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delicate connective tissue membrane that covers specialized skeletal muscle fibers


tough connective tissue binding together fascicles


coarse sheath covering the muscle as a whole


point of attachment that does not move when the muscle contracts


point of attachment that moves when the muscle contracts

prime mover

a muscle or group of muscles that directly performs a specific movement


muscles that, when contracting, directly oppose prime movers; relax while prime mover in contracting to produce movement; provide precision and control during contraction of prime movers


muscles that contract at the same time as the prime movers; they facilitate prime mover actions to produce a more efficient movement

fixator muscles

joint stabilizers


plasma membrane of muscle fibers

sarcoplasmic reticulum

network of tubules and sacs found within muscle fibers, stores calcium ions within its sacs


numerous fine fibers packed close together in sarcoplasm


segment of myofibril between two successive Z lines, myofibrils consists of many of these, contractile unit of muscle fibers


triplet of tubules; allows an electrical impulse traveling along a T tubule to stimulate the membranes of adjacent sacs of the sarcoplasmic reticulum

T tubule

sandwiched between two sacs of sarcoplasmic reticulum


within myofibrils, thick and thin; thin attach to both Z lines of a sarcomere and extend part way toward the center; thick do not attach to the Z lines

motor unit

motor neurons plus the muscle fibers to which it attaches

twitch contraction

a quick jerk of a muscle that is produced as a result of a single, brief threshold stimulus


the staircase phenomenon; gradual, step like increase in the strength of contraction that is seen in a series of twitch contractions that occur 1 second apart


smooth, sustained contractions

isotonic contractions

contraction in which the tone or tension within a muscle remains the same but the length of the muscle shortens (same tension)

isometric contraction

contraction in which muscle length remains the same while the muscle tension increases (same length)

first class

fulcrum lies between the pull and the load, not abundant in the human body, serve as levers of stability

second class

load lies between the fulcrum and the joint at which the pull is exerted, presence of these levers in the human body is a controversial issue

third class

pull is exerted between the fulcrum and load, permit rapid and extensive movement, most common type of lever found in the body

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