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Each axon terminal contains thousands of membrane-bound sacs called vesicles, which in turn contain thousands of neurotransmitter molecules each. Neurotransmitters are chemical messengers which relay, amplify and modulate signals between neurons and other cells.
1 Sensory neurones carry signals from receptors receptors: organs which recognize and respond to stimuli to the spinal cord and brain. 2  Relay neurones carry messages from one part of the CNS CNS: Central Nervous System (brain and spinal cord). to another.here two neurones meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neurone releases the chemical into the gap. The chemical diffuses across the gap and makes the next neurone transmit an electrical signal.