Vestibular System - SSA

Question 1

Focal point of the vestibular system

Answer 1

Position of the head

• rotate - angular acceleration, dynamic equilibrium
• move in straight line - linear acceleration, static equilibrium

Question 2

Simplified concept of vestibular system

Answer 2

Stimulus -> vestibular nuclei (cerebellum) -> muscle changes (2 types that either move eyes or maintain posture/balance/equilibrium)

Question 3

2 experiments done in class

Answer 3

1) turn head -> eyes move

2) postular mm. tense up as lean to one side so you don’t fall over (lateral and medial vestibulospinal tracts)

Question 4

Where’s are vestibular receptors located (3)

Answer 4

• bilateral system located in inner ear in petrous temporal bone
• 3 receptor sites in semicircular ducts (bilateral)
• 2 receptor sites in vestibule (bilateral)

Question 5

Bony labyrinth (4)

Answer 5

• filled with perilymph
  a) semicircular canals - 3 pairs on each side
  b) vestibule - where n. fibers attach
  c) cochlea - part of auditory system (don’t care about)

Question 6

Membranous labyrinth (4)

Answer 6

• filled with endolymph
  a) semicircular duct - in semicircular canal, used in dynamic equilibrium (rotary movement)
  b) utricle and saccule - in vestibule, used in static equilibrium
  c) cochlea duct - in cochlear canal

Question 7

Hair cell (receptor)

Answer 7

Kinocilium or stereocilia - modified epithelial cells, each has connection surrounded by vestibular n. cell

Question 8

Receptor units - rotary movement/dynamic equilibrium

Answer 8

Crista ampullaris (cristae ampullares) = ridge of the ampulla
-embedded in the cupula in each ampulla of the semicircular ducts

Question 9

Pathway from endolymph to brainstem/cerebellum

Answer 9

Endolymph bobs cupula -> stimulates hair cell -> stimulates vestibular n. -> dendrites send impulse to brainstem or cerebellum

Question 10

Receptor units - linear acceleration/static equilibrium

Answer 10

Macula (maculae) = blob with hair cells

-embedded in otolithic membrane of each utricle and saccule

Question 11

Vestibular ganglion and fiber cell type (how stimulus detected and transmitted)

Answer 11

Bipolar sensory neurons

Question 12

Primary vestibular fibers

Answer 12

Axons coming from vestibular ganglion going to:

• vestibular nuclei in brainstem
• fastigial nucleus in cerebellum

Question 13

Utriculi and sacculi - which are horiz/vert and what kind of movement do they sense

Answer 13

Utriculi - horiz, sense up and down movement

Sacculi - vertical, sense side to side movement

Question 14

Cerebellomedullary angle

Answer 14

Where CN VIII, cerebrum (ventral), and rostral extent of medulla meet; frequent site for tumor growth -> see vestibular signs

Question 15

Vestibular nuclei and fibers (4 pairs)

Answer 15

• rostral - to extraocular motor nuclei; CN 3, 4, 6; conjugate eye movement
• caudal - to cerebellum
• lateral - forms lateral vestibulospinal tract to regulate muscle tone and balance (extensor tone -> don’t fall over)
• medial - forms medial vestibulospinal tract to regulate muscle tone in cervical muscle and thoracic limb

Question 16

Secondary vestibular fibers

Answer 16

Axons from vestibular nuclei of the brainstem to their targets of distribution

Question 17

Targets of secondary vestibular fibers (3)

Answer 17

• spinal cord
• brainstem
• cerebellum

Question 18

Spinal cord - lateral and medial vestibulospinal tracts (VSTs)

Answer 18

• lateral VST - inc ipsilateral extensor tone, dec contralateral extensor tone
• medial VST - helps to coordinate activity of limb and trunk with movement of head

Question 19

2 targets of secondary vestibular fibers in brainstem

Answer 19

• extraocular nuclei to regulate conjugate eye movement

- vomition center - site of collateral fiber synapse (motion sickness)

Question 20

Vestibulocerebellar tract (target of secondary vestibular fibers in cerebellum)

Answer 20

Tract goes to fastigial nucleus (primary fiber) and flocculonodular lobe (secondary fiber) of cerebellum for balance

Question 21

Medial longitudinal fasciculus

Answer 21

Special tract formed by secondary vestibular fibers from all the vestibular nuclei

Question 22

Ascending branch of medial longitudinal fasciculus

Answer 22

Forms vestibulomesencephalic tract and goes to extraocular LMN nuclei

Question 23

Descending branch of medial longitudinal fasciculus

Answer 23

Contributes to formation of the medialvestibulospinal tract to regulate extensor tone (mainly neck and upper TL)

Question 24

Vestibular dz signs - eyes

Answer 24

Pathologic nystagmus - involuntary oscillation of the eye

Question 25

Vestibular dz signs - posture

Answer 25

Asymmetric ataxia, falls over, circles **characteristic head tilt

Question 26

Vestibular dz signs - changes in extensor tone

Answer 26

Decreased ipsilaterally, increased contralaterally (lesion on same side decreases tone, on opposite side increases tone)