Motor Cortex and Pathways

Motor homunculus

Area of cortex is proportional to the degree of motor innervation on contralateral side of body
Lower limb more medial and head more lateral
More neurones mean more precise movement

Separation between motor and sensory cortex

Central sulcus
Primary motor cortex is in pre-central gyrus, sensory is in post-central gyrus

Main descending motor pathways

Corticospinal, corticobulbar, reticulospinal, vestibulospinal

Corticospinal pathway

Voluntary control of movement

Vestibulospinal pathway

Posture, balance, muscle tone reflexes

Reticulospinal pathway

Facilitates and inhibits voluntary muscle contraction - regulates muscle tone (readiness for contraction)

Corticospinal tract

Starts in precentral gyrus, moves down ipsilaterally through midbrain and pons, crosses to contralateral side in medulla, into the spinal cord where it synapses with an alpha motor neurone (lower motor neurone) and then information travels to limb where extrafusal muscles are innervated to produce voluntary movement

Reticulospinal tract

Begins in reticular formation in the brainstem which sits in between the pons and medulla, travels down into spinal cord on ipsilateral side and synapses in spinal cord to innervate gamma motor neurones in muscle spindles to regulate muscle tone

Vestibulospinal tract

Begins in vestibular nucleus in the medulla and pons of the midbrain and travels down the ipsilateral side of the spinal cord where it synapses and goes on to innervate axial extensors (muscles of the trunk) to maintain posture

Corticospinal pathway influence on movement production

Enables subconscious and conscious movement control which is needed for effective backmovement
Innervates alpha motor neurones which facilitate muscle contraction
Subconscious control provides background for effective voluntary movement