Neurons and Nerve Impulses
Neurons fire action potentials along axons.
About this topic
Neurons are specialised cells: dendrites receive signals, the cell body contains the nucleus, and a long axon, often wrapped in an insulating myelin sheath, carries impulses away. At rest the neuron is polarised (about −70 mV). When stimulated past a threshold, sodium channels open, producing an action potential that travels along the axon.
At synapses, the impulse triggers release of neurotransmitters that cross the gap and bind to receptors on the next neuron. Myelin speeds up conduction by saltatory jumping.
At rest, the neuron's inside is about minus 70 millivolts, kept by the sodium-potassium pump. A stimulus opens sodium channels, depolarising the membrane, and the electrical signal, the action potential, sweeps along the axon, then potassium leaves to restore the resting state. The impulse is all-or-nothing: a stronger stimulus gives more frequent impulses, not bigger ones.
At the synapse, impulses cause release of neurotransmitters such as acetylcholine, which cross the tiny gap and bind to receptors on the next neuron. Myelin allows jumping between gaps called nodes of Ranvier, speeding transmission; multiple sclerosis damages myelin. Many drugs, including caffeine and anti-depressants, act on synapses. A common error is thinking impulses are like electricity in a wire, carried by electrons; they are made by ion movements.
Key ideas
- Dendrites receive
- Axon carries signals
- Synapses use neurotransmitters
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Frequently asked questions
What is Neurons and Nerve Impulses?
Neurons fire action potentials along axons.
What will I learn in Neurons and Nerve Impulses?
Dendrites receive. Axon carries signals. Synapses use neurotransmitters.
Is Neurons and Nerve Impulses part of Biology?
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