Auditory System

Question 1

Structures of outer/ external ear

Answer 1

1 - Pinna /Auricle

2 - external auditory canal - connects outer ear to middle ear

Question 2

Structures of middle ear (tympanic cavity)

Answer 2

Tympanic membrane (eardrum)
Ossicles (3 small bones) - (1) malleus; (2) incus; (3) stapes
Eustachian Tube - equalizes pressure

Question 3

Inner Ear structures

Answer 3

1 - Cochlea - nerves for hearing
2 - Vestibule - receptors for balance
3 - Semicircular canals - receptors for balance

Question 4

The cochlear:

Answer 4

–> Amplifies sound waves & converts them into neural signals
Contains fluid-filled chambers:
1 - Superior chamber - scala vestibuli
2 - Inferior chamber - scala tympani
–> filled with perilymph
3 - Scala media - filled with endolymph (containing the organ of corti)

Question 5

Organ of Corti

Answer 5

Resides on the basilar membrane (base) permeable to perilymph
Sensory epithelium containing hair cells (inner & outer hair cells)

Question 6

Membranes associated with organ of corti

Answer 6

1 - Tectorial membrane (bathed in endolymph): upper parts of hair cells bathed in endolymph with tight junctions that prevent endolymph moving down hair cells
2 - Basilar Membrane (permeable to perilymph): base of hair cells bathed in perilymphs

Question 7

The hair cells

Answer 7

Epithelial cell contain stereocilia with one taller kinocilium
Tip links connect tips of adjacent stereocilia (CAMs)
two types: 1 - Inner hair cells: receive afferents from cranial nerve/vestibular cochlear nerve
2 - outer hair cells - receive efferent innervation

Question 8

Neurophysiology of auditory transduction

Answer 8

1 - Displacement of stereocilia toward kinocilium
2 - tip links stretches & force cation channels open near tips of stereocilia
3 - K+ enters & causes depolarisation
4 - V-gated-Ca channels open - influx of Ca
5 - NT released by hair cells onto afferent nerve

Question 9

Function of organ of corti in hearing

Answer 9

• Sound waves enter ear via auditory canal, vibrates tympanic membrane –> vibrates within ossicles –> transfer of energy to cochlea through oval window
• Waves transfer to perilymph fluid (scala vestibuli & scala tympani) –> basilar membran shifts respective to tectorial membrane
• Shifts move stereocilia & activate/deactivate receptors on hair cells surface –> cation channels open –> K+ influx –> depolarisation –> influx of Ca2+
• NT release (glutamate) onto auditory nerve –> sends info about sound waves to brain

Question 10

Topographical Mapping of Frequency (Tonotopy)

Answer 10

Points responding to high frequencies at the base of basilar membrane: narrower & stiffer
Points responding to low frequencies are at the apex: wider & more flexible