Muscular Physiology Flashcards

Flashcards covering skeletal muscle physiology, contraction, relaxation, and energy sources.

What is the resting membrane potential in muscle fibers?

About -85 mV because cytosol is 85 mV more negative than extracellular fluid.

What causes an action potential?

Opening and closing of ion channels that moves Na+ and K+ across the membrane.

What are the two types of gated ion channels in action potentials?

Ligand-gated channels and Voltage-gated channels

What is the primary function of the neuromuscular junction?

To transmit a nerve impulse from a neuron to the sarcolemma.

What are the three main components of the neuromuscular junction?

Axon terminal, synaptic cleft, and motor end plate.

What is the role of acetylcholinesterase in the synaptic cleft?

Breaks down acetylcholine (ACh).

What are the three phases of skeletal muscle contraction?

Excitation, excitation-contraction coupling, and contraction phases

What triggers the opening of voltage-gated calcium channels in the axon terminal during muscle excitation?

Action potential arriving at the axon terminal.

What happens when enough voltage-gated Na+ channels open during excitation-contraction coupling?

It will stimulate an action potential.

What is the role of the T-tubules in excitation-contraction coupling?

To propagate the action potential along the sarcolemma.

What triggers the release of Ca2+ from the sarcoplasmic reticulum (SR) during excitation-contraction coupling?

Depolarization stimulates a voltage sensor in the T-tubule.

What blocks the active sites on actin at rest?

Tropomyosin

What are the three subunits of troponin?

Troponin C, troponin T, and troponin I.

What happens when Ca2+ binds to troponin C?

It releases the inhibition of troponin I on troponin T, allowing tropomyosin to expose active sites of actin.

What is a cross bridge in muscle contraction?

A myosin head bound to an actin.

What is the role of ATP hydrolysis in the cross bridge cycle?

To "cock" the myosin head into a high-energy position.

What causes Rigor Mortis?

No ATP for pumps to remove Ca2+ in cytosol, so Ca2+ remains bound to troponin C and muscle fibers are unable to relax.

What are the two main steps involved in muscle relaxation?

Stopping ACh release and breakdown of ACh in the synaptic cleft, and removing Ca2+ from the cytosol.

What is the role of acetylcholinesterase (AChE) in muscle relaxation?

Degrades remaining ACh in the synaptic cleft.

What happens to the sarcolemma during muscle relaxation?

It returns to resting membrane potential and Ca2+ channels in SR close.

What are the three main processes that regenerate ATP for muscle contraction?

Immediate sources of ATP in cytosol, glycolytic or anaerobic catabolism, and oxidative catabolism.

How is ATP quickly regenerated for muscle contraction?

By creatine phosphate and the enzyme creatine kinase (CK).

How many ATP are produced per glucose molecule in glycolytic or anaerobic catabolism?

2 ATP

What happens to pyruvate if O2 is present during glycolytic catabolism?

It enters the mitochondria for oxidative catabolism.

What is the role of myoglobin in oxidative energy sources?

It is an oxygen-binding protein in the cytosol that stores oxygen.