1. What kinds of coordinated movements does skeletal muscle contraction lead to?

• Voluntary movement

• Reflexes

• Maintenance of posture

• Repetitive and rhythmical movements, e.g. breathing All of these types of movement are under the control of an integrated motor system.

2. What are the components of the motor system that initiate, coordinate and execute these movements?

The components can be thought of as forming an interactive hierarchy. They consist of:

• Cerebral cortex: consisting of the motor cortex and associated areas

• Subcortical areas: the cerebellum, basal ganglia and brainstem

• Spinal cord: this carries fibres from the cerebral cortex to motoneurones, but is also capable of its own intrinsic reflex activity

• Motoneurones: these form the final common pathway

• Motor units: the functional contractile unit

• Receptors and afferent pathways: these sensory pathways relay information back to the other components, which can in turn adjust movement, e.g. proprioceptive information

3. Where is the motor cortex located?

This is found at the precentral gyrus (Brodmann's area 4). This controls contralateral muscular activity. There is also an associated motor cortex, found in Brodmann's areas 6. This helps control movement on both sides of the body.

4. Where in the spinal cord are cell bodies of the motoneurones located?

These are located in the ventral horns of the spinal cord. They congregate together as motor nuclei in specific parts of this ventral horn depending on whether they supply muscles of the axial or appendicular skeleton, and whether they supply proximal or distal limb muscles.