CHAPTER 8 EXSS PHYS

What are the main functions of skeletal muscle?

Movement, posture support, and heat production.

How much of body weight is skeletal muscle?

About 40–50% of total body weight.

What is another name for a muscle fiber?

A muscle fiber is also called a myocyte or myofiber.

What is the epimysium?

The connective tissue that surrounds the entire muscle.

What is the perimysium?

The connective tissue that surrounds bundles of muscle fibers called fascicles.

What is the endomysium?

The connective tissue that surrounds an individual muscle fiber.

What is a fascicle?

A bundle of muscle fibers.

What is the sarcolemma?

The cell membrane of a muscle fiber.

What are satellite cells?

Cells that help with muscle growth and repair by adding nuclei.

What is the myonuclear domain?

The area of cytoplasm controlled by one nucleus.

Why are more nuclei important in muscle cells?

More nuclei allow for greater protein synthesis and muscle growth.

What are myofibrils?

Structures inside muscle fibers that contain the contractile proteins.

What is actin?

The thin filament in muscle fibers.

What is myosin?

The thick filament in muscle fibers.

What is a sarcomere?

The functional unit of muscle from one Z line to the next.

What happens to the I band during contraction?

It shortens.

What happens to the H zone during contraction?

It shortens.

What happens to the A band during contraction?

It does not change.

What is the sarcoplasmic reticulum?

A structure that stores and releases calcium.

What are T-tubules?

Tubes that carry electrical signals deep into the muscle fiber.

What is the neuromuscular junction?

The connection point between a motor neuron and a muscle fiber.

What is a motor unit?

A motor neuron and all the muscle fibers it controls.

What is acetylcholine?

A neurotransmitter that triggers muscle contraction.

What is an end plate potential?

The depolarization of the muscle fiber membrane.

What is the sliding filament theory?

The process where actin slides over myosin to cause muscle contraction.

What is a cross-bridge?

The binding of myosin to actin.

What is the power stroke?

The pulling action of the myosin head during contraction.

Why is ATP required for muscle contraction?

It provides energy and allows myosin to detach from actin.

What are the three sources of ATP?

Phosphocreatine, glycolysis, and oxidative phosphorylation.

What is excitation-contraction coupling?

The process that links a nerve signal to muscle contraction.

What role does calcium play in contraction?

It binds to troponin and exposes binding sites on actin.

What does troponin do?

It binds calcium and shifts tropomyosin.

What does tropomyosin do?

It blocks the binding sites on actin until moved by calcium.

What happens during muscle relaxation?

Calcium is pumped back into the sarcoplasmic reticulum.

What is muscle fatigue?

A decrease in force production and contraction speed.

What causes fatigue during high-intensity exercise?

Accumulation of lactate, hydrogen ions, ADP, and inorganic phosphate.

What causes fatigue during long-duration exercise?

Glycogen depletion, free radicals, and electrolyte imbalance.

What are Type I muscle fibers?

Slow-twitch fibers that are fatigue resistant and used for endurance.

What are Type IIa muscle fibers?

Fast-twitch fibers that are both oxidative and glycolytic.

What are Type IIx muscle fibers?

Fast-twitch fibers that produce high power but fatigue quickly.

What is motor unit recruitment?

The activation of more motor units to increase force.

What is summation?

Increased force from repeated stimulation.

What is tetanus?

A sustained, maximal muscle contraction.

What is the length-tension relationship?

The idea that muscles produce the most force at an optimal length.

What is the force-velocity relationship?

Muscles contract faster at lower force and slower at higher force.

What is the power relationship?

Power is greatest at moderate speeds of contraction.

What is sarcopenia?

The age-related loss of muscle mass.

How can resistance training affect aging muscle?

It slows muscle loss and helps maintain strength.

What would happen if ATP was not available in muscle?

Cross-bridges could not detach, leading to a rigid state.

What triggers calcium release in muscle cells?

Depolarization traveling down T-tubules.