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Quiz!
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functions of muscle tissue |
-produce body movements |
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excitability |
property of muscle tissue ability to respond to stimuli and produce electrical signals |
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contractability |
property of muscle tissue ability to shorten and generate force once excited |
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extensibility |
property of muscle tissue ability to stretch w/out damaging the tissue |
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elasticity |
property of muscle tissue ability to return to normal length after being extended |
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thermal |
property of muscle tissue ability to produce heat energy |
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Skeletal muscle tissue |
attaches to bone, skin or fascia (connective tissue) striated w/ light and dark bands voluntary control of contraction & relaxation multi-nucleated |
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epimysium |
connective tissue layer that surrounds the whole muscle |
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perimysium |
connective tissue that surrounds the fascicles/bundles of 10-100 muscle cells/fibers |
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endomysium |
connective tissue that separates individual muscle cells/fibers |
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sarcoplasma |
name for the cytoplasm in a muscle contains lots of glycogen for energy production and myoglobin for oxygen storage |
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sarcolemma |
cell membrane in a muscle |
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sarcoplasmic reticulum (SR) |
storage network of calcium system of tubular sacs stores Ca2+ in relaxed muscle, release of Ca2+ triggers muscle contraction |
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transverse (t) tubule |
brings electrical signal into the muscle cell tiny invaginations of the sarcolemma filled with ECF and quickly spread the muscle action potential to all pts of the fiber |
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myofibrils have 3 kinds of protein |
1. contractile proteins |
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contractile proteins |
myosin and actin |
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regulatory proteins |
troponin and tropomyosin |
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structural proteins |
titin, myomesin, nebulin, dystrophin provide proper alignment, elasticity and extensibility; link myofibrils to sarcolemma and extracellular matrix |
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sarcomere |
functional unit of muscle contraction one Z disc/line to the next |
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thick filaments |
myosin each molecule resembles 2 golf clubs twisted 2gether myosin heads (cross bridges) extend toward the thin filaments held in place by the M line proteins |
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thin filaments |
made up of actin, troponin & tropomyosin at rest, want myosin binding sights on actin covered by tropomyosin |
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troponin |
tells tropomyosin when to cover/expose binding sites on actin |
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Z disc |
thin filaments are held in place by this disc |
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H zone |
only myosin almost disappears during contraction |
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A band |
"all" actin & myosin doesn't change length during contraction |
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I band |
actin only almost disappears during muscle contraction |
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contraction |
when myosin pulls actin inward |
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motor unit |
one motor neuron (nerve) & all the skeletal muscle cells/fibers it innervates (10-2,000 cells) why so many? |
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one; multiple |
each muscle cell is supplied by ____ motor neuron terminal branch each motor neuron supplies _______ muscle cells |
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motor unit recruitment |
increasing the # of active motor units |
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motor units in a whole muscle fire asynchronously |
-some fibers are active others are relaxed precise mvmts require smaller contractions/smaller motor units (less fibers/nerve) |
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the all-or-none response |
for a motor unit to be recruited into activity the motor nerve impulse must meet or exceed the threshold if the threshold is not met no fibers in that unit act |
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muscle tone |
involuntary contraction of a small # of motor units (alternately active and inactive in a constantly shifting pater) keeps muscles firm even though relaxed (always keep some level of overlap) doesn't produce movement essential for maintaining head posture; important in maintaining BP* |
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how muscle contraction begins |
1. nerve impulse arrives at axon terminal & synaptic vesicles release ACh |
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steps in the contraction cycle |
1. myosin heads hydrolyze ATP and become reoriented and energized (ready to bind) |
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the contraction cycle keeps repeating as long as there is... |
calcium, ATP, and the signal/theAP/stimulus |
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leaky SRs |
theory that muscle fatigue may be the result of calcium leaking out of the SR (then calcium isnt there for contraction) |
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Relaxation |
Acetylcholinesterase (AChE) breaks down ACh within the synaptic cleft [neurotransmitter can't go across] Muscle AP ceases Ca2+ release channels are closed Active transport pumps Ca2+ back into SR Troponin holds tropomyosin in position to block myosin-binding sites on actin |
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Contraction |
Ca2+ release channels are open Ca2+ binds to tropinin, which changes the shape of the troponin-tropomyosin complex & uncovers the myosin-binding sites on actin sarcomeres, muscle fiber and muscle shorten *can't generate anymore force or tension in full contraction |
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acetylcholinesterase (AChE) |
enzyme that breaks down ACh within the synaptic cleft in order to relax muscle |
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rigor mortis |
state of muscular rigidity that begins 3-4 hrs after death and lasts ab 1day After death, Ca2+ ions leak out of the SR and allow myosin heads to bind to actin since ATP synthesis has ceased, crossbridges cannot detach from actin until enzymes start to digest decomposing cells |
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types of skeletal muscle fibers |
1) Type I, slow oxidative, slow-twitch |
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Type I |
aka slow oxidative, slow-twitch red in color (lots of mitochondria, myoglobin & blood vessels) prolonged, sustained contractions for maintaining posture great ability to make energy fatigue resistant, bc have lots of mitochondria, blood & oxygen (aerobic fuels) small fiber size, small motor unit, slow twitch speed, highest capillary density, low glycogen content, slow fatigability rate |
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Type IIa |
aka fast oxidative-glycolytic (FOG) pinkish in color (lots of mitochondria, myoglobin & bvs) -not as much as Type I split ATP at very fast rate; used for walking & sprinting Fast twitch speed, high capillary density, aerobic & anaerobic, intermediate glycogen content, fatigability rate, fiber size, and motor unit size |
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Type IIb |
aka fast glycolytic, fast-twitch white in color (few mitochondria & BV, low myoglobin) anaerobic movements for short duration; used for weight lifting respond quickly, fatigue quickly large fiber size, large motor unit & NMJ size, fast twitch speed, low capillary density, anaerobic , high glycogen content |
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shoulder & arm muscles have a higher proportion of... ____ fibers |
fast glycolytic (Type II) |
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neck, back and leg muscles have a higher portion of _____ fibers |
postural, slow oxidative (Type I) |
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distribution & recruitment of dif types of fibers |
# of muscle fibers doesn't change growth is enlargement of existing cells (hypertrophy) characteristics can be altered (takes a while) |
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atrophy |
wasting away of muscles caused by disuse (castin, space travel) or severing of the nerve supply the transition to connective tissue can't be reversed |
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hypertrophy |
inc in the diameter of muscle fibers resulting from very forceful, repetitive muscular activity and an inc in myofibrils, SR & mitochondria |
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anabolic steroids |
similar to testosterone increases muscle size, strength & endurance side effects: |
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aging & muscle tissue |
skeletal muscle starts to be replaced by fat beginning @ 30 |
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aging & muscle tissue |
skeletal muscle starts to be replaced by fat beginning @ 30 |
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types of contractions |
1)concentric |
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concentric contractions |
muscle shortens to produce force & movement, like biceps curl upward |
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eccentric contractions |
muscle lengthens while maintaining force & movement |
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isometric contractions |
tension generated, no muscle shortening, no movement maintaining posture & supports objects in a fixed position |
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increased force |
increased motor units activated |
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increased force |
increased # of fast-twitch motor neurons activated |
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increased force |
inc'd muscle fiber size |
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more interaction of cross bridge b/w actin & myosin |
equals more force (cross bridge) |
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length tension curve |
at rest we develop the most tension, at about 80-120% of the optimum length |
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joint angle |
optimal joint angle maximizes the force transmitted to the bone (via # of crossbridges) |
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speed of reaction in relation to force production |
decrease force, increase velocity (the lighter the load, the quicker we can shorten the muscle) increase load, decrease velocity (the heavier the load, the slower we can shorten the muscle) |
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parts of a twitch contraction |
1. Latent Period (2msec) |
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wave summation |
second stimulus applied before muscle has completely relaxed after theprevious stimulus; results in increased strength of contraction |
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incomplete/unfused tetanus |
sustained muscle contraction that permits partial relaxation b/w stimuli (several APs) |
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complete/fused tetanus |
sustained contraction w/ NO relaxation b/w stimuli (just applies to skeletal muscle) muscle gets stuck/stays stimulated @ highest pt |
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3 sources of ATP production w/in muscle |
1) Creatine Phosphate (CP) |
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creatine phosphate |
source of ATP production in muscle excess ATP w/in resting muscle used to form creatine phosphate CP 3-6x more plentiful than ATP w/in muscle empties quickly (~15 sec); quick breakdown 1 P from ATP goes to creatine phosphate (waiting to b released quickly); creatine P drops P to produce ATP for contraction during relaxation-build more creatine p stores |
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anaerobic cellular respiration |
aka glycolysis ATP produced from glucose brkdwn into pyruvic acid during glycolysis If no O2 present, pyruvic acid converted to lactic acid, which diffuses into the blood 30-40 seconds of maximal activity (200 m run) |
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aerobic cellular respiration |
source of ATP production in muscle reqs O2 fats, carbs, proteins brk down aerobically through cellular respiration in mitochondria |
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factors that contribute to muscle fatigue |
-feeling of tiredness & desire to stop (protective mechanism) |
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muscle cramps |
cause not known |
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cardiac muscle |
-striated lots of mitochondria (larger than skeletal, thus req more O2) |
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cardiac muscle |
-striated |
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smooth muscle |
-attached to hair follicles in skin |
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contraction of smooth muscle |
-no sarcomeres |
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multiunit smooth muscle |
individual fibers with OWN motor neuron ending, fibers operate individually (no gap junctions; not as a unit) found in large arteries, large airways, arrector pili, iris & ciliary muscles |
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visceral (single-unit) smooth muscle |
in the walls of hollow viscera and small BV autorhythmic; fibers contract in unison (gap junctions) all fibers act 2gether in a single unit |
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physiology of smooth muscle |
-contraction starts slowly and lasts longer |
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calmodulin |
in smooth muscle; activates the enzyme myosin light chain kinase, which facilitates myosin-actin binding and allows contraction to work at a relatively slow rate |
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smooth muscle tone |
•Prolonged presence of calcium in the cytosol leads to |
