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A&P - Ch 9
Muscle tissue
| Question | Answer |
|---|---|
| skeletal muscles maintain __ | posture |
| skeletal muscles __ joints | stabilize |
| skeletal muscles generate __ | heat |
| skeletal muscles __ __ but tires easily | contracts rapidly |
| in skeletal muscles, each muscle is a(n) | organ composed of muscle tissue, blood, & connective tissue |
| striated; involuntary; responsible for pumping blood through body; specialized muscle | cardiac muscle |
| cardiac muscle contracts at steady rate set by __ __ | heart’s pacemaker |
| neural controls, in cardiac muscles | allow heart to respond to changes in body needs |
| spindle-shaped cells w/1 centrally located nucleus; no externally visible striations; involuntary; forces food, feces & other substances through internal body channels | smooth muscles |
| smooth muscles are found | walls of hollow visceral organs, such as stomach, urinary bladder, & respiratory passages |
| ability to recoil & resume resting length after being stretched | elasticity |
| ability to be stretched/extended | extensibility |
| muscle cell's ability to move by shortening | contractility |
| ability to respond to stimuli | excitability |
| most skeletal muscles __ __ & are attached to bone in at least __ places | span joints; two |
| attachment of a muscle that remains relatively fixed during muscular contraction | muscle’s origin |
| epimysium of muscle is fused to periosteum of a bone/perichondrium of cartilage | direct or fleshy attachment |
| muscle's CT wrapping extends beyond muscle via tendons/aponeurosis | indirect attachment |
| sheath of CT surrounding each muscle fiber; consists of fine areolar CT | endomysium |
| connective tissue surrounding groups of fascicles | perimysium |
| dense irregular connective tissue that surrounds entire muscle | epimysium |
| sarcolemma | plasma membrane os muscle cell |
| each __ __ is a long, cylindrical cell with multiple nuclei just beneath sarcolemma | muscle fiber |
| sarcoplasm | cytoplasm of muscle cell |
| contains glycosomes & myoglobin; abundant mitochondria; usual organelles | sarcoplasm |
| myofibrils, sarcoplasmic reticulum, & T tubules are found in the muscle fiber's | cytoplasm |
| made of hundreds of myofibrils | muscle fiber (cell) |
| found within myofibril | striations, sarcomere & myofilaments |
| striations of myofibril are due to | arrangement of myofilaments |
| sarcomere is region of myofibril between 2 | Z discs |
| banding pattern produced by thick myosin & thin actin filaments | myofilaments |
| thin myofilaments; chiefly composed of the protein | actin |
| thick myofilaments composed of protein | myosin |
| each myosin molecule has | rod-like tail & 2 globular heads |
| two interwoven, polypeptide chains are found in myosin molecule's | tails |
| form cross bridges, found in myosin molecules | heads |
| subunits of thin myofilaments contain active sites to which | myosin heads attach during contraction |
| regulatory subunits bound to actin | tropomyosin & troponin |
| sarcoplasmic reticulum is elaborate smooth __ __ that runs longitudinally & surrounds each myofibril | endoplasmic reticulum |
| sarcoplasmic reticulum has paired terminal cisternae form | perpendicular cross channels |
| sarcoplasmic reticulum stores __ __ & releases them when muscle is stimulated to contract | calcium ions |
| extensions of sarcolemma, penetrate deep into cell’s interior | T tubules |
| T tubules associate w/paired terminal cisternae to form __ | triads |
| upon __ __, myosin heads bind to active sites on actin & sliding begins | nerve stimulation |
| thin filaments __ __ thick ones so that actin & myosin filaments __ to greater degree | slide past; overlap |
| in the __ __, thin & thick filaments overlap only slightly | relaxed state |
| as muscles relax, sarcomeres __ & muscle cell __ | shorten; shortens |
| stimulated by a nerve ending; electrical current or action potential is propagated along its sarcolemma; results in a rise in intracellular Ca2+ levels | skeletal muscle contraction |
| the final trigger for skeletal muscle contraction | rise in intracellular Ca2+ levels |
| sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments; linking electrical signal to contraction is called | excitation-contraction coupling |
| skeletal muscles are stimulated by | motor neurons |
| __ of motor neurons branch as they enter muscles | axons |
| each __ __ forms a neuromuscular junction w/muscle fiber | axonal terminal |
| axon branch; folds of sarcolemma at motor end plate w/acetyl choline receptors; synaptic vesicles in axon terminal; synaptic cleft; are all components of a(n) | neuromuscular junction (NMJ) |
| __ __ reaches axon terminal at NMJ | nerve impulse |
| at NMJ, voltage-gated __ __ in axon terminal open, allowing __ enter axon | calcium channels; Ca++ |
| at NMJ, Ca++ inside axon terminal causes synaptic vesicles to fuse with __ __ | axonal membrane |
| at NMJ, fusion of synaptic vessels w/axonal membrane releases ACh into synaptic cleft via __ | exocytosis |
| at NMJ, binding of ACh to its receptors on sarcolemma opens Na/K __ __ | gated channels |
| at NMJ, more Na+ diffuses in & interior of sarcolemma becomes less negative (depolarization), which initiates a(n) | action potential in muscle |
| at NMJ, ACh is quickly destroyed by __ acetylcholinesterase | enzyme |
| predominant extracellular ion is Na+; predominant intracellular ion is K+ | resting state |
| in resting cell inside of sarcolemma is | negative compared to outside |
| difference in charge of sarcolemma, negative compared to outside, is known as | resting membrane potential |
| action potential, depolarization, takes place when | ACh binds to its receptors on sarcolemma Na/K channels open |
| once ACh binds to its receptors on sarcolemma Na/K channels open, sodium channels open first- Na+ diffuses in & causes a patch of sarcolemma to become | less negative |
| change in resting potential is | depolarization |
