Term
| how are conjugate horizontal eye movements generated? |
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Definition
| abducens motorneurons innervate LR muscle on ipsilateral side. abducens internuclear neurons cross, ascend in MEDIAL LONGITUDINAL FASCICULUS (MLF) and synapse in the oculomotor nucleus, exciting motorneurons for medial rectus on contralateral eye. END RESULT: eye movement in same direction and thru same angle in both eyes |
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Term
| how are disjunctive eye movements generated? |
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Definition
| near response (NR) premotor vergence neurons send bilateral input to the appropriate motor neuron nucleus (i.e. oculomotor nucleus), producing convergence |
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Term
| define a disjunctive eye movement in terms of the muscles innervated and the eye movements produced |
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Definition
-opposite muscles of each eye are innervated - i.e. lateral rectus on one side, medial rectus on the other side
-eyes move in same direction |
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Term
| define a conjugate eye movement in terms of the muscles innervated and the eye movements produced |
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Definition
-same muscle innervated bilaterally
-eyes move in different directions (both look in/out, but one eye moves left, other moves right) |
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Term
| what is internuclear ophthalmoplegia (INO) and what is the pathology? |
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Definition
-lesion in MLF; cuts the internuclear pathway, disrupts conjugate eye movements
-lesion in MLF will disrupt the innervation to the contralateral eye during conjugate eye movement. Abducting eye will more normally, the adducting eye will get stuck at midline |
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Term
| how can you differentiate INO from oculomotor paralysis/lesions? |
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Definition
in INO, the lesion is at MLF.
-the person can still produce vergence movements b/c these don't require MLF, so you know CNIII is in tact |
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Term
| what are the different projections from the FEF in saccadic eye movement pathways? |
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Definition
FEF projects to: 1. superior colliculus; 2. premotor neuron nucleus (PMN); 3. basal ganglia (caudate nucleus, substantia nigra pars reticulata); 4. neurons in parietal cortex
-FEF and neurons in parietal cortex are reciprocally linked |
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Term
| what is the role of the PMN? |
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Definition
| the premotor neurons generate the motor command |
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Term
| T/F: The same population of neurons in the cortical structures are involved in initiating pursuit or saccadic eye movements? |
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Definition
| F - different populations of neurons are involved in each pathway |
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Term
| in smooth pursuit, which cortical structures are involved in initiating eye movements? |
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Definition
| MT, MST - integrate eye movement and visual signals to determine the eye velocity needed to track a target; final decision to track a target is also made here |
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Term
| what is the general pathway for generating smooth pursuit/tracking eye movements? |
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Definition
| FEF -> LIP (parietal cortex) -> MT/MST -> pons -> superior colliculus -> cerebellum -> vestibular nucleus |
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Term
| how is the motor command encoded? |
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Definition
by the discharge frequency of motor neuron APs (firing rate)
-firing rate increases when the eye rotates into the pulling direction of a muscle |
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Term
| what is the motor command sequence for a saccade? |
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Definition
1. pulse - burst of APs
2. step - step change in tonic discharge rate (to overcome rebound of stretched muscle) |
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Term
| where is the motor command for saccadic eye movements generated? |
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Definition
pulse: PPRF
step: medial vestibular nucleus (MVN) and nucleus prepositus hypoglossi (NPH) |
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Term
| where is the motor command for smooth pursuit and the vestibular ocular reflex generated? |
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Definition
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Term
| what is the effect of a lesion at PPRF? |
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Definition
| slow or absent saccades on the ipsilateral side |
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Term
| what is the effect of a lesion at the MVN? |
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Definition
| eyes will drift back to center from the eccentric position; can't maintain the increased tonic firing rate to hold the eye in position |
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Term
what are 4 major ways that inflow from the vestibular system is used?
