The Muscular System: Written

Flashcards for Dr. Lin chapter 7 written exam

Five primary functions of skeletal muscle

Move the skeleton, maintain posture and body position, support soft tissues, guard entrances and exits, and maintain body temperature.

Skeletal muscle

An organ made mainly of skeletal muscle tissue, plus connective tissues, blood vessels, and nerves.Its cells are called muscle fibers.

Epimysium

Collagen-fiber connective tissue surrounding the entire muscle and separating it from surrounding tissues and organs.

Perimysium

Connective tissue that divides a muscle into compartments containing bundles of muscle fibers called fascicles; it also carries blood vessels and nerves.

Fascicle

A bundle of skeletal muscle fibers.

Endomysium

Connective tissue surrounding each muscle fiber and tying adjacent fibers together; it contains capillaries and nerve fibers.

Tendon vs. aponeurosis

A tendon is a band of collagen fibers that attaches skeletal muscle to bone. An aponeurosis is a broad connective-tissue sheet that connects muscles.

Muscle blood supply and nerve supply

Blood vessels deliver oxygen and remove metabolic wastes. Motor-neuron axons stimulate muscle fibers; skeletal muscle contracts only when stimulated by the nervous system.

Voluntary muscle

Skeletal muscle is called voluntary because its contractions can be consciously controlled, although some skeletal muscles (such as those used in breathing) also work subconsciously.

Muscle fiber size and nuclei

A skeletal muscle fiber can be very long and contains hundreds of nuclei just beneath its plasma membrane, so it is multinucleate.

Sarcolemma and sarcoplasm

The sarcolemma is a muscle fiber's plasma membrane; the sarcoplasm is its cytoplasm.

Transverse tubules (T tubules)

Tubules extending deep into the muscle fiber that carry electrical impulses inward so all regions of the fiber can contract together.

Myofibrils and myofilaments

Myofibrils are long structures inside a muscle fiber, made of protein myofilaments. Thin filaments contain actin; thick filaments contain myosin.

ATP in muscle fibers

ATP powers contractions. Mitochondria and the breakdown of glucose help supply it; glycogen granules store a source of glucose.

Sarcoplasmic reticulum (SR)

Specialized smooth endoplasmic reticulum forming a network around myofibrils; it stores calcium ions needed to start contraction.

Terminal cisternae and triad

Terminal cisternae are expanded SR chambers rich in calcium. Two terminal cisternae with a T tubule between them form a triad.

Sarcomere

The smallest functional unit of a muscle fiber; repeating units of thick and thin filaments whose interactions produce contraction.

Striations

The banded appearance of skeletal muscle fibers caused by the regular arrangement of thick and thin filaments in sarcomeres.

Z lines

Mark the boundaries of each sarcomere; thin filaments attach to them.

A band

The dark sarcomere band that contains thick filaments; its length does not change during contraction.

I band

The light band that includes a Z line and it’s between adjacent A bands; it becomes shorter during contraction.

H band and M line

The H band is the central region containing only thick filaments. The M line contains proteins connecting the central portions of thick filaments.

Titin

Protein strands extending from Z lines to the ends of thick filaments; they help keep filaments aligned.

Actin, tropomyosin, and troponin

Actin forms thin filaments and has active sites for myosin. At rest, tropomyosin covers these sites; troponin holds tropomyosin in position.

Myosin

Protein forming thick filaments; each molecule has a tail and a globular head that can bind to actin during contraction.

Calcium's role in contraction

Calcium binds to troponin, changing its shape and moving tropomyosin away from actin's active sites so myosin can bind.

Sliding filament theory

Thin filaments slide toward the center of the sarcomere alongside thick filaments; the filaments themselves do not need to shorten.

Sarcomere changes during contraction

Z lines move closer; I bands and H bands shrink; zones of overlap increase; A-band length stays the same.

Cross-bridge cycle

Myosin heads attach to actin, pivot toward the sarcomere center to pull the thin filaments, detach, and return to their original position.

Neuromuscular junction (NMJ)

The specialized connection where a motor neuron communicates with a skeletal muscle fiber.