(a) Polarisation of the membrane of a nerve fibre
Ans. Polarisation is when the neuron is at rest. Inside of the neuron is negatively charged relative to the outside due to uneven distribution of Na⁺ and K⁺ ions. This is called resting potential.

(b) Depolarisation of the membrane of a nerve fibre
Ans. Depolarisation occurs when a stimulus triggers Na⁺ channels to open. Na⁺ rushes into the cell, making the inside temporarily positive, which creates an action potential.

(c) Transmission of a nerve impulse across a chemical synapse
Ans. When an impulse reaches the end of a neuron (axon terminal), neurotransmitters are released into the synaptic cleft. They bind to receptors on the next neuron, triggering a new action potential. This allows signal transmission from one neuron to another.