vestibular physiology Flashcards
List two functions of the vestibular system.
detect the stationary position of the head relative to gravity
detect linear and angular acceperation
List the types of accelerations that hair cells in the utricle, saccule, and
semicircular ducts, respectively, detect.
utricle detects horizontal linear acceleration and relation to gravity
saccule detects vertical linear acceleration and relation to gravity
semicircular ducts detect rotational acceleration
Explain how hair cells in the utricle and saccule detect linear accelerations
movement towards kinocilium (big cilium) is depolarization, away is hyperpolarization, cause change from basla firing rate (which is 100 Hz)
the macule is the bed of hair cells in these recpetors, and the otolithic membrane is a gelatinous membrane with otolinths embedded in it
otolinths are calcium carbonate, make otolithic membrane dense, cause acceleration to pull hair cells
Describe how artificial linear accelerations may produce a false sense of
spatial orientation
the mechanism of artificial linear acceleratin produces exactly the same type of forces on the utricle and saccule as head tilt
Explain how hair cells in the semicircular ducts detect angular acceleration and
why they do not normally detect linear accelerations.
three canals in orthogonal planes, the anterior and posterior canals are diverted 45 degress out from lateral so that anterior of one side works with posterior of contralateral side
angular acceleration causes endolymph to push the cupula and thus excite or inhibit hair firing
# Define the term nystagmus and explain the convention for naming the direction of nystagmus.
nystagmus is the process of smooth tracking movements followed by saccadic (rapid) movements back to midline once smooth tracking reaches lateral limit
nystagmus is in direction of saccadic movement
rotate patient one way, they become accustomed to angular momentum, rapid stop causes angular acceleration, smooth movement is in the opposite rotational direction of the sudden stop, nystagmus in the direction of sudden rotational acceleration, feels like world is spinning to opposite side of nystagmus
Describe the signal sent to the central nervous system by the vestibular nerve
and its interpretation:
a. under normal physiological conditions (short duration angular
accelerations).
b. during sustained, constant, angular acceleration (duration > ~30 sec).
c. During sustained, constant, angular velocity (duration > ~30 sec).
Describe the vestibulo-ocular reflex.
it subconsciously allows for the eyes to correct for rotational and horizontal movement
vestibular nerve synapses in vestibular nuclei which project to extraocular nuclei via medial longitudinal fasciculus
Describe a subject’s nystagmus and perception of motion as he/she is rotated
in a Barany chair from a complete stop, to constant angular velocity and then
brought to a complete stop.
initial nystagmus is to the direction of chair rotation with patient percieving their rotation to the direction of chair rotation (patient’s percieved rotation is always in direction of nystagmus)
during middle phase there’s no percieved motion
during stop nystagmus is to opposite to the direction they were just rotating in
Draw a schematic showing the inputs and outputs of the vestibular nuclei and
explain the functions associated with each efferent connection.
input is the vestibular nerve
output is to abducens, trochlear, and oculomotor nuclei via medial longitudinal fasciculus
output to lateral vestibulospinal tract for ipsilateral motor execution of balance in lower limbs (righting reflex)
medial vestibulospinal tract projects bilaterally to cervical spinal cord for neck stabilization and extraocular nuclei
vestibulocerebellar tract allows for cancellation of vestibuloocular reflex (by rotating head) and provides sensory info to cerebellum
