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200 Cards in this Set
- Front
- Back
Skeletal muscle
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an organ of the muscular system, composed of skeletal muscle tissue, nervous tissue, blood, & connective tissues.
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Fascia
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is dense connective tissue that separates individual skeletal muscles
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A tendon
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is a cordlike structure that consists of dense connective, Tendons connect a muscle to a bone
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Aponeurosis
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is a sheetlike structure composed of dense connective tissue
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Epimysium
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is a layer of connective tissue that closely surrounds a skeletal muscle
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Perimysium
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is connective tissue that separates muscles into fascicles
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A fascicle
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is a section of a muscle
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Endomysium
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is connective tissue that surrounds individual muscle cells
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Subcutaneous fascia
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is fascia just beneath the skin
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Subserous fascia
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is connective tissue layer of the serous membranes covering organs in various body cavities & lining those cavities.
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A skeletal muscle fiber
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is a single muscle cell
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The sarcolemma
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is the cell membrane of a muscle cell
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The sarcoplasm
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is the cytoplasm of a muscle cell
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The sarcoplasm contains
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many small nuclei, mitochondria & myofibrils
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Myofibrils
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are threadlike structures & are located in the sarcoplasm, Myofibrils play a fundamental role in the muscle contraction mechanism
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Thick myofilaments are composed of
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myosin
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Thin myofilaments are composed of
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actin
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The organization of myofilaments produces
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the alternating light & dark striation characteristic of skeletal muscles
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A sarcomere
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is a repeating pattern of a myofibril
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Myofibrils
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may be thought of as sarcomeres joined end to end
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I bands are composed of
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thin actin filaments
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Z lines are structures
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that anchor I bands
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A bands are composed of
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thick myosin filaments overlapping thin actin filaments
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The H zone
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is a central region of an A band that only contains thick filaments
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The M line
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is a region of an A band which consists of proteins that help hold the thick filaments in place
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Titin connects
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proteins that connect myosin filaments to Z lines
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A sarcomere extends from
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one Z line to another Z line
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Each myosin molecule consists of
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two twisted protein strands with globular parts called cross bridges that project outward along their lengths
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Thin filaments consist of
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double strands of actin twisted into a helix
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Actin
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has a binding site to which the cross bridges of a myosin molecule can attach
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Troponin & tropomyosin associate with
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actin filaments
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Sarcoplasmic reticulum
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is endoplasmic reticulum of a muscle fiber
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Transverse tubules
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are membranous channels that extend into the sarcoplasm as invaginations continuous with the sarcolemma & contain extracellular fluid
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Cisternae
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are enlarged portions of sarcoplasmic reticulum
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A triad
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is formed by one transverse tubule & two cisternae
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Each skeletal muscle is functionally connected to
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an axon of a motor neuron
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A motor neuron passes outward from
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brain or spinal cord
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Normally, a skeletal muscle fiber contracts only
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upon stimulation by a motor neuron
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A neuromuscular junction is
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the site where an axon & muscle fiber meet
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A motor end plate
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is a specialized portion of the muscle cell membrane that is extensively folded
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A motor unit
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is a motor neuron & the muscle fibers it controls
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A synaptic cleft
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separates the membranes of the neuron & the membrane of the muscle fiber
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Synaptic vesicles
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store neurotransmitters
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Acetylcholine
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is the neurotrasnmitter that motor neurons use to control skeletal muscle
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ACh is synthesized and stored in
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the cytoplasm of the motor neuron & is stored in synaptic vesicles in axons
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When a nerve impulse reaches the end of an axon
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acetylcholine is released into the synaptic cleft
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ACh combines
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with ACh receptors on the motor end plate, & stimulates the muscle fiber
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A muscle impulse
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is an electrical signal that is like a nerve impulse
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A muscle impulse changes
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the muscle cell membrane in a way that transmits the impulse in all directions along & around the muscle cell
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Ultimately the muscle impulse reaches
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the sarcoplasmic reticulum & cisternae
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The sarcoplasmic reticulum has
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a high concentration of calcium
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In response to a muscle impulse
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the membranes become more permeable to calcium, & the calcium diffuses out of the cisternae into the cytosol of the muscle fiber
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When a muscle fiber is at rest
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the troponin tropomyosin complexes block the binding sites on the actin molecules
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Calcium ions
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bind to troponin, changing its shape & altering the position of the tropomyosin
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The movement of the tropomyosin molecule
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exposes the binding sites of the actin filaments, allowing linkages to form between myosin cross bridges & actin
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The functional unit of skeletal muscles is the
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sarcomere
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According to the sliding filament model, when sarcomeres shorten
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the thick & thin filaments slide past one another
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As contraction occurs
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the H zones & the I bands get narrower & the Z lines move closer together.
