1. Overview of CNS Structure and Function
The Main Motor systems

2. 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.

3. 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

4. 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.

5. 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

6. 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.

7. 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

8. Signs of Upper Motor Neurone damage
The Babinski Sign