The Motor Cortex

The motor cortex is the part of the brain which controls most of our movement (a few reflexes are regulated by the spinal cord). There is a motor area on both the left and right hemispheres, with the left hemisphere motor cortex controlling the right side of our body, and vice versa.

Here is a diagram of the brain showing where the motor cortex is located:

The motor cortex can be divided into several different sub-sections:

the primary motor cortex is the main area controlling the execution of movement.

the premotor cortex is thought to be responsible for the preparation of movement – cells in this area fire just before movement takes place.

the supplementary motor area (SMA) is thought to be involving in planning sequences of movement and coordinating movement on both sides of the body.

However, it is not just the motor cortex which is responsible for controlling our movement. The cerebellum, basal ganglia, posterior parietal cortex and the primary somatosensory cortex have also been shown to be involved.

It has also been shown that different areas of the motor cortex are involved in controlling movement in different parts of the body. Much of this work was carried out by Penfield during the 1930’s. In his most famous experiment, he applied electrical stimulation to different parts of the motor cortex in the brains of patients who were undergoing surgery for epilepsy. As the patients were conscious, they could tell him which part of their body they felt movement in when each part of the motor cortex was stimulated. From this research, he mapped the body onto the motor cortex – he called this a homunculus.

As you can see from the homunculus map, different parts of the body are represented over larger areas of the motor cortex, regardless of the size of the body part. The fact that the hand covers such a large area reflects how the hand is one of the most mobile areas of the body.

If a part of the body has to be amputated then this causes disruption to the motor cortex. Due to neural plasticity, patients can feel as though they have ‘phantom limbs’ – the feeling that the limb that has been amputated is still there.

Check back soon for my next post about phantom limbs 🙂