Read the following statements with respect to skeletal muscle and its components.

(a) The junction between a motor neuron and the sarcolemma of the muscle fibre is called the muscle spindle.

(b) A neural signal reaching this junction releases a neurotransmitter, the acetylcholine.

(c) Neurotransmitter generates an action potential first in the sarcosome.

(d) Action potential spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm.

In the above, the correct statements are

The junction between a motor neuron and the sarcolemma (cell membrane) of a muscle fibre is called the neuromuscular junction (NMJ) or motor-end plate. It is a specialised synapse where the nerve impulse from the motor neuron is transmitted to the muscle fibre.

When an action potential (electrical signal) reaches the end of the motor neuron, it triggers the release of a neurotransmitter called acetylcholine (ACh) into the synaptic cleft. The synaptic cleft is the small gap between the motor neuron and the sarcolemma of the muscle fiber.

Acetylcholine diffuses across the synaptic cleft and binds to receptors on the sarcolemma. This binding of acetylcholine to its receptors generates an action potential in the sarcolemma, propagating an electrical impulse along the muscle fiber.

This action potential eventually reaches the sarcoplasmic reticulum, a specialised internal membrane system in the muscle fiber, leading to the release of calcium ions. The presence of calcium ions triggers the sliding of actin and myosin filaments, leading to muscle contraction.