| initially, depolarization, is a local electrical event called | end plate potential |
| if stimulus is strong enough, a(n) __ __ is initiated | action potential/propagation |
| if action potential initiated, voltage-gated Na+ channels open in adjacent areas of sarcolemma causing it to | depolarize |
| action potential travels | across sarcolemma |
| ultimately action potential results in | contraction of a muscle |
| in action potential/repolarization, sarcolemma permeability | changes |
| in action potential/repolarization, Na+ channels __ & K+ channels __ | close; open |
| in action potential/repolarization, K+ __ out from cell, restoring __ membrane potential (becoming negative again) | diffuses; resting |
| occurs in same direction as depolarization | repolarization |
| in excitation/contraction coupling, action potential propagates | along sarcolemma to T-tubules |
| in excitation/contraction coupling, action potential propagated along sarcolemma to T-tubules triggers | Ca2+ release from terminal cisternae |
| in excitation/contraction coupling, Ca++ bind to __; blocking action of tropomyosin released- actin binding sites __ | troponin; exposed |
| in excitation/contraction coupling, myosin heads attach forming a __ __; power stroke of myosin head causes sliding of __ __ toward center of sarcomere | cross bridge; thin filaments |
| binding of ATP to myosin heads results in their detachment from actin during | excitation/contraction coupling |
| during excitation/contraction coupling, as action potential ends, removal of Ca+2 by __ __ | active transport |
| stiffening of muscles after death; cross bridge detachment requires ATP | rigor mortis |
| because of lack of __ after breathing stops- actin & myosin irreversibly cross linked causing rigor mortis | ATP |
| refers to activation of cross bridges | contraction |
| force exerted by contracting muscle on an object | muscle tension |
| opposing force exerted on muscle by weight of object | load |
| occurs when tension generated by cross bridges exceeds forces opposing it | shortening |
| when cross bridges become inactive, tension declines & relaxation occurs | contraction ends |
| contraction in which muscle does not shorten (load is too heavy) but its internal tension increases; load not moved | isometric contraction |
| isometric contraction is used in | standing, sitting, posture |
| muscle changes in length; muscle tension overcomes load & moves load | isotonic contraction |
| isotonic contraction are used in | walking/moving any part of body |
| motor neuron & all muscle fibers it supplies | motor unit |
| muscles that control fine precise movements e.g. fingers, eyes (few muscle fibers) have | small motor units |
| large weight-bearing muscles (many muscle fibers) e.g. thighs, hips have | large motor units |
| muscle contraction in response to a single stimulus | muscle twitch |
| phase of a muscle twitch; first few m/sec after stimulus; no response seen yet | latent period |
| phase of a muscle twitch when cross bridges form | period of contraction |
| phase of a muscle twitch when Ca2+ re-enters SR; muscle tension decreases | period of relaxation |
| factor affecting muscle tension in which muscle stimulated rapidly, contractions are summed up become stronger | frequency of stimulation |
| factor affecting muscle tension in which the more the motor fibers are contracting (by recruitment of more motor units) the stronger the contraction | number of muscle fibers contracting |
| factor affecting muscle tension in which muscles contract strongest when muscle fibers are moderately stretched before contraction | degree of muscle stretch |
| degree of muscle stretch is optimum muscle length at which they can | generate maximum force of contraction |
| degree of muscle stretch, number of muscle fibers contracting, & frequency of stimulation | factors that affect muscle tension |
| single stimulus results in a single contractile response | a muscle twitch |
| with increased frequency of stimulus muscle does not relax completely; contraction force increasing | wave summation |
| shorter & shorter relaxation | incomplete tetanus |
| smooth continuous contraction without any relaxation | complete tetanus |
| produces weak contraction because overlapping thin filaments interfere with each other | unstretched sarcomere |
| cross bridges too far apart to cycle | overstretched sarcomere |
| maximum tension develops at this optimum overlap of thick & thin filaments; all cross bridges can cycle | moderately stretched sarcomere |
| constant, partial state of muscle contraction which does not produce active movements | muscle tone |
| muscle tone keeps muscles __ & ready to __ to stimulus | firm; respond |
| account for muscle tone by responding to stretch receptors in muscles & tendons | spinal reflexes |
| ATP in muscle contraction is used for energizing | power stroke of myosin head |
| ATP in muscle contraction is used for ___ myosin head from actin | detaching |
| ATP in muscle contraction is used for pumping __ back into sarcoplasmic reticulum | calcium |
| creatine phosphate (CP), anaerobic glycolysis of glucose, & aerobic respiration are sources of | ATP regeneration |
| during contraction: hydrolysisphosphate group combines w/ADP to form ATP (immediate source) | creatine phosphate (CP) |
| during contraction: when muscle contractile activity reaches 70% of maximum, bulging muscles compress blood vessels; impaired O2 delivery | anaerobic glycolysis of glucose |
| during contraction, largest amount of ATP formed | aerobic respiration |
| muscle is being stimulated but is in a state of physiological inability to contract | muscle fatigue |
| muscle fatigue can be due to __ ATP production | low |
| muscle fatigue can be due to __ __ accumulation | lactic acid |
| a functional characteristic of muscle fiber type, slow & fast fibers on basis of | speed of contraction |
| a functional characteristic of muscle fiber type, according to ATP-forming pathways | oxidative or glycolytic fibers |
