ch 19 – modulation of movement by cerebellum (motor control)

upper

cerebellum modifies the activity of _____ motor neurons

laminated cortex and nucleu

two main gray matter structures:

laminated cortex

• surface of gray matter

nuclei

• deep in white matter

• neurons are the main source of output of the cerebellum

detect and correct the error between intended and actual movements

primary function of cerebellum:

3 parts of the cerebellum

• cerebrocerebellum

• spinocerebellum

• vestibulocerebellum

cerebrocerebellum

• lateral hemispheres

• largest in humans

• receives input from cerebral cortex

• controls highly skilled movements + speech

spinocerebellum

• middle section

• receives input from the spinal cord

• vermis (center) → movements of proximal muscles

• lateral areas → movements of distal muscles

vestibulocerebellum

• receives inputs from brainstem

• vestibulo-ocular reflex (VOR) → involuntary movement of the eyes when the head is moving

• posture

• equilibrium

deep cerebellar nucleu

• send outputs (efferents) to the thalamus, which projects to the motor cortex

  • cerebellum → thalamus → cortex

input projections TO the cerebellum

• cerebral cortex axons project → pontine nuclei (brainstem) on the same side → pontine nuclei axons cross the midline → cerebellum

• receives sensory info about body position and movement

spinocerebellar maps

• spinocerebellum contains topographic maps for sensory inputs

• fractured = areas of the body appear several times

• inputs are ipsilateral

  • brain inputs are contralateral

output projections FROM the cerebellum

• cerebellar cortex neurons → deep cerebellar nuclei → axons cross to other side of cerebral cortex

• cerebral cortex neurons control contralateral musculature

• each cerebellar hemisphere controls ipsilateral musculature

fastigial nuclei

• neurons (deep cerebellar) send projections to brainstem

• control medial tracts in spinal cord that regulate axial and proximal limb muscles

purkinje cells

inputs to the cerebellum target _______ _____

cerebellum circuit

cortex → pontine nuclei (brainstem) → cerebellum (contralateral)

mossy fibers

• axons of pontine nuclei

• connect to granule cells

granule cells

• connected to mossy fibers

• send parallel fibers to Purkinje cells = T branches

  • via excitatory synapses

• 50 billion

parallel fibers

• at right angles to the plane of purkinje dendrites

• connects many Purkinje cells

  • each Purkinje cell receives inputs from around 200,000

• granule cells = wires - connecting to - Purkinje cells = poles

  • minimum contacts between wires

  • maximum number of contacts

  • spreading of information

climbing fibers

• connect Purkinje cell dendrites (wrapping around them) to form numerous connections

• when fired, causes a Purkinje cell to fire

• funneling of information

deep cerebellar nuclei neurons

• receive excitatory inputs from mossy fibers and climbing fibers

• Purkinje cells are GABAergic → modulate excitation via inhibition

  • Purkinje cells form a cortical inhibitory loop = can correct errors and modify movements

motor learning model

• modulated by cerebellum

• Purkinje cells compare climbing fiber input and parallel fiber input

  • if inputs arrive at the same time: depression of synapse with parallel fiber

    • via LTD = endocytosis of AMPAR

  • next time: similar input will have the Purkinje cells fire less → less inhibition from cerebellar loop → brain motor program controlled by that Purkinje cell will be more activated

movement control

• during movements, pattern of cerebellar activity in Purkinje cells and deep nuclei neurons changes continuously

vestibulo-ocular reflex

• when the head turns, the eyes move in the opposite direction to keep a stable image in the retina

• if there is damage to the cerebellum, VOR can’t adapt to new conditions → cerebellar ataxia

• minifying glasses:

  • glasses alter the size of the visual image

  • healthy cerebellum adapts VOR to compensate

  • damaged cerebellum prevents this adaptation

appendicular ataxia

• irregular movements that typically overshoot or undershoot the visual target

• require frequency corrective movements