muscle tissue
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| three major types of MT | skeletal, cardiac, smooth
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| skeletal MT | F/can be operated voluntarily || F/general function is to move bones of the skeleton (occasionally, to move areas of skin) || SA/striated
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| cardiac MT | L/comprises most of the heart wall || SA/striated || F/involuntarily operates the heart
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| smooth MT | SA/nonstriated, smooth || L/the walls of hollow interior structures, such as blood vessels, airways, and most organs of the abdominopelvic cavity || F/operates involuntarily
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| four basic functions of MT | producing body movements, stabilizing body positions, storing and moving substances within the body, generating heat
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| four basic properties of MT | electrical excitability, contractility, extensibility, elasticity (i.e., the ability to return to its original shape after contraction or extension)
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| muscle tension | When a muscle contracts, it generates tension (force of contraction) while pulling on its attachment points. If the tension generated is great enough to overcome the resistance of the object to be moved, the muscle shortens and movement occurs.
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| term for individual muscle cells | muscle fiber
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| fascia | a sheet or broad band of dense CT that supports and surrounds muscles and other organs || F/holds muscles with similar functions together, allows free movement of muscles, carries nerves and blood and lymphatic vessels, fills spaces between muscles
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| three layers of CT extending from the fascia | epimysium, perimysium, endomysium
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| epimysium | outermost layer of the fascia, encircling the entire muscle
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| perimysium | an inner layer of the fascia, surrounding fascicles
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| endomysium | the innermost layer of the fascia, separating individual muscle fibers from one another
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| tendon | a cord of dense regular CT that connects muscle to the periosteum of a bone || C/comprised of an extension of all three layers of fascia
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| aponeurosis | a type of tendon in which the CT extends as a broad flat layer || EX/the epicranial ----, which lies between the occipital and frontal bellies of the occipitofrontalis muscle
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| muscular dystrophy | term for a number of heriditary disorders that cause weakening of muscle function
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| muscular hypertrophy | the dramatic muscle growth that occurs after birth || occurs via enlargement of existing muscle fibers, not the creation of new fibers
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| muscular atrophy | a loss of MT size and strength, associated with lack of use
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| sarcolemma | the plasma membrane of a muscle fiber || F/receives and conducts stimuli
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| T-tubule | a small invagination of the sarcolemma into the cytoplasm of the muscle fiber; each fiber has thousands of these || F/ensures that all superficial and deep parts of the muscle fiber become excited by an action potential at the same time
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| myofibril | "threads" that extend the entire length of a muscle fiber
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| sarcoplasmic reticulum | a fluid-filled system of membranous sacs that surrounds each myofibril || F/in a relaxed muscle fiber, stores calcium ions
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| sarcomere | the contractile unit of a muscle; the basic functional unit of a myofibril
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| Z discs | zones of dense protein material that separate sarcomeres from one another
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| myosin | L//thick filaments || F/a motor protein (i.e., converts chemical energy of ATP to the mechanical energy of motion or the production of force || SA/each ---- molecule is shaped like 2 golf clubs twisted together
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| actin | L/thin filaments || SA/individual ---- molecules join to form an ---- filament that is twisted into a helix || F/a contractile (motor) protein
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| tropomyosin and troponin | L/thin filaments || regulatory proteins that (in relaxed muscle) cover actin's myosin-binding site; when a muscle action potential occurs, the SR releases Ca ions, which in turn remove these proteins from actin's myosin-binding site, and contraction occur
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| neuromuscular junction (NMJ) | the structural site of synaptic contact and functional site of communication between a motor neuron and a skeletal muscle fiber
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| synapse | general term for a region where communication occurs between a neuron and another cell
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| synaptic cleft | a small gap between a neuron and another cell; neurotransmitters communicate signals across the ----
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| acetylcholine (ACh) | the neurotransmitter released at a NMJ
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| synaptic vesicles | hundreds of membrane-enclosed sacs within each synaptic end bulb
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| motor end plate | in a NMJ, the region of sarcolemma that is opposite the synaptic end bulb; each contains 30 to 40 million ACh receptors
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| acetylcholinesterase (AChE) | an enzyme in the synaptic cleft that rapidly breaks down ACh
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| excitation of a muscle fiber | when two molecules of ACh attach to a receptor, an ion channel opens; Na cations (and others) flow across sarcolemma into the muscle fiber, thus generating a muscle action potential
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| excitation-contraction coupling | general term for the steps that link muscle excitation to muscle contraction
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| effects of Ca2+ concentration in the sarcoplasm | an increase starts muscle contraction; a decrease stops it
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| four basic steps in the contraction cycle | ATP splits || myosin attaches to actin || power stroke occurs || myosin detaches from actin
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