| cells that rely on oxygen-using aerobic pathways for ATP generation | oxidative fibers |
| cells that rely more on anaerobic glycolysis pathways for ATP generation | glycolytic fibers |
| characteristics intermediate btwn oxidative & glycolytic fibers | fast oxidative fibers |
| red fibers; depend on aerobic ATP production; have more myoglobin, capillaries, mitochondria, low glycogen; contract slowly, are fatigue resistant & have high endurance | slow oxidative fibers |
| example of slow oxidative fibers | muscles maintaining posture; activities- running a marathon |
| white fibers; mainly use glycolysis for ATP production; large diameter fibers, have abundant glycogen, but few capillaries, mitochondria & low myoglobin; contract quickly, and are easily fatigued; muscles used for short time in powerful activities | fast glycolytic fibers |
| example of fast glycolytic fibers | hitting baseball, pushing piano |
| most muscles contain a(n) __ of fiber types | mixture |
| shrinkage of muscle due to decrease in size of cells | atrophy |
| example of disuse atrophy | immobilization |
| example of atrophy due to loss of nerve supply | paralysis |
| enlargement of a muscle; more capillaries & more mitochondria; greater bulk through increase in size, but not in number of cells | hypertrophy |
| example of hypertrophy | strenuous exercise in body builders |
| composed of spindle-shaped fibers w/central nuclei | smooth muscle |
| smooth muscle is found in | walls of blood vessels, digestive, urinary, respiratory & reproductive tracts |
| smooth muscle is organized in two layers of | sheets |
| organized sheets of smooth muscle are sheets of | longitudinal & circular |
| smooth muscle lack the __ __ junctions of skeletal muscle | structures neuromuscular |
| smooth muscles autonomic nerve fibers have __ that release neurotransmitters | varicosities |
| smooth muscle sarcoplasmic reticulum is | less developed |
| smooth muscle T tubules are | absent |
| in smooth muscle, actin & myosin filaments are present but | there are no sarcomeres |
| in smooth muscle, there is no | troponin complex |
| slow & prolonged; has low energy requirements | smooth muscle contraction |
| mostly whole sheets of smooth muscle contract together, because of __ __, as __ __ spread from cell to cell | gap junctions; action potentials |
| each skeletal muscle fiber is stimulated to __ by its own NMJ | contract |
| in smooth muscle, actin & myosin interact by the | sliding filament mechanism |
| in smooth muscle, final trigger for contractions is a(n) | rise in intracellular Ca2+ |
| in smooth muscle, sliding filament mechanism | requires ATP |
| in smooth muscle, Ca2+ enter mainly from the __ __ | extracellular space |
| in smooth muscle, some Ca2+ is __ __ SR | released from |
| when stretched to an optimal length contract more strongly | cardiac & skeletal muscles |
| smooth muscle responds to stretch briefly by __ __ then adapts to its new length & relaxes | increased contraction |
| enables organs such as the stomach and bladder to be able to store contents without strong contractions expelling contents | stress-relaxation response of smooth muscles |
| found in walls of hollow visceral organs; cells contract as a unit (have gap junctions); arranged in sheets; show stress-relaxation response | smooth muscle single unit |
| found in airways, large arteries, internal eye muscles; have individual NMJs & muscle fibers independent of each other | smooth muscle multiunit |
| increase in cell numbers | hyperplasia |
| smooth muscles can undergo hyperplasia | when stimulated |
| examples of smooth muscle hyperplasia stimulation is | estrogen’s effect on the uterus |
| during pregnancy, estrogen stimulates uterine growth to accommodate the increasing size of the growing fetus, causing | smooth muscle hyperplasia |
| because skeletal & smooth muscles are __ they are called muscle fibers | elongated |
| whenever you see prefixes myo-/mys- or sarco- the reference is to | muscle |
| word root means muscle | myo-/mys- |
| word root means flesh | sarco- |
| word root means husk | -lemma |
| muscle composed of cylindrical, multinucleate cells w/obvious striations; attached to skeleton; voluntary muscle | skeletal muscle tissue |
| skeletal muscle tissue is packaged; organs that attach to & cover bony skeleton; responsible for body movements | skeletal muscles |
| cardiac muscles tissue constitutes bulk of __ __ | heart walls |
| allow heart to speed up for brief periods of exertion | neural controls |
| response to stimuli; generation of electrical impulse that passes along plasma membrane of muscle cell & causes cell to contract | conductivity |
| produces movement, maintains posture, stabilizes joints, generates heat, etc. | muscle functions |
| skeletal muscles are responsible for all __ & __ | locomotion; manipulation |
| skeletal muscles enable you to __ __ to changes in external environment | respond quickly |
| cardiac muscle of heart & smooth muscle in walls of blood vessels help to | maintain blood pressure |
| skeletal muscles account for at least 40% of | body mass |
| skeletal muscles are muscle type most responsible for | generating heat |
| form valves to regulate passage of substances through internal body openings, dilate/constrict pupils of eyes, & forms arrector pili muscles attached to hair follicles | smooth muscles |
| predominately muscle fibers, but also blood vessels, nerve fibers, & CT | composition of skeletal muscles |
| in general, __ __ is served by one nerve, artery, & 1/more veins | each muscle |
| only cardiac & smooth muscles can | contract in without nerve stimulation |
| long & winding w/numerous cross-links, which is feature that accommodates changes in muscle length | muscle capillaries |
| muscle capillaries __ when muscle is stretched | straighten |
| muscle capillaries __ when muscle contracts | contort |
| support each muscle cell & reinforce muscle as a whole; prevents bulging muscle from bursting during strong contractions | CT sheaths |
