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Cerebellum

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imissyou419's version from 2017-01-29 02:17

Section 1

Question Answer
How many neurons does the cerebellum have?it consists of only 10% of volume of the brain but contains >1/2 of all neurons in the brain
How many cell types are there in cerebellar cortex?5 cell types that are connected the same way in all regions (3 are inhibitory)
Lesion of the cerebellumNo change in sensory perception, sensory threshold, or strength of movements. Movements are inaccurate and uncoordinated (ataxic)
Purkinje cellhas up to 200,000 synapses (dendritic tree)
What are the 5 features of input-output connections of the cerebellum KNOW THESE1. Widespread sensory input. None reaches consciousness.
2. Only output from cerebellar cortex to deep nuclei is via Purkinje cells - always inhibitory.
3. medial and lateral division
4. in primates, there is an increased development of lateral cerebellum.
5. lateral cerebellum projects to motor cortex and frontal cortex (cognitive function?)
What is the pathway of lateral cerebellum?cerebellar cortex -> [Purkinje fibers] (inhibits w/ GABA) dentate interposed -> thalamus -> frontal cortex & motor cortex (limbs MNs)
What is the pathway of medial cerebellum?cerebellar cortex -> [Purkinje fibers] (inhibits w/ GABA) fastigial -> lateral vestibular nucleus or medial vestibular nucleus/reticular formaion -> postural muscle MNs or eye MNs
Lesion of lateral cerebellumDysmetric limb movements, intention tremor, arm ataxia
Lesions of medial cerebellumDysmetric saccades, disorder smooth pursuit, disorder equilibrium, balance, gait ataxia
Alcoholcerebellar lesions can be mimicked by alcohol (act at GABA gated ion channels between Purkinje fibers and Vestibular nucleus) = bad balance + sacchades
Why does lesions cause the movement disorders?failure of cerebellum to "tune up" the different functions, e.g. failure to tune-up the generation of saccades (in brainstem reticular formation), limb movements (motor cortex), balance (vestibular postural reflexes)
What is the overall function of the cerebellum?subconscious computer that tunes up reflexes (VPR, VOR), motor programs (saccades, accurate arm movements), cognition to make them more accurate
what are the 4 specific functions of the cerebellum?1. contributes to the generation of accurate saccades, accurate limb movements. 2. feedforward, anticipatory, predictive movement control. 3. motor recalibration, error correction, motor learning. 4. contributes to cognition
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Section 2

Question Answer
How does the cerebellum contribution to the generation of accurate saccades, accurate limb movements?Everytime make saccade/arm movement, the cerebellum helps start it and stop it, make it accurate
How does the cerebellum do feedforward control?when a perturbation is expected, the movements are via feedforwad control
e.g. when catching a ball dropped from height, visual info feedforward into cerebellum which then predict the time of ball impact, cerebellum sends relay info to motor cortex, then motor cortex sends command to muscle to contract before the ball hits the hand (anticipatory activity come from before ball hits hand TO ALLOW FOR ELECTRICAL MECHANICAL COUPLING TIME)
If only feedback mechanism occurs (no vision), stretch reflex only would not catch ball - stretch reflex 30 ms + EM coupling time (50ms) = 80 ms!!!!, takes too long
How does cerebellum do motor recalibration, error correction, motor learning?change strength of parallel fiber - Purkinje cell synapse (excitable synapse at cerebellar cortex) by means of climbing fiber (the teacher) (Inferior olive does error detection)
How does throwing with shifted visual world impact the modifiable synapse for healthy person?Starts throwing to left and after 50 throws, recalibrates and get back on target; when take off glasses, throws to right and slowly get back to target (negative after effect demonstrates recalibration has taken place); it is only that visual action that is affected
How does throwing with shifted visual world impact the modifiable synapse for a cerebellar patient?Patient cannot recalibrate and after 50 throws, would still throw to left. when take off glasses, throws on target (no negative after effect so no recalibration)
Why do people warm up before an athletic event?cerebellum to do fine-tuning of smooth pursuit, VOR, vestibular postural reflexes, etc
Examples of recalibration, error correction, motor learningrecalibrating throwing after wearing glasses that shift visual world, modifying strength of reflexes (VPR ice skating (do not stick out hand when head accelerating), VOR glasses), switching between sets of reflexes (walking/skating, no-glasses/glasses), classical Palvovian conditioning
How does cerebellum contribute to cognition?sensory discrimination of time (cerebellar patients cannot discriminate accurately the duration of auditory tones or the velocity of moving objects i.e. cannot judge time), spatial cognition (cerebellar patients cannot do spatial tasks e.g. pegboard puzzles), linguistic processing (noun - verb task) (cerebellar patients do not do well on matching noun - verb, e.g. dog-bark)
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