Vestibular Anatomy & Physiology

Question 1

Overall size of the vestibule-cochlear apparatus

Answer 1

3x5 mm

Question 2

Endolymph resides in the bony or membranous labyrinth

Answer 2

Membranous

Question 3

Purpose of vestibular system

Answer 3

• Equilibrium, sense of balance
• Sense motion and position of head and body
• Maintains head upright on body
  -Helps maintain balance and influences how we perceive space (fires at resting tonic rate)
• Postural reflexes
• Influences eye movements

Question 4

How many sets of organs in the vestibular system detect motion

Answer 4

Two (angular and linear acceleration)

Question 5

Semicircular canals detect

Answer 5

Angular acceleration ie. shaking or nodding head

Question 6

Utricle and Saccule (otolith organs) detect

Answer 6

Linear acceleration (motion along a line ie. elevator dropping)

Question 7

Utricle detects

Answer 7

Horizontal-plane motion ie. Side to side motions, forward/backward, car movement and tipping of the head

Question 8

Saccule detects

Answer 8

Vertical-plane motion ie. Up and down, elevator

Question 9

How many utricle and saccule in each ear

Answer 9

One

Question 10

Macula

Answer 10

The sensor of the utricle and saccule, hair cells attached here

Question 11

Embedded in the gelatin substance of calcium carbonate crystals and provide inertia

Answer 11

Otoconia

Question 12

Vestibular hair cells contain…

Answer 12

One kinocilium and many stereocilia

Question 13

What happens when stereocilia are bent toward the kinocilium

Answer 13

Hair cell depolarizes (triggers excitatory stimulus)

Question 14

What happens when stereocilia are bent away from the kinocilium

Answer 14

Hair cell hyperpolarizes (triggers an inhibitory stimulus)

Question 15

How many semicircular canals are on each side

Answer 15

3 - anterior, posterior, horizontal; arranged in perpendicular planes (x, y, and z)

Question 16

How complimentary pairs work with semicircular canals

Answer 16

One ear will signal the motion by increasing the firing rate of its nerve the complementary canal of contralateral ear will signal same movements by decreasing its firing rate
- Ie. The left AC and right PC form a pair

Question 17

Ampulla

Answer 17

Small swelling at the base of the semicircular canal - houses sensory receptors

Question 18

Crista

Answer 18

Elevated ridge of tissue inside ampulla. Akin to the macular
- Where cilia (hair cells) emerge from

Question 19

Cupula

Answer 19

Gelatinous mass in which hair cells (cilia) are embedded
- Connected to the roof of the ampulla
-Hair cells are covered by

Question 20

The transition from PNS to CNS for vestibular info occurs where

Answer 20

As CN VIII enters the brainstem and terminates in the 4 vestibular nuclei; superior, inferior, lateral, and medial

Question 21

Distal processes of Scarpa’s ganglion aka vestibular ganglion innervate what

Answer 21

Hair cells

Question 22

Proximal processes of Scarpa’s ganglion aka vestibular ganglion form what

Answer 22

CN VIII or vestibulocochlear nerve

Question 23

Where may afferent fibers also terminate if they bypass the brainstem (and thus the vestibular nuclei)

Answer 23

Directly in the cerebellum on the flocculonodular lobe

Question 24

Where is the vestibular nuclei complex housed

Answer 24

Lateral part of the brainstem just below the floor of the 4th ventricle

Question 25

The possible vestibular nuclei connections

Answer 25

- Vestibulo-ocular reflex - Peripheral vestibular organs - Cervical proprioceptors (head movements) - MVST & LVST (vestibulospinal reflexes) - Cerebellum (compensation) - Autonomic nervous system (nausea) - Thalamus -> cerebral cortex (perception)

Question 26

Lateral vestibulospinal tract arises from

Answer 26

The lateral vestibular nuclei

Question 27

Medial vestibulospinal tract arises from

Answer 27

The medial vestibular nuclei

Question 28

Lateral vestibulospinal tract acts to

Answer 28

Maintain posture and activate extensor muscles via descending pathway

Question 29

Medial vestibulospinal tract has effect on

Answer 29

Reflexive head/neck control (vestibulocolic reflex) via descending pathway *only effects head/neck function)

Question 30

Input to cerebellum from vestibular nuclei give info about

Answer 30

Head movement

Question 31

Output from cerebellum to the LATERAL vestibular nucleus gives info about

Answer 31

- Muscle tone regulation and coordination -> vestibulospinal tract to body - Adjust/coordinate eye movements

Question 32

Effects of reticular formation connection with vestibular nuclei complex

Answer 32

- Locomotion - Postural control - Integration of signals that trigger nausea/vomiting

Question 33

Vestibular nuclei connect to cranial nerves III, IV, VI by way of

Answer 33

The medial longitudinal fasciculus

Question 34

The vestibular nuclei involved with oculomotor nuclei

Answer 34

Lateral, medial, and superior nuclei

Question 35

Vestibular-ocular reflex

Answer 35

Conjugate eye movement in response to vestibular stimulation, faster than visual tracking

Question 36

Effects of cortex connection to vestibular nuclei

Answer 36

Perception of body orientation in extra personal space via thalamocortical pathways (posterior parietal)

Question 37

Gaze stabilization

Answer 37

Maintains visual fixation while the head moves - Head turns, walking, jogging

Question 38

What happens in the eye muscles a right head turn

Answer 38

- Right horizontal semicircular canal (+) Activates L lateral rectus & R medial rectus -Left horizontal semicircular canal (-) Inhibits L medial rectus & R lateral rectus

Question 39

VOR gain

Answer 39

Ratio of eye movement to head movement Ideal = 1