The Vestibular System

An introductory lecture on the anatomy and physiology of the vestibular system.

1. The Vestibular System
Csilla Egri, KIN 306 Spring 2012
Will Ferrell and Jon Heder are challenging their vestibular
systems

2. Outline
Vestibular system
Function
Structure
Semicircular canals
Sensory transduction
Otolith organs
Vestibular pathways
Vestibular reflexes
2

3. Vestibular System: Function
3
Detects angular and linear acceleration
Important in maintaining balance, posture, and
vision
Connections with brainstem, cerebellum, and
somatic sensory cortices to provide info about
the motions & position of the head & body

4. Vestibular System: Structure
4

5. Vestibular System: Structure
5
utricle
saccule
Otolith
organs

6. Semicircular canals: structure
6
each semicircular canal
contains an ampulla
Contains hair cells
embedded in
sensory epithelium
called crista
ampullaris
Cilia of hair cells
project into
gelatinous cap called
cupula
Enlargement of
ampulla
Crista ampullaris
Semicircular
canals

7. Semicircular canals:
function
7
Specialized for responding to
rotational acceleration of the head
Head rotation results in intertial
movement of endolymph in
opposite direction
Bends cupula which bends hair
cells
Same mechanical/electrical
coupling as in auditory hair
cells
Excites/suppresses release of
NTs from hair cells depending on
direction of movement
B&B Figure 13-18

8. Semicircular canals: sensory
transduction
8
B&L Figure 8-26
Steriocilia maintain directionality on both sides of the head
Bending towards kinocilium  opens mechanically gated cation
channels  K
+
influx  depolarization
Bending away from kinocilium  closes channels that are open
during resting state  hyperpolarization

9. Semicircular canals: sensory
transduction
9
Kandel Figure 40-7
Paired canals work
together to signal head
movement
With turning of the
head, hair cells on
one side of the body
send excitatory
signals to the brain
while hair cells on the
opposite side are
inhibited

10. Otolith Organs: Structure
10
Two otolith organs; utricle and
saccule
Each contains a sensory
epithleium called the
macula
Horizontally oriented in
utricle
Vertically oriented in
saccule
cilia of hair cells embedded in
gelatinous otolithic membrane
Embedded on surface are
calcium carbonate crystals
called the otoliths
otoliths

11. Otolith Organs: Function
11
Specialized to respond to gravity and linear acceleration
Otoliths have a higher density than endolymph
Shift when angle of head changes
Causes otolithic membrane to shift in same direction
Cilia of certain hair cells deflected
Excites/suppresses release of NTs from hair cells
depending on orientation of cilia

12. Otolith Organs: Function
12
kinocilia of each hair cell are oriented in
different directions in relation to striola
Utricle: towards striola
Saccule: away from striola
striola

13. Otolith Organs: Function
13
Same sensory
transduction as
semicircular canals
Bending of cilia towards
kinocilium depolarizes
the hair cell
Kandel Figure 40-3
otoliths
Is this a picture of a
macula from the utricle
or saccule?

14. Vestibular Pathways
14
vestibular afferents synapse on vestibular nuclei located in medulla & pons
Nuclei integrate information from vestibular, visual, and somatic receptors and send
collaterals to
1.cerebellum
Sends corrective adjustments to motor cortex: maintenance of balance and posture

15. Vestibular Pathways
15
2.nuclei of cranial nerves
Control coupled movements of the eyes, maintain focus and visual field
3.nuclei of accessory nerves
Control head movement and assist with equilibrium

16. Vestibular Pathways
16
4.ventral posterior nucleus of thalamus and vestibular area in cerebral cortex
(part of primary somatosensory cortex)
Conscious awareness of the position and movement of head
Areas 1,2,3

17. Vestibular Reflexes
17
Vestibulospinal Reflexes
Senses falling/tipping
contracts limb muscles for postural support
Vestibulocollic Reflexes
acts on the neck musculature to stabilize the head if
body moves
Vestibulo-ocular Reflexes
stabilizes visual image during head movement
causes eyes to move simultaneously in the opposite
direction and in equal magnitude to head movement

18. Vestibulo-Ocular Reflex (VOR)
18
Example: head movement to the
LEFT
1.inertia of endolymph movement to the
right in horizontal vestibular canals
causes:

a
’d firing of left vestibular
afferent

b
’d firing of right vestibular
afferent
2.Excitatory connections with
contralateral abducens nuclei and
inhibitory connections to ispilateral side
3.Excitatory connection to inhibitory
interneuron in contralateral vestibular
nuclei
4.Movement of the eyes to the right
abducens nuclei
occulomotor nuclei
vestibular nuclei
B&L Figure 9-
27

19. Objectives
After this lecture you should be able to:
Relate the anatomical organization of the semicircular
canals and otolith organs to sensation of
movement/acceleration
Describe the mechanism of sensory transduction in these
structures
Outline the vestibular pathways and projections to
various brain regions
Describe the pathway of the horizontal vestibulocular reflex
19

20. 20
1.What specific part of the vestibular system would
sense
1.Movement in an elevator
2.Abrupt stop of a moving vehicle
3.Shaking your head side to side
2.In the utricle, if hair cells bend away from the striola,
will this cause depolarization or hyperpolarization of
the receptor?
3.Based on what you know about the vestibular system,
if you spin around for 5-10 seconds, why do you feel
dizzy even after you stop?
Test your knowledge