Balance

Question 1

what is the vestibular sense

Answer 1

sense of movement, tilt, and rotation

Question 2

what are the vestibular stimuli

Answer 2

1) angular acceleration (head turning)
2) linear acceleration (head tilt with respect to gravity)

Question 3

how does vestibular sense affect behavior

Answer 3

reflexes that maintain balance and posture, visual fixation, orientation in space

Question 4

kinetic labyrinth

Answer 4

*part of the vestibular labyrinth
*contains semicircular canals
*detects angular acceleration and deceleration

Question 5

static labyrinth

Answer 5

*path of the vestibular labyrinth
*utricle and saccule
*detects linear acceleration and gravity

Question 6

endolymphatic sac

Answer 6

a drainage pathway for endolymph into subarachnoid space

Question 7

bony labyrinth of inner ear

Answer 7

a very dense, bony shell containing perilymph, which resembles extracellular fluid in general

Question 8

vestibular labyrinth of inner ear

Answer 8

*comprises the otolith organs (utricle & saccule) and 3 semicircular canals (superior, posterior, and lateral/horizontal)

Question 9

anterior (superior) semicircular canal

Answer 9

located in the sagittal plane

Question 10

lateral (horizontal) semicircular canal

Answer 10

located in the transverse plane

Question 11

posterior (inferior) semicircular canal

Answer 11

located in the frontal plane

Question 12

how are semicircular canals stimulated by angular acceleration

Answer 12

1) all hair cells are located on a crest in the ampulla of each semicircular canal; the hair bundles of cells are oriented or polarized in the same direction
2) the bundles extend into a gelatinous structure called the cupula
3) when the head turns, inertia of fluid resists movement and deforms the hair bundle, displacing the cupula in the OPPOSITE direction
4) turning the head in one direction causes depolarization of the hair cell and hyperpolarization in the other, thereby increasing or decreasing the firing rate of afferent nerve fibers that synapse on the cell
5) the change in firing rate of the afferent nerve fibers is proportional to the angle and degree of acceleration and deceleration

Question 13

ampulla

Answer 13

duct at base of semicircular canal, filled with endolymph

Question 14

cupula

Answer 14

gelatinous mass inside ampulla

Question 15

vestibular hair cells and kinocilium

Answer 15

*rows of stereocilia with a single kinocilia
*pushing kinocilium in one direction OPENS CATION CHANNELS (depolarization)
*neurotransmitter is released and activates primary vestibular afferent fibers

Question 16

flow of endolymph toward kinocilium is ?

Answer 16

excitatory

Question 17

maculae

Answer 17

*within the saccule and utricle, the maculae are the sensory organs of the static labyrinth that detect head position and linear acceleration

Question 18

vestibulocerebellar pathway

Answer 18

*bidirectional (between cerebellum and vestibular nuclei)
*helps with motor planning, movement, balance, etc

Question 19

lateral vestibulospinal tract

Answer 19

*descending
*originates in the lateral vestibular nucleus; axons descend IPSILATERALLY down spinal cord to motor neurons of limbs and trunk to maintain balance

Question 20

lateral vestibulospinal tract - functions

Answer 20

*senses falling/tripping
*contracts leg muscles for postural support
*descending = motor; lateral = limbs

Question 21

medial vestibulospinal tract

Answer 21

*descending
*originates in the medial ventricular nucleus; axons descend bilaterally to the cervical and thoracic spinal card

Question 22

medial vestibulospinal tract - functions

Answer 22

*head and shoulder reflexes
*acts on neck musculature to stabilize the head if the body moves

Question 23

vestibular projections to thalamus and cortex

Answer 23

*ascending
*projects to the ventroposterior (VP) nucleus of the thalamus
*then projects to the cortex
*provides awareness of motion and body position

Question 24

vestibulo-ocular reflexes

Answer 24

*ascending
*originate in vestibular nucleus and travel up the medial longitudinal fasciculus to the nuclei responsible for eye movements (CN III, IV, and VI)

Question 25

vestibulo-ocular reflexes - functions

Answer 25

*eye reflexes
*stabilizes visual image during head movement
*causes eyes to move simultaneously in the opposite direction and in equal magnitude to head movement

Question 26

vestibulo-ocular reflex: step by step

Answer 26

*if you rotate head to left, eyes move to right
*MLF connects abducens nucleus on one side to the oculomotor nucleus on the contralateral side
*if the right eye abducts via CN VI, connections through MLF to left oculomotor nucleus causes left medial rectus to ADDUCT the left eye

Question 27

oculocephalic reflex (doll’s head reflex)

Answer 27

*used in unconscious patients to test brainstem function
*NORMAL/positive (reflex present) = head rotated to R, eyes move to L
*ABNORMAL/negative (reflex absent) = head rotated to R, eyes follow to R
*absence of reflex bilaterally can indicate damage to lower brainstem

Question 28

vertigo

Answer 28

*an illusion of body motion, like spinning or turning, when no real motion occurring
*typically uncontrollable
*usually accompanied by nausea, vomiting, sweating
*onset is usually sudden; could persist for hours to days

Question 29

peripheral vertigo

Answer 29

*commonly associated with a problem in the inner ear
*most common type of vertigo
*many causes: excessive alcohol intake, meningitis, etc
*may also include hearing loss, nystagmus, and gait abnormalities

Question 30

central vertigo

Answer 30

caused by vertebrobasilar stroke or cerebellar stroke

Question 31

nystagmus

Answer 31

*abnormal deviations or beating movements of the eyes
*slow drift of eyes in one direction, followed by fast beat in opposite direction

Question 32

how is the direction of nystagmus defined

Answer 32

direction of FAST BEAT = direction of nystagmus

Question 33

caloric testing for nystagmus

Answer 33

*irrigation of the external ear canal with either cold or warm water to determine nystagmus
*NORMAL (COWS): cold water causes nystagmus to the OPPOSITE side; warm water causes nystagmus to the SAME side [COWS: cold, opposite; warm, same]
*no response can help you determine where the issue is

Question 34

benign paroxysmal positional vertigo (BPPV)

Answer 34

*most common cause of vertigo
*etiology = canalithiasis (displaced otoconia end up in semicircular canals)
*usually lasts seconds to minutes

Question 35

Meniere’s disease

Answer 35

*excess endolymph
*4 major symptoms:
1) periodic episodes of rotary vertigo
2) fluctuating, progressive hearing loss
3) tinnitus
4) a sensation of “fullness” or pressure in the ear
*episodes last for hours

Question 36

labyrinthitis

Answer 36

*infection of the inner ear and labyrinth, usually caused by viral infection
*can lead to nystagmus, tinnitus, hearing loss
*vertigo and dizziness persist even when head remains still
*lasts for several days

Question 37

Dix-Hallpike test

Answer 37

*testing for BPPV
1) patient’s head is first turned 45 degrees
2) patient is laid supine with neck extended below the table
3) after a few seconds, observe vertical and rotatory nystagmus and assess for vertigo

Question 38

romberg test

Answer 38

inability to keep balance with eyes closed indicates either vestibular dysfunction or loss of proprioception (sensory ataxia)