Question

Sequence the events that take place when a motor neuron's action potential triggers a muscle contraction.

Answer 1

Answer:

The correct sequence is: A) The motor neuron's action potential arrives at the neuromuscular junction, C) The muscle fiber's plasma membrane depolarizes in response to the arrival of acetylcholine, F) The action potential moves throughout the muscle fiber along transverse (T) tubules, E) The sarcoplasmic reticulum becomes more permeable in response to the action potential, causing a release of calcium ions, D) Calcium ions bind to troponin, which changes the conformation of the tropomyosin so the actin-binding sites are exposed, B) Myosin cross‑bridges attach to actin fibers.

Explanation:

The question is referring to the process of muscle contraction thanks to the action potential transmission in the neuromuscular junction.

This process begins when the motor neuron's action potential arrives at the neuromuscular junction and excites the muscle fiber with the presence of acetylcholine, which depolarizes the membrane. This information is transmitted through every myocyte thanks to the T tubes, this is important because myocytes must coordinate in order to produce an effective contraction of the muscle. The action potential makes the sarcoplasmic reticulum release calcium ions that will arrive at the sarcomeres and bind to troponin molecules in order to uncover the hidden actin-binding sites. With the actin-binding sites now uncovered, the myosin heads can form cross bridges with it, which will lead to the shortening of the sarcomere and finally produce the contraction of the muscle.

Answer 2

Answer:

A,C,F,E,D,B

Explanation:

The is the sequence of  action potential transmission at  at the neuromuscular junction. Generally the arrival of action potential from the presynptic neuron caused influx of ca+ which causes migration and  the  release of the the acetycholine to the synaptic cleft.

The acetycholine binds with the receptors  on the saccolemma to causes opening of Na+ , its influx to causes depolarizarion  of the sacolemma. The depolarization of the latter spreads along the transverse tubules, This depolarization causes increases in the permeability of the sacorplasmic reticulum, with opening of ca+ channels and diffusion of Ca+ out of the  S. reticulum.

The Ca+ binds to troponin,and tropomyosin  exposed the myosin-binding sites on actin filament . The myosin head forms the cross bridges with the filament, and therefore the sacomere shortens leading causing muscle contraction.