The nervous system allows us to communicate with the outside world while controlling many internal mechanisms at the same time. It is made up of all the nerve cells in your entire body, and by taking in information through our senses, it processes the information and triggers reactions, allowing your muscles to move or causing you to feel pain. Metabolic processes are also controlled by the nervous system. Nervous systems are exceedingly complex: it has been determined that as much as 70% of an animal’s genome is expressed in a single nerve cell.
There are billions of nerve cells, known as neurons, in the nervous system — the brain alone has about 100 billion neurons. Each neuron has a cell body and various extensions; the shorter extensions (dendrites) act like antennae, receiving signals from other neurons and passing them on to the cell body through a long extension (the axon), which can be up to a meter long.
The nervous system is made of two parts: the central nervous system and the peripheral nervous system. The central nervous system (CNS) includes the nerves in the brain and the spinal cords, contained within the skull and vertebral canal of the spine. All the other nerves in the body are part of the peripheral nervous system (PNS). The neurons that carry out integration form the CNS, while neurons that carry information into and out of the CNS form the PNS.
The central nervous system is referred to as such because it combines information from the entire body and coordinates activity across the whole organism. The brain is the most complex organ in the body and uses 20% of the total oxygen we breathe in. It can be divided into four main lobes: temporal, parietal, occipital, and frontal. The brain is protected by the skull (the cranial cavity), and the spinal cord travels from the back of the brain to the center of the spine, stopping in the lumbar region of the lower back. In vertebrates, the spinal cord runs inside the vertebral column, conveying information to and from the brain. It generates basic patterns of locomotion, but it can also act independently as part of the simple nerve circuits that produce certain reflexes.
Both the brain and the spinal cord contain grey and white matter. Grey matter is made up of neuron cell bodies. White matter consists of bundled axons, making up the outer layer of the spinal cord. It links the CNS to sensory and motor neurons of the PNS. In the brain, white matter is located mostly in the interior.
The CNS also contains fluid-filled spaces, called the central canal in the spinal cord and ventricles in the brain. The cerebrospinal fluid is formed in the brain by filtering arterial blood, supplying the CNS with nutrients and hormones and carrying away waste. It circulates through the ventricles and central canal before draining into the veins.
While the CNS consists of, arguably, the most important organ in the body, it does …
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