Vestibular System

Question 1

O1: describe the structure of the vestibular apparatus of the inner ear, the receptive organs and hair cells:

Answer 1

1: bony labyrinth = semicircular canals and cochlea, containing membraneous labyrinth. Utricle & saccule in vestibule with utricle attached to semicircular canals. Endolymphatic duct connects vestibule to sac near sigmoid sinus where endolymph is reabsorbed. Cochlear duct connects perilymph and CSF (= spread of infection&raquo_space; deafness). Hair cells: stereocilia in contact with endolymph; each stereo cilia connected by tip filaments. Base of hair cell in contact with perilymph.
Receptive organs: cristae w/in ampulla of semicircular ducts w/ hair cells all oriented in one direction
maculae in saccule and utricle w/hair cells orientated in multiple directions

Question 2

O2: explain how movement is transducer to an electrical signal and the particular sensitivities of the maculae and cristae

Answer 2

2: maculae sense linear acceleration. Have hair cells oriented in all directions so any movement is sensed. Hair cells (in both M & C) extend into gelatinous mass, & transduce movement to electrical signal via stereo cilia. Movement away from large, kinocilia&raquo_space; hyper polarization and closure of K+ channels&raquo_space; decreased neurotransmitter release. Movement toward kinocilia&raquo_space; depolarization via opening of K+ channels. K+ moves from endolymph into hair cell&raquo_space; Opening of Ca+ channels on base and Ca+ influx&raquo_space;RELASE OF NT&raquo_space; ACTION POTENTIAL and opening of K+ channels on base and K+ efflux into perilymph.
Distinction between cristae and maculae: maculae gelatinous mass (cupola) contains otoliths (ca crystals) that make it dense, increases sensitivity to gravity. Cristae cupola is same density as fluid around it. Cristae activated by currents.
Cristae: angular movement via three semicircular canals arranged at right angles to each other.

Question 3

O3: describe the projection of vestibular afferents and the functional roles of central vestibular structures

Answer 3

3: maculae and cristae&raquo_space; action potentials to axons w/cell bodies in Scarpa’s ganglion (vestibular ganglion)&raquo_space; vestibular nerve. central projections > vestibular nuclei, flocculus and nodulus (vestibulocerebellum).

Question 4

O4: discuss the vestibulo-ocular reflex, its regulation and the central connections involved in it

Answer 4

4: vestibular nerves connected to extraocular nuclei via the MLF. Reflex stabilizes eyes/vision during movement.

Question 5

O5: explain the role of the connections of the vestibular system with other areas of the brain

Answer 5

5: vestibular nucleus connected to flocculonodular lobe; spinal cord via tracts for regulating body muscle tone in response to vestibular stimuli (vestibular righting reflex) ;
to reticular formation for autonomic responses like motion sickness;
to thalamus > sensory cortex for perception of movement (responsible for vertigo)

Question 6

Connections between the vestibulocerebellum (floculonodulus) and the vestibular nuclei are important for:

Answer 6

adaptation to changing conditions, adjustments to vestibulo-oculuar reflex.

Question 7

what is nystagmus?

Answer 7

eyes slowly move in response to change in body position, like spinning. They “stay focused on an object while body moves, then jerk back to center. damage to left inner ear or vestibular nerve will cause sensation of spinning to the right