1.4 Nervous system

Watch Video 1 which introduces the overall structure of the nervous system and how it is made up of the brain, the spinal cord, and a complex network of nerves that run throughout the whole body.

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All animals have nervous systems. The specialised cells that make up a nervous system are nerve cells or neurons. They are able to conduct an electrical signal from one to another, passing information quickly from one part of the body to another. We'll talk about neurons specifically in a later video. For now, we're going to look at the overall structure of the nervous system.

In simple animals, like jellyfish, the nervous system may be no more than a simple nerve net, a net of neurons that are connected together loosely, which controls the pulsing of the jellyfish's body and its tentacles to allow it to move and draw in food. In more complex creatures, however, the nervous system has many more complex jobs to do. And so it has evolved a much more complicated structure, involving specialised organs that are made from neurons. We're going to look at humans as our prime example. But keep in mind that all animals, even things like worms, spiders, and insects have a nervous system.

The nervous system has two main parts-- the central nervous system, CNS, and the peripheral nervous system, PNS. In this diagram, the CNS, the central nervous system, is colored in yellow. And the peripheral nervous system, PNS, is colored in blue.

The central nervous system is composed of the brain and the spinal cord. This is where most of the information processing happens, kind of like the processor chip in the laptop. The CNS receives information from the rest of the body, decides what to do about it, and then sends instructions back.

Note that for humans, some of this information processing is conscious. You're aware of making the decision. But a very large part of it happens in the brain without you being aware of it.

The peripheral nervous system, PNS, is so named because the periphery of something is its outside, its edge. You can see from the diagram that the PNS connects the central nervous system to the rest of the body, including right out to your skin. It consists of long nerve fibres or bundles that reach from the spinal cord out to all the various organs and parts of the body.

It collects information from other organ systems about how the body's going and what the external environment is like. It's cold today and sends that to the CNS. It also receives signals from the CNS and directs the body to change in some way. Muscles move, intestines contract, heart beats faster, and so on.

So to summarise, in the body, information passes in two directions. It can pass from the PNS to the CNS. So that's information about how the body is doing. And it can pass from the CNS back to the PNS, which is instructions about what the body needs to do next.

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The nervous system consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made up of the brain and spinal cord. The PNS is made up mainly of nerves, which are bundles of long fibres called neurons, that connect the CNS to every part of the body.

This system allows different parts of the body to communicate and enables the brain to control and regulate what is going on. Through the nervous system, the brain detects environmental changes that impact the body, then works in tandem with other body systems to respond and maintain equilibrium.

For example, if it is hot, the brain tells the blood vessels to dilate (become wider) to reduce body temperature, if it is cold, the brain sends shiver signals out to warm the body up.