Vestibular function

Question 1

what is the function of the utricle and saccule?

Answer 1

1. measure linear acceleration 2. utricle - oriented horizontal to ground when head is upright - maximal response to head tilt when head is in upright position 3. saccule - oriented vertical to ground when head is upright

Question 2

what is the function of the semicircular canals?

Answer 2

measure angular acceleration

Question 3

what is the function of the vestibular hair cell?

Answer 3

1. sensory receptor 2. if stereocilia are bent toward kinocilium then cell depolarizes and releases additional NT 3. if stereocilia are bent away from kinocilium then cell hyperpolarizes and decreases NT release

Question 4

what is the function of endolymph?

Answer 4

located in the vestibular divison of the membranous labyrinth - pushes against cupula to bend stereocilia of hair cells

Question 5

why would a patient show post-rotatory nystagmus?

Answer 5

inertia of endolymph causes signals from semicircular canals to make person feel that they are turning in opposite direction from original movement

Question 6

what is “slow phase of vestibular nystagmus”?

Answer 6

compensates for rotation - opposite of rotation

Question 7

what is “fast phase of vestibular nystagmus”?

Answer 7

movement of eyes back to midline - same side as rotation

Question 8

what are the directions for nystagmus during turning? after rotation?

Answer 8

opposite - to allow for fixation

Question 9

what is the probable cause of positional vertigo?

Answer 9

when part of an otoconium becomes detached from the otoconial membrane of the utricle then lodged in or near an ampulla (usually of posterior canal)

Question 10

what is the probably cause of Meniere syndrome?

Answer 10

imbalance between production and reabsorption of endolymph

Question 11

what are the symptoms associated with Meniere syndrome?

Answer 11

1. sensation of ear fullness and pressure with transient decreased sensorineural hearing loss and tinnitus 2. vertigo, nausea, vomiting

Question 12

what are the main inputs to the vestibular nuclei?

Answer 12

1. primary vestibular afferents 2. neck proprioceptors

Question 13

what are the main outputs of the vestibular nuclei? what are their functions?

Answer 13

1. medial longitudinal fasciculus to motor nuclei of extraocular muscles - VOR 2. lateral vestibulospinal tract - maintenance of balance and posture 3. medial vestibulospinal tract - neck and head position 4. higher centers via thalamus to cerebral cortex - conscious awareness of orientation and motion

Question 14

what are the three major roles of the vestibular system? what sensory systems help the vestibular system fulfill these roles?

Answer 14

1. subjective awareness of body position and movement in space 2. postural tone and equilibrium 3. stabilization of eyes in space during head movements 4. visual and proprioceptive systems

Question 15

what is the doll’s eye maneuver? what is being tested?

Answer 15

1. checking for slow phase nystagmus 2. evaluates brainstem function in an unconscious patient

Question 16

how do the eyes move if cold water is put in the ear canal? warm water?

Answer 16

1. cold - slow phase toward irrigated ear, fast phase away from irrigated ear 2. fast - slow phase away from irrigated ear, fast phase toward irrigated ear COWS (for fast phase) - cold opposite, warm same

Question 17

what kind of eye movement would you see in a comatose patient?

Answer 17

slow phase but NO fast phase