Skeletal Muscle Structure

Epimysium

Layer of connective tissue surrounding the whole muscle

Perimysium

Layer of connective tissue surrounding fascicles

Endomysium

Layer of connective tissue surrounding individual muscle fibers

Muscle fiber

Muscle cell or myocyte

Fascicle

Bundle of muscle fibers

Cardiac muscle tissue

Found in the heart; striated; single nucleus; branched and connected at intercalated discs; involuntary

Smooth muscle tissue

Found in blood vessels and glands; NOT striated; single nucleus; short and tapered; involuntary

Skeletal muscle tissue

Found in the muscles attached to the bones of the skeleton; striated; multinucleated; elongated; voluntary

Myofibril

Long, smaller fibers that are found in muscle cells; consists of thick and thin filaments giving it a banded appearance

Sarcolemma

Plasma membrane of a muscle fiber

Myofilaments

Filaments of myofibrils; contains actin and myosin

Actin

Thin filament

Myosin

Thick filament

Troponin

One of the "bodyguards" for actin; calcium ions bind to this protein to allow muscle contraction

Tropomyosin

One of the "bodyguards" for actin; "covers" or blocks the binding sites on actin

Sarcoplasmic reticulum (SR)

Specialized endoplasmic reticulum of muscle fibers; stores calcium

Terminal cisternae

Enlarged areas of the sarcoplasmic reticulum (SR) adjacent to the transverse tubules (T tubules)

Sarcomere

Contractile unit of a muscle fiber

Transverse tubules

Channels extending from the sarcolemma to the SR; allows for the propagation of an action potential deep into a muscle fiber

Sarcoplasm

Cytoplasm of a muscle fiber

Triad

Group of three; in a muscle fiber, consists of a t-tubule and the two adjacent terminal cisternae

Mitochondria

Powerhouse of the cell; organelle that is the site of ATP (energy) production

Prime mover (agonist)

Muscle with the major responsibility for a certain movement; muscles that produce the most force during a contraction

Synergists

Muscles that act together; these muscles assist other muscles during a contraction

Flexor muscles

Decrease the angle between two bones at a joint

Extensor muscles

Increase the angle between two bones at a joint

Muscle body (head)

Largest/main portion of a muscle

Origin

Immovable end to which a muscle is attached; point of muscle attachment to bone that remains stationary

Muscle insertion

Movable end to which a muscle is attached; point of muscle attachment to bone that remains stationary

Z line (disc)

Where actin attaches