Question

Place the following events in the correct order they occur during excitation-contraction coupling in skeletal muscle:

1. Myosin forms a tight bond with actin and undergoes the ‘power stroke’.
2. The troponin/tropomyosin complex shifts, exposing the myosin binding sites on the actin filament.
3. Ca2+ binds to troponin.
4. Ca2+ moves out of the sarcoplasmic reticulum (called a “calcium spark”).
5. An action potential in the alpha motor neuron leads to the release of neurotransmitter at the neuromuscular junction.
6. Nicotinic receptors on the motor end plate open, enabling an influx of Na+ ions (end plate potential).
7. The action potential travels along the sarcolemma and down the t-tubules.
8. Ryanodine receptors coupled to the t-tubules open, allowing Ca2+.

Answer 1

An action potential in the alpha motor neuron leads to the release of neurotransmitter at the neuromuscular junction.

Nicotinic receptors on the motor end plate open, enabling an influx of Na+ ions (end plate potential).

The action potential travels along the sarcolemma and down the t-tubules.

Ryanodine receptors coupled to the t-tubules open, allowing Ca2+.

Ca2+ moves out of the sarcoplasmic reticulum (called a “calcium spark”).

Ca2+ binds to troponin.

The troponin/tropomyosin complex shifts, exposing the myosin binding sites on the actin filament.

Myosin forms a tight bond with actin and undergoes the ‘power stroke’.