| bundle of nerve/muscle fibers bound together by CT | fascicles |
| CT sheaths contribute to __ of muscle tissue | elasticity |
| CT sheaths provide entry & exit routes for | blood vessels & nerve fibers serving muscle |
| movable attachment of a muscle | muscle's insertion |
| when muscle contracts movable bone, __ moves towards immovable/less movable bone | insertion |
| cord of dense fibrous tissue attaching muscle to bone | tendon |
| fibrous/membranous sheet connecting muscle & part it moves | aponeurosis |
| anchors muscle to CT covering of skeletal element or fascia of other muscles | aponeurosis/tendon |
| indirect attachments are more common because of | their durability & size |
| more __ than fleshy muscle can pass over __ | tendons; joint |
| granules of stored glycogen that provide glucose during periods of muscle cell activity | glycosomes |
| oxygen-binding, red pigment in muscle | myoglobin |
| myoglobin is similar to | hemoglobin |
| rod-like bundle of contractile filaments (myofilaments) found in muscle fibers (cells) | myofibril |
| myofibrils account for about 80% of | cellular volume |
| repeating series of dark & light bands, evident along length of each myofibril | striations |
| dark striations within muscle cells | A bands |
| light striations within muscle cells | I bands |
| lighter region in midsection of A band | H zone |
| dark line that bisects each H zone vertically; formed by molecules of protein myomesin | M line |
| darker, midline interruption in I bands; coin-shaped sheet composed largely of protein alpha-actinin; anchors thin filaments | Z disc |
| smallest contractile unit of muscle; extends from 1 Z disc to next | sarcomere |
| sarcomere is __ __ of skeletal muscle | functional unit |
| sarcomere contains __ band flanked by 1/2 __ band | A; I |
| located in center; contain myosin; extend entire length of A band | thick filaments |
| more lateral; contain actin; extend across I band & partway into A band | thin filaments |
| contain desmin; extend from Z disc; connect each myofibril to next throughout width of muscle cell | intermediate filaments |
| consists of 2 heavy & 4 light polypeptide chains; has rod-like tail attached by flexible hinge to 2 globular heads | myosin molecule |
| rod-shaped protein, spiral about actin core & hep stiffen & stabilize it | tropomyosin |
| in relaxed muscle fiber, tropomyosin __ myosin-binding sites on actin | block |
| globular, three-polypeptide complex | troponin |
| troponin & tropomyosin help control __ __ involved in contraction | myosin-actin interactions |
| composed of titin | elastic filament |
| protein extending from Z disc to thick filament, & then runs within thick filament to attach to M line | titin |
| titin forms __ of thick filament | core |
| titin holds thick filaments in place, thus maintaining | organization of A band |
| titin holds thick filaments in place, helping muscle cell to | spring back into shape after being stretched |
| titin does not resist stretching in | ordinary range of extension |
| titin stiffens as it uncoils, helping muscle to | resist excessive stretching |
| structural protein that links thin filaments to integral proteins of sarcolemma | dystrophin |
| nebulin, myomesin, & C proteins are other proteins that act to | bind filaments or sarcomeres together & maintain their alignment |
| SR & T tubules are two sets of intracellular tubules that | participate in regulation of muscle contractions |
| tubules of SR run longitudinally along | myofibril communicating at H zone |
| major role of SR is to regulate | intercellular levels of ionic calcium |
| T tubules increase muscle fiber's __ __ | surface area |
| successive groupings of 2 membranous structures (terminal cisterna, T tubule, & terminal cisterna | triads (definition) |
| because T tubules are extensions of sarcolemma they | conduct impulses to deepest regions of muscle cell to every sarcomere |
| protruding integral proteins of T tubules act as | voltage sensors |
| form gated channels through which Ca2+ can be released from SR cisternae | foot proteins |
| term contraction refers to | activation of myosin's cross bridges |
| states that during contraction thin filaments slide past thick ones so that actin & myosin filaments overlap to greater degree | sliding filament model of contraction |
| for skeletal muscle to contract it must be | stimulated by nerve ending so change in membrane potential occurs |
| large transient depolarization event, including polarity reversal, that is conducted along membrane of muscle cell/nerve fiber | action potential |
| for skeletal muscle to contract it must be activated, then must | generate & propagate action potential along its sarcolemma |
| for skeletal muscle to contract it must be activated, generate/propagate action potential, then final trigger is | short-lived rise in intracellular calcium ion levels |
| nerve cells that activate skeletal muscle fibers are called | somatic motor neurons |
| long thread-like extensions of somatic motor neurons | axons |
| synaptic connection of axon of motor neuron with muscle fiber | neuromuscular junction |
| when axon of motor neuron divides when entering muscle, the short curling branches it gives off are collectively called | elliptical neuromuscular junctions |
| each muscle fiber has | only one neuromuscular junction |
| fluid-filled (with ACh) space at a synapse | synaptic cleft |
| chemical transmitter substance released by some nerve endings; neurotransmitter | acetylcholine (ACh) |
| trough-like part of muscle fiber's sarcolemma | junctional folds |
| junctional folds provide __ __ __ for location for millions of ACh receptors | large surface area |
| neuromuscular junction includes | axonal endings, synaptic cleft, junctional folds |
| enzyme present at NMJ & synapses that degrades acetylcholine & terminates its action | acetylcholinesterase |
