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Location, Structure, And Function of the Motor Cortex

Motor Cortex: Location, Structure, and Function
The part of the brain that does the job of executing voluntary movements is the motor cortex. The required movements are carried out in such a way that they best suit the individual's current position.
Nicks J
Last Updated: Dec 21, 2017
Did You Know?
The left motor cortex is involved in regulating movement of the right side of the body, while the right motor cortex co-ordinates movements of the left side of the body.
Have you ever thought which part of the brain plays a crucial role in generating voluntary movement? Well, it is the motor cortex. It lies slightly at the back side of the frontal lobeā€•one of the 4 major lobes that sits at the front portion of the brain. The motor cortex lies prior to the central sulcus, a fissure-like structure that allows us to distinguish the frontal lobe and parietal lobe.
As the name suggests, the motor cortex deals with the motor function of the body, meaning it is involved in the movement of muscles to perform a specific task. Our ability to produce movements, such as picking up small objects, are linked to the proper working of the motor cortex.
Be it small movements, such as moving the fingers, or the large movements, such as sitting and rolling, the motor cortex plays a crucial role right from initiation to execution of movement. To put it simply, the voluntary contraction of muscles for normal movement is something that is supervised by the motor cortex.
At the time of initiating movement, the upper motor neurons located in the motor cortex transmit electrical signals, which run through other structures of the brain, such as basal ganglia and brain-stem, and is received by the lower motor neurons located in the spinal cord. The signal then travels down from one lower motor neuron to another and finally arrives at the desired muscle group. Upon receiving the signal, the muscles contract causing voluntary movement.
Different Regions of the Motor Cortex
Labeled human brain
Premotor Cortex
In order to execute a specific movement, certain muscles need to be contracted. The premotor cortex analyzes and accurately determines the group of muscles that need to be used to carry out the specific movement. It takes into account the current position and posture of the body when choosing the set of muscles to execute the movement. For instance, for kicking a soccer ball, the premotor cortex rightly decides to move the leg muscles to initiate the action.
Primary Motor Cortex
This part of the brain actually communicates with the motor neurons of the spinal cord to stimulate the intended muscles. In short, the primary motor cortex is involved in sending signals that contribute directly in generating movement.
Supplemental Motor Area (SMA)
One of the main functions of the SMA is to supervise bi-manual coordination. In bi-manual coordination, multiple movements need to be executed at simultaneously to achieve desired action or task.
For example, actions that involve the use of both hands will require coordination between the left and right motor cortex. This is done by the SMA, which helps to produce a combination of movements simultaneously to execute the complex action. So our ability to move both hands simultaneously to complete a specific task has been attributed to the proper working of the SMA.

The SMA also assists in deciding the sequence of movements so as to arrive at a optimum movement path, to carry out a complex action.

A point to note here is that the motor cortex does not decide whether to execute a movement or not. For instance, upon seeing a piece of chocolate lying on the floor, the decision to pick it up is taken by the prefrontal cortex, which lies just ahead of the premotor cortex. The prefrontal cortex then, accordingly, signals the motor cortex to carry out the movement. Also, the motor cortex is not the only area involved in carrying out precise movements. Other parts of the brain, such as the basal ganglia and cerebellum, equally contribute to produce motor output.