Nervous System - For Students

What Are the Nerve Cells and Nerves

All nervous system from those of the simplest multicellular animal, to the human body, are made up of cells whose job is to carry 'messages', called nerve impulses, to and from all parts of the body. Like all other cells, a nerve cell or neuron has a nucleus and cytoplasm. Each neuron has several 'inputs' called dendrites, along which nerve impulses travel into the cell. Leading out from the cell, the cytoplasm forms a single long fibre, called the axon. From the axon impulses travel out to another nerve, or to a muscle or some other cell. Axons can be tiny, but the longest runs from the spinal cord down to your toes, and can be up to one metres long. It can take less than a fiftieth of a second for an itch signal to travel from your big toe to your brain.

Sensory Nerves

Nerves are bundles of axons or nerve fibres. There are two types of nerves. Sensory nerves carry messages to and from the skin and other sense organs.

Simple Definition:

1. Sensory neurons are nerve cells that transmit sensory information (sight, sound, feeling, etc.). They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord.

Motor Nerves

Motor nerves communicate with the muscles, making them contract and relax so that we can move.

Synapses

Neurons do not touch one another. There are gaps between them called synapses. Messages cross the gap between one neuron and the next with the help of a chemical.

What is the Central Nervous System

Spinal Cord

Human and other vertebrate animals have a single tubular nerve cord, called the spinal cord. It is safely protected by the vertebrae, the bones of the backbone or spines. The brain is an enlarged and very complicated swelling on the end of the spinal cord. Together, the brain and spinal make up what is we call the central nervous system.

The central nervous system has many nerves branching from it. The human brain not only coordinates many activities in the body, it is also capable of remembering and thinking. A complex nervous system allows an animal to behave in a complex way. In fact, humans have the most highly developed nervous system and behaviour of any animal.