Motor System Overview

Motor System Objectives

• Students should understand how skilled movements are planned and executed.
• Students should be able to identify the motor cortex.
• Students must describe pyramidal and extrapyramidal motor tracts.
• Students need to discuss the cerebellum and basal ganglia functions.

Motor Cortex Subareas

• The motor cortex is divided into three subareas: primary motor cortex, premotor area, and supplementary motor area.
• The primary motor cortex controls specific muscle movements.
• The premotor area is involved in planning and coordinating movements.
• The supplementary motor area is responsible for complex and sequential movements.

Primary Motor Area (PMC)

• Located within the precentral gyrus.
• Topographically organized: the representation is proportional to the movement complexity of body parts. (e.g. hands, face and fingers are larger).
• Representation is upside-down.
• Innervates opposite side of the body, with some bilateral representation for the upper face.
• Stimulation of a specific part generates specific muscle contractions, without coordinated movement.

Control of Movement

• Inputs to motor neurons have three functions: initiating voluntary activity; adjusting posture for stable movement; and coordinating muscle action for smooth, precise movements.
• Posture adjustment occurs continually, even during movement, and is coordinated by the cerebellum.

Motor Output Types

• Two types of motor output exist: reflexive (involuntary) and voluntary.
• Reflex responses, e.g. chewing, swallowing, scratching, walking, can be adjusted voluntarily.

Planning of Movement

• Movement planning is a function of the cortex (association area), basal ganglia, and cerebellum (lateral portions).
• Basal ganglia and cerebellum relay information to the premotor and motor cortex.
• The cerebellum sequences motor activities and makes corrective adjustments during execution.

Motor Function

• Two parallel systems of descending pathways originate in the cerebral cortex (upper motor neurons): the pyramidal (corticobulbar and corticospinal) and extrapyramidal systems.
• Pyramidal tracts terminate in the brainstem (corticobulbar) or spinal cord (corticospinal) and control voluntary movements.
• Extrapyramidal tracts govern motor functions beyond the pyramidal system, for postural control, gross movements, and muscle tone.

Descending Spinal Pathways - Pyramidal System

• The pyramidal system mainly controls precise movements.
• At the medulla, 80% of corticospinal fibres cross over, innervating distal muscles.
• Remaining 20% innervate proximal muscles, directly synapsing with lower motor neurons.

Descending Spinal Pathways - Extrapyramidal System

• Includes rubrospinal, reticulospinal, tectospinal, and vestibulospinal tracts.
• Basal ganglia and thalamus influence these descending tracts.
• The extrapyramidal system establishes the postural background for skilled movements, controlling gross subconscious movements and muscle tone.

Summary of Control of Movement

• Movement Planning: basal ganglia, cerebellum, and cortical areas (association area).
• Movement Execution: pyramidal tract controls precise skilled movements, while the extrapyramidal tract provides the necessary background for skilled movements and subconscious gross motor actions (e.g. walking).
• Coordination: primarily performed by the cerebellum.

Upper and Lower Motor Neurons

• Upper Motor Neurons: cell bodies in the cortex of the brain; synapse with lower motor neurons.
• Lower Motor Neurons: cell bodies in the gray matter of the spinal cord and brainstem; synapse with muscles; also divided into alpha and gamma types.

Lesion Effects

• Lower Motor Neuron Lesion: lesion at the anterior horn cells (or below); results in flaccid paralysis, hypotonicity, hyporeflexia, areflexia, fasciculation, and muscle atrophy.
• Upper Motor Neuron Lesion: lesion above the anterior horn cells; results in spastic paralysis, hypertonicity, hyperreflexia, clonus, and a positive Babinski sign.

This quiz explores the key concepts of the motor system, including the planning and execution of skilled movements, and the various functions of the motor cortex. Students will learn about the different subareas of the motor cortex, such as the primary motor cortex, premotor area, and supplementary motor area, as well as the roles of the cerebellum and basal ganglia. Test your understanding of these essential components and their interconnections!