Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
46 Cards in this Set
- Front
- Back
|
What is roll?
|
Rotation around x axis (which goes ventral to dorsal on head)
|
|
|
What is pitch?
|
Rotation around y-axis (which is the left-right axis on head)
|
|
|
What is yaw?
|
Rotation around z-axis, (which is rostral to caudal axis)
|
|
|
Where does the vestibular organ lie?
|
Within petrous portion of temporal bone
Membranous labyrinth within bony labyrinth |
|
|
What 5 structures make up the vestibular organ?
|
3 semicircular canals (horizontal, anterior, posterior)
2 otolith organs (utricle, saccule) |
|
|
How are the structures of the vestibular organ arranged?
|
Semicircular canals at right angles
Otolith organs also at right angles |
|
|
What do otolith organs sense?
Semicircular canals? |
Linear movements of the head
Angular or rotational movements of the head |
|
|
Where is endolymph?
Properties? |
Endolymph within the membranous labyrinth
Low in Na, high in K |
|
|
Where is the perilymph?
Properties? |
Outside membranous labyrinth but inside bony labyrinth
High Na, Low K |
|
|
What happens when endolymph moves?
|
Hair cells deflected (stereocilia moves toward kinocilium) --> mechanical opening of channels --> K in from endolymph --> depolarization --> NT release
|
|
|
What happens when the kinocilium is moved towards the stereocilia?
|
Mechanical closure of ion channels --> stop inward K flow --> hyperpolarize --> shut off NT release
|
|
|
What is the status of ion channels when the kinocilium are in 'mid-position'?
What does this cause? |
Some ion channels open
Causes spontaneous activity of vestibular nerves |
|
|
What do utricle and saccule sense?
|
Linear displacements and accelerations
|
|
|
What is the macula?
|
Area on otolithic organs where hair cells are imbedded in a gelatinous layer, topped by otolithic membrane which contains otoconia
|
|
|
How are left and right horizontal canals angled relative to horizontal?
|
30 degrees up
|
|
|
What is otoconia?
What does it do? |
Ca carbonate crystals embedded in otolithic membrane
Provides mass that amkes the otolithic membrane move relative to hair cells during movement --> hair cells deflect --> neurons activate |
|
|
How is the macula organized?
|
Hair cells on one side of the striola (dividing line) are oriented in the opposite direction from hair cells on the other side
|
|
|
How is the macula in the utricle arranged? What does this help it do?
Saccule? |
Utricle = macula arranged horizontally --> senses movements in horizontal plane
Saccule = macula arragned vertically --> senses movements in the vertical plane |
|
|
How are otolith organs on the two sides of the head arranged?
|
As mirror images
|
|
|
How does the firing rate of vestibular axons compare between the sensation of static movement vs. dynamic movement?
|
Firing rate higher in dynamic movement (slightly)
|
|
|
What do semicircular canals sense?
|
Rotation and angular accelerations
|
|
|
Where is the ampulla?
What does it contain? (2) |
At base of each semicircular canal bulb
1. Crista (epithelium containing hair cells) 2. Cupula (gelatinous mass encompassing the hair bundles) |
|
|
What happens in semicircular canals when endolymph moves?
|
Displacement of the cupula
--> hair cells move --> signaling |
|
|
How are semicicular canals oriented to each other?
To other side of the head? |
Orthogonally
Mirror-image |
|
|
What do vestibular nerves innervate?
Where is their cell body? |
Innervate hair cell on one end, vestibular nuclei on the other
--> directly to cerebellum Cell body in Scarpa's ganglion |
|
|
What 3 systems are used to maintain balance?
What is needed for upright balance? |
Vestibulocerebellum
Visual input from the floor Proprioceptive input Intact vestbulocerebellum and one of the other systems |
|
|
What is a positive Romberg sign?
|
With normal vestibulocerebellar function, standing is steady with intact vision but no proprioception
Diminished when you close your eyes |
|
|
How do vestibular sensations reach consciousness?
|
Projections from vestibular nuclei --> ventral posterior thalamus --> vestibular cortex (in somatosensory cortex)
|
|
|
What are two pathways for projections down spinal cord from vestibular nuclei?
|
Lateral vestibular nucleus -->
vestibulospinal tract medial vestibular nucleus --> descending MLF |
|
|
To where does the MLF project?
What does it influence? |
Bilaterally to cervical levels
Influences head and neck movements through the vestibulo-cervical reflex |
|
|
To where does the vestibulospinal tract project?
What does it influence? |
Unilaterally, throughout spinal cord
Activates extensor motorneurons to maintian upright posture through the vestibulo-spinal reflex |
|
|
In general, what does the oculocephalic or vestibular-ocular reflex (VOR) do?
|
adjusts eye movements to accomodate head movemnts so vision is continuously smooth
|
|
|
What is the VOR when you move your head to the left?
|
Left horizontal semicircular canal activated (R is inhibited) --> med. vestibular nucleus excites R CN6 and L CN3 --> maintain forward gaze
|
|
|
To what 2 structures does the medial vestibular nucleus sne excitatory projections in VOR?
|
1. Excitatory to contralateral CN6 in pons
2. Excitatory to ipsilateral CN3 via ascending MLF Inhibitory to the opposite structures |
|
|
What happens with an intact VOR?
Abnormal VOR? |
Intact = maintain forward gaze when head turns (because eyes turn the opposite way)
Abnormal = eyes turn with head |
|
|
What does the VOR do in upward head movements?
|
Excites posterior semicircular canals --> activation of contralateral inferior rectus and ipsilateral superior oblique --> downward movement of eyes
|
|
|
What does the VOR do in downward head movements?
|
Excitation in anterior semicircular canals --> activation of contralateral inferior oblique, ipsilateral superior rectus --> upward eye movement
|
|
|
What is the cause of Nystagmus?
What are 2 possible sources of this? |
Asymmetric activity of vestibular afferents
1. Physiological - subject rotates quickly for some time and then stops 2. Pathological - problem with the vestibular afferent nerves |
|
|
What are the components of Nystagmus?
How is Nystagmus named? |
Low dirft in one direction, followed by rapid corrective phase in the opposite direction
Named Right or Left depending on direction of rapid ccorrective phase |
|
|
What is happening with vestibular afferents in Nystagmus?
|
Firing at higher rates relative to the contralateral sides --> activation of contralateral lateral rectus and ipsilateral medial rectus --> slow drift towards less active vestibular afferents
|
|
|
What initiates the fast corrective phase?
|
Frontal eye fields of the supplementary motor cortex through lateral gaze center in the parapontine reticular formation
|
|
|
What is the effect of cold water in the ear canal on vestibular afferents?
Warm water? |
Cold water --> decreases firing rate in vestibular afferents
Warm water --> increases firing rate in vestibular afferents |
|
|
What happens when cold water is presented to the right ear (caloric testing)?
|
Decreased activity in right vestibular system --> left vestibular system activates right CN6 and left CN3 --> slow drift of eyes right
Frontal eye fields on right --> PPRF --> rapid leftward correction |
|
|
What are the results of the caloric test in the case where the brainstem is intact but there is no input from the cortex to the brainstem?
|
Lateral drift occurs, but corrective rapid component towards opposite side does not occur
|
|
|
What is the result of the cold water test if there is a disconnect between the pons and midbrain (affecting ascending MLF) or injury to the midbrain?
|
Activation of CN6 normally, but CN3 on opposite side will not be activated
Internuclear opthalmoplegia |
|
|
What is the results of the cold water test if there is damage to the vestibular organ, vestibular nerve, vestibular nuclei, or the pons?
|
Cold water will have no efect on eye movements
|
