The Vestibular System

Question 1

Vestibular system information is faster/slower than information coming from Golgi tendon organs and muscle spindles.

Answer 1

faster

Question 2

T/F Anti-gravity support by the vestibular system is non-volitional.

Answer 2

True

Question 3

Vestibulospinal system works in conjunction with the _____________ system to stabilize the girdle.

Answer 3

rubrospinal

Question 4

Ocular reflex.

Answer 4

eyes fixate on object that is moving, less effective than vestibulo-ocular reflex

Question 5

Vestibulo-ocular reflex (VOR).

Answer 5

reflexive movement of the eyes stimulated by rotational movements of the head, stabilizes the visual image on the retinas, eyes stay fixated on object even though head is moving

Question 6

Feed-Forward (anticipatory) Mechanisms.

Answer 6

movements made by the body to anticipate danger or change in direction (visual input–>vestibular system–>motor output)

Question 7

Feed-Back (compensatory) Mechanisms.

Answer 7

• Lowers center of gravity, widens base of support, etc to prevent falling over when pushed
• Relies on proprioceptives (joint receptors, GTOs, muscle spindles etc)
• Relatively slow because it takes time to gather the info and relay to and from vestibular system
• pt. with proprioceptive issues will have greater fall risk (elder population, as a result of demyelination)
  (proprioceptive input–>vestibular system–>motor output)

Question 8

What occurs when the head moves to one side and the eyes stay fixated on an object in the other direction?

Answer 8

• info will come from semicircular canals of vestibular system, through vestibular nuclei, to two of the nuclei for extraocular muscles (oculomotor and abducens nucleus)
• medial rectus on one eye and the lateral rectus on the contralateral eye both have to contract

Question 9

Vestibular apparatus semicircular canals.

Answer 9

• Anterior canal in coronal plane
• Posterior in sagittal plane
• Lateral in transverse plane
  Ampulla (hair cells similar to auditory system)
  Utricle
  Saccule
• Utricle and Saccule have specialized detectors called otolithic organs

Question 10

Scarpa’s ganglion.

Answer 10

come from otolithic organs to join up with the cochlear portions to create CN VIII

Question 11

Physiology of the ampulla.

Answer 11

filled with fluid so detects angular acceleration and deceleration, independent of gravity

Question 12

Otolith Organs physiology.

Answer 12

Macula-Saccule and Utricle, detects linear acceleration (macula moves back), detects linear deceleration (macula moves forward), head tilt, gravity dependent

Question 13

Anatomy of ampulla.

Answer 13

• series of air cells located in enlarged mounded area within the ampulla, surrounded by supporting cells
• hairs of hair cells are embedded in gelatinous matrix, aka Cupula
• as fluid moves within the semicircular canals, it causes a deflection of the cupula, causing the hair cells to bend one way or another

Question 14

Hair cell physiology.

Answer 14

• depending on direction of bend of hair cells they are either depolarized or hyperpolarized
• towards kinocilia its increase in firing rate
• away from kinocilia there is a decrease in firing rate (inhibited)
• ampulla are set up so that when one side is being stimulated the other is being suppressed

Question 15

Anatomy of Otolithic Organs.

Answer 15

• series of hair cells surrounded by supporting cells

- hair cells embedded in gelatinous matrix, on top of which are calcium carbonate crystals known as Otoliths

Question 16

Vertigo

Answer 16

caused by calcium carbonate crystals breaking off and floating around in canals, creating the sensation of movement when stationary

Question 17

Explain otolith movement during forward, neutral, and backward head movement.

Answer 17

• Move head forward, otoliths are pulled downward
• Move head to neutral, otoliths are at normal location
• Move head backwards, otoliths are pulled backwards

Question 18

Primary purpose the otoliths serve.

Answer 18

• Otoliths give weight to the macula, which causes the hair cells to bend one way or another

Question 19

Medial vestibulospinal tract.

Answer 19

control of head movement

Question 20

Lateral vestibulospinal tract.

Answer 20

control of trunk movement

Question 21

Are the medial and lateral vestibulospinal tracts ascending or descending.

Answer 21

descending

Question 22

There is a series of connection to the ________ ________ to and from the vestibular nuclei.

Answer 22

cerebellar cortex

Question 23

Vestibular nuclei.

Answer 23

Superior - ipsilateral and contralateral interconnections to oculomotor complex
Medial - contralateral input to the trochlear nucleus for control of superior oblique and to oculomotor complex for inferior rectus, ipsilateral and contralateral connection to abducens nuclei and then to lateral rectus
Lateral - First 3 are directly associated with occulomotor muscles
Inferior