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Physiology 3120
Tom Stavraky

Human Physiology Friday, November 20, 2009 “Neuro XIII” Cerebellum • Comes from Latin for little brain  Has a cortex, just like the cerebrum (big brain)  Also has deep nuclei, which are further inwards from the cortex  10% of the volume of the brain; said to have more than half the neurons in the brain • Cell types in the cerebellum  Granule cell  Give rise to an axon called a parallel fibres that run down to Purkinje cells  Large numbers of granule cells  Purkinje cell  3 other cell types in the cerebellar cortex; all are inhibitory interneurons • Lesions  No change in sensory perception  No change in sensory thresholds and no change in strength of movement  Movements becomes inaccurate & uncoordinated (i.e. ataxic) • Input/output  Input comes from neurons in the pons; excitatory; collateral from this afferent axon goes to the deep nuclei in an excitatory manner  Connection from Purkinje cells to deep nuclei is ALWAYS inhibitory  Lateral area  Involved in vestibular postural reflexes  Medial area  Input from vestibular, auditory, and visual systems  Project to fastigial neurons to the lateral (vestibular ocular reflexes) or medial/reticular formation (saccades) vestibular nucleus • Effects of lesions  Medial  Dysmetric (deficit in length of) saccades; overshoot = hypermetria, undershoot = hypometria  Gaze-evoked nystagmus (can’t maintain gaze on extreme point in visual system; eyes drift away from the object; occurs with alcohol intoxication as well)  Disorder in smooth pursuit; make series of saccades instead  Disorders in equilibrium & balance (associated with lateral vestibular nucleus)  Gait ataxia (uncoordinated stagger); also associated with lateral vestibular nucleus  Lateral; as you progress phylogenetically, there is a large increase in the size of the lateral cerebellum in monkeys & man  Dysmetric limb movements; classically tested in the nose-to-finger task
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