Question

Which of the following is incorrect about stimulation of striated muscle contraction by the neuromuscular junction?

A) Acetylcholine is stored in vesicles in the axon terminal.
B) Acetylcholine is secreted in response to a nerve action potential.
C) Acetylcholine binds to soluble receptors in the extracellular environment.
D) Acetylcholine binding stimulates sodium ions to enter the muscle cell.
E) T tubules carry action potentials into the muscle cell.

Answer 1

hi elp sorry secuestro 36

Answer 2

Acetylcholine binds to receptors on the sarcolemma, allowing an action potential to move to the endoplasmic reticulum where calcium ions are stored. When Ca²+ is released in response to the change in voltage, it binds to actin, causing actin filaments to shift position and revealing myosin binding sites for the cross-bridges. The enzyme acetylcholinesterase removes lingering acetylcholine from the synaptic cleft. The correct option is D) Acetylcholine binding stimulates sodium ions to enter the muscle cell.

Step-by-step explanation:

Motor neuron axons connect to muscle fibers at a neuromuscular junction. This is a specialized synaptic structure at which multiple axon terminals synapse with the muscle fiber sarcolemma.

Acetylcholine binds to receptors on the sarcolemma, allowing an action potential to move to the endoplasmic reticulum where calcium ions are stored. When Ca²+ is released in response to the change in voltage, it binds to actin, causing actin filaments to shift position and revealing myosin binding sites for the cross-bridges.

The muscle contracts until the nerve impulse stops and Ca²+ returns to its storage sites. The enzyme acetylcholinesterase removes lingering acetylcholine from the synaptic cleft. The correct option is D) Acetylcholine binding stimulates sodium ions to enter the muscle cell.