-what is the central pathway associated with each? |
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Definition
1. to stabilize retinal images (vestibular-ocular reflex)
2. in postural control of head and body (vestibulo-spinal)
3. spatial navigation and spatial memory (vestibulo-cortical)
4. autonomic fxns (vestibulo-medullary) |
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Term
| what organs in your head sense angular rotation? |
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Definition
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Term
| which organs sense head translation and orientation in relation to the ground/gravity? |
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Definition
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Term
| what part of the CNS is responsible for perceptions of self motion, spatial navigation and memory? |
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Definition
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Term
| what part of the CNS is responsible for VOR/image stability? |
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Definition
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Term
| what part of the NS is responsible for regulating blood pressure, respiration? |
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Definition
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Term
| what is the flow of vestibular information from the periphery to the CNS? |
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Definition
| hair cells (the primary sensory organ of the vestibular system) -> Scarpa's ganglion -> vestibular nuclei -> project to appropriate higher structure (i.e. cortex, cerebellum, etc.) |
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Term
| how do semicircular canals detect acceleration? |
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Definition
| accel in one direction causes flow of endolymph in opposit directoin; endolymph deflects cupula and hair cell stereocilia are deflected --> deflection towards kinocilia opens membrane channels --> depolarization |
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Term
| what kind of inputs are flowing to hair cells on each side of the head during angular accel? |
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Definition
-excitatory input flows to horizontal semicircular canal on the ipsilateral side (side on the direction in which head is moving)
-inhibitory input to semicirc canal of contralateral side (i.e. activity in CN VIII is decreased) |
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Term
| what is the angular vestibular ocular reflex (AVOR)? |
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Definition
| reflexive eye movements that are equal in amplitude but opposite in direction to head movements |
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Term
| what are the 3 neurons involved in the VOR reflex arc? |
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Definition
1. primary sensory neurons in Scarpa's ganglion
2. secondary neurons in vestibular nuclei
3. extraocular motoneuron |
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Term
| map out the VOR pathway that takes place when there is a leftward head turn: |
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Definition
1. left horizontal semicir canal is excited; right canal is inhibited
2. LHC goes to the RIGHT abducens nucleus - excitory pathways are crossed. (note: left medial rectus is also innervated via internuclear pathway and MLF)
3. LHC send inhibitory signal to left abducen nucleus; inhibitory pathways are uncrossed |
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Term
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Definition
| an alternating pattern of fast and slow eye movements where the flow phase is the VOR and the fast is a saccade movement to return the eye to a central position |
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Term
| what is the relationship between the vestibular nuclei? |
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Definition
| they are connected across the midline by commissural fibers |
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Term
| what kind of input comes from the cerebellar Purkinje cells? |
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Definition
| direct inhibition of vestibular neurons |
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Term
| what is the general scheme of info flow for how we are able to align our heads and neck in relation to the earth? |
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Definition
| otoliths (saccule and utricle) detect head orientation and are linked to vestibulospinal pathways that re-orient the head and body to align with earth |
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Term
| the vestibular nuclei are located around the level of the pons and medulla and have both ascending and descending projections. name two descending pathways |
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Definition
spinal projections:
1. medial vestibulospinal tract (MVST)
2. lateral vestibulospinal tract (LVST) |
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Term
| trace the path of the medial vestibulospinal tract. what is its fxn? |
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Definition
most fibers arise from medial vestibular nucleus -> project BILATERALLY downward to cervical motor neurons and propriospinal neurons
-mediates head movements |
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Term
trace the path of the lateral vestibulospinal tract (LVST)
-fxn? |
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Definition
vestibular nuclei -> project IPSI downward to alpha and gamma motor neurons (mostly to extensors), and spinal interneurons throughout cord
- mediates postural tone and antigravity reflexes |
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Term
| what is the path of ascending tracts from the vestibular nucleus? what kind of info do they carry? |
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Definition
-vestibular nuclei -> posterior nuclei of thalamus -> cortical areas 3a (via VPL) and area 2v (via posterior nuclei)
-carry perceptions of self-motion |
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Term
| what is a possible fxn for ascending vestibular signals to the hippocampus? |
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Definition
| spatial memory and spatial navigation |
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Term
| what pathways evoke changes in BP, resp rate, cerebral blood flow in response to translation? |
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Definition
| pathways linking vestibular nuclei to medullary brain stem autonomic centers |
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Term
| describe the phenomenon of habituation to vestibular stimulation |
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Definition
| habituated individuals will have a faster decrease in vestibular output following a vestibular stimulation |
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