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Structure and Function of the Muscular System



thin protein filaments that connect to the ends of the sarcomere


muscle cell that is found in cardiac muscle and generates the heart contractions

concentric contraction

muscle contraction during which the muscle shortens in length

creatine phosphate

molecule present in muscle fibers that acts as an energy reserve

eccentric contraction

muscle contraction during which the muscle lengthens


thin, wispy connective tissue that surrounds the individual muscle fibers and connects them within the fascicle


thick, elastic tissue composed of collagen that surrounds whole muscles and prevents them from rubbing against each other, or against the bones


loose connective tissue that surrounds and supports organs throughout the body


bundle of individual muscle fibers surrounded by connective tissue and grouped together into muscles

isometric contraction

muscle contraction during which the muscle generates force, but does not change in length

isotonic contraction

muscle contraction during which the muscle changes in length (increases or decreases)

lactic acid

acid compound produced in muscles when glucose breaks down and oxidizes faster than the body can break it down

motor unit

single neuron and skeletal muscle fibers that work together with other motor units to contract one muscle


rod-like structure present in muscle fibers that contains the proteins actin and myosin, contained in regular repeating units called sarcomeres


protein filament that makes up myofibrils


red pigment (related to hemoglobin) that carries and stores oxygen in muscle tissues for use by muscle cells


protein on the thick filaments that sit in the center of each sarcomere


connective tissue composed of collagen and elastin fibers that surrounds bundles of muscle fibers, dividing them into fascicles


cell membrane of muscle fibers


regular repeated structures consisting of thick and thin filaments, present in the myofibrils of muscle fibers

sarcoplasmic reticulum

muscle-specific type of smooth endoplasmic reticulum that contains a reserve of calcium ions, ready to release upon muscle fiber stimulation

synaptic cleft

in a neuromuscular junction, the region between the presynaptic bouton and the post-synaptic junctional fold

synaptic vesicle

small, membrane-lined sac filled with neurotransmitters, which fuse with the presynaptic membrane and release their contents into the synaptic cleft

terminal cisternae

portion of the sarcoplasmic reticulum that sits on either side of the transverse tubules, structures of muscle fiber membrane that intersect the muscle fiber


the point at which a muscle is in the state of sustained contraction

transverse tubule

channel of the cell membranes that runs through the myofibril bundles of a muscle fiber, allowing membrane signals to quickly reach all of the myofibrils in the muscle fiber


single contract cycle of a muscle, following a single muscle stimulation or action potential