24 Lecture Vestibular System

Question 1

What part(s) of the vestibular system sense angular acceleration (rotation) v. linear acceleration and gravity?

Answer 1

semicircular canals sense head angular acceleration where as otoliths sense linear acceleration and gravity

Question 2

Where are 3 places the vestibular system sends afferent signals to?

Answer 2

cerebral cortex (movement sensation), 3 reflex paths that act in reflexive movements, and the cerebellum to feed back and modify reflexes

Question 3

Describe the three reflex pathways that the vestibular system contributes to.

Answer 3

input to oculomotor systems for gaze stabilization (eye movement), input to control head stabilization during head movements (vestibulocollic or vestibulcervical) as well as input to control body stabilization during movement and limb movement (vestibulospinal)

Question 4

How do the visual and vestibular system work together?

Answer 4

the visual system complements /aids the vestibular system, therefore visuo-vestibular conflict causes acute discomfort

Question 5

Name the three semicircular canals.

Answer 5

Anterior vertical, horizontal and posterior vertical canal

Question 6

Where are hair cells located within the semicircular canals?

Answer 6

in the ampulla (bulge of canal at its base)

Question 7

Branches of what artery supply the vestibular organ?

Answer 7

basilar a. branches to the AICA which gives off the internal auditory a.

Question 8

What is the sensory mechanism for the utricle and saccule (otoliths)?

Answer 8

hair cells (in an area called the macula) sit in a thick gelatin and atop that gelatin sits otoconia which are sensitive to changes in gravity due to their weight, causing the bending of hair cells

Question 9

How is the sensory macula in the saccule and utricle oriented?

Answer 9

saccule (vertically) and utricle (horizontally) hair cells are oriented in many directions and switch direction in certain places (remember the direction of kinocilium denote the direction in which they are excited)

Question 10

Describe the sensory portion of the semicircular canals

Answer 10

inside each ampulla is a sensory epithelium (crista) where the hair cells sit inside a gelatinous mass (cupola) and hair cells are excited by the movement of fluid in the semicircular canals

Question 11

How do corresponding semicircular canals bilaterally compare?

Answer 11

in the opposite ear, the horizontal canal is the mirror image, so the opposite response is occurring ( ie. excitation vs. inhibition)

Question 12

Where does output via the vestibular nerve head?

Answer 12

vestibular nerve sends fibers to several sub nuclei span the pons/medulla border and also some that project directly to the cerebellum BONUS: nuclei have strong connections across the midline

Question 13

What are the major vestibular nuclei projections? (4)

Answer 13

1. cerebellum and contra vestibular n. 2. cerebral cortex via the thalamus 3. extra ocular muscles via CN. nuclei 4. spinal cord via the vestibulospinal paths

Question 14

What areas are thought to be stimulated by the vestibulocortical tracts? (4)

Answer 14

primarily the parietal operculum (little lid) and also the temporal operculum, the primary somatosensory and the insula

Question 15

Name the 3 major vestibular reflexes

Answer 15

vestibule-ocular, vestibule-cervical and vestibular-spinal

Question 16

What information is contained in the lateral vestibulospinal tract? (vestibulospinal)

Answer 16

otolith signal that project to the cervical, thoracic and lumbar segment, entirely ipsilateral, acts primarily in the (ortoliths, vestibular nerve, vestibular nuclei, ipsi ventral funiculus, LMN to proximal mucles, body position)

Question 17

What information is contained in the medial vestibulospinal tract (vestibulo-collic)

Answer 17

semicircular signal that projects to the vestibular nucleus, and on to cervical segments via the medial longitudinal fascicules

Question 18

Which semicircular canals are in the same plane and therefore work together in feedback for reflexes?

Answer 18

both horizontal canals
left anterior and right posterior
(vertical plane 45 anteriorly tilted to the left)
right anterior and left posterior
(vertical plane skewed 45 anteriorly to the right)

Question 19

Each pair of semicircular canals in a given plane use/turn on the extra ocular muscles that move the eyes in the ____ plane (same/opposite)

Answer 19

semicircular canals int eh same use the extra ocular muscle that move the eyes int hat same plane

Question 20

How is the vestibular system connected to the frontal eye fields?

Answer 20

semicircular hair cells send a signal via the vestibular nerve and nuclei that synapse on the abducens nuclei/PPRF to coordinate with eye movements

Question 21

What movement causes opt kinetic nystagums.

Answer 21

when you move your head so quickly that the object your eye is focused on leaves the frontal field, then the eye snaps quickly back to center of field to find something to focus on, do this rapidly and repeatedly and you’ll get nystagumus

Question 22

If you are rotating to the right, what directly will your nystagmus travel?

Answer 22

the left (opposite direction)

Question 23

How do you artificially activate OKN?

Answer 23

by perfusing warm/ old water into the ear (COWS- cold will cause nystagmus to opposite side, warm will cause nystagmus to same side) NOTE that the temperature of the water will cause a current in the horizontal semicircular canals and produce the sensation of spinning

Question 24

What is the practical use of OKN?

Answer 24

test the integrity of a conscious patients vestibular system by comparing the amplitude of the 2 sids or to test the brainstem/ cortex integrity of the unconscious patient (no fast movement is a cortical problem, abnormal slow movement is a brainstem problem)

Question 25

What is benign paroxysmal vertigo?

Answer 25

the otoconia fall of the trickles otolitic membrane and get into the semicircular canals causing those hair cells in the cupola to be sensitive to gravity- causes vertigo; can be treated with an Epley maneuver to relodge the otoconia to lodge in the utricle again.