Question

Acetylcholine is a neurotransmitter that is important in the transmission of signals from the motor neurons to the muscles.
Which of the following describes the action of acetylcholine?

• A. Acetylcholine travels through the nerve fibers to the muscle cell where is breaks down inhibitors blocking the active sites on the muscle cell.
• B. Acetylcholine triggers the production of other neurotransmitters in the muscle cell. The new neurotransmitters stimulate contraction.
• C. Acetylcholine is released from the axon of the motor neuron, diffuses across the synapse and binds to receptors on the muscle cell, leading to contraction.
• D. Acetylcholine binds to G-protein receptors on the muscle cells, resulting in the production of cAMP within the muscle cells. cAMP then stimulates transcription.

Answer 1

The correct option is C Acetylcholine is released from the axon of the motor neuron, diffuses across the synapse and binds to receptors on the muscle cell, leading to contraction.

• A neural signal reaching neuromuscular junction releases a neurotransmitter Acetylcholine which generates an action potential in the sarcolemma.
• This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm.
• Increase in Ca++ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin and facilitates muscle contraction.
  
• Hence Acetylcholine is released from the axon of the motor neuron, diffuses across the synapse and binds to receptors on the muscle cell, leading to contraction.

So, the correct answer 'Acetylcholine is released from the axon of the motor neuron, diffuses across the synapse and binds to receptors on the muscle cell, leading to contraction.'.