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The force that shortens the sarcomeres comes from
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cross bridges pulling on the actin filaments
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A myosin cross bridge attaches to
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actin in order to pull on the actin filament
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The cross bridge can
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release, straighten, & combine with another binding site further down the actin filament, & pull again
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Myosin cross bridges contain the enzyme
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ATPase
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ATPase catalyzes the breakdown of
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ATP to ADP
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The force for muscle contraction is provided by
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the breakdown of ATP into ADP
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Breaking down of ATP puts the myosin cross bridge in a
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“cocked” position
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When a muscle is stimulated to contract
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a cocked cross bridge attaches to actin & pulls the actin filament toward the center of the sarcomere, shortening the muscle
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When another ATP binds
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the cross bridge is released, & then breaks down the ATP to return to the cocked position
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The cross bridge cycle
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may repeat over & over as long as ATP is present & nerve impulses cause ACh release at the neuromuscular junction
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In order for a muscle fiber to relax
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acetylcholine must be decomposed by an enzyme called acetylcholinesterase.
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The action of acetycholinesterase
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prevents a single nerve impulse from continuously stimulating a muscle fiber.
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When acetylcholine breaks down
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the stimulus to the sarcolemma & the membranes within the muscle fiber ceases.
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The calcium pump moves
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calcium back into the sarcoplasmic reticulum
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When calcium is removed from the cytoplasm
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the cross bridge linkages break & tropomyosin rolls back into its groove, preventing any cross bridge attachment
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ATP is necessary for
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both muscle contraction & relaxation
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The trigger for contraction is
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the increase in cytosolic calcium in response to stimulation by ACh from a motor neuron
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Creatine phosphate
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is an energy source available to generate ATP from ADP
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Creatine phosphate includes
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a high energy phosphate bond
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As ATP is decomposed to ADP
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the energy from creatine phosphate is transferred back to ADP to produce ATP
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After creatine phosphate is used
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a muscle cell must depend on cellular respiration of glucose to synthesize ATP
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Typically a muscle stores glucose in the form of
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glycogen
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Glycolysis occurs
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in the cytoplasm & is anaerobic
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Glycolysis releases
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a few ATP molecules
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The complete break down of glucose occurs
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in mitochondria & requires oxygen
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The citric acid cycle & electron transport
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chain produce water, carbon dioxide & a large amount of ATP
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Oxygen is carried in the blood stream bound to
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hemoglobin
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Myoglobin is ____ in color
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red
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Myoglobin stores oxygen in
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muscle tissue
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Lactic acid threshold
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is the shift in cellular metabolism from breaking down pyruvic acid into carbon dioxide to pyruvic acid breakdown leading to lactic acid formation
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Under anaerobic conditions, glycolysis breaks down
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glucose into pyruvic acid & converts it to lactic acid
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Lactic acid is carried by
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the blood to the liver
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Liver cells can convert lactic acid to
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glucose
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Oxygen debt reflects the amount of
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oxygen liver cells require to use the accumulated lactic acid to produce glucose, plus the amount the muscle cells require to resynthesized ATP & creatine phosphate, & restore their original concentrations
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Fatigue
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is the condition in which a muscle fiber cannot contract
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Fatigue may result from
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decreased blood flow, ion imbalances across the sarcolemma, & the psychological loss of the desire to continue to exercise
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A cramp
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is a sustained, painful, involuntary muscle contraction
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The strenuous exercise of aerobic training
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stimulates new capillaries to grow within the muscles, supplying more oxygen & nutrients
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Heat
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is a by product of cellular respiration, Blood transports heat throughout the body, which helps to maintain body temperature.
