Muscles Test


ASU Summer '11 Muscle Test 
  
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Muscle cells capable of shortening and converting the chemical energy of ____ into ______ energy
 
ATP; mechanical
3 types of muscle
 
cardiac, smooth, skeletal
5 characteristics of muscle
 
responsiveness, conductivity, contractility, extensibility, and elasticity
Skeletal muscle
 
voluntary, striated, attached to bones. Myofibers as long as 30 cm. Alters light and dark transverse bands (striations) ((overlapping arrangement of internal contractile proteins))
Fascicles
 
myofibers bundled together
perimysium
 
separates each fascicle from neighboring ones
epimysium
 
outer edge of muscle, holds all fibers together; grade imperceptibily into connective tissue sheets of fassciae
characteristics of collagen (2)
 
extensible and elastic; stretches slightly under tension and recoils when released (this protects muscle from injury and return it to resting length)
2 types of elastic components
 
parallel components to parallel muscle cells; series components joined to ends of muscle
muscle fiber nuclei; fused and unfused
 
flattened inside cell membrane; fusion by multiple myoblasts during development; unfused satellite cells nearby can multiply to produce a small number of new myofibers if needed
Sarcolemma
 
plasma membrane of a muscle fiber; has tunnel-like infoldings or transverse (T) tubules that penetrate the cell and carry electric current to cell interior
sarcoplasm
 
cytoplasm; filled with myofibrils (bundle of myofilaments) and glycogen for stored energy and mygloblin for binding oxygen
sarcoplasmic reticulum
 
smooth ER; network around each myofibril; dilated end-sacs (terminal cisternea) that store calcium
triad
 
T tubule and 2 terminal cisternea
myofilament
 
bundle of parallel protein microfilaments
3 types of myofilaments
 
thick, thin, elastic
thick filaments
 
made of 200-500 myosin molecules; 2 entwined polypeptides (golf clubs); arranged in a bundle with heads directed outwards in a spiral array around bundled tails
central area
 
bare zone with no heads in thick filaments
thin filaments
 
two intertwined strands of fibrous (F) actin; composed of globular (G) actin with an active site; form beadlike necklace
tropomyosin
 
held in groove of thin filaments; each block 6-7 active sites of G actin to prevent myosin from binding to them
troponin
 
calcium-binding molecule attached to each tropomyosin molecule
Elastic filaments
 
composed of springy protein called titin; anchor each thick filament to Z disc. Prevents over stretching of sarcomere
contractile proteins
 
myosin (thick filaments) and actin (thin filaments); do the work of shortening the muscle fiber
regulatory proteins
 
tropomyosin and troponin; switch that starts/stops shortening of muscle cell; contraction activated by release of calcium into sarcoplasm and its binding to troponin; troponin moves tropomyosin off the actin active site
A band
 
thick filament region; lighter, central H band area contains no