Overview of CNS Structure and Function The Main Motor systems

Motor Control Primary Motor Cortex Premotor Cortex Key brain areas managing motor activities and control of movement. Upper motor neurones The Motor Cortex. Primary Motor Cortex Premotor Cortex Role: Act together to initiate, control and integrate movement and movement control through motor pathways linking different areas of the brain and spinal cord.

Upper Motor Neurone Pathways Large nerve cells (e.g. Betz Cells) in the motor cortex. Give rise to: a) direct pathways to spinal motor centres -Corticospinal tract b)indirect pathways that relay in brain stem -Corticoreticulospinal tract. c) other motor spinal tracts

Direct and indirect motor tracts Diagram of key motor pathways Motor nerve tracts arising within the primary motor cortex and the premotor cortex synapse either directly or indirectly with spinal motor neurone pools Direct cortical projections decussate at the level of the brain stem. They serve the contralateral spinal motor centres. The corticoreticulospinal tracts synapse with motoneurone pools on both sides of the spinal cord.

Corticoreticulospinal Tract Reticular (net like) formation –a complex formation of groups of neurones serving a number of functions and systems Motor functions are: Modulatory:- neurones project to spinal cord and to cerebral cortex Premotor functions:- long pathways influencing spinal motor neurone function. Important for motor planning and anticipation E.g. Maintains balance and posture

Sample experiment showing “anticipatory” muscular activity Experimental Design The subject pulls a lever on hearing a sound. To maintain a safe posture he automatically adopts a “braced leg” position to counteract the impact upper limb movement on body stability His gastrocnemius muscles contract a few ms before his biceps apply pull to the lever. This braces his body against the upper limb action.

Clinical Correlates of Damage to Upper Motor Neurone Pathways Early response Flaccid paralysis of extremities Loss of reflex activity Trunk control (proximal muscle control) generally preserved Late response Recovery of some spinal control but loss of upper motor neurone control some of which is inhibitory Upward Babinski sign Increased muscle tone (spasticity) Clonus

Signs of Upper Motor Neurone damage The Babinski Sign