Transcript Document

• Corticospinal and corticobulbar
pathways: upper motor neurons that
initiate complex voluntary movements
• Functional organization of the primary
motor cortex
• Premotor cortex
• Damage to descending motor pathways
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Corticospinal and corticobulbar pathways:
upper motor neurons that initiate
complex voluntary movements
• Upper motor neurons in cerebral cortex
(primary motor cortex)
– In adjacent and interconnected areas of
the frontal lobe
– Together mediate planning & initiation of
complex temporal sequences of voluntary
movements.
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Corticospinal and corticobulbar pathways
Primary motor cortex receives regulatory input:
• From basal ganglia and cerebellum
-> relays in ventrolateral thalamus
• From sensory regions of the parietal lobe
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Primary motor cortex
• Low threshold for eliciting movements
through electrical stimulation
• Descending pathways to lower motor
neurons in the brainstem and spinal
cord.
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Organization of the primary
motor cortex
• Upper motor neurons are pyramidal
cells in layer V.
– Their axons descend to the brainstem and
to spinal motor center in the corticobulbar
and corticospinal tracts.
– --> then run to the base of the pons
– --> to medulla through medullary
pyramids….
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Lateral corticospinal tract
• Direct pathway from the cortex to the
spinal cord (lateral portions of the
ventral horn and intermediate gray
matter)
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Indirect pathway
• from motor cortex to 2 sources of upper
motor neurons in the brainstem (red
nucleus and reticular formation)
• Motor cortex--> reticular formation -->
medial region of the spinal cord.
• Motor cortex--> red nucleus--> lateral
region of the spinal cord.
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Functional organization of the
primary motor cortex
• When stimulated, muscles on the
opposite side of the body contract.
• Has complete representation of body’s
musculature.
• Greater space for fine motor control
than for less precise motor control
• Very focal stimulation --> organized
movement (excitation and inhibition)
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Motor Cortex
• Overlap of regions that initiate different
movements.
• A particular movement can be elicited
by widely separated sites.
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Motor cortex
• Recorded neural activity during
voluntary movement.
– Motor cortex neurons direct recruitment of
lower motor neurons
– Force
– Direction
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Motor cortex
• Upper motor neurons encode a
movement rather than individual
muscles.
• A movement can involve several
different lower motor neuron pools
• Each arm movement is encoded by
concurrent discharges of a large
population of neurons
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Premotor cortex
-movement selection
• Reciprocal connections
• with the primary motor cortex
• And project axons through corticobulbar
and corticospinal pathways
• Uses information from other cortical
regions
• Active during association of visual
(sensory) to movement.
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