45a - Balance, Dizziness, Vertigo Flashcards
What is the vasovagal reaction?
common fainting.
If patient says room is spinning to the left, which way is the nystagmus?
fast beat of the nystagmus is also to the left and slow is to the right.
If patient says room is spinning to left, which side is the lesion on?
if room is spinning to the left, nystagmus is to the left so slow phase is to the right, meaning right side is lesioned.
What is rotation around the z axis called?
yaw
How many degrees of freedom are there in standard human motion?
- 3 translational and 3 rotational
What structure is responsible for detecting angular movements?
semicircular canals with the ampulla (cupula)
What structure is responsible for detecting translational movement in the horizontal axis?
utricle
What structure is responsible for detecting translational movement in the vertical axis?
sacculus
What are otholiths/otoconia?
crystals of calcium carbonate stuck in the membrane that distort the matrix when linear force movments occur.
Describe the action potential of stereocillia in the vestibule
force can either open or close K+ on the kinocilium by moving them. If gravity opens the channels, K will flow in and depolarize the cell membrane, opening Ca channels, increasing intracellular Ca. Calcium will open Ca-dependent K channels that leak K into the perilymph
What is the midline of the kinocilium called?
striola. This is the midline that the kinocilium of the utricle all face. In the sacculus they face away from it.
What is a major difference between the sacculu/utricle and the cupula inside the ampulla?
the kinocilia of the cupula always point in one direction only, whereas the utricle and saccule have mirror images across the striola (pointing in opposite directions).There are also no otoliths in the hair cells of the semicircular canal.
If you suddenly turn your head to the left, which vestibular canal will be stimulated and which direction should your eyes turn?
left horizontal semicircular canal will be stimulated and right canal will be inhibited. This will mediate a reflex movment of the eyes to the right to maintian visual fixation. AKA vestibulo-ocular reflex (VOR)
What side should you administer cold water irigation to to ease the symptoms of a perosn with left beating nystagmus?
if it’s left beating nystagmus, eyes are slowly moving to right, so lesion is on the right. If you administer cold water to left, the eyes will pull back towards midline and symptoms will abate temporarily
How does ice-water caloric testing differentiate psychogenic coma?
In true coma, there is a disconnect from the brainstem. When you do ice-water caloric testing, eyes will deviate towards irrigated side with no nystagmic corrections. If patient is in psychogenic coma, cortex recognizes mismatch between vestibular info and other sensory input so it directs eys back to midline with a nystagmus.TLDR: if ice water induces nystagmus = psychogenic coma