Neurones are nerve cells, which carry messages from one part of the body to another. These messages are carried as tiny electrical signals.
Motor neurones are located in the central nervous system and by projecting their axons outside the CNS, can indirectly or directly control muscles. Motor neurones receive messages from the CNS to effectors (like muscles). Motor neurones have a motor end plate, which is in muscles and passes the electrical signals onto the muscles, via the muscle fibres. This makes them contract. Motor neurones can be as long as 1m and their motor end plate are found in a muscle, while the dendrites are found inside the spinal cord. Axons run in groups – forming nerves.
Relay neurones simply connect a sensory neurone and a motor neurone. Relay neurones are found in the CNS (Central Nervous System), often in the spinal cord. They have evolved as a part of the reflex arc and, through bypassing the journey for a signal to the brain, they make reactions quicker.
Sensory neurones are the neurones inside the nervous system which are responsible for changing external stimuli, such as chemicals, into electrical impulses, and to send these messages from the receptor cell to the CNS across synaptic gaps linking neurones. The sensory neurones are found very close to the spinal cord. There are two long threads of cytoplasm – the axon end extends into the spinal cord, and the dendron into the receptor cell.