AO1

• There are three main types of neurons: sensory, relay and motor.
• Each neuron has a different function, depending on its location in the body and its role within the nervous system.
• Sensory neurons are found in receptors such as the eyes, ears, tongue and skin.
• Sensory neurons carry nerve impulses to the spinal cord and the brain.
• Not all sensory neurons reach the brain, as some neurons stop at the spinal cord allowing for quick reflex actions.
• Motor neurons are the neurons that carry the impulses from the CNS to the muscles.
• Relay neurons are neurons that connect sensory neurons to motor neurons in the central nervous system.
• An axon transmits the action potential to the axon terminal.
• neurons

  A) sensory

  B) relay

  C) motor

  D) myelin sheath

  E) node of ranvier

  F) dendrite

  G) cell body

  H) receptor cell

  I) axon

  
• The synaptic vesicles containing the neurotransmitter are only present on/released from the presynaptic membrane and the receptors for the neurotransmitters are only present on the postsynaptic membrane. It is the binding of the neurotransmitter to the receptor which enables the signal/information to be passed/transmitted on (to the next neuron). Diffusion of the neurotransmitters mean they can only go from high to low concentration, so can only travel from the presynaptic to the postsynaptic membrane. This means neurons can only transmit information in one direction at a synapse.