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The Nervous System:

The nervous system consists of the brain, spinal cord, and billions of neurons acting as a network of communicating cells. The central nervous system, or CNS, consists of the  spinal cord and brain, responsible for processing information, coordinating responses, and controlling several bodily functions. The peripheral nervous system, or PNS, includes all the sensory and motor neurons that allow us to sense, feel, and move our bodies. These two systems work hand-in-hand, giving us cognitive control over our actions. Just as a car without any internal wiring would just be a box with four wheels capable of going nowhere, a human body without the nervous system would be unable to observe the environment and execute movements.

What is a Neuron?

Before getting into the anatomy of the spinal cord and brain, it is important to understand how the neuron is built to communicate. The neuron is a type of cell specialized for transmitting and receiving electrical and chemical signals throughout the body. Each neuron consists of a dendrite – a receptive-like structure that transmits signals to the cell body – which then sends electrical impulses down a slender, wire-like axon to neighboring neurons or muscle cells (as discussed in Chapter 4).

White and Grey Matter:

Within the nervous system, nervous tissue is classified as either grey or white matter. While neurons are naturally grey, some have axons coated in a fatty, insulating tissue called myelin, which gives them a white appearance. Myelin not only protects the neuron but also significantly increases the speed of signal transmission—much like a phone charger relies on a thick, intact coating to efficiently deliver power. This insulation is essential for rapid communication with the brain; without myelinated white matter, there would be a noticeable delay between a stimulus and our awareness of it, just as a damaged charger struggles to deliver energy. In the spinal cord, this distinction is visible: the outer layer is made of white matter (myelinated axons), while the central region consists of grey matter (cell bodies and unmyelinated neurons).

• Grey matter, generally located deep within the spinal cord and shaped like a butterfly, these areas contain neuronal cell bodies which communicate with nearby neurons. Within the brain, the grey matter is located superficially on the outer surface of the brain.

• White matter is organized superficially to the grey matter within the spinal cord and composed of bundles of axons to send quick messages to and from the brain. Within the brain, white matter is located deep to communicate messages to the superficial grey matter. Therefore, damage to white matter can affect one’s ability to move or react to stimuli.