Muscle Anatomy, Contraction, and Physiology: Skeletal Muscle Structure and Function

What is the connective tissue sheath surrounding individual muscle fibers called?

Endomysium

What is the connective tissue sheath that surrounds each fascicle?

Perimysium

What is the connective tissue covering the exterior of a muscle organ?

Epimysium

What is a bundle of muscle fibers called?

Fascicle

What are the rodlike organelles located inside skeletal muscle fibers formed by sarcomeres placed end to end?

Myofibrils

What is the cell membrane of a muscle fiber called?

Sarcolemma

What structural term refers to actin and myosin proteins?

Myofilaments

What is the unit of muscle contraction?

Sarcomere

What forms the boundaries of a sarcomere?

Z discs

What are the dark bands produced by overlapping myosin and actin filaments in a sarcomere called?

A bands

Which myofilament uses energy from ATP to bind to actin to perform contractions?

Myosin

What happens when actin binds to myosin heads?

It gets pulled and stretched, causing the sarcomere to shorten.

What is the first step in muscle contraction?

Na+ ions enter the sarcolemma causing local depolarization.

What binds to receptors on the sarcolemma to open chemically-gated ion channels?

Acetylcholine

What causes acetylcholine to be released from the axon terminal?

Ca2+ ions

What is the role of Ca2+ ions in muscle contraction?

They bind to troponin, causing tropomyosin to uncover myosin-binding sites on actin.

What is rigor mortis?

A state where ATP is no longer available, preventing myosin heads from detaching from actin.

What is an isometric contraction?

A contraction in which the muscle remains the same length but muscle tension is present.

What is an isotonic concentric contraction?

A type of contraction where the muscle develops enough tension to shorten and lift a load.

What are the smallest muscle fibers activated first when lifting a load called?

Smallest muscle fibers

What are the largest muscle fibers activated last for powerful contractions called?

Largest muscle fibers

What is a motor unit?

A motor neuron and all the muscle fibers it innervates.

What is an isotonic eccentric contraction?

A contraction where muscle tension is present as the muscle lengthens.

What is the oxygen-binding protein found in muscle cells?

Myoglobin

Why do skeletal muscles store glycogen?

To readily convert glucose to ATP for energy.

How does creatine phosphate supply energy for muscle contractions?

By storing a phosphate group and transferring it to ADP to make ATP.

What is the role of creatine phosphate (CP) in ATP regeneration during muscle contraction?

CP transfers a phosphate group and energy to ADP to regenerate ATP.

How many ATP molecules are produced from one creatine phosphate molecule?

One ATP molecule.

How long does the creatine phosphate pathway supply energy during intense activity?

About 15 seconds.

What triggers the anaerobic glycolysis pathway during exercise?

Insufficient oxygen due to compressed blood vessels.

What is produced alongside ATP during anaerobic glycolysis?

Lactic acid.

How many ATP molecules are produced from one glucose molecule in anaerobic glycolysis?

Two ATP molecules.

Where does the anaerobic glycolysis pathway take place?

In the cytosol.

What are the energy sources used in the aerobic cellular respiration pathway?

Glucose, pyruvic acid, fatty acids, and amino acids.

How many ATP molecules are produced from one glucose molecule in aerobic respiration?

Thirty-two ATP molecules.

What are the byproducts of aerobic respiration?

Carbon dioxide and water.

What is the resting membrane potential (RMP) of a cell?

Approximately -70mV.

What maintains the resting membrane potential in a cell?

Na+/K+ pumps using active transport.

What happens during depolarization in muscle fibers?

Na+ voltage-gated channels open, causing sodium to enter the sarcolemma.

What is the absolute refractory period?

A period when no action potential can be received, regardless of stimulus strength.

What is the relative refractory period?

A period when a strong enough stimulus can generate an action potential despite hyperpolarization.

What occurs during hyperpolarization?

K+ ions continue to leave the cell, making the inside of the membrane more negative.

What is the function of Na+/K+ pumps?

To maintain the resting membrane potential by ejecting 3 Na+ ions out for every 2 K+ ions in.