Neurones carry electrical signals. A motor neurone, for example, carries a message from the brain to a specific muscle or gland. Its cell bodies are located within the spinal cord or the brain. The dendrites transport impulses to the cell. The terminal branches contain vesicles, which release transmitter substances, and mitochondria.

The axon can be very long, some even stretch from your brain all the way to your foot. The Schwann cells contain the axon, enclosing it in a myelin sheath. They’re not found on all neurones. This increases the rate at which the signal is conducted. The uncovered points are called nodes of Ranvier which also help to speed up the rate of conduction.

Nerve Impulse Propagation

After an action potential has started it’s automatically moved or propagated along an axon. The surrounding voltage-gated ion channels detect the reversal of the membrane potential and then open once the potential change is high enough.

Once the threshold has been reached voltage-gated sodium channels in one part of the axon, called the trigger zone, open and sodium ions flood in. The membrane in the trigger zone depolarizes and more sodium channels open. The positive charge moves by local current flow into the adjacent parts of the axon. While the trigger zone is in its refractory period the potassium gates open and the sodium gates close. As the potassium flows out the membrane repolarizes. In the adjacent active region the membrane depolarizes and so the impulse continues to move up the axon.