Neuronal Structure

Sensory Neurone
The nerve impulses travel from left to right in this diagram of a sensory neurone. A stimulus causes the impulse to be produced by a sense organ. (skin / ears / eyes / tongue / nose)
Dendrites and Synapses are both nerve endings at the ends of neurones. Dendrites are located at the ends that receive the nerve impulses (at the left of diagram above). Synapses are found at the transmitting ends of the neurone where the impulse is transferred to another neurone. Synapses use chemicals to transmit their electrical signal.
Relay Neurone
This neurone does exactly what its name suggests. Relay neurones are situated in the spinal cord. This, along with the brain, acts as the central nervous system.
Reflex actions are caused when a stimulus creates an electrical impulse that is relayed via the relay neurone straight to the effector. The message never actually reaches the brain.
Motor Neurone
A motor neurone is connected to an effector and when an electrical nerve impulse is transmitted, the effector is stimulated into action. (muscles / glands)