Neurons and synapses: how nervous signals travel — Biology, 14–17
Nervous systems combine fast electrical changes with chemical messages between cells. This explains how a signal can travel along one neuron and then cross a tiny gap to affect the next cell.
The idea
A neuron can change the voltage across its membrane and send a brief electrical impulse along its axon. At the end, it releases chemical messengers into a synapse, a tiny gap where the message can influence another neuron, muscle or gland cell.
Why it matters
The problem is communication across a whole body: electrical signals are fast along a cell, but cells do not normally touch end to end. Synapses solve that gap while allowing signals to be strengthened, weakened or stopped, so the nervous system is more than simple wiring.
A worked example
Touch a hot pan: heat activates receptors in your skin, which trigger impulses in a sensory neuron. At a synapse in the spinal cord, chemicals pass the message to another neuron; motor neurons then signal arm muscles, which contract and pull your hand away.
The common trap
It is reasonable to picture a nerve message as electricity flowing continuously from skin to muscle. In reality, the electrical impulse travels within a neuron, while chemicals cross most synapses; this separation is why a signal has direction and can be modified.
Where it is used
This biology helps explain reflexes, learning, pain and movement. Medicines and recreational drugs can change synapses by imitating a messenger, blocking its receptor or slowing its removal, which is why small chemical changes can alter mood, alertness or coordination.
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