Cortical Control of Movement Prof. K. Sivapalan

Cortical motor control Upper Motor Neuron. Corticospinal fibers coming from pyramidal cells regulate voluntary movements This is generally known as the upper motor neuron. Other descending tracts are concerned with reflexes and facilitatory or inhibitory roles. 2/28/2019 Cortical motor control

Cortical motor control Cortical Motor areas. Motor cortex [M1] is the precentral gyrus. Supplementary motor area- superior bank on and above the cingulate sulcus. Premotor cortex- lateral surface in front of the motor cortex. 30% of corticospinal tract from motor cortex, 30 % from premotor cortex and 40 % from parietal cortex sensory area. 2/28/2019 Cortical motor control

Cortical motor control Other motor areas. Supplementary motor area projects to motor cortex. It appears to be involved in programming motor sequence. Premotor cortex projects to motor cortex and brainstem areas concerned with posture. It also contributes to corticospinal and corticobulbar fibers. It appears to set appropriate posture before and during movement . Posterior parietal cortex gives rise to fibers in corticospinal and corticobulbar tracts and projects to premotor area. Important for sensory coordination: eye- hand coordination -eating with fork and knife. 2/28/2019 Cortical motor control

Cortical representation In motor cortex, legs up, in the opposite side. Cranial motor nerves up to upper half of facial nerve have bilateral representation. Hand and vocalization are represented in large area. Area is proportional to the skill involved. 2/28/2019 Cortical motor control

Cortical motor control Pyramidal tract. Axons from the pyramidal cells descend through the internal capsule and brain stem. Decussation in medulla appears as pyramid [80 % of the corticospinal fibers]. Crossed fibers descend in the lateral corticospinal tract and synapse with anterior horn cells. Uncrossed fibers [20%] descend in the ventral corticospinal tract They synapse with interneuron which crosses and synapses with anterior horn cells. 2/28/2019 Cortical motor control

Cortical motor control Internal Capsule All corticospinal fibers enter the internal capsule through the corona radiata. Corticospinal fibers lie in the posterior limb of the internal capsule, legs anterior and head posterior. 2/28/2019 Cortical motor control

Decussation of the Pyramids 80 % of the pyramidal fibers decusssate in the medulla. The crossed fibers form the lateral corticospinal tract. 2/28/2019 Cortical motor control

Cortical motor control Tracts in Spinal Cord. Descending [motor] Ascending [sensory] 2/28/2019 Cortical motor control

Motor Neurons in Spinal Cord The anterior horn of the lower cervical and lumbar segments are large corrosponding to the number of muscles and the degree of control of movements. 2/28/2019 Cortical motor control

Cortical motor control Connection to AHC Lower motor neurons of the head area are supplied as the fibers descend. The lateral Corticospinal fibers innervate the limb muscles with skilled movements The anterior corticospinal tract innervates the postural muscles with posture control. Axons end in either AHC or Inter neurons. The innervation controls movements and not individual muscles. 2/28/2019 Cortical motor control

Axial and Distal Muscles Axial muscles are concerned with control of posture and gross movements. Distal muscles are in the limbs, concerned with fine, skilled and complex movements. Neurons and fibers in the medial and ventral parts of the neural axis control trunk and proximal limb muscles. Lateral pathways are concerned with distal limb muscles. 2/28/2019 Cortical motor control