Vestibular Anatomy

Question 1

what are the roles of the vestibular system?

Answer 1

1. estimate body position and movement
2. postural control
3. control of eye movements
4. autonomic function and consciousness
5. project info throughout cortex, brainstem and cerebellum

Question 2

define pitch

Answer 2

rotation around y-axis

nodding yes

Question 3

define yaw

Answer 3

rotation around the z-axis

shaking head no

Question 4

define roll

Answer 4

rotation around the x-axis

tilting head side to side

Question 5

what structures are included in the central vestibular system?

Answer 5

1. vestibular nuclei (4)
2. vestibular tracts (6)
3. vestibulocerebellum
4. vetibular cortex

Question 6

what structures are included in the peripheral vestibular system?

Answer 6

1. vestibular apparatus
   
   1. bony labyrinth
   2. otolith organs
   3. semi-circular canals
2. CN 8 - vestibular branch

Question 7

what are the primary functions of the peripheral vestibular system?

Answer 7

1. stabilize visual images on fovea of the retina during head movement allowing for clear vision
2. maintain postural stability (especially during movement of head)
3. provide info for spatial orientation

Question 8

the peripheral vestibular system is mainly responsible for ______________

Answer 8

relaying info (velocity and acceleration of the head)

Question 9

what is included in the vestibular apparatus?

Answer 9

1. bony labyrinth
2. membranous labyrinth

Question 10

what structures make up the membranous labyrinth?

Answer 10

1. Vestibule
   
   • Otolith organs (utricle and saccule)
2. Semicircular canals
   
   • anterior canal
   • posterior canal
   • horizontal canal
3. Cochlea

Question 11

what is the role of the otolith organs?

Answer 11

linear acceleration/deceleration

static head position

Question 12

what is the role of the utricle and saccule?

Answer 12

1. Utricle → detects movement in the horizontal plane
2. Saccule → detects movement in the verticle plane

Question 13

what are stereocilia?

Answer 13

• gravity-dependent motion sensitivity
• hair cells encased in gelatinous layer (macula)
• layered on top: Otoconia
  
  • calcium carbonate crystals
  • heavier than structures it overlays

Question 14

describe how stereocilia work

Answer 14

• Motion receptors → transduce minute displacements into behaviorally relevant potentials
  
  • movement of stereocilia towards kinocilium = excitatory
  • movement of stereocilia away from kinocilium = inhibitory

Question 15

how do the semicircular canals function?

Answer 15

they are encased in the bony labyrinth and filled with endolymph

• head rotation → movement of endolymph in corresponding canal → movement of hair cells → depolarization/hyperpolorization

Question 16

what are ampulla?

Answer 16

bulbous formation at the start or finish of each canal

contains cupula, which houses stereocillia

which are sensitive to angular movements only

Question 17

hair cell displacement towards the utricle is called _______

Answer 17

utriculopedal cupular displacement

Question 18

hair cell displacement away from the utricle is called _________

Answer 18

utriculofugal cupular displacement

Question 19

utriculopedal cupular displacement is excitatory/inhibitory for what?

Answer 19

1. Excitatory → horizontal canall
2. Inhibitory → anterior/posterior canal

Question 20

utriculofugal cupular displacement is excitatory/inhibitory for what?

Answer 20

1. excitatory → anterior/posterior canal
2. inhibitory → horizontal canal

Question 21

list and briefly describe the vestibular reflexes

Answer 21

1. Vestibulo-Ocular Reflex (VOR)
   
   • stable vision during head motion
2. Vestibulo-Spinal Reflex (VSR)
   
   • stable body during head motion
3. Vestibulo-Collic Reflex (VCR)
   
   • stable neck during head motion

Question 22

Describe VOR connections to ocular nuclei

Answer 22

labyrinth → vestibular nuclei → ascending tracts (cross at MLF) → ocular motor nuclei (III, IV, VI)

excite/inhibit the agonist/antagonist muscles needed to move the eyes in the desired direction

Question 23

describe what occurs within the horizontal canals when turning the head to the left

Answer 23

• left horizontal semicircular canal → the endolymph is pushed towards the utricle → utriculocupular displacement = excites horizontal canal
• right horizontal semicircular canal → the endolymph is displaced away from utricle → utriculofugal displacement = inhibits horizontal canal

Question 24

what is the purpose of the VSR?

Answer 24

generation of compensatory body movements to maintain head and postural stability

Question 25

list the steps involved in the VSR

Answer 25

1. head tilts to side 2. ipsilateral SCC/otoliths excitation 3. increased input from vestibular nerve → vestibular nuclei ipsilaterally 4. MVST/LVST descending drive to truncal muscles 5. increased truncal extension ipsilaterally and increased truncal flexion contralaterally

Question 26

what is the purpose of the VCR?

Answer 26

similar to VSR only works on the cervical musculature it counters a movement sensed by our labyrinth otolithic or SCC and modulates neck movements accordingly to help with postural stability

Question 27

list the cervical reflexes

Answer 27

1. Cervico-ocular reflex (COR) 2. Cervicospinal reflex (CSR) 3. Cervicocollic reflex (CCR)

Question 28

describe the COR

Answer 28

* interacts closely with VOR * can supplement VOR under certain circumstances * eye movements driven by neck proprioceptors

Question 29

describe the CSR

Answer 29

* changes in limb position driven by neck afferent activity * can supplement VSR under certain circumstances

Question 30

describe the CCR

Answer 30

* helps stabilize head on body * afferent input caused by changes in neck position (stretch) → contralateral reflexive contraction of appropriate neck muscles

Question 31

what structures are involved in the central vestibular system?

Answer 31

1. Vestibular nuclei * Lateral/Medial nucleus * Superior/Inferior nucleus 2. Vestibular tracts * Medial/Lateral vestibulospinal * vestibulocerebellar 3. Vestibulocerebellum 4. Vestibular Cortex

Question 32

what are the functions/relay points of the vestibular nuclei?

Answer 32

1. eye movement control for gaze stability during movment (oculomotor) 2. postural control and movement (brainstem) * aid in maintaining tone 3. spatial orientation (cortex) 4. autonomic nervous system control

Question 33

describe the lateral vestibulospinal tract

Answer 33

travels to the thoracic spinal cord to extensor muscles * head and body position in space * walking upright * righting and equilibrium reactions

Question 34

describe the medial vestibulospinal tract

Answer 34

travels bilaterally to the MLF to the cervical cord to extensor muscles * head movements * integrating head and eye movements

Question 35

what is the role of the vestibulocerebellum?

Answer 35

responsible for postural and gaze stabilization * modulating VOR * VOR suppression/cancellation * VSR suppression/cancellation

Question 36

how is the thalamus involved in vestibular function?

Answer 36

1. VPL of thalamus connects subcortical structures to the vestibular cortex * connection w/vestibular cortex and reticular formation for arousal and conscious awareness of body 2. specific vestibular info processed in VPL

Question 37

what specific vestibular info is processed in the VPL?

Answer 37

1. discrimination between self movement vs. that of environment 2. spatial awareness and perceived vertical 3. "personal space"

Question 38

List cortical regions involved in the Vestibular Cortex

Answer 38

1. PIVC (parieto-insular vestibular cortex) * junction between parietal and insular lobe * thalamus connects it to cerebellum and vestibular nuclei 2. Medial superior temporal region * visuo-vestibular integration * self-motion perception 3. Ventral Intraparietal region * multisensory spatial coding * proprioception, auditory, visual, tactile, vestibular

Question 39

How is the vestibular system involved in autonomic function?

Answer 39

it has many projections throughout the brainstem to the reticular formation and other regions involved in autonomic function