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24 Cards in this Set

  • Front
  • Back
vestibular system
primarily a reflex system that maintains the upright anatomical position
maintenance of equilibrium
three principal sources of sensory information:
1. vision
2. somatosensory (including position and touch)
3. vestibular apparatus of the internal ear
*balance can usually be maintained with 2/3 inputs
vertigo
dizziness (sensation of spinning or whirling motion), sometimes accompanied by nausea, vomiting, and pallor, caused by labyrinthine irritation
Meniere's disease
recurrent vertigo with tinnitus (sensation of noises in the ears) and deafness caused by complex pathology leading to degeneration of vestibular and cochlear hair cells
stria vascularis
produces endolymph in the cochlear duct, important for proper function of vestibular and cochlear receptors
macula
sensory epithelium found in the utricle and saccule
vestibular hair cells
sensitive mechanoreceptors located w/in cristae ampullares and maculae.
stereocilia extend from surface of hair cell.
kinocilium=single, eccentrically placed especially long cilium arising from centriole.
deflection of stereocilia toward kinocilium=increased depolarization in hair cell firing
crista ampullaris
stereocilia protrude into gelatinous cupula, sensitive to kinetic (rotary or angular) movement
macula utriculus
sensory hair cells oriented in the horizontal plane (sensitive to linear acceleration or deceleration), stereocilia protrude into otolithic membrane (contains crystals of calcium carbonate=otoliths)
macula sacculus
vertically oriented and sensitive to vertical movement
vestibular (Scarpa's) ganglion
located w/in internal auditory meatus, composed of bipolar neurons
areas of brain contributing to the control of eye movements
retina
cerebral cortex
cerebellum
superior colliculus
Edinger-Westphal nucleus
GVE innervation to ciliary ganglion, which in turn innervates the constrictor pupillae and ciliary muscles of the eye
conjugate deviation
rotation of the eyes equally and simultaneously in the same direction, problem=diplopia
paramedian pontine reticular formation (PPRF)
projects to the ocular nuclei via the MLF, stimulation results in horizontal eye movements
ascending medial longitudinal fasciculus
contains crossed and uncrossed projections originating from abducens, trochlear, and oculomotor nuclei, the PPRF, and vestibular nuclei.
crossed ascending from vestibular nuclei have excitatory effects, uncrossed have inhibitory effects
vestibuloocular reflexes (VOR)
eyes reflexively move in direction opposite of head movement, absence indicates brain stem damage
superior colliculus
receives afferents from retina, inferior colliculus, and cerebral cortex.
tectospinal and tectoreticular tracts...mediate orienting (startle) response, turning of head and eyes and raising of arms to an unexpected visual or auditory stimulus
saccades
voluntary, rapid, ballistic eye movements made to turn eye toward objects in periphery of visual field, controlled by cerebral cortex or superior colliculus
tracking or smooth pursuit movements
"locking" eyes onto a perceived moving object, involves the occipital eye field. movements voluntary, but cannot be done in the absence of visual stimuli
vergence
reflex convergence or divergence of the eyes in order to focus on objects moving toward or away from the viewer, controlled by occipital cortical projections to the superior colliculus
nystagmus
oscillating eye movements, slow and fast component (described in terms of fast component)
lateral gaze paralysis
results from lesion to abducens nucleus=inability to move both eyes to side of lesion because lesion disrupts connections between the abducens and oculomotor nucleus
anterior internuclear ophthalmoplegia
due to MLF lesion rostral to abducens nucleus=inability to move affected eye medially, horizontal nystagmus present in opposite abducting eye, commonly found in MS patients