| disease characterized by drooping upper eyelids, difficulty swallowing & talking, & generalized muscle weakness, involves shortage of ACh receptor | myasthenia gravis |
| resting sarcolemma is | polarized |
| loss of a state of polarity; loss/reduction of negative membrane potential | depolarization |
| depolarizations of skeletal muscle fibers caused by neurotransmitters binding to post-synaptic membrane in NMJ | end plate potential |
| movement of membrane potential to initial resting state | repolarization |
| period of time it takes for an excitable membrane to be ready for 2nd stimulus once it returns to its resting state following an excitation | refractory period |
| repolarization only restores __ __ of resting state | electrical conditions |
| ATP-dependent sodium-ion pump restores __ __ of resting state | ionic conditions |
| once initiated, the action potential is __ | unstoppable |
| events of excitation-contraction coupling take place during __ __ btwn action potential initiation & beginning of mechanical activity | latent period |
| intracellular Ca levels low & active (myosin-binding) sites on actin are physically blocked by tropomyosin | muscle is relaxed |
| tropomyosin is __ when sufficient Ca is present | removed |
| continues as long as Ca signal & adequate ATP are present | sliding of thin filament |
| when impulses delivered rapidly, intracellular Ca2_ levels __ __ due to successive rounds of Ca2_ released from SR | increase greatly |
| except for brief period following muscle cell __, Ca ion concentrations in cytosol are kept low | excitation |
| graphic recording of mechanical contractile activity produced by apparatus that measures muscle contraction | myogram |
| latent period | period of time btwn stimulation & onset of muscle contraction; excitation-contraction coupling occurs here |
| period of contraction | when cross bridges are active, from onset-peak tension development, myogram tracing rises to peak |
| period of relaxation | final phase; initiated by reentry of Ca2+ into SR |
| muscle twitches may result from | some neuromuscular problems |
| relatively smooth; vary in strength as different demands placed on them | healthy muscle contractions |
| variations in degree of muscle contraction by changing either frequency/strength of stimulus | graded muscle responses |
| nervous system achieves __ __ __ by increasing firing rate of motor neurons | greater muscular force |
| occurs in transmission of nerve impulses when volley of impulses arrives at synapse so that duration of impulses is briefer than post-synaptic potential & their deliveries of transmitter are combined to create larger than normal response | temporal/wave summation |
| each stimulus causes contraction to be initiated when muscle has only partly relaxed from previous contraction | unfused/incomplete tetanus |
| sustained muscular contraction caused by series of nerve stimuli repeated so rapidly that individual muscular responses are fused | complete tetanus |
| fused/complete tetanus happens __ in real world | infrequently |
| __ tetanus eventually leads to muscle __ | prolonged; fatigue |
| wave summation contributes to __ force | contractile |
| is to produce smooth, continuous muscle contractions by rapidly stimulating specific number of muscle cells | primary function of wave summation |
| smooth but steady increase in muscular tension produced by increasing number of active motor units | recruitment/multiple motor unit summation |
| stimulus too weak to evoke a response | subthreshold stimulus |
| one stimulus just strong enough to excite; weakest stimulus capable of producing response in irritable tissue | threshold stimulus |
| stimulus strong enough to evoke greatest possible response; represents point at which all muscle's motor units are recruited | maximal stimulus |
| increasing stimulus intensity beyond maximal stimulus | does not produce stronger contraction |
| recruitment process is __ by size principle | dictated |
| motor units of small, highly excitable motor neurons (found in smallest muscle fibers) tend to be activated first; as motor units w/larger & larger muscle fibers begin to excited, contractile strength increases | size principle |
| size principle dictates that largest motor units containing large, coarse muscle fibers controlled by largest least excitable neurons & are activated only when | most powerful contraction is necessary |
| size principle is important because it allows for increases in force during weak contractions to | occur in small steps |
| according to size principle, gradations in muscle force are __ __ when large amounts of force are needed | progressively greater |
| although all motor unit of a muscle may be recruited simultaneously to produce strong contraction, they are more commonly activated __ in body | asynchronously |
| even __ muscles are almost always __ | relaxed; contracted |
| muscle contraction that occurs while muscle is shortening as it develops tension & contracts to move resistance | concentric contraction |
| type of muscle contraction that occurs as muscle fibers lengthen; contractile force generated by muscle is weaker than opposing force, which causes muscle to stretch | eccentric contraction |
| eccentric contractions are about 50% __ __ than concentric ones | more forceful |
| eccentric contractions put body in position to | contract concentrically |
| CP-ADP reaction is catalyzed by | creatine kinase |
| initial phase of glucose breakdown; anaerobic pathways; glucose broken down into pyruvic acid molecules releasing enough energy to form small amount of ATP | glycolysis |
| 2 ATP produce | per glucose broken down |
| product of anaerobic metabolism, especially in muscle | lactic acid |
| lactic acid is produced when bulging muscles (from vigorous activity) compress blood vessels within them causing | impaired blood flow & O2 delivery |
| energy-yielding conversion of glucose to lactic acid in muscle, when sufficient oxygen is not available | anaerobic glycolysis |
