Special senses III: vestibular system

Question 1

vestibular apparatus: features

Answer 1

• inner ear also has structures for self motion -> vestibular labyrinth
• sensory receptors (hair cells) in labyrinth function as acceleration detectors

Question 2

vestibular apparatus: 2 structures for different motions

Answer 2

semicircular canals:
- detect rotational acceleration (turning head, nodding)

otolith organs:
- linear (straight line) acceleration, force of gravity

Question 3

vestibular hair cells: differs from auditory

Answer 3

• possess true cilium (kinocilium) like longer stereocilium
• relative orientation of stereocilia and kinocilium: polarity of hair cells, confers directional sensitivity
  hyperpolarisation

Question 4

vestibular hair cells: - bending stereocilia towards kinocilium causes

Answer 4

• bending stereocilia towards kinocilium causes depolarisation,

Question 5

vestibular hair cells: - bending stereocilia away from kinocilium causes

Answer 5

hyperpolarisation

Question 6

dynamic (kinetic) labyrinth: semicircular canals features

Answer 6

• transduce rotational acceleration
• oriented perpendicular to each other, code acceleration in 3 directions
• sensory end organ (crista ampullaris) located in ampulla at bae of each canal

Question 7

dynamic (kinetic) labyrinth: semicircular canals name canals

Answer 7

• ant
• lateral
• post

Question 8

dynamic (kinetic) labyrinth: semicircular canals- ant

Answer 8

• up down motion

- yes nod

Question 9

dynamic (kinetic) labyrinth: semicircular canals- lateral

Answer 9

• side to side motion

- no shake

Question 10

dynamic (kinetic) labyrinth: semicircular canals- post

Answer 10

• rocking motion

- ear to shoulder

Question 11

crista ampullaris: features

Answer 11

• each have several hair cells
• hair cell’s stereocilia (40-70/ cell) project into membrane bound gelatinous mass= cupula
• hair bundles polarised in same direction- directionality provided by canal shape
• hair cells synapse onto 1˚ vestibular sensory afferents that travel to brain via CN VIII

Question 12

semicircular canals: response to rotational motion

Answer 12

• rotation of head rotates canal
• endolymph lag behind and exerts force on cupula
• pressure on cupula bends stereocilia in opposite direction to head
• bending towards kinocilium - depolarisation of hair cell (MET channels, same as auditory system in cochlea)
• increase NT onto 1˚ afferent neuron -> increased spiking

Question 13

static labyrinth- otolith organs: features

Answer 13

• utricle and saccule are bulges in labyrinth located btw semicircular canals and cochlea
• each have patch of sensory cells= macula

Question 14

static labyrinth- otolith organs: moving head

Answer 14

• hair cell cilia embedded in gelatinous matrix
• matrix have small crystals of Ca carbonated = otoliths
• otoliths add mass
• head moves -> matrix lags behind and bend stereocilia

Question 15

static labyrinth- otolith organs: direction sensitivity

Answer 15

• hair cells in different zones of macula of utricle and saccule are oriented in opp directions:

Question 16

static labyrinth- otolith organs: saccule direction

Answer 16

• kinocilium away from striola

- hair cells detect up and down linear acceleration (going up in lift)

Question 17

static labyrinth- otolith organs: utricle direction

Answer 17

• kinocilium towards striola

- hair cells detect forward and backwards (walking forwards, nodding head)

Question 18

neural pathways for vestibular info:

Answer 18

• vestibular (bipolar) neurons supply all 5 vestibular organs
• afferent fibres project via vestibular n (vestibular branch of CN VIII)
• synapse in vestibular nuclei (brainstem), heavily influenced by flocculonodular lobe of cerebellum

Question 19

functional role of dynamic labyrinth (semicircular canals): VOR

Answer 19

• vestibuloocular reflex (VOR)- fastest reflexes in body
• compensatory movements of eyes, keep visual gaze on target during rotational movements of head, stabilises image on retina (prevents blur)
• doesn’t need visual input
• proprioceptive info (from muscle spindles in deep mm around cervical vertebrae) relayed to cerebellum via spinocerebellar tracts

Question 20

functional role of dynamic labyrinth (semicircular canals): vestibular nuclei receive input from

Answer 20

• flocculonodular lobe of cerebellum

- semicircular canals

Question 21

functional role of dynamic labyrinth (semicircular canals): vestibular nuclei neurons

Answer 21

• project into cranial n inn extraocular mm of eye (CN III, IV, VI)
• mm contract to move eyes in opp direction to head movement
• [caloric test for brain function]

Question 22

functional role of static labyrinth (otolith organs): VSR

Answer 22

• vestibulospinal reflex (VSR) v fast reflex

- controls balance, coordinated head/ neck movements w those of trunk/ limbs (stationary, walking)

Question 23

functional role of static labyrinth (otolith organs): project into

Answer 23

• vestibular nuclei (receive input from cerebellum, visual system, proprioceptors)

Question 24

functional role of static labyrinth (otolith organs): neurons in vestibular nuclei project into

Answer 24

• spinal cord

- via lateral vestibulospinal tract

Question 25

functional role of static labyrinth (otolith organs): features

Answer 25

• increases tone in antigravity (extensor mm) in trunk, limbs on the side which head is tilted
• works in concert w proprioceptors and retina to maintain upright posture, keep head upright

Question 26

functional role of static labyrinth (otolith organs): absence of vision,

Answer 26

• fall likely if either vestibular/ conscious proprioceptive system has been compromised (Romberg’s sign)

Question 27

vestibular cortex: features

Answer 27

• parietoinsular vestibular cortex (PIVC) and adjacent region of sup temporal gyrus
• spatial orientation, conscious awareness of self motion and equilibrium
• more multimodal association area than true unimodal 1˚ sensory cortex
• integrates vestibular, visual, somatosensory (proprioceptive) info
• modulate brainstem vestibular function via descending fibres