Primary motor cortex

From Psy3241

Revision as of 15:37, 24 April 2008

Picture of Primary Motor Cortex

Background

• Primary motor cortex is also called M1

• One of the principle areas involved in motor function

• Located in the frontal lobe of the brain along the precentral gyrus

• The role is to generate neural impulses that control the execution of movement

• Signals from M1 cross the body’s midline to activate skeletal muscles on the opposite side of the body

• The right hemisphere controls the left side of the body

• The left hemisphere controls the right side of the body

Somatotopic Representation

• Every part of the body is represented in the primary motor cortex

• Body part representations are arranged somatotopically

• The foot is next to the leg, next to the trunk, next to the arm, which is next to the hand

• The amount of brain matter devoted to a particular body part represents the amount of control that the primary motor cortex has over that body part

• A lot of cortical space is devoted to complex hand and finger movements; therefore, they have larger representations in M1

Corticospinal Tract

• Neurons in M1, supplementary motor area, and premotor cortex give rise to fibers of the corticospinal tract

• The corticospinal tract is the only direct pathway from the cortex to the spine

• This tract is composed of over a million fibers

• The fibers descend through the brainstem and cross to the opposite side of the body

• The fibers then continue to descend through the spine, terminating at the appropriate spinal levels

• This tract is the main pathway for control of voluntary movement in humans

Damage to Primary Motor Cortex

• Lesions in the primary motor cortex result in paralysis of the contralateral side of the body