| during __ __, lactic acid is end product of cellular metabolism of glucose | oxygen deficit |
| 95% of ATP used for muscle activity from from | aerobic respiration |
| when ATP demands are within capacity os aerobic pathway, light to moderate muscular activity can | continue for several hours in well-conditioned person |
| when exercise demands begin to exceed ability of muscle cells to carry out necessary reactions quickly enough, | glycolysis contributes more & more of total ATP generated |
| length of time muscle can continue to contract using aerobic pathways | aerobic endurance |
| point at which muscle metabolism converts to anaerobic glycolysis | anaerobic threshold |
| activities requiring surge of power lasting only few seconds (i.e. weight lighting, diving, etc.) rely | entirely on ATP & CP stores |
| more on-and-off or burst-like activities (i.e. tennis, soccer, etc.) appear to be fueled | almost entirely by anaerobic glycolysis |
| prolonged activities (i.e. marathons, jogging) where endurance over power is goal, depend | mainly on aerobic respiration |
| levels of CP & ATP do not change much during __ __ because ATP is generated at same rate it is use | prolonged exercise |
| states of continuous contraction because cross bridges are unable to detach | contractures |
| example of temporary contracture | writer's cramp |
| several __ __contribute to muscle fatigue | ionic imbalances |
| lactic acid is more important in provoking __ fatigue than __ fatigue | central; physiological |
| excessive intracellular accumulation of lactic acid raises concentration of H+ and alters __ __ | contractile proteins |
| lactic acid has been shown to __ high K+ levels, which do lead to muscle fatigue | counteract |
| intense exercise of short duration produces fatigue rapidly via disturbances that | alter E-P coupling |
| short-duration exercise damages SR, interfering with Ca2+ __ & __, and thus with muscle activation | regulation; release |
| O2-requiring muscle metabolism activities occur more slowly & are deferred until O2 is again available during | anaerobic muscle contraction |
| volume of O2 required after exercise to replenish stores of O_2, ATP, creatine phosphate, & glycogen & oxidize lactic acid formed during exercise | oxygen deficit (definition) |
| oxygen deficit represents difference btwn amount of oxygen __ for totally aerobic muscle activity & amount __ __ | need; actually used |
| only about 40% of energy released during muscle activity is | converted to useful work |
| greater muscle's __ __, more tension can develop & greater its strength | cross-sectional area |
| force generated by cross bridges, inside contracting muscle fibers | internal tension |
| force generated in extracellular fibers | external tension |
| length at which muscle can generate maximum force | optimal operating length |
| relationship btwn length of fiber & force that fiber produces at that length; permits sliding along nearly entire length of thin filaments | ideal length-tension relationship |
| in slow/fast fibers, difference in speed reflects how fast their myosin ATPases __ __ | split ATP |
| in slow/fast fibers, difference in speed reflects on pattern of __ __ of motor neurons | electrical activity |
| depending on pathways for forming ATP, skeletal muscles cells can be classified as | slow oxidative (SO), fast oxidative (FO), or fast glycolytic (FG) fibers |
| exercise that increases the need for oxygen | aerobic exercise |
| moderately weak but sustained muscle activity | endurance exercise |
| high-intensity exercise in which the muscles are pitted against high resistance or immovable forces and, as a result, muscle cells increase in size | resistance exercise |
| smooth muscle fibers run parallel to long axis of organ; when muscle contracts organ dilates & shortens | longitudinal layer |
| smooth muscle fibers run around circumference of organ; contraction constricts lumen causing it to elongate | circular layer |
| junction of varicosities & synaptic cleft of smooth muscle cells | diffuse junctions |
| epimysium | surround entire muscle |
| endomysium | surround each muscle fiber |
| perimysium | surround each muscle bundle |
| deep fascia | bind muscles into functional groups |
| sarcolemma | plasma membrane of skeletal muscle fiber |
| sarcoplasm | cytoplasm of a skeletal muscle fiber |
| sarcoplasmic reticulum | series of membranous channels (modified ER) that surround each myofibril |
| myofibril | rod-like contractile elements within a muscle fiber |
| sarcomere | functional unit of a skeletal muscle fiber |
| A band | area of the sarcomere with overlapping thick and thin filaments |
| I band | area of sarcomere containing only thin filaments |
| H band | are in center of A band containing only thick filaments |
| myosin molecules | cross bridges |
| synaptic knob | contains vesicles filled w/ACh |
| synaptic cleft | space btwn neuron & muscle |
| motor end plate | contains receptors for ACh |
| twitch | type of contraction represented by a single stimulus/contraction/relaxation sequence |
| incomplete tetanus | muscle producing peak tensions with visible relaxation during rapid cycles of contraction and relaxation |
| complete tetanus | muscle that is stimulated so frequently that the relaxation phase is completely eliminated |
| wave summation | when muscle is stimulated repeatedly for several seconds with a constant stimulus, the amount of tensions gradually increases to a maximum |
| endurance-type activities | best suited for slow oxidative fibers |
| 400M or 800M sprint | best suited for fast oxidative fibers |
| short-term intense movements | best suited for fast glycolytic fibers |
| skeletal muscle fibers | single, very long, cylindrical, multinucleate cells with striations |
| cardiac muscle cells | branching chains of cells; uni- or binucleate striations; intercalated discs |
| smooth muscle cells | single, fusiform, uninucleate; no striations |
| excitability | ability to receive and respond to a stimulus |
| contractility | ability to shorten forcibly when adequately stimulated |
| extensibility | ability to be stretched or extended |
| elasticity | ability of a muscle to resume its resting length after being stretched |
| isotonic contraction | contraction of muscle during which the muscle changes in length and the tension remains constant through most of the contractile period |
| isometric contraction | contraction of muscle during which the tension continues to increase but the muscle neither shortens nor lengthens |
| concentric contraction | contraction of the muscle in which the muscle shortens and does work |
| eccentric contraction | contraction of muscle in which the muscle contracts as it lengthens |
| skeletal muscle voluntary via __ __ of the somatic nervous system | axonal endings |
| involuntary; intrinsic system regulation, hormones and autonomic nervous system controls | cardiac muscles |
| involuntary, autonomic nerves, hormones, local chemicals | smooth muscles |
| acetylcholine (ACh) | neurotransmitter at the neuromuscular junction |
| creatine phosphate | high-energy compound in muscle |
| myoglobin | O2 storage molecules in muscles |
| lactic acid | product of anaerobic glycolysis |
| fast oxidative fibers | muscle fibers that contract quickly and rely on aerobic respiration for ATP |
| slow oxidative fibers | muscle fibers that are most resistant to fatigue |
| fast glycolytic fibers | muscle fibers that have few mitochondria |
| sustained spasm, or tetanic contraction | cramp |
| inflammation of a muscle, its connective tissue coverings and tendons, and capsules of nearby joints | fibromyositis |
| muscle pain resulting from any muscle disorder | myalgia |
| excessive stretching and possible tearing of a muscle caused by muscle overuse or abuse | strain |
| latent period | time btwn stimulus/electrical event & mechanical event of contraction |
| contraction period | time during which the muscle is shortening |
| relaxation period | time during which the muscle is returning to its original length |
| refractory period | very brief time after one stimulus during which the muscle is unresponsive to a second stimulus |
| action potential | propagation of an electrical current along sarcolemma |
| resting potential | initial polarized state |
| repolarization | restoration of membrane potential to resting potential |
| refractory period | time when fiber cannot be stimulated until repolarization is complete |
| end plate potential | electrical event occurring only at neuromuscular junction |
| Ca2+ | released by terminal cisternae into the sarcoplasm to bind with troponin |
| acetylcholinesterase | enzyme released into neuromuscular junction to break down acetylcholine |
| calmodulin | cytoplasmic, calcium-binding protein |
| electrical conditions of a resting sarcolemma | outside positive relative to the inside |
| depolarization & generation of action potential | production of an end plate potential at the motor end plate and consequent depolarization of adjacent areas |
| propagation of action potential | increased positive charge inside sarcolemma changes permeability of adjacent areas, opening voltage-regulated Na+ channels |
| repolarization | change in sarcolemma after the wave of depolarization; Na+ channels close and K+ channels open, allowing K+ to create a positive charge outside the membrane |
| producing movement | pulling on something to change its position |
| maintaining posture | development of tension to prevent movement, as in keeping the vertebral column upright |
| stabilizing joints | attaching to bones and keeping them in close proximity to one another |
| generation of heat | release of energy during metabolism |
| myosin | changes shape during the contraction cycle |
| actin | slides toward the M line during a contraction |
| tropomyosin | covers the binding site |
| troponin | binds Ca2+ and starts the contraction cycle |
| __ skeletal muscle is surrounded by epimysium | entire |
| as an axon enters a muscle, it branches into a number of axonal terminals, each of which forms a neuromuscular junction with a single muscle fiber. A motor neuron and all the muscle fibers it supplies is called a(n) | motor unit |
| What is the ion released from the terminal cisternae that combines with troponin and removes the blocking action of tropomyosin, resulting in the formation of cross bridges? | Ca2+ |
| each skeletal muscle fiber is controlled by a neuron at a single | NMJ |
| terminal cisterna, transverse tubule, and terminal cistern | composition of the structure known as a triad in a skeletal muscle fiber |
| In the __ __ __ of muscle contraction, the myofilaments slide over each other, resulting in the overlapping of actin and myosin | sliding filament model |
| epimysium is the | dense layer of collagen fibers that surround an entire skeletal muscle |
| muscle tone | means a continued mild or partial contraction of an entire muscle is muscle |
| isometric | type of muscle contraction in which the muscle fibers produce increased tension, but the muscle neither shortens nor lengthens |
| lactic acid | substance that increases in quantity during repetitive muscle contraction |
| action potential | sequence of electrical changes that occurs along the sarcolemma when a muscle fiber is stimulated |
| calmodulin | binds calcium ions in a smooth muscle, causing contraction |
| sarcomere is part of | a myofibril |
| "cross bridges" that link between the thick and thin filaments are formed by the | globular heads of thick filaments |
| refractory period in which the muscle will not contract if stimulated occurs during | refractory period of muscle cell |
| cause of rigor mortis | calcium influx into the cell after death |
| 95% of the energy needed for contraction during moderate exercise | comes from ATOP |
| T-tubules | serve as a communication network that coordinates the contraction of each myofibril that makes up the muscle fiber |
| actin | myofilaments are composed chiefly of |
| when an action potential arrives at the neuromuscular junction, the most immediate result is | release of acetylcholine |
| if a muscle is applied to a load that exceeds the muscle's maximum tension | muscle length will not change during contraction |
| graded muscle response | variation of stimulation needed in skeletal muscle contraction in order to have controlled movement |
| aerobic respiration | most efficient means of producing ATP |
| if muscle became totally depleted of ATP | muscle would remain in a contracted state due to an inability to break actin-myosin cross bridges |
| smooth muscle depends on the __ system to regulate contraction | calcium-calmodulin |
| skeletal muscle relies on the __ __ system to regulate contraction | calcium-troponin |
| peristalsis | progressive, wavelike contractions that move foodstuffs through alimentary tube organs/move other substances through other hollow body organs |
| smooth muscle lacks highly structured, __ __ of skeletal muscles | specific NMJs |
| smooth muscles are controlled by | innervating nerve fibers, part of autonomic nervous system |
| varicosities | knob-like swellings of certain autonomic axons containing mitochondria and synaptic vesicles |
| diffuse junctions | wide synaptic cleft in general area of smooth muscles |
| smooth muscles have __ __ SR | less developed |
| some SR tubules of smooth muscle touch __ at several sites, forming what resembles __ | sarcolemma; half-triads |
| pouch-like infoldings that sequester bits of extracellular fluid containing high concentration of Ca2+ close to membrane | caveolae |
| when calcium channels in caveolae open, Ca2+ | influx occurs rapidly |
| in smooth muscles, SR does release some calcium that triggers contraction, but most | enters through the calcium channels |
| contraction of smooth muscle ends when calcium is | actively transported to SR & out of cell |
| smooth muscles contain | interdigitating thick & thin filaments |
| in smooth muscle, __ filament are fewer, but have __ __ along their entire length | thick; myosin heads |
| in smooth muscle, there is no __ __ in thin filaments | troponin complex |
| in smooth muscle, thick & thin filaments are __ __ allowing muscles to contract in __ __; thus peristalsis | arranged diagonally; twisting way |
| in smooth muscles, the lattice-like arrangement of non-contractile __ filaments attach to __ __ | intermediate; dense bodies |
| cytoplasmic structures; tethered to sarcolemma; act as anchoring points for thin filaments; correspond to Z discs of skeletal muscles | dense bodies |
| forms strong, cable-like intracellular cytoskeleton that harnesses pull generated by sliding of thick & thin filaments in smooth muscles | intermediate filament-dense body network |
| dense bodies, of smooth muscles, bind muscle cell to | endomysium & adjacent cells |
| synchronizistic contraction of smooth muscles reflects | electrical coupling by gap junctions |
| allow smooth muscles to transmit action potentials from fiber to fiber | gap junctions |
| some smooth muscles in stomach & small intestines are | pacemaker cells |
| smooth muscle's pacemaker cells have fluctuating __ __ & are __ | membrane potentials; self-excitatory |
| smooth muscle's pacemaker cells __ __ in absence of stimuli | depolarize spontaneously |
| rate & intensity of smooth muscle contraction may be modified by | neural & chemical stimuli |
| in order to phosphorylate myosin, calmodulin interacts with | myosin kinase/myosin light chain kinase |
| smooth muscle takes 30x longer to | contract & relax than skeletal muscle |
| smooth muscle myofilaments may __ __ during prolonged contractions, saving energy | latch together |
| smooth muscle cells may maintain __ __ even after dephosphorylation of myosin | latch state |
| __ __ of smooth muscle is extremely important to overall body homeostasis | ATP-efficient contraction |
| graded contraction depends on level of calcium and # of cross bridges formed | smooth muscle tone |
| smooth muscle makes ATP through __ __ | aerobic pathways |
| some smooth muscles respond to neural stimulation with __ __ only | graded potentials |
| smooth muscles react to __ __ in different ways depending on receptors present | different neurotransmitters |
| smooth muscles without nerve supply depolarize __ or in response to chemical stimuli that bind to __ __ receptors | spontaneously; G protein-linked |
| certain hormones, lack of O2, histamine, excess CO2, & low pH are different chemical factors that cause smooth muscle contraction & relaxation | without an action potential |
| smooth muscle responds differently to | stretch |
| smooth muscle can __ more than other muscle types | shorten |
| stretch of smooth muscle provokes contraction, but soon muscle | adapts to length & relaxes with retaining ability to contract on demand |
| lack of sarcomeres & irregular, overlapping arrangement of smooth muscle filaments allow them to | generate considerable force, even when they are substantially stretched |
| smooth muscle can contract when it is anywhere from | twice to half its resting length |
| smooth muscles are categorized as | single-unit or multiunit |
| type of smooth muscle; cells contract as unit & rhythmically, are electrically coupled by gap junctions; often exhibit spontaneous action potentials | visceral muscle |
| visceral muscle is also known as | single-unit smooth muscle |
| visceral muscle is found in walls of all hollow organs except | the heart |
| smooth muscles in large airways to lungs & in large arteries, arrector pili muscle attached to hair follicles, & internal eye muscles are examples of | multiunit smooth muscle |
| in multiunit smooth muscle | gap junctions are rare & spontaneous synchronous depolarization are rare |
| multiunit smooth muscle is innervated by | autonomic nervous system |
| embryonic mesoderm cells from which all muscle fibers develop | myoblasts |
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lfrancois
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