Muscle Physiology: Contraction Mechanics, Fiber Types, and Muscle Categories

Flashcards covering muscle contraction, rigor mortis, the length-tension relationship, fiber typing (slow vs. fast twitch), energy systems, smooth muscle characteristics, and cardiac muscle anatomy.

What initiates rigor mortis in deceased muscle tissue?

Calcium leaks out of the sarcoplasmic reticulum into the muscle cell.

Why do muscles remain locked in a rigid state during rigor mortis?

There is no ATP left to bind to the myosin heads and cause them to release from actin.

How long does rigor mortis typically persist before the muscle stiffness begins to release?

About a day or two, maybe three days.

What role does ATP play after myosin completes a power stroke during muscle contraction?

A new ATP molecule binds to myosin to trigger detachment from actin and reload it for the next power stroke.

Why is it difficult to generate significant force when a muscle is at its maximum extended length?

There is minimal overlap between the thick and thin filaments, reducing the number of cross-bridges that can form.

What type of muscle fibers compose dark meat in chickens, and why are they suited for constant walking?

Slow twitch fibers, which contract repeatedly, recharge continuously, and resist fatigue over long periods.

Which cellular components give slow twitch oxidative fibers their darker appearance?

High concentrations of myoglobin, mitochondria, and blood capillaries.

How much ATP is produced by aerobic respiration compared to anaerobic fermentation per glucose molecule?

Aerobic respiration generates $32\text{ ATP}$, whereas anaerobic fermentation produces only $2\text{ ATP}$.

What is the function of myoglobin within muscle fibers?

It serves as an intracellular oxygen storage reservoir that holds oxygen for immediate metabolic use.

How does the phosphagen system provide immediate energy during short bursts of exertion?

Creatine phosphate donates its phosphate directly to ADP to rapidly regenerate ATP.

How long does the creatine phosphate energy reserve typically last during high-intensity activity?

About two, three, or four seconds, which can be extended up to roughly eight seconds with sprint training.

What metabolic byproduct accumulates during sustained fast glycolytic activity, requiring heavy post-exercise breathing to process?

Lactic acid.

What fiber type exists intermediary between slow twitch oxidative and fast twitch glycolytic fibers?

Fast oxidative glycolytic fibers.

What structural shape describes individual smooth muscle cells?

Spindle-shaped (oval with tapered, pointy ends).

How does the physical motion of smooth muscle contraction differ from striated muscle contraction?

Smooth muscle cells bunch up in an irregular fashion rather than shortening along a linear axis.

What are the roles of the two smooth muscle layers surrounding the digestive tube?

The inner circumferential layer squeezes food, while the outer longitudinal layer propels food forward along the tract.

How much volume does an empty human stomach typically hold compared to a fully expanded stomach?

It holds around $100\text{ cc}$ when empty and stretches up to $1{,}500\text{ cc}$ ($1.5\text{ liters}$) when full.

What unique contractile feature enables smooth muscle to prevent involuntary leakage of contents over extended periods?

It can lock itself in a contracted state and maintain tension without continuously expending energy.

What microscopic structural features distinguish cardiac muscle from skeletal muscle?

Cardiac muscle fibers are branching and joined by intercalated discs containing gap junctions, rather than running in strictly linear, multinucleated strands.