20.5 Vestibular

Question 1

What are the otoliths?

Answer 1

2 otolith organs (utricle and saccule) → sense linear acceleration and head position

Question 2

What are the semi-circular canals?

Answer 2

3 semi-circular canals (anterior, posterior, horizontal) → sense rotational velocity/ angular acceleration.

Question 3

What is the vestibular system?

Answer 3

A somatosensory portion of the nervous system that provides us with awareness of the spatial position of our head and body (proprioception) and self motion (kinesthesia)

Question 4

Where is the vestibular system found?

Answer 4

deep in the temporal bone

Question 5

Label the semi-circular canals and the otolith organs.

Answer 5

Question 6

What is the name of the terminal end of each semi-circular canal?

Answer 6

Ampulla = opens into the vestibule

Question 7

What are the clusters of hair cells in the utricle and saccule called?

Answer 7

Maculae (sensory epithelium)

Question 8

Which cranial nerve innervates the semicircular canals and otolith organs?

Answer 8

Vestibular portion of the vestibularcochlear nerve (VIII) which originates from a different nuclei in the brain to the cochlear portion. It enters posterior cranial fossa and synapses with vestibular nuclei in the brainstem and cerebellum directly

Question 9

What is the origin of the vesitubulocochlear nerve?

Answer 9

vestibular and cochlear nuclei in the brainstem which merge to form the vestibulocochlear trunk in the posterior cranial fossa in the petrous part of the temporal bone

Question 10

Where does the vestibulocochlear nerve split?

Answer 10

When it reaches the inner ear (special somatic afferent as provides special sensory funciton of hearing and balance)

Question 11

Where is the vestibular area?

Answer 11

Lateral corner of the rhomboid fossa of the brainstem

Question 12

How are the vestibular ganglia formed?

Answer 12

Vestibular ganglia → formed from cell bodies which receive NTs from HCs + project to brainstem vestibular nuclei + cerebellum
4 at junction between pons + medulla:
medial/ lateral
superior/ inferior (aka descending)

Question 13

How many vestibular nuclei are there? Where do they get their inputs?

Answer 13

Four nuclei (medial, lateral, superior and inferior)
Receive inputs from receptors of the utricle, saccule and semi-circular ducts

Question 14

What are the vestibulo-spinal tracts?

Answer 14

*Lateral vestibulospinal tract
*Medial vestibulospinal tract

Question 15

Which nuclei form the lateral column of the vestibular tract?

Answer 15

Inferior, lateral and superior nuclei

Question 16

Describe the lateral vestibulospinal tract

Answer 16

From vestibular nuclei descends to lumbar regions to influence limb extensors involved in balance.
It adjusts the posture of the body and tone of extensors.

Question 17

What is the vestibulospinal reflex mediated by?

Answer 17

lateral vestibulospinal tract

Question 18

What is the vestibulospinal reflex?

Answer 18

Uses vestibular organs and skeletal muscles to maintain balance and posture in an environment with gravity to evoke a response from the muscular system below the neck
ENGAGES EXTENSOR MUSCLES
Inhibition of ispilteral flexors and facilitates contralateral flexors

Question 19

Which nuclei form the medial vestibular tract?

Answer 19

Medial nuclei

Question 20

Describe the medial vestibulospinal tract.

Answer 20

projects bilaterally to cervical spinal cord to mediate the vestibulocollic reflex

Question 21

What is the vestibulocollic reflex?

Answer 21

a neural reflex that activates neck muscles when head motion is sensed by the vestibular organs in the inner ear

Question 22

Where are the second order nuclei in the vestibular system found?

Answer 22

In the vestibular nuclei

Question 23

Where do second order vestibular fibres project?

Answer 23

Oculomotor nuclei
Cerebellum (floculo-nodular lobe)
Reticular formation
Spinal cord to motor nuclei
Thalamus to cortex

Question 24

What is the vestibulo-Ocular Reflex?

Answer 24

Maintaining gaze on fixed object/location during head movement (eye move to counter head movement).

Question 25

Which part of the cerebellum receives inputs from vestibular nuclei and fibres?

Answer 25

Flocculonodular lobe for eye movements and posture

Question 26

What is highlighted?

Answer 26

Vestibular ganglion (ganglion of Scarpa)

Question 27

What does the superior and medial vestibular nuclei receive most their inputs from?

Answer 27

Cristae ampullaes of semi-circular canals

Question 28

Which pathways do vestibular nerves take to enter the cerebellum?

Answer 28

Synapse directly as mossy fibres
Synapse with Vestibular nuclei –> flocculonodular lobe
Synapse with vestibular nuclei –> inferior olivary nucleus –> vermis and flocculonodular lobe
For balance

Question 29

What is vertigo?

Answer 29

Vertigo is a condition in which a person has a false sensation that either him or surroundings are in motion . It can cause nausea, dizziness, sweating and vomiting.

Question 30

What are the causes of vertigo?

Answer 30

-Benign paroxysmal positional vertigo (BPPV) = Pieces of otolithic membrane break off and fall into semicircular canal displacing fluid. Common in elderly.
-Vestibular neuritis (labyrinthitis),
-Meniere’s disease
-VIII nerve damage

Question 31

What is motion sickness?

Answer 31

Motion sickness is a condition characterized by nausea and vomiting due to the travelling, it is most often seen in some people travelling by vehicle.

Question 32

What causes motion sickness?

Answer 32

fluctuations in the maculae (otolith organs for linear acceleration)

Question 33

What is nystagmus?

Answer 33

Alternating slow phase (compensatory) and quick phase (anti-compensatory) eye movements
Vestibular nystagmus is normal when a person is being rotated. It is pathological when the head is still.