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Describe how information passes from a relay neurone to a motor neurone. (3 marks)

Information in the form of electrical impulses is the way in which the nervous system communicates. The neurones have a long axon that is insulated with myelin sheath at intervals. This insulation helps the electrical impulses to jump along the neurone and be transmitted. However, these impulses cannot pass from one neurone to another neurone as there are gaps between them. There are three types of neurones: sensory, relay and motor. The receptors detect stimuli and pass the information to sensory neurones that then make a junction with a relay neurone in the central nervous system. Then, the information is passed on to the motor neurone which then directs the effector to make a response. Between all of the neurones, there is a gap that is called a synapse. Also, between a neurone and an effector, there are synapses present.  
When the information reaches the relay neurone, they trigger the release of chemical messengers called neurotransmitters like acetylcholine from vesicles which fuse with the presynaptic neurone (relay neurone). Then, they diffuse in the synapse and move from a high concentration to a low concentration, and bind to the receptors on the postsynaptic neurone’s membrane (motor neurone). Hence, this will generate an electrical impulse in the motor neurone.

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