Brain And Behavior 2011-Vestibular System

Front 1

smooth pursuit

Back 1

voluntary conjugate eye movement; follow slow moving object (30 deg/sec); can't do without moving object

Front 2

optokinetic

Back 2

conjugate eye movement; reflex following movements elicited when large portions of visual field moves slowly (i.e. train); mediated by brainstem

Front 3

VOR

Back 3

conjugate eye movement driven by VIII; stabilizes gaze in spite of head movements or tilt

Front 4

saccades

Back 4

rapid conjugate eye movement designed to move object onto fovea (i.e. reading) - associated with shift in attention

Front 5

vergence

Back 5

disjunctive eye movement; i.e. convergence (both eyes intort); very slow movements of eyes in third dimension (towards objects either beyond or within fixation plane)

Front 6

fixation movements

Back 6

involuntary conjugate eye movements required for vision to ensure that object doesn't stay still on retina (or else it will fade)

Front 7

extraocular innervation

Back 7

trochlear -> contra SO; oculomotor -> ipsi IR, MR, IO and conta SR; abducens -> ipsi LR

Front 8

extraocular motorneurons fire pattern in order to generate saccade

Back 8

large high frequency pulse in order to overcome inertia/viscous resistance (proportional to eye velocity) followed by small step to overcome elastic restoring forces and hold eye in new position (proportional to deviation size)

Front 9

abducens nuclei connections

Back 9

excites contralateral oculomotor nucleus via MLF so that it does the same thing (right LR moves at same rate as left MR when eye moves to right) and inhibits ipsilateral oculomotor nucleus so it does the opposite thing (right MR relaxes so eye can move to right)

Front 10

paramedian pontine reticular formation

Back 10

PPRF near the abducens nucleus; under control from superior colliculus and frontal eye fields that decide on location of next saccade; directly excites abducens nucleus in order to produce pulse so eye will move and also excites integrator which calculates what size step is needed for the given pulse and excites abducens nuclei to produce that step to hold the eye in the new position

Front 11

neural pepositus hypoglossi

Back 11

location of the neural integrator for horizontal eye movements

Front 12

express saccades

Back 12

mediated by superior colliculus; short latency saccades in response to the sudden appearance of a visual or auditory stimulus (orienting reflex, which also may include head movements)

Front 13

voluntary saccade

Back 13

mediated by frontal eye fields

Front 14

vestibular organs

Back 14

otolith organs (utricle and sacculus) report static head position and linear acceleration; semicircular canals report angular acceleration

Front 15

Scarpa's ganglion

Back 15

vestibular portion of VIII has cell bodies in this ganglion

Front 16

semicircular canal action

Back 16

konocilia embedded in cupula (gelatinous mass) which spans the width of the ampula (sensory swelling of the canal) and forms a barrier blocking the circulation of the fluid; when the head turns in the plane of the canal, the inertia of the fluid distorts the cupula in the direction OPPOSITE the head movement (fluid moves away from head movement due to inertia); this bends the cilia and produces increased or decreased firing of VIII

Front 17

otolith organs action

Back 17

cilia protrude thorugh otoconia (gelatinous layer with calcium carbonate crystals suspended); head tilt or linear acceleration cause cilia (oriented in various orientations) to bend -> increased or decreased VIII firing (tonic in the case of head tilt, transient in the case of linear acceleration)

Front 18

linear acceleration

Back 18

detected by otolith organs -> causes transient firing due to crystals bending cilia; not detected by semicircular canal because linear acceleration produces equal forces on both sides of the canal and thus no net signal

Front 19

angular acceleration

Back 19

causes increases in firing on the side TOWARDS which the head is rotating and decreases in firing on the other side

Front 20

VOR driven by

Back 20

VIII only - not vision nor neck proprioceptor

Front 21

VOR angles

Back 21

angle gaze = angle eyes + angle head

Front 22

VOR mechanism

Back 22

head moves left -> L VIII fires more than right VIII -> excites R abducens nuclei via right MLF -> right LR contracts; L VIII also inhibits L abducens nuclei via left MLF -> left LR relaxes; R abducens nuclei, stimulated by L VIII, then excites contra (L) oculomotor nuclei via MLF -> left MR contracts (the opposite happens between the L abducens and the R oculomotor -> inhibitin L abducens ends up inhibiting R oculomotor via MLF) -- this is ALL the slow phase, designed to make the eyes move right

Front 23

physiological nystagmus

Back 23

eyes move R when head moves L (slow phase) followed by fast phase to reset eyes in the opposite direction (L) -> named for the fast phase (i.e. head moves L, slow phase moves R, fast phase moves L -> "left nystagmus")

Front 24

spontaneous nystagmus

Back 24

nystagmus that occurs w/o head movement - us. due to damage to VIII; nystagmus is away from lesion (i.e. fast phase is away)

Front 25

caloric nystagmus

Back 25

COWS - cold water produces nystagmus in opposite direction to the ear side (i.e. cold water in right ear causes left nystagmus), hot water produces nystagmus in the same direction as the ear side

Front 26

vestibulospinal tract

Back 26

from vestibular nerve to medial motorneurons -> maintains posture

Front 27

vestibular cerebellum connections

Back 27

vestibular nerve is the only sensory afferent to project directly to the cerebellum; sends mossy fibers via the ICP to the flooculonodular lobe; Purkinje cells project back to the vestibular nuclei (act as deep cerebellar nuclei for flooculonodular lobe); this system maintains long-term accuracy of VOR (calibration)