It is separated from the inner bony surfaces of the vertebrae by an epidural space. Neurons Many different types of neurons contribute to the complex circuitry of the central nervous system. Two relatively simple types of neurons are sensory neurons, with their cell bodies located part-way along their axons outside the spinal cord, and motor neurons, with their cell bodies located within the spinal cord. Dendrites are small root-like branches that provide the input to motor neuron cell bodies and to the axons of sensory neurons. Information is communicated along axons by waves of ionic activity called action potentials .
Information is communicated between neurons by the release and reception of chemical transmitters.
A synapse is a junction between two neurons, or between a neuron and a muscle fiber. The cell bodies, dendrites and axons of a neuron are bounded by a cell membrane that is able to pump sodium ions outwards. This allows the concentration of potassium ions to build up inside the neuron. Because of the unequal distribution of these and other ions, the neuronal membrane carries an electrical charge of 50 to 70 millivolts, with the negative charge on the inner face of the membrane. If the membrane is briefly short circuited by a change in its ionic permeability, sodium ions rush inwards and potassium ions rush outwards for a brief instant.