Muscle Contraction

What occurs at the neuromuscular junction when a motor neuron stimulates a muscle fiber?

An impulse from the brain causes calcium to enter the neuron, leading to vesicle movement and the release of ACh.

What are the types of ACh receptors located on the muscle fiber sarcolemma?

The two types of ACh receptors are nicotinic and muscarinic.

What happens to ACh after it binds to its receptors on the muscle fiber?

Acetylcholinesterase immediately breaks down ACh into choline and acetic acid.

What is the resting potential of a muscle fiber sarcolemma?

The resting potential is polarized at -70mv.

What is the initial depolarization called when ACh binds to post-synaptic receptors?

The initial depolarization is called an end plate potential.

What occurs to the sarcolemma after an action potential is initiated?

Repolarization occurs, closing Na+ channels and opening K+ channels.

What triggers the release of Ca++ from the sarcoplasmic reticulum during E-C coupling?

The action potential propagated along the sarcolemma and down the T-tubule system.

What happens to Ca++ in the sarcoplasm after its release?

An ATP-driven calcium pump moves Ca++ back into the sarcoplasmic reticulum.

What happens when Ca++ binds to the troponin complex on the thin filament?

A conformational change occurs that moves tropomyosin from the myosin-binding site on actin.

What is the state of myosin heads when they form cross-bridges with actin?

Myosin heads are in a high energy state.

What occurs during the power stroke of muscle contraction?

Myosin heads bend and pull the thin filament towards the center of the sarcomere.

What happens to myosin heads after ATP binds to them?

Cross-bridges are detached from actin, putting myosin heads in a low energy state.

How does the energy needed to 're-cock' myosin heads come about?

Hydrolysis of ATP by ATPase on myosin heads provides the necessary energy.

What condition must be met for myosin to reattach and form cross-bridges after a contraction?

The presence of a Ca++ signal that exposes active sites on the thin filaments.