Vestibular System

Question 1

Vestibular Organ

Answer 1

adjacent to Cochlea, consists of two complex structures that provide info for movement, balance

Question 2

Otolith (“Ear Stone”) Organs

Answer 2

Detect changes in head tilt relative to body

• Hair Cell receptors, embedded in gelatinous substance on which sit Calcium Carbonate crystals
• Two chambers (“Vestibular Sacs”)

Question 3

Vestibular Sacs

Answer 3

Saculle, lined with Hair Cells on its walls,

Utricle with Hair Cells on its floor

Question 4

Head tilts…

Answer 4

gravity makes crystals shift against & deform cilia of Hair Cells => alters NT release

Question 5

Semi-Circular Canals

Answer 5

• Detect angular ac/deceleration (e.g from walking, turning)
• Three looped canals
• Hair Cell receptors

Question 6

Three looped canals

Answer 6

• each in a different orthogonal (X, X, Z) plane, filled with viscous, potassium-rich (K+) Endolymph
• When head begins to rotate, fluid in canal lags behind movement; when head stops, fluid overshoots movement

Question 7

Hair Cell receptors

Answer 7

embedded in gelatinous base of each canal; fluid lags & overshoots, deforms cilia => alters NT release

Question 8

deforming Hair Cells results in …

Answer 8

….graded responses to subtle, 3D changes

Returns to Spontaneous rate when static or at constant velocity

Question 9

Bend cilia toward tallest cilia…

Answer 9

….open K+ gates wide, K+ enters => hypo-polarization, increase Spontaneous firing rate

Question 10

bend cilia toward shortest cilia

Answer 10

close K+ gates => hyper-polarization, decrease Spontaneous firing rate

Question 11

Vestibular System only detects change in

Answer 11

velocity/orientation

Question 12

Pathway

Answer 12

Hair Cells => Vestibular Ganglions, whose axons form tract within 8th Cranial Nerve (nerve shared w/Audition)

=> Vestibular Nuclei of Medulla (source of nausea); some directly to Cerebellum (as feedback for acts that require balance)

=> Spinal Cord and many Brain Stem nuclei, including Pons, & Midbrain’s Red Nucleus (Tegmentum) – regulate posture
and to Superior Colliculus to coordinate with vision (help determine which movements on retina from head vs. environment)
and to Cranial Nerves (3,4,6) that control Eye Movement, to compensate for head (e.g. so can keep focus while head moves)
=> ?? Temporal Lobe – higher pathway little known

Question 13

Motion Sickness

Answer 13

When visual and/or motor feedback inconsistent with vestibular info, Medulla connections cause nausea

e. g. In car, see environment stream by, but constant velocity so no vestibular change & no motor feedback
e. g. In outer space, move muscles & see environment change, but no gravity and rare acceleration so no vestibular change
e. g. Spin around, stop – vestibular system still detects change for a while, eyes do not (=>Nystagmus, eyes jump to compensate)