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One way to observe muscle contraction is to
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remove a single muscle fiber from a skeletal muscle & connect it to a device that measures contraction
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An electrical impulse
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is usually used to produce muscle contraction.
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Threshold stimulus
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is the minimal stimulus needed to start a muscle contraction
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An impulse
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in a motor neuron normally releases enough ACh to bring the muscle fibers in its motor unit to threshold
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A twitch
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is the response of a single muscle fiber to the ACh released by a single action potential
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A myogram
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is a recording of the events of a muscle twitch
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Three periods of a muscle fiber contraction are
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latent, contraction, & relaxation
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During the period of contraction
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a muscle fiber is generating force or contracting
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The latent period
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is the period before contraction
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The period of relaxation
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is the period in which a muscle fiber is decreasing tension
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The refractory period
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is the brief moment when a muscle fiber remains unresponsive to stimulation
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An all or none response
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is one in which a muscle fiber contracts completely or not at all
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The length to which a muscle is stretched before stimulation affects
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the force it will develop when stimulated
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If a muscle is stretched well beyond its normal resting length
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the force will decrease
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At very short muscle lengths, the sarcomere becomes
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compressed & shortening is not possible
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In the whole muscle, the degree of tension reflects
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the frequency at which individual fibers are stimulated & how many fibers take part in the overall contraction of the muscle
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Twitches in a muscle can
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combine to become sustained
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Summation
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is the combination of the force of individual twitches
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Tetanic contractions
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are contractions that lack relaxation.
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The fewer muscle fibers
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in the motor units, the more precise the movements can be produced in a particular muscle
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All muscle fibers in a motor unit are
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stimulated at the same time
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Multiple motor unit summation is
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recruitment
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Recruitment
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is an increase in the number of activated motor units
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As the intensity of stimulation increases
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recruitment continues until all possible motor units are activated in a muscle
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During sustained contractions
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smaller motor units are recruited earlier
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The larger motor units respond
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later & more forcefully
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Muscle movements are smooth because
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the spinal cord stimulates contraction in different sets of motor units at different times
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Muscle tone
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is the amount of sustained contractions in a muscle
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Muscle tone is important for
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maintaining posture.
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An isotonic contraction
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is a type of contraction that produces movement of a body part
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A concentric contraction
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is an isotonic contraction in which shortening of the muscle occurs
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An eccentric contraction
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is an isotonic contraction in which lengthening of the muscle occurs
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An isometric contraction
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is a contraction in which muscle tension increases but no movements of body parts are produced
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An example of an isometric contraction is
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standing
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An example of an isotonic contraction is
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walking
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Type I fibers are
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slow twitch fibers
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Examples of type I fibers are
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those in the long muscles of the back
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Type I fibers are
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red in color because they contain a relatively large amount of myoglobin
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Type I fibers are
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resistant to fatigue
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Type IIa fibers are
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fast twitch glycolytic fibers, white in color because they contain relatively small amounts of myoglobin, they are fast twitch oxidative fibers
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All muscles include
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a combination of fiber types
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Compared to skeletal muscle fibers, smooth muscle fibers are
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shorter & they have single nuclei
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Two major types of smooth muscle are
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visceral & multiunit
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Multiunit smooth muscle is located
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in the irises & the walls of blood vessels
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Visceral smooth muscle is located
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in the walls of hollow organs except for the heart
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Fibers of visceral smooth muscle are connected by
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gap junctions
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Rhythmicity
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is a pattern of spontaneous repeated contraction
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Peristalsis
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is a wavelike motion produced by smooth muscle contraction
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Peristalsis helps
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force the contents of a tube along its length
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Compared to skeletal muscle fibers, smooth muscle fibers lack
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troponin & use calmodulin to bind calcium instead
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Two neurotransmitters that affect smooth muscle are
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acetylcholine & norepinephrine
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Hormones affect smooth muscle by
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stimulating or inhibiting contraction in some cases & lettering the degree of response to neurotransmitters in other cases
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Stretching of smooth muscle can trigger
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contractions
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Smooth muscle is slower to contract & relax than
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skeletal muscle
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Unlike skeletal muscle, smooth muscle fibers can change length without
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changing tautness
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Cardiac muscle appears only in
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the heart
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Cardiac muscle is composed of
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striated cells, forming fibers that are interconnected in branching, three dimensional networks
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Cardiac muscle fibers can contract longer than
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skeletal muscle fibers
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Intercalated discs are
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membrane junctions that join cardiac muscle fibers together
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Intercalated discs allow muscle impulses to travel
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rapidly from cell to cell.
