vestibular system Flashcards
1
Q
define Otoliths
A
- found in utricle and saccule
- Calcium carbonate crystals that are denser than any other tissue and can bend cilia of hair cells RESULTING in organs sensitive to LINEAR ACCELERATION and position of head with respect to gravity
- nerves have relatively steady high firing rate when head is upright and changes in response to head tilt
2
Q
define macula
A
- found mainly on the floor of the utricle
- when head is uprightm macula of the utricle is oriented almost PARALLEL TO THE GROUND
- when head is upright, macula of the SACCULE is VERTICAL TO THE GROUND
3
Q
define semicircular cannals
A
- ROTATIONAL ACCELERATION to head
- anterior (superior), posterior, and horizontal canals are arranged at RIGHT ANGLES to each other
- if the head is bent forward 30 degrees, horizontal cells become parallel to the ground
- BRAIN COMPARES firing rate in nerves coming from right and left ears
- -> anterior canal output on one side is compared to output from the posterior canal from the other ear
- -> respond to angular acceleration by CHANGING FIRING RATE from TONIC FIRING LEVEL (PHASIC) = endolymph stops moving)
4
Q
vestibular hair cells
A
- receptors of the estibular system deteriorate w age
- 40% decrease by 70 years old
5
Q
describe the vestibule-ocular reflexes in response to head tilt or head turns
A
- reflex developed to move eyes in response to small head turns
- eye move opposite to head turn to facilitate fixation on visual target (even if eyes are closed)
- LOSS of the reflex would make fixation difficult or impossible while the head was turning
- VOR sensory input
- -> reflex is driven by vestibular input
- -> reflex occurs even when pts have eyes closed or are in the dark
- -> visual input keeps this reflex accurate. Amount of eye mov’t can be experimentally manipulated
6
Q
post-rotatory nystagmus
A
- vestibular nystagmus that occurs AFTER a person stops turning
- Endolymph (increase K+) has inertia so it continues to move after head stops turning
- signals from semicircular canals make person feel they are turning in OPPOSITE DIRECTION from preceding actual head turn
- Eye movements correspond to ILLUSIONARY turning
7
Q
Define slow phase nystagmus
A
- if turn head to the RIGHT slow phase of nystagmus is to the LEFT
8
Q
Define fast phase nystagmus
A
- moves eye back to the midline, so if turning patient to RIGHT, fast phase is to the RIGHT
- DEPENDENT ON DIFFERENT NEURAL CIRCUIT and DOES NOT OCCUR in COMATOSE PATIENTS
9
Q
What type of nystagmus occurs during turning
A
- SLOW phase in opposite direction of the turn
10
Q
what type of nystagmus occurs after turning
A
- FAST phase back to midline, in the SAME DIRECTION of the turn
11
Q
Describe positional vertigo
A
- BPPV is one of the MOST common types of vertigo
- Benign term used because vertigo not caused by intracranial neoplasm but by free floating particles within the posterior semicircular canal
- BPPV can be severe disabling problem
- ADDITIONALLY patients experiences nystagmus, usually with both torsional and vertical components
12
Q
What is the cause of Meniere syndrome
A
- caused by an imbalance between the production and reabsorption of endolymph
- endolymphatic hydrops leading to rupture of membraneous labyrinth
- contamination of endolymph with sodium ions depolarizes afferent and hair cells can be killed
13
Q
describe the symptoms of Meniere syndrome
A
- include transient attacks (lasting minutes to hours of:
- -> vertigo, Nausea, vomiting, abnormal eye movements, sensorineural hearing loss
- disease has variable course
- some patients have spontaneous recovery
- many patients have permanent damage and become deaf in the affected ear
14
Q
what is the main input into vestibular nuclei
A
- primary vestibular afferents, neck proprioceptors
15
Q
what are the main outputs of vestibular nuclei
A
- main outputs via:
- -> thalamus to cerebral cortex (provide conscious awareness of body orientation and motion)
