What are the steps involved in impulse transmission across neurones?

Impulse transmission across neurones involves the steps of resting potential, action potential, propagation, and synaptic transmission.

In the first stage, the neurone is at rest, known as the resting potential. This is when the inside of the neurone is negatively charged compared to the outside. This is due to the distribution of ions across the neurone's membrane, with more sodium ions (Na+) outside and more potassium ions (K+) inside. The resting potential is maintained by the sodium-potassium pump, which actively transports Na+ out and K+ into the neurone.

The second stage is the action potential, which is the actual nerve impulse. When a stimulus is received, the neurone's membrane becomes permeable to Na+, allowing them to rush into the neurone. This causes the inside of the neurone to become positively charged, creating an action potential. This is a rapid, temporary change in the electrical potential across the membrane.

The third stage is the propagation of the action potential. The action potential is propagated along the length of the neurone, from the dendrites to the axon terminals. This is achieved through a wave of depolarisation and repolarisation. Depolarisation is when the inside of the neurone becomes positively charged due to the influx of Na+. Repolarisation is the process of restoring the negative charge inside the neurone, achieved by the outflow of K+.

The final stage is synaptic transmission. When the action potential reaches the axon terminals, it triggers the release of neurotransmitters. These chemicals cross the synapse, the gap between neurones, and bind to receptors on the next neurone. This can either trigger or inhibit an action potential in the next neurone, depending on the type of neurotransmitter and receptor.

In summary, impulse transmission across neurones involves a complex sequence of electrical and chemical changes. These changes are driven by the movement of ions across the neurone's membrane and the release of neurotransmitters at the synapse.