How are action potentials propagated along an axon?

Action potentials are propagated along an axon through a process called saltatory conduction, involving depolarisation and repolarisation.

In more detail, an action potential is essentially an electrical signal that travels along the axon of a neuron. This process begins when a neuron is stimulated by another neuron or by a specific signal from the environment. The stimulation causes a sudden change in the neuron's membrane potential, causing it to depolarise. Depolarisation is the process where the inside of the neuron becomes less negative compared to the outside. This is due to the rapid influx of positively charged sodium ions into the neuron through voltage-gated sodium channels.

Once the membrane potential reaches a certain threshold, an action potential is triggered. This action potential then propagates along the axon, moving from the cell body towards the axon terminals. This propagation is due to the sequential opening and closing of voltage-gated ion channels along the length of the axon. As the action potential moves along the axon, the area behind it repolarises, restoring the negative membrane potential. This is achieved by the efflux of positively charged potassium ions out of the neuron through voltage-gated potassium channels.

Interestingly, in myelinated neurons, the action potential doesn't move continuously along the axon but jumps between the gaps in the myelin sheath, known as the nodes of Ranvier. This process is known as saltatory conduction and it significantly speeds up the transmission of the action potential.

In summary, the propagation of action potentials involves a complex interplay of ion movements across the neuron's membrane, driven by changes in membrane potential. This process is crucial for the transmission of information within the nervous system, allowing us to respond to our environment and carry out all sorts of functions.