Vestibular System

Question 1

Balance

Answer 1

Needs all 3 factors
Vestibular system
Vision
Proprioception

Question 2

Vestibular apparatus

Answer 2

Found in inner ear, petrous part of temporal for protection

Bony labyrinth

• 3 semicircular canals
• vestibule
• cochlea

Membranous labyrinth found in bony

• semicircular duct opens up into utricle and saccule
• surrounded by perilymph (high Na, low K)
• filled with endolymph (low Na, high K
• endolymphatic duct allows fluid circulation
• voltage difference across membranous labyrinth aids with vestibular function

Question 3

Describe the structure of the ampulla in the semicircular ducts
How do the semicircular ducts respond to motion

Answer 3

Gelatinous cupula surrounded by endolymph
Kinocilium embedded in height order in axis of polarity in cupula
All face the same direction
Axons from kinocilium => CN8

Ends of lower stereocilia connected by tip links to taller ones above
At rest, there is a passive movement of ions at RP

If ampulla moved along axis of polarity
-channels at tiplinks stretch => ion influx => depolarisation

If ampulla moved against axis of polarity
-channels at tiplinks compressed => prevent ion influx => hyperpolarisation

When accelerating whilst rotating => increased firing via CN8 afferents on 1 side and decreased on the other

Question 4

Describe the structure of the macula in the utricle

Describe how the utricle responds to motion and positional changes

Answer 4

DETECT STATIC HEAD POSITION and LINEAR ACCELERATION
Stereocilia hairs embeded in otolithic membrane
Otoliths found ontop
Axons from stereocilia form CN8

Saccule - verticle, hair cells point away from striola
Utricle - horizontal, hair cells point towards striola

When head tilted, gravity acts on heavy otoliths move and bends otolithic membrane => bends hair cells
-tilt in any direction depolarises and hyperpolarises some cells => accurate measure of head position

Question 5

Where does CN8 join the brainstem

Answer 5

CN8 joins brainstem at CPA

Ascending/descending tracts from vestibular nuclei to

• extraoculomotor nerves, cervical spinal cord to coordinate head mv with eye mv (vestibuloocular reflex)
• project to lower spinal levels to coordinate extensor and flexors to maintain balance, posture