Dendrites convey signals towards the cell body. Axons conduct signals away from the cell body. Dendrites are short and numerous and branch extensively. Most neurons have only a single axon which is usually very long. Schwann cells are arranged along the length of the axon. All together these Schwann cells form an insulating layer which is called the myelin sheath. Axons can be branched and each branch can terminate in hundreds or thousands of small branchlets called telodendria which end in a small bulbous end called the synaptic knob. Synaptic knobs relay messages to other cells via neurotransmitters. Between the synaptic knobs are gaps called synapses. In the body cells usually carry a negative charge. Nervous cells are able to alter their charge in order to conduct signals. Cells that are able to do this are called excitable cells. Neurons are able to alter their charge largely due to ions. Cells in which a signal begins are called pre-synaptic cells. Cells which receive the signal are called post-synaptic cells. There are two types of synapses: electrical and chemical. An electrical synapse allows the signal to spread directly from the pre-synaptic to the post-synaptic cells. Chemical synapses allows for cells that so not have an electrical connection to spread their messages. This happens by converting the electrical signal to a chemical signal that then travels across the synapse and is then converted back to an electrical signal on the other side of the synapse. These chemicals are called Neurotransmitters. |
