Functional organization of the primary motor cortex Premotor cortex 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

Wed. Jan. 24, 2006 03-55-485

Upper motor neurons in cerebral cortex (primary motor cortex) 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

Wed. Jan. 24, 2006 03-55-485

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

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

Wed. Jan. 24, 2006 03-55-485

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

Wed. Jan. 24, 2006 03-55-485

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

Wed. Jan. 24, 2006 03-55-485

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

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

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

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

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

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