Subcortical Motor Systems:

Cerebellum & Basal Ganglia

Lecture 21

Motor Loops

Cortex Subcortex Cortex Spinal cord

Cerebellum coordination of movement

Basal Ganglia selection & initiation of voluntary

movements ~

Cerebellum

Nonmotor functions - memory/language Coordination of complex movements Programs ballistic movements

no feedback during execution direction, force, & timing

Motor learning shift from conscious unconscious ~

Cerebellum: Anatomy

Folia & lobules analogous to sulci & gyri

Vermis - along midline output ventromedial pathway

Hemispheres output lateral pathway

Deep cerebellar nuclei analogous to thalamus ~

Motor Loop Through Cerebellum

Lateral cerebellumsimplest circuit

20 million axons Cortex pons & cerebellum

Prefrontal, Motor, PPC Pons & Cerebellum thalamus

VLc - ventrolateral nucleus VLc M1 lateral pathway ~

Prefrontal PPCM1M2

Pons, CerebellumVLc

Distal Limbs

Lateral CerebellarMotor Loop

Cerebellum: Damage

Lesions - loss of motor coordination Dysynergia

no simultaneous movement of jointsserial movement only

Dysmetric movements to wrong coordinates

Alcohol intoxiction depression of cerebellar circuits ~

Basal Ganglia

Caudate nucleus Putamen

Globus Pallidus Substantia Nigra Tegmentum

Control slow movements Using immediate sensory feedback ~

Striatum

StriatumGlobusPallidus

Substantia Nigra

Thalamus

Cross section of Tegmentum

Substantia Nigra

Prefrontal PPCM1M2

BasalGanglia VLo

Distal Limbs

Basal GangliaMotor Loop

Basal Ganglia Movement Disorders

Parkinson’s Disease

1% of population Nigrostriatal pathway

Substantia nigra neurons die Progressive loss

Hypokinesia Rigidity Bradykinesia Akinesia ~

SMA

Putamen

-Globus

Pallidus (GPi)

-

SubstantiaNigra

+

VLo

SubthalamicNucleus

+

Cortex

+X

Parkinson’s Disease+

Parkinson’s Disease: Treatment

Basal Ganglia - Cholinergic Substantia Nigra - Dopaminergic Drug Therapy

L-DOPA Pallidectomy Tissue transplants ~

Huntington’s Disease (Chorea)

Rare onset 30-40s

early as 20s Degeneration of Striatum

Caudate Putamen

GABA & ACh neurons ~

Symptoms

Khoros = dance Uncontrollable, jerky movements Dementia Progressive

eventually fatal ~

SMA

Putamen

-

-

+

VLo

SubthalamicNucleus

+X

Huntington’s Disease

GPiGPe

-

+

Huntington’s Disease: Cause

Genetic disorder Single dominant gene on chromosome 4 HD mutation -

unstable trinucleotide repeat - CAG # of repeats correlated w/ age of onset ~

HD gene huntingtin 3 forms

mutated form binds to protein involved in energy production neuron starves

Excitotoxicity contributes to degeneration glutamate Nitric oxide (NO) Potential treatment:: Inhibit NO synthase ~

Huntington’s Disease: Cause

Hyperkinesia

Excessive movement Ballism

violent, flinging movements Lesions in subthalamus

less inhibition of VLo excitation of SMA ~

SMA

Striatum

- GlobusPallidus

-

+

VLo

SubthalamicNucleus

+

X

Hyperkinesia(e.g. ballism)