Muscle Lecture Vocabulary

skeletal muscle

associated with the skeleton, striated and voluntary

striated

exhibits alternating dark and light bands

voluntary

innervated by the somatic nervous system and subject to voluntary control

cardiac muscle

occurs in the wall of the heart, striated and involuntary

involuntary

innervated by the autonomic nervous system - contractions not under conscious control

smooth muscle

found in the walls of hollow organs and tubes (blood vessels, stomach and intestines

nonstriated

having no striations

muscle fiber

a single skeletal muscle cell

myoblasts

undifferentiated, mononucleated cells

sarcolemma

the plasma membrane that covers each muscle fiber

fasciculi

arranged bundles of muscle fibers

myofibrils

cylindrical organelle of a muscle cell that consists of alternating light and dark bands (I and A bands)

I-bands

light area consisting of the portion of thin filaments that do not project into the A band

A-bands

dark area consisting of a stacked set of thick filaments along with the portions of the thin filaments that overlap on both ends of the thick filaments

Z discs

narrow zones of dense material which separated sarcomeres

sarcomeres

contractile unit made of thin and thick filaments and are the basic functional unit of striated muscle fibers

thick filaments

composed of the protein myosin

thin filaments

made up primarily of the protein actin and smaller amounts of the proteins tropomyosin and troponin

myosin

fibrous protein that, together with actin, forms the contractile filaments of muscle cells

tropomyosin

actin-binding proteins that are central to the control of calcium-regulated contraction in striated muscle

troponin

a globular protein complex involved in muscle contraction

cross bridges

the force-generating sites in muscle cells

contractile proteins

proteins that mediate sliding of contractile fibres (contraction) of a cell's cytoskeleton, and of cardiac and skeletal muscle

sliding-filament mechanism

the basis of contraction is sarcomere shortening due to sliding of the thin filaments inward between the thick filaments

cross-bridge cycle

the steps occurring between binding of a cross bridge to a thin filament and the time it again binds to a thin filament to repeat the process (4 steps)

sarcoplasmic reticulum (SR)

a modified endoplasmic reticulum, consisting of a network of interconnected tubules surrounding each myofibril

excitation-contraction coupling

the sequence of events that link an action potential to mechanical contraction

action potential

a rapid sequence of changes in the voltage across a membrane

transverse tubules

invaginations of the plasma membrane into the muscle fiber occurring at each junction of an A band and I band

twitch

a single, brief contraction of the muscle

tetanus

sustained contraction lacking partial relaxation between stimuli

motor unit

a single motor neuron and all the fibers it innervates

hypertrophy

enlargement of tissue without cell division

creatine phosphate

an energy store in muscle, which like ATP contains a high energy phosphate group

slow-twitch muscle fibers

adapted for extended, aerobic work

fast-twitch fibers

adapted for generating maximum forces for short periods

intermediate filaments

one of the three cytoskeletal systems in smooth muscle.

dense bodies

anchoring sites for actin filaments

intercalated discs

thickened portions of the sarcolemma

gap junctions

facilitate conduction of muscle action potentials