Neuromuscular Junction

Revision resource

What ions are crucial for propagating an action potential in neurons?

Sodium (Na+) and Potassium (K+)

What is the state of the cell at rest in terms of ion concentration?

Higher concentration of sodium ions extracellularly compared to a higher concentration of potassium ions intracellularly.

What leads to depolarisation of the muscle fiber membrane?

Influx of sodium ions moving into the cell from the extracellular fluid.

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine (ACh)

What effect does acetylcholine have on nicotinic receptors?

It binds to nicotinic receptors which promotes influx of sodium ions, leading to depolarisation of the muscle fiber membrane.

What is a miniature end-plate potential?

The result of the release of a single vesicle of ACh at rest.

What is an end-plate potential (EPP)?

The summation of several ACh releases when the motor neuron is activated.

What does the myelin sheath do for nerve conduction?

Insulates the nerve and speeds up conduction velocity.

What is the function of the sub-neural clefts on muscle fibers?

Increases surface area for neurotransmitter binding.

What is the structural unit of skeletal muscle called?

Sarcomere.

How are sarcomeres arranged in skeletal muscle?

In parallel, separated by Z lines.

What happens during sliding filament contraction?

Actin filaments slide past myosin filaments, shortening the sarcomere.

What initiates the release of calcium ions from the sarcoplasmic reticulum?

An action potential propagating down the sarcolemma and T tubules.

What is the role of calcium ions in muscle contraction?

Calcium binds to troponin, causing tropomyosin to expose myosin binding sites on actin.

Describe the power stroke in cross-bridge recycling.

Myosin heads bend towards the center of the sarcomere, pulling actin filaments towards it.

What dictates the rate of muscle contraction?

The rate of action potential propagation down muscle fibers and the conversion of ATP to ADP and Pi.