Muscle Types, Structure, and Contraction Mechanisms in Human Skeletal and Cardiac Muscles

What are the three types of muscle tissues in the body?

Smooth, Skeletal, Cardiac

Which muscle type is striated and under voluntary control?

Skeletal

How many nuclei are present in skeletal muscle fibers?

Many (multinucleated)

What surrounds each muscle fiber?

Endomysium

What is the connective tissue that surrounds a muscle fascicle?

Perimysium

What is the outermost connective tissue layer surrounding a skeletal muscle?

Epimysium

What is the role of the sarcolemma in muscle fibers?

It is the plasma membrane that surrounds the sarcoplasm.

What initiates a contraction in skeletal muscle fibers?

A sudden change in membrane potential.

What are myofibrils?

Long, rod-shaped organelles in muscle fibers that contain myofilaments.

What are the two types of myofilaments?

Thin filaments (Actin) and Thick filaments (Myosin)

What are the two chains of actin monomers

Tropomyosin, troponin

What is the smallest functional unit of a muscle fiber?

Sarcomere

What is the sliding-filament theory?

It describes how muscle contraction occurs through the sliding of thin filaments over thick filaments.

What happens to the A band during muscle contraction?

The width of the A band remains constant.

What is the role of calcium ions in muscle contraction?

They bind to troponin, exposing active sites on myosin.

What is the power stroke in muscle contraction?

It is the action when the myosin head pivots toward the M line, releasing ADP and phosphate.

What occurs during cross-bridge detachment?

ATP binds to myosin, breaking the link between myosin and actin.

What is the function of titin in muscle fibers?

It keeps filaments in proper alignment and aids in restoring resting sarcomere length.

What is the function of tropomyosin in muscle contraction?

It covers active sites on G-actin, preventing actin-myosin interaction.

What is the role of troponin in muscle fibers?

It binds to tropomyosin, G-actin, and calcium ions to regulate muscle contraction.

What is the significance of the Z lines in a sarcomere?

They mark the boundaries between adjacent sarcomeres.

What is the purpose of the sarcoplasmic reticulum

It allows passage through the middle of muscle fibers to release calcium much faster.

What is Isometric

the load increases as muscle contracts. more tension but length stays unchanged

what is isotonic

length decreases but load remains constant. less tension but more movement along the crossbridge.

What is a twitch?

a mechanical response to a single action potential

what is a unfused tetanus

continuous unrelaxed contractions

what is tetanus

completely no relaxation between contractions