Meghan has taught undergraduate and graduate level science courses and has a PhD in Immunology.
Brain and Motor Neurons
Think of an electronic device that requires a power source and delivers a controllable output. A kitchen mixer, a remote control car, and a vacuum cleaner are all good examples. Once these devices are plugged in, an invisible, electrical current sends a signal to the machine, giving it power. As the controller, you are then able to turn on the device and change the speed. Our brains are similar to these everyday items, in that they contain a power source of nerves and allow you to control your muscle movements.
The brain is a very complex organ. The main parts of the brain include the cerebrum, cerebellum, and brainstem, as seen in the image below. The cerebrum and cerebellum control the cognitive and voluntary functions of the body. The brainstem connects to your spinal cord, which together can be thought of as the power cord to your household device. The brainstem is responsible for regulating your heartbeat and breathing, but it also contains nerves that control your motor or movement functions.
The Corticospinal Tract
The nerve fibers that travel from the brain through the stem to your spinal cord are considered part of the corticospinal tract. The corticospinal tract conducts impulses from the brain to your muscles in a voluntary manner - this means that you're in control of the movements conducted by this tract. The corticospinal tract mainly controls your upper and lower limbs. Picking up a plate, sitting down, and flexing your feet are all examples of voluntary motions controlled by your corticospinal tract. The rest of the voluntary motions, such as swallowing, chewing, and facial expressions are regulated by the corticobulbar tract.
Anatomy of the Corticospinal Tract
Within the cerebrum, the motor cortex contains the origin of the motor nerves. The motor nerves are bundled together as they travel down through the cerebrum to enter the brainstem. This bundling composes the corticospinal tract. The brainstem itself is made up of multiple layers, including (from top to bottom) the forebrain, midbrain, pons, medulla, and pyramidal decussation. At the pyramidal decussation the nerve fibers within the corticospinal tract split into what is called the lateral and anterior corticospinal tracts. Nerve fibers that cross over to the opposite side of the spinal cord make up the lateral corticospinal tract, whereas the remaining nerves that remain descending make up the anterior corticospinal tract. This divergence of the tracts enables control of the limbs (lateral) and control of the pelvis and other mid-body muscles (anterior). The lateral nerve bundle is also larger than the anterior. In the event of damage to the lateral corticospinal tract, muscles on the same side of the body will be affected; whereas, if there is damage to the motor cortex within the cerebrum, muscles on the opposite side of the body will be affected.
The brain is a highly complex organ consisting of electrical impulses and nerve fibers that travel down through your spinal cord, controlling your muscles. Similar to an electronic device, the corticospinal tract contains the nerves that regulate voluntary movement - or, the muscles that you can control. The limbs are primarily controlled by the corticospinal tract. Within the brainstem, different layers help maintain the flow of the corticospinal tract. Once the nerve fibers reach the pyramidal decussation, the tract splits into the lateral and anterior corticospinal tracts.
Medical Disclaimer: The information on this site is for your information only and is not a substitute for professional medical advice.
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