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Lecture

Physiology 3120 Lecture Notes - Lateral Vestibular Nucleus, Vestibular Nuclei, Deep Cerebellar Nuclei


Department
Physiology
Course Code
PHYSIO 3120
Professor
Tom Stavraky

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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
Intention tremor; occurs when you’re trying to move (may be called an action tremor as
well)
Arm ataxia; occurs when intention tremors combine across various joints to produce
impression of clumsiness
Functions
Overall: subconscious computer that tunes-up reflexes & motor programs
Specific
1. Generation of accurate saccades & limb movements
Starts it, stops it, and makes it as smooth as possible
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