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Chapter 14: Brain Control of Movement (Cerebellum (Anatomy (Lobules (10),…
Chapter 14: Brain Control of Movement
Descending Spinal Tracts
Lateral Pathways-voluntary movement; cortical control
Corticospinal Tract- carries info from motor cortices to brain stem, spinal cord. "Pyramidal Tract" (contralateral)
Rubrospinal Tract- originates in red nucleus of midbrain; decussates in pons rather than medulla
Lesions
Both pathways- deficit in fractionated movements
Corticospinal tract alone- same phenotype
Ventromedial Pathways- posture & locomotion, under brain stem control
Tectospinal Tract
Originates in Superior Colliculus; receives projections from retina
Axons decussate immediately after leaving S.C.
Neck, shoulders, upper trunk
Pontine Reticulospinal Tract
Enhances antigravity reflexes of spinal cord
Helps maintain standing posture
Vestibulospinal Tract
Medial vestibulospinal tract- terminates bilaterally in medial ventral horn (neck & back muscles)
Lateral Vestibulospinal Tract- projects ipsilaterally to LMN pools that innervate proximal muscles of the limbs
Medullary Reticulospinal Tract
Liberates antigravity muscles from reflex control
Both reticulospinal tracts controlled by cortex
Babinski sign- toes curl in normally. Used to test for motor tract damage
Motor Cortex
Area 4: M1
Precentral gyrus (aka motor strip)
Lowest threshold for electrical stimulation
Input-Output organization
Layer V- Betz cells (pyramidal); project to LMNs, excite monosynaptically
Also excite local inhibitory neurons (reciprocal inhibition)
Sources of Input to Betz Cells:
BAs 6, 3, 2, 1
Thalamus- VLc relays info from cerebellum
Activity occurs immediately before & during movement
Population coding
Area 6: "Higher" motor area (Penfield)
Lateral region: Premotor area (PMA)
Medial Region: Supplementary Motor Area (SMA)
Movement planning
"Set"= Supplementary & premotor areas
"Go" = Area 6
"Ready" = parietal & frontal lobes
Mirror neurons- understanding intentions of others?
Basal Ganglia
Direct Pathway
Cortical activation excites putamen
Putamen inhibits internal Globus Pallidus
Releases VLo from inhibition
VLo excites SMA
Motor Loop
Basal ganglia projects to VLo of thalamus, then MAJOR input to BA 6
Cortex projects back to basal ganglia
Forms a 'loop': CSTC
Willed movements
Indirect Pathway
Striatum inhibits external Globus Pallidus
Releases inhibition of internal Globus Pallidus & STN
Activation by cortex inhibits thalamus
Disorders
Parkinson's Disease
Increased inhibition of Thalamus by basal ganglia
trouble initiating willed movements
Huntington's Disease
Polyglutamine disease
Loss of neurons in caudate nucleus, putamen, globus pallidus
Loss of inhibitory output to thalamus
Hemiballismus
Violent, involuntary movements of limbs
Damage to subthalamic nuclei
Cerebellum
Intentional tremor: tremor only when trying to move
Dyssynergia: composition of synergistic multi-joint movements
Ataxia: uncoordinated & inaccurate movements
Dysmetria: overshoot or undershoot target
Anatomy
Lobules (10)
Vermis- midline bump (ventromedial pathways)
Folia- transverse
Cerebellar hemispheres: limb movements- contributes to lateral pathways
Cells & Layers of cerebellar cortex
Granule Cells: tiny excitatory neurons
Purkinje cells- largest in cerebellum; get input from granule cells- send inhibitory axons to deep cerebellar nuclei
Pontine Nuclei- axons from layer V pyramidal cells to pons
Corticopontocerebelllar projection
Lateral cerebellum projects back to motor cortex via VLc