccule

Question 9

Describe structure of semicircular canals

Answer 9

• bony on the outside
• endolymph filled membrane inside

Question 10

Macula

Answer 10

-Information on head position, acceleration & deceleration

-One in each utricle & saccule

-structure of macula:
Otoliths
Otolithic membrane
Hair bundle
Hair cell
Supporting cell
Vestibular branches of vestibulocochlear nerve

Question 11

Otoliths

Answer 11

Calcium carbonate