Corticospinal and corticobulbar pathways upper motor neurons that
• 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 Wed. Jan. 24, 2006 03 -55 -485 1
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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. Wed. Jan. 24, 2006 03 -55 -485 3
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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 Wed. Jan. 24, 2006 03 -55 -485 5
Primary motor cortex • Low threshold for eliciting movements through electrical stimulation • Descending pathways to lower motor neurons in the brainstem and spinal cord. Wed. Jan. 24, 2006 03 -55 -485 6
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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…. Wed. Jan. 24, 2006 03 -55 -485 8
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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) Wed. Jan. 24, 2006 03 -55 -485 10
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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. Wed. Jan. 24, 2006 03 -55 -485 12
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) Wed. Jan. 24, 2006 03 -55 -485 13
Motor Cortex • Overlap of regions that initiate different movements. • A particular movement can be elicited by widely separated sites. Wed. Jan. 24, 2006 03 -55 -485 14
Motor cortex • Recorded neural activity during voluntary movement. – Motor cortex neurons direct recruitment of lower motor neurons – Force – Direction Wed. Jan. 24, 2006 03 -55 -485 15
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 Wed. Jan. 24, 2006 03 -55 -485 16
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. Wed. Jan. 24, 2006 03 -55 -485 17
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