PT 22 LEC: Cerebellum & BG

cerebellum functions

- major role in timing of motor activities & in rapid, smooth progression of mov't

- control intensity

- corrective adjustments

- aids cortex in planning sequential movements

cerebellum considered as

silent area; electrical excitation does not cause any conscious sensory or motor response

cerebellar lesions can lead to:

no paralysis but loss of coordination

Corticopontocerebellar pathway

from cerebral motor and somatosensory cortex to opposite LATERAL CEREBELLAR HEMISPHERES

Olivocerebellar tract

FROM the inferior olive TO all parts of cerebellum(excitation in the olive via cerebral motor cortex, BN, RF, SC)

Vestibulocerebellar fibers

FROM the vestibular apparatus, BS vestibular nuclei TO flocculonodular lobe and fastigial nucleus

Reticulocerebellar fibers

FROM reticular formation TO midline cerebellar areas (mainly vermis)

dorsal spinocerebellar tracts

- via inf peduncle on same side

- from mm spindle & GTO

- mm contraction, tension, position, forces acting

ventra spinocerebellar tracts

- via sup peduncle on both sides

- motor signals from anterior horn

- feedback efference copy

Afferent input through spinal dorsal column

to the dorsal column of the medulla then relayed to the cerebellum

spinoreticular & spinoolivary pathway

signals relayed from these areas to cerebellum

deep cerebellar nuclei

dentate, interposed globose and emboliform, fastigial; receive signals from cerebellar cortex & deep sensory afferent tracts to the cerebellum

2 directions when signal is received in DCN

- directly to cerebellar nuclei

- corresponding part over deep nuclei

efferent pathway from vermis

goes to fastigial nucleus; equilibrium & posture

efferent pathways from intermediate zone

to red nucleus & RF; coordinates reciprocal contractions

efferent pathways from lateral zone

to cortex; coordination sequential motor activities

Purkinje cells

site of inhibition

other inhibitory cells

basket * stellate

layers of cortex

- granular

- Purkinje

- molecular

granule cells

- excitatory; glutamate

- parallel fibers run perpendicular to the Purkinje cell dendrites

molecular layer

basket, Golgi, stellate cells

Basket cells

receive excitatory signals from parallel (granular) fibers & project these signals to Purkinje cells to INHIBIT

Stellate cells

receive excitatory signals from parallel fibers & send back to Purkinje cells to INHIBIT

Golgi cells

receive excitatory inputs from parallel & mossy fibers and send back to granule cells to INHIBIT

Purkinje cells in Purkinje layer

Dendrites fan out in a single plan like a Japanese fan

Primary output from cerebellar cortex

Projects ipsilaterally to the deep cerebellar nuclei, especially DENTATE nucleus

Forms inhibitory synapses

2 types of afferent input

climbing & mossy fibers

climbing fibers

strong; single impulse causes complex spike

mossy fibers

weak; causes simple spike

deep cerebellar nuclei in neuronal circuit

Receives inhibitory inputs from the Purkinje and excitatory from the other areas

signals from mossy & climbing fibers

excite deep nuclear cells

signals from Purkinje

inhibit deep nuclear cells

damping

prevent overshooting of movements

Turn-on signals

for the agonist muscles; rapid

Turn-off signals

for the antagonist muscles; reciprocal & simultaneous with turn-on signals

cerebellar lesions

hardly noticeable affectation as long as activities as performed slowly

basal nuclei

complex patterns; accessory motor system

lesion in globus pallidus

athetosis

lesion in subthalamus

hemiballismus

lesion in putamen

chorea

lesion in substantia nigra

Parkinson's

putamen circuit

patterns of motor activity

caudate circuit

cognitive control

agnosia

inability to identify objects

Dopamine

from substantia nigra to caudate and putamen; inhibitory neurotransmitter that can function as stabilizer

Glutamate

provide mostly excitatory response to balance inhibitory signals from dopamine, GABA and serotonin

GABA

from caudate and putamen to the globus and substantia nigra; functions in negative feedback loops to lend stability to motor control systems

ACh

from cortex to caudate nucleus and putamen

NE, serotonin, enkephalin, etc.

multiple general pathways from the brainstem