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88 Cards in this Set
- Front
- Back
skeletal muscle
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- strong, quick discontinuous voluntary contraction
- bundle of fibers - muscle cells - myofibril |
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cardiac muscle
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- strong, quick continuous involuntary contraction
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smooth muscle
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- weak, slow involuntary contraction
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myofibril
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- rods of proteins inside muscle fibers
- myofilaments = thick and thin filaments - arranged in specific way = thick filament surrounded by six thin filaments |
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sacromere
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- functional unit of muscle
- z line and I band to the next z line - I band split between 2 sacromeres - sacroplasmic reticulum - terminal sisterny = stores calcium - I tubule, terminal sisterny, sacroplasmic reticulum = triad |
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thick filament
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- made of myosin
- myosin composed of 6 polypeptides - myosin lines up tail to tail = heads pointed in opposite directions - 4 light chains and 2 heavy chains |
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thin filament
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- made of many proteins
- actin composed of globular actin - actin has myosin binding site - tropomyosin wraps around actin and covers binding site - troponin has 3 subunits - tropomyosin exposes binding sites when calcium present |
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troponin 3 subunits
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- TnT = binds to tropomyosin
- TnC = binds to calcium - TnI = inhibitory |
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titin
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- huge protein that helps center thick filament
- elastic element - links thick filaments to Z lines - largest protein in human genome |
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nebulin
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- acts as molecular ruler
- determines how long the thin filament will be - actin binding protein |
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sliding filaments
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- produce muscle contraction
- H zone and I band disappear - sacromere shortens = thin filament pulled over thick filament |
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cap-Z
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- binds to thin filaments and stabilizes it on the Z line
- caps the plus ends of actin filaments at Z-disk |
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muscle contraction
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- dystroglycan complex = proteins that interact with extracellular matrix and bound to sacroglycan complex
- sacroglycan = enormous gene that is capable of having mutations - muscle dystrophy = dystrophin is absent or mutated |
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sequence of muscle contraction
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- rigor is a transient state
- ATP binding dissociates myosin from actin - myosin ATPase hydrolyzes ATP to ADP and P - hydrolization causes myosin to have a cocked position - myosin binding site on actin binds to actin binding site on myosin making a cross bridge - conformation change called a power stroke and ADP is released - binds to ATP and myosin releases from actin |
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power stroke
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- thin filament is pulled over the thick filament toward the M line
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regulation of contraction
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- myosin binding site on actin is controlled
- tropomyosin covers the myosin binding site and won't let myosin connect to actin - Ca binds to troponin causing a conformational change that pulls down the tropomyosin exposing myosin binding sites |
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vertebrate plan
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- based on muscles organized into motor units
- motor units = motor neuron and all muscle fibers it innervates |
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motor end-plate
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- region of the muscle cell membrane covered by the terminal bud
- has clefts and ridges = junctional folds |
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T tubule
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- contains dihydropyridine receptor (DHPR)
- blocks channel for ryanodine |
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excitation-contraction coupling sequence
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- action potential in motor neuron triggers exocytosis of ACh
- ligand-gated channels bind ACh and open generating an action potential - action potential propagates over cell membrane and depolarizes the t-tubules - depolarization reaches the DHPR and causes a conformation change that opens a RyR calcium channel of the SR and Ca diffuses out of SR into cytoplasm - Ca ions bind to troponin and tropomyosin moves to expose myosin-binding sites on actin - acetylcholinesterase in the extracellular matrix of synaptic cleft hydrolyzes ACh to terminate the action potential - cross bridges go through several cycles as long as Ca remains bound to troponin - once wave of depolarization ceases, DHPRs return to their original conformation and RyR Ca channels close - as ATP-depenedent Ca pumps decrease the Ca concentration in cytoplasm, Ca leaves TN, TM blocks myosin binding sites on actin, and contraction ends |
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excitation-contraction coupling
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- Ca is stored in the SR both free and bound to the protein calsequestrin
- ATP dependent Ca pumps are continuously active, before, during, and after contraction - each ATP hydrolyzed, 2 Ca are moved from cytoplasm into the SR |
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excitation-contraction coupling diagram
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excitation-contraction coupling diagram
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whole skeletal muscles
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- prime mover
- synergist - antagonist - fixator |
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prime mover
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- agonist
- produces most of force |
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synergist
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- aids prime mover
- stabilizes the nearby joint - modifies direction of movement |
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antagonist
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- opposes prime mover
- prevents excessive movement and injury |
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fixator
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- prevents movement of bone
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force
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- generated only by contracting
- lengthen passively |
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contraction
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- tension generated by a muscle during cross bridge activity
- may or may not involve shorteining |
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twitch
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- mechanical response of a muscle to a single action potential
- latent period - contraction phase - relaxation phase |
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latent period
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- period of time that elapses between the generation of an action potential and the start of the contraction
- Ca release cross bridge formation |
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contraction phase
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- starts at the end of latent period and ends at tension peak
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relaxation phase
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- period of time from end of the tension peak until the end of the contraction
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types of muscle contraction
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- isotonic
- isometric |
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isotonic contraction
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- changes in length
- muscle attempts to move a load that is equal to or less than the tension generated by muscle - tension in the muscle remains constant despite a change in muscle length - shortening can occur only when a muscle's maximal force of contraction exceeds the total load on the muscle |
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types of muscle contractions
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- concentric = shortening
- eccentric = lengthening |
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concentric
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- tension generated is sufficient to overcome the resistance, and the muscle shortens as it contracts
- occurs throughout the length of the muscle, generating tension at musculo-tendinous junction, causing the muscle to shorten and changing the angle of the joint - cross-bridge cycling |
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eccentric
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- tension generated is insufficient to overcome the external load on the muscle and the muscle fibers lengthen as they contract
- an opposing force is greater than the force generated by the muscle - used as a means of decelerating a body part or object, or lowering a load gently rather than letting it drop, or hiking uphill - unknown mechanism - leads to minor muscle damage that causes soreness following exercise |
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recording isometric and isotonic contraction
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- tension developed is sufficient to move the load, and the muscle shortens
- latent period is followed by rise in tension - not enough tension to move a load - plateau = force produced by the muscle remains constant - isotonic/same tension allowing the muscle to shorten |
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work of contraction
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- isotonic contractions show that muscle shortens the greatest distance with no load
- shortens progressively shorter distances with increasing loads - multiply the force developed by distance shortened for each load gives a curve that represents work performed by muscle |
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muscle force
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- decreases with increased velocity of contraction during concentric contraction
- increases with increased velocity of contraction during eccentric contraction |
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isometric contraction
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- tension without changing length
- muscle attempts to move a load that is greater than the tension generated by the muscle - muscles of hand and forearm grip an object, joints of hand don't move but muscles generate sufficient tension to prevent the object from being dropped |
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power
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- equal to force times velocity
- muscle generates no power at either isometric force (due to zero velocity) or maximal velocity (due to zero force) - maximal force produced by a muscle is proportional to cross-sectional area of its contractile elements - velocity of shortening is influenced by the myosin isoforms expressed by the motor units of muscle |
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tension/muscle force
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- amount a muscle can do depends on its volume
- force/cross sectional area - tension generated by a muscle fiber that is directly proportional to number of attached cross bridges |
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threshold
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- minimal stimulus needed to depolarize the sarcolemma
- point at which sodium ions start to move into the cells = depolarization - ability to reach threshold is determined by the magnitude of stimulation and duration of stimulation |
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length-tension relationship
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- tension that a muscle generates varies with its length
- found when a muscle is under isometric contraction and maximum activation of the muscle - in a singe muscle fiber, peak force is noted at a normal resting length - bell-shaped curve - too much overlap of thick and thin filaments results in less tension - overlap of thick and thin filaments is ideal to generate maximal force - sacromere set longer than ideal length doesn't have enough overlap so fewer sites of cross sectional formation |
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length-tension for isometric contraction
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- shows tension produced by a muscle when it is set a different lengths prior to simulation
- shorter = tension drops - maximal tension was achieved when muscle was set a lengths near normal relaxed lengths |
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motor units
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- skeletal muscles of vertebrates
- independent - single alpha motor neuron and all the corresponding muscle fibers it innervates - when activated all of its fibers contract |
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motor unit recruitment
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- progressive activation of a muscle by successive recruitment of contractile units/motor units to accomplish increasing gradations of contractile strength
- each vertebrate muscle twitch fiber is innervated by a single axon that branches to make many synaptic contacts at the middle of multiple fibers |
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tension varies
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- varying the frequency of impulse in a single motor unit
- varying number of active motor units |
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multiple fiber summation
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- weak signal is sent by the CNS to muscle
- smaller motor units are stimulated first - smaller motor units are more excitable than the larger ones - as strength of signal increases = more motor units are excited in addition to larger ones - largest motor units having as much as 50 times the contractile strength as the smaller ones - as more and larger motor units are activated = force of muscle contraction becomes progressively stronger |
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size principle
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- allows for a gradation of muscle force during weak contraction
- occur in small steps which then become progressively larger when greater amounts of force are required |
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contractile and elastic components
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- to achieve maximal tension all structures in series must be stretched taut
- sustained high calcium concentration must be present from multiple individual twitches |
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summation
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- muscle is stimulated repeatedly
- stimuli arrive one after another within a short period of time - twitches can overlap and result in a stronger muscle contraction |
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tetanus
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- stimuli continue to be applied frequently to a muscle over a prolonged period of time
- muscle will eventually reach a plateau - twitches fuse |
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tension force
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- minimum produced by single twitch in smallest motor unit
- maximum produce by simultaneous fused tetanic contraction in all motor units |
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fiber firing
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- 1/3 of fibers in muscle firing at once under conscious muscle exertion
- actual number firing affected by various physiological and psychological factors = Golgi tendon organs and Renshaw cells - low level of contraction is protective mechanism to prevent avulsion of tendon - force generated by 95% contraction of all fibers is sufficient to damage the body |
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mechanical model of muscle
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- contractile component = muscle fiber
- series elastic component = tendon - parallel elastic component = muscle membrane |
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elastic elements
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- series elastic elements
- non-contractile component of muscles - lies in series - store energy when stretched - tendons - cross bridges between actin and myosin also contribute |
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parallel elastic elements
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- non-contractile component of a muscle
- provides resistive tension when muscle is passively stretched - muscle membranes which lie in parallel to muscle - Hook's law |
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Hook's law
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- F=KL
- F is force exerted on spring - K is constant - L is displacement |
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viscous resistance
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- muscle cells contents become compressed
- increase with maximal force - contributes to passive resistance - produce by parallel elastic components |
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parallel fibers
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- parallel to longitudinal axis of the muscle
- sartorius, masseter, biceps branchi - each fiber attached to its own tendon with tendons converging on a common point - gets shorter and increases diameter when contracts - fibers shorten in direction parallel to direction shortening of muscle - located in positions requiring longer movements with less power of faster movements - greater length and less cross sectional area = greater velocity |
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convergent fibers
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- fibers spread over a broad area
- all the fibers converge at one common attachment site - fibers typically spread out, like a fan or a broad triangle, with tendon at apex - pectoralis major muscle - versatility because stimulation of only one portion of muscle can change direction of pull - pull in different directions - allow maximum force production |
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pennate fibers
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- at angle to longitudinal axis of muscle
- rectus femoris, deltoid - attach to a common tendon - direction of shortening of individual fibers is different from direction of shortening of whole muscle - fewer sarcomeres in series - cannot shorten as much as parallel - located in positions requiring small but powerful movements - fatigue quickly - force produced is greater than force produced by parallel - greater cross sectional area and less length = greater force |
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angle of pennation
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- greater it is the smaller the amount of effective force transmitted to tendon
- increases as tension progressively increases in the muscle fibers - contains more muscle fibers - produces more tension |
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muscle architecture
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- muscle force is proportional to physiologic cross-sectional area
- muscle velocity is proportional to muscle fiber length |
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contraction and temperature
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- most efficient at 38.5 C
- elevated muscle temperature causes a shift in force-velocity curve - increased maximum isometric tension - increased maximum velocity of muscle shortening - requiring less motor unit to sustain a given load - body temperature too high = heat exhaustion or heat stroke |
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2 types of skeletal muscles
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- red muscles
- white muscles |
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red muscles
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- contain myoglobin
- highly vascularized - receiving and using more oxygen than white muscles - require lower minimum rate of stimulation for tetanic fusion - contain many mitochondria - gets most of its ATP form oxidative phosphorylation = rapid - sustain contraction longer without fatiguing - produce large tension |
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white muscles
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- contain little myoglobin
- more rapidly contracting fast muscles - poorly vascularized - contain few mitochondria - ATP from glycolysis - produce small tension |
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muscle fibers specialized
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- different muscles contain different types of fibers
- specialized for slow or quick response |
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3 different forms of myosin
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- type 1
- type 2a - type 2x |
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type 1
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- slow oxidative
- hydrolyze ATP slowly - slow Ca uptake by SR - slow contraction - long duration of twitches - high resistance to fatigue - many mitochondria, myoglobin, and capillaries - red muscle - small fiber diameter - posture - slow myosin ATPase activity - specialized for endurance - require constant oxygen = no lactate dehydrogenase - energy from aerobic metabolism - slow cross-bridge formation |
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type 2a
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- fast oxidative glycolytic
- hydrolyze ATP rapidly - fast Ca uptake by SR - fast contraction - short twitch duration - intermediate resistance to fatigue - many mitochondria, myoglobin, and capillaries - red muscle - intermediate fiber diameter - standing, walking, rapid repetitive movements - generate great deal of power - myosin ATPase activity is high - energy from glycolysis and oxidative phosphorylation |
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type 2x
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- fast glycolytic
- hydrolyze ATP rapidly - fast Ca uptake by SR - fast contraction - short duration of twitch - low resistance to fatigue - few mitochondria, myoglobin, and capillaries - white muscle - large fiber diameter - jumping, bursts of high speed locomotion - generate great deal of power and force - myosin ATPase activity high - energy from glycolysis |
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motor unit 1
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- small alpha motor neurons
- innervate relatively few muscle fibers - form motor units that generate small forces - innervate small red muscle fibers = slow oxidative - small motor units - especially important for activities that require sustained muscular contraction - more excitable |
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motor unit 2
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- intermediate alpha motor neurons
- properties that lie between those for the other two - use type 2a - fast fatigue resistance motor units - not quiet as fast as FF units - generate about twice the force of a slow motor unit |
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motor unit 3
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- large motor neurons
- innervate large, more powerful motor units - type 2x - fast fatigable motor units - especially important for brief exertions that require large forces - fire last - small axon diameter - least excitable |
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plasticity
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- muscle capable of changing in both mass and cellular characteristics
- change mass by hypertrophy - atrophy occurs when muscle fibers lose actin and myosin or from loss of cells |
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endurance training
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- elicits changes in fiber type, capillary density, mitochondrial density
- proportion of type1 fibers remain unchanged - proportion of type 2a fibers increase - proportion of type 2x fibers decrease - changes in gene activity - increase density of capillaries - exercised muscle produce and release cytokine vascular endothelial growth factor - increases aerobic capacity of muscle fibers by increasing mitochondria and lipid droplets - increased Mhc 2a isoform and decreased amount of Mhc 2x isoform |
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vascular endothelial growth factor
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- increases with exercise
- increases less in trained muscles than in untrained muscles |
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hypertrophy
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- adding structural proteins
- occurs in cardiac muscle - doesn't add cell numbers by mitosis |
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regulating muscle mass
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- myostatin
- PI3-K-Akt1 pathway |
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myostatin
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- prevents from getting to much muscle
- decreases PI3 - Akt1 pathway - negative growth regulator - binds to a R on muscle PM - initiates an intercellular signaling pathway - controls cell growth - decreases amount of fat deposited between muscle fibers - limits protein production and satellite cell activation |
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PI3-K-Atk1 pathway
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- provides molecular signals that regulate balance between synthesis and degradation
- insulin like growth factor (IGF-1) secreted when struiated (skeletal and cardiac) muscle exerts force against a load - insulin also activates - IGF-1 binds to R - activates phophoinositol 3-kinase (PI3-K) that phophorylates Akt-1 making it active - increased protein synthesis by entering nucleus and binding to genes that make products that control protein degradation |
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muscle energetics
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- ATP is immediate source of energy for powering muscle contraction
- ATP binding required for detachment of myosin and actin - ATP hydrolysis activates acting binding site on myosin - ATP drives the ATPase-Ca pump that transports Ca into the SR |
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3 biochemical mechanisms produce ATP in muscle
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- use of phosphagen creatine phosphate
- aerobic glycolysis - aerobic catabolism |