Biology · Locomotion and Movement · NEET
They are almost the same idea and NCERT uses them together. The neuromuscular junction (NMJ) is the whole meeting point between the motor neuron ending and the muscle fibre. The motor end plate is the specialised part of the muscle's sarcolemma at this junction. For NEET, treat 'neuromuscular junction / motor end plate' as the site where the nerve signal is passed to the muscle.
A motor unit is one motor neuron together with all the muscle fibres it supplies and controls. When that neuron fires, every muscle fibre in its unit contracts at once. Fine-control muscles (like eye muscles) have few fibres per neuron, while big power muscles (like thigh muscles) have many fibres per neuron. Do not confuse a motor unit with a single muscle fibre.
No. There is a very small gap (a synaptic cleft) between the neuron ending and the sarcolemma. The neuron does not touch the muscle. It releases the neurotransmitter acetylcholine into this gap; acetylcholine then binds to the muscle membrane and starts an action potential on the sarcolemma.
When the nerve signal reaches the neuron ending, acetylcholine is released and crosses the synaptic cleft. It binds to receptors on the motor end plate (the muscle side). This generates an action potential that spreads over the sarcolemma and into the muscle fibre, leading to release of calcium and then contraction.
NEET regularly starts the muscle-contraction sequence from this junction: CNS sends a signal through a motor neuron to the sarcolemma, acetylcholine is released, and an action potential begins. The disorder myasthenia gravis (an autoimmune disease affecting the NMJ) is also asked. Knowing the NMJ links nerve control to the whole contraction pathway.
Muscle contraction is initiated by a signal sent by the central nervous system by the release of _____.
Choose the correct statements regarding muscle contraction. A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre. B. The neural signal generates an action potential which causes the release of Ca2+ into sarcoplasm. D. Myosin hydrolyses ATP during cross-bridge cycling. E. The reaction time of the fibre depends on the number of motor units involved.
Chronic autoimmune disorder affecting neuromuscular junction leading to fatigue, weakening and paralysis of skeletal muscle is called as:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the meeting point where the ending of a motor neuron reaches the membrane (sarcolemma) of a muscle fibre. Here the nerve passes its message to the muscle using the chemical acetylcholine.
A motor unit is one motor neuron plus all the muscle fibres it controls. When the neuron fires, all those fibres contract together.
Acetylcholine. It is released by the motor neuron ending and starts an action potential on the muscle's sarcolemma.
Myasthenia gravis, an autoimmune disorder that damages the neuromuscular junction and causes muscle fatigue, weakness and paralysis.
It creates an action potential that spreads over the sarcolemma, which then triggers release of calcium ions into the sarcoplasm, leading to muscle contraction.