F. A syncytium is a group of muscle fibers that contract as a unit
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Skeletal muscles generate
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a great variety of body movements
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The action of each muscle mostly depends upon
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the kind of joint it is associated with & the way the muscle is attached on either side of that joint
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Bones & muscles interact as
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levers
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The four basic components of a lever system are
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rigid bar, fulcrum, object that is moved against resistance, & a force
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In scissors, the handle & blades form
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a rigid bar
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The fulcrum of scissors is
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the screw
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The resistance of scissors is
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the material to be cut
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The force of scissors is supplied by
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the person on the handles
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In a first class lever system
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the parts are arranged resistance, fulcrum, force
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Besides scissors, other examples of first class lever systems are
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seesaws & hemostats
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In a second class lever system
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the parts are arranged fulcrum, resistance, force
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An example of a second class lever system is a
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wheelbarrow
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In a third class lever system, the parts are
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arranged resistance, force, & fulcrum
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An example of a third class lever system is
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a pair of tweezers
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In the action of bending the upper limb at the elbow
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the rigid bar is the forearm bones, the fulcrum is the elbow joint, the resistance is the hand, & the force is applied by muscles on the anterior side of the arm.
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Bending the arm at the elbow is an example of
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a third class lever system
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When the upper limb straightens at the elbow
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the rigid bar is forearm bones, the pivot is the elbow, the resistance is the hand, & the force is applied by the triceps brachii muscle located on the posterior surface of the arm
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Straightening the arm at the elbow is a first class lever system because
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the parts of the lever are arranged resistance, fulcrum, force
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An example of a second class lever system in the body is
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a movement produced at the temporomandibular joint (opening of the mouth)
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The origin of a muscle
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is the immovable end of the muscle
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The insertion of a muscle is
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the movable end of a muscle
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When a muscle contracts, its insertion is pulled toward
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its origin
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The head of a muscle is the part nearest
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its origin
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The origins of the biceps brachii are
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the attachment to the coracoid process of the scapula, & the attachment to a tubercle above the glenoid cavity of the scapula
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The insertion of the bicep brachii is
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the radial tuberosity of the radius
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When the biceps brachii contracts
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the elbow bends
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A prime mover
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is the muscle primarily responsible for producing an action
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A synergist
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is a muscle that assists the prime mover
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An antagonist
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is a muscle that resists the action of a prime mover
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The name of a muscle may reflect
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its size, shape, function, number of origins, attachment sites, or direction of its muscle fibers
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An example of a muscle named for it size is
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pectoralis major
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An example of a muscle named for its shape
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is deltoid
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An example of a muscle named for its function
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is extensor digitorum
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An example of a muscle named for its number of origins is
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biceps brachii
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An example of a muscle named for it attachments sites
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is sternocleidomastoid
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An example of a muscle named of the direction of its muscle fibers is
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external oblique
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As a group, muscles of facial expression connect
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the bones of the skull to connective tissue in region of the overlying skin
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Life Span Changes
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Signs of aging of the muscular system begin to appear one’s forties
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Life span changes At a microscopic level
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myoglobin, ATP, & creatine phosphate decline
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Connective tissue & adipose tissue
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begin to replace some muscle tissue
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Exercise can help maintain
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a healthy muscular system
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According to the National Institute on Aging, exercise should include
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strength training, aerobics, & stretching
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Deep fascia |
is fascia that surrounds or penetrates muscles |