There are roughly 100 billion neurons in the human nervous system, each one is made up of three basic part the Soma, or cell body, the dendrites and the axon. They will have only one axon, but usually many dendrites branching off to receive "messages". These nerve cells cooperate with each other, make connections with each other, and are responsible for producing behaviour in all of us. They are the information processing units of the brain, and because of this they have varied and complex jobs and a lot of responsibility. These jobs include receiving sensory information, and passing along that information, interpreting that information and making our muscles produce a reaction of behaviour, they encode our memories, produce thoughts and emotions, and of course they regulate our body processes such as breathing and our heartbeat (you know just the little things)! The cell body contains the nucleus and cytoplasm. The axon extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals.Dendrites extend from the neuron cell body and receive messages from other neurons. Synapses are the contact points where one neuron communicates with another. The dendrites are covered with synapses formed by the ends of axons from other neurons.When neurons receive or send messages, they transmit electrical impulses along their axons, which can range in length from a tiny fraction of an inch (or centimeter) to three feet (about one meter) or more. Many axons are covered with a layered myelin sheath, which accelerates the transmission of electrical signals along the axon. This sheath is made by specialized cells called glia. In the brain, the glia that make the sheath are called oligodendrocytes, and in the peripheral nervous system, they are known as Schwann cells. We will talk more about these in the next page.
neurotransmitters play an important role in communication between neurons. They carry signals across the synaptic gap allowing two neurons to communicate. Chemicals, called neurotransmitters, are released from one neuron at the presynaptic nerve terminal. Neurotransmitters then cross the synapsewhere they may be accepted by the next neuron at a specialized site called a receptor.When they do not do their jobs this can cause problems such as depression. They were discovered in 1921 by an Austrian scientist called Otto Loewi in an experiment involving frog hearts. There are many different types of neurotransmitters all of which trigger different types of reactions.