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49 Cards in this Set
- Front
- Back
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What is the relationship between the initial length of the sarcomere (or muscle fiber) and the amount of tension it can produce?
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- length-tension relationship; must have optimal overlap b/w thick ant thin filaments b4 onset of contraction
- Optimal resting length - where there is potential for the max amount of crossbridge interactions - Shapes of joints prevent muscles from going too far outside of this, in body it is near-optimal |
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Describe the relative positions of actin and myosin when the muscle is at its optimal length for strength production.
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- Fillaments overlap somewhat
- Max. amt. of crossbridge interactions - "optimal overlap" b/w them |
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What happens to force production in a muscle that is extreme stretch or contraction?
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- Muscle is unable to create much tension in the muscle fibers, because either the thin/thick filaments aren't overlapping enough, or the muscle is already contracted and fillaments are jammed up at the end/can't move anymore
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What is a muscle twitch?
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Response of isolated muscle/motor unit to single brief threshold stiumulus
Threshold stiumulus = twitch doesn't vary with size of stimulus |
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What is the latent period and what is taking place during the latent period?
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- Period b/w delvery of stimulus and noticible response/onset of tension and force production
- SEE creates slackness in muscle, which we have to take up; Ca2+ is flooding sarcoplasm;excitation - contraction coupling is getting underway; rxns occurring |
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Explain the all-or-none law as it relates to skeletal muscle fibers and motor units.
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Single nerve impulse = single contraction event in all muscle fibers of motor unit
Muscle fiber is either on or off, not in the middle Applies to single alpha motor unit and all of the fibers that it activates; doesn't apply to the skeletal muscle |
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What are graded muscle responses? What are the two general ways of producing a graded muscle response?
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- Sustained muscle contractions of varying intensities
- Changing frequency of stimulation (wave summation, unfused tetanus, complete tetanus etc) - Changing strength of stimulus (multiple motor unit summation) |
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What happens to the strength of contraction when two or more identical stiumuli are delivered to the muscle in rapid succession (i.e., before complete relaxation occurs)? What is this phenomenon called?
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- Wave summation and tetanus
- Identical stiumuli delivered so muscle doesn't have time to relax fully; contractions get bigger - Occurs b/c some Ca is still in sarcoplasm; stimulus must wait till after refractory period - Contract at this rate to produce sustained contraction while delaying fatigue |
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What is a motor unit?
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Single motor neuron + all skeletal muscle fibers it stimulates
Vary in size depending on size of contractions you want to generate Scattered throughout muscle; not all in a clump |
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What is the difference between unfused tetanus and complete tetanus?
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Complete - stimuli frequent; no relaxation phase; smooth continuous maximal force production; not under normal conditions in body
Incomplete - frequent stimulation; doesn't relax completly; peak tension, but vascillating; sustained contraction but delays fatigue |
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How is complete tetanus achieved in a muscle fiber?
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Stimulation so frequent that relaxation phase eliminated entirely
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What role does complete tetanus play in voluntary movements?
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- Required for maximal contraction; created by maximal stimulus
- Does not normally occur in body |
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What is recruitement (i.e., multiple motor unit summation)?
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- Greater external force created by activating more muscle units
- Large motor neurons =less excitable, greater force/less precise - Small motor neurons = fine motor control; more excitable Recruited synchronously and asynchronously for smooth longer contractions w/less fatigue |
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Threshold stimulus
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- Stimulus strengh @ which you first see twitch response from muscle
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Maximal stimulus
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- Stimulus supplied to get strongest force production by the muscle
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What is muscle tone and why is it important?
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Low level of asynchronous motor unit recruitment creating sustained partial contraction in relaxed skeletal muscle
Triggered by sensory input from stretch receptors Stabalizes joints + body position; essential for normal neuromuscular functioning; no stimulation = atrophy and spastic contractions Resistance training - increase muscle tone, so increase basal metabolic rate |
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What type of tension does a muscle develop when it is acting as an agonist?
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Agonist = prime mover
Concentric contraction; type of isotonic; tension exceeds resistance, muscle shortens; how mucles cause movement Least efficient |
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What type of tension is being produced when internal tension is being developed, but no movement occurs?
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Isometric contraction
Occurs either by choice (holding a book still in the air) or because you can't move Contraction doesn't overcome external resistance |
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What type of tension is being produced when the overall length of the muscle is increasing while the muscle is functioning?
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Eccentric tension
Outside force doing work, contraction controlls movement Often occurs with gravity; the contraction is in the opposing muscle group Repeated eccentric contractions cause more damage/tears in muscles than concentric Lowering a book, sitting in chair |
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What type of tension is developed most efficiently (i.e. requires less ATP expenditure per unit of work accomplished)? Least efficiently?
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- Eccentric is most efficient b/c muscle isn't doing the work
- Isometric is middle b/c no work is occurring Concentric = least efficient because muscle has to expend ATP for every bit of work |
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What factors influence the amount of force that a muscle can generate?
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Degree of muscle stretch - optimal sarcomere length; length-tension relationship
Number of fibers activated - motor units recruited Relative size of muscle - shape, cross sectional area of belly of muscle; bigger = packed w/more myofibrils (hypertrophy = muscle fibers increase in size) SEE and external tension dev. - the non-contractile structures (CT wrappings, tendons, muscle attachment), have ability to stretch and recoil; little can be measured as external tension |
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What are the series elastic elements (SEE) and how do they influence force production?
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SEE = CT wrappings (epi, peri and endomysium), Tendons, Muscle attachment
Ability to stretch and recoil, create internal tension, but relatively small amt. can be measured as exernal tension After internal tension is developed crossbridge cycling starts generating external tension - explains wave summation and tetanus, b/c we never loose SEE tightness, so more e. can be spent on external tension |
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When does a muscle begin to develop (or exert) external tension?
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When all of the slack is taken up, so the cross-bridge cycling can generate extern. tens.
Internal - generated by SEE External - the pull you make on the attatchment/bone |
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How does the size of a motor unit influence the strength of contraction and the control of a movement?
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Small motor units - fine motor control, most excitable neurons, so activated first
Large motor units - less excitable, greater force production, so less precise |
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Classify each muscle fiber type with respect to its predominant pathway for ATP synthesis, the amount of myoglobin present, and the activity of its myosin ATPase.
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Slow Oxidative - Aerobic pathway; high myoglobin to attract O2, Slow myosin ATPase activity
Fast Oxidative Glycolytic - Aerobic pathway; intermediate myoglobin, fast Myosin ATPase activity Fast Glycolytic - Anaerobic glycolysis pathway, low myoglobin, fast myosin ATPase activity |
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Which fiber type receives the richest blood supply?
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Slow oxidative fibers (slow twitch)
Many capillaries Red, b/c of high myoglobin content |
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Which fiber type has the fastest contraction sped? The slowest?
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Fastest - Fast Glycolytic fibers(FG) /fast twitch fatiguable fibers
Intermediate - Fast Oxidative Glycolytic (FOG); fast-twitch fatigue-resistant fibers Slowest - Slow Oxidative (SO); slow twitch or fatigue-resistance fibers |
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Describe the major structural differences between smooth and skeletal muscle.
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Smooth: Smaller in diameter; shorter
Endomysium and centrally located nucleus No tendons or aponeroses; no epi or perimysium; only one nucleus, no t-tubules or terminal cisternae, SR is a loose network throughout the sarcoplasm, so little Ca is released; SR touches sarcolema in some places No sarcomeres or myofibrils, so nonstriated; can contract even when stretched a lot; more thin + fewer thick filaments; arranged obliquely/angled so cell contracts in corkscrew way Network of dense bodies and intermediate filaments to tramsmit tension; unstructured neuromuscular jcts.; nerve fibers end in varicosities, releasing neurotransmiters in general region; no motor end plate |
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Describe the functional differences between smooth and skeletal muscle.
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neuromuscular junctions called diffuse junctions, with neurotransmitters released in general region
Increased sarcoplasmic Ca, but less, goes straight from extracellular fluid via calcium channels = slow onset/prolonged contraction b/c diffuses through sarcoplasm to find active sites no troponin = active sites always open |
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What structures anchor smooth muscle fibers and transmit the tension they develop?
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Dense bodies - proteinous plaques scatered in sarcoplasm, attatch 2 sarcolema at perifery and/or intermediate/thin filaments; corresponds to z line in skeletal mscle
Intermediate Filaments - lengthwise through sarcoplasm, attach periodically to dense bodies Anchor thin filaments and adjacent cells together so they can act as sheets;sphyncters |
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What are the sources of the sarcoplasmic Ca2+ which triggers smooth muscle contraction? Which of these is the main source?
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Most enters through Ca channels directly from extracellular space - caveolae (infoldings of membrane w/extracellular fluid that has high Ca2+ conc)
SR releases some Ca |
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Identify the regulatory protein in smooth muscle which binds to Ca to activate the contraction process.
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Calmodulin - binds to Ca and becomes active, acting as enzyme to activate MLCK (myosin light chain kinase)
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What is the role of myosin light chain kinase (MLCK)?
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Activated by calmodulin
Mydrolizes ATP; transfers an inorganic posphate to myosin head, so it can interact with the active site Slow acting enzyme, so crossbridge cycling is slow;contracts for long time with low e. / no fatigue Can latch on for long time = contraction sustained without effort/energy |
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Which contracts more quickly - smooth or skeletal muscle?
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Skeletal muscle
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Which contracts more efficiently - smooth or skeletal muscle?
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Smooth muscle
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Which is most fatigue-resistant - smooth or skeletal muscle?
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Smooth muscle
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How is smooth muscle contraction regulated?
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Neural factors - extrinsic control; neural stimulus and NT release; or difft. NT's released w/o a nerve stimulus, exerted by fibers of the autonomic nerve system
Effect of NTs depends on the ion that ligand gated channel lets through - acH = Ca = strong contraction; - Norepinepherin = contraction or relaxation depending on gate Local factors - intrinsic control focus on care of the organ rather than of the system; caused by hormones, low pH, chem factors, CO2 buildup, low O2, |
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Describe the relationship b/w resting length and tension development in smooth muscle.
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Tension nor directly related to resting length
Contract forcefully when stretched little or lots Thin and thick fibers scattered throughout; no sarcomere |
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Describe the stress-relaxation response.
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Smooth muscle stretched = inherantly contracts for 30-60 sec
Hollow organ full = contracts to push substance along Stomach, urinary bladder, etc |
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What are the two types of smooth muscle?
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Single-unit smooth muscle - common, (bladder, gallbladder, arteries, veins, hollow smooth organs); fibers in sheets; gap junctions+ pacemaker cells are there
Multiunit smooth muscle - smooth muscle fibers structurally independent (arrector pilli muscle, iris, respiratory, largest arteries); few gap junctions; no pace maker, not self excitatory, innervated by nerve fibers from autonomic nervous system; responds to stimuli through graded stimuli responses |
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Where is each type of smooth muscle located?
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Single-unit smooth muscle (visceral muscle) - most common; hollow smooth organs, urinary bladder, gallbladder, arteries, veins
Multiunit smooth muscle - arrector pilli muscle, iris of eye, respiratory, largest arteries |
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What is the role of gap junctions in single-unit smooth muscle?
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Connects adjacent cells
Excitation impulses spread rapidly through sheet Sheet contracts/functions as a unit |
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What is the role of pacemaker cells in single-unit smooth muscle?
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Set rhythmic pattern of contraction
Spontaneously depolarize/excite at regular intervals Pattern/rate of contraction can be altered Self excitatory |
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Which type of smooth muscle exhibits rhythmicity and self excitation?
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Single-unit smooth muscle
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Synergist
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An organ (as a muscle) that acts in concert with another to enhance its effect
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Agonist
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Prime mover
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What is taking place during the relaxation period?
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Reentry of Ca into SR
Contractile force declining Muscle tension decreases to zero Returns to original lengh Muscle contracts faster than relaxes |
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What is the refractory period? Why is it significant?
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Cell can't be stimulated again until repolarization is complete
Restores electrical conditions - K diffuses rapidly out of fiber, restoring negative charged conditions inside |
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Name and describe the muscle fiber's three avenues of ATP production.
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Creatine phosphate (CP) - rapidly available (fuels 10 sec); forms ATP and creatine; reversible; catalized by creatine kinase (CK)
Anaerobic glycolysis + lactic acid formation - anaerobic in cytoplasm; forms pyruvic acid; too much = converted into lactic acid (used as fuel in liver, skeletal, cardiac muscle and kidney, can be converted back), lowers pH, interfering w/enzymes Aerobic respiration - long term; oxidative phosphorylation uses fats protens and carbs; 60-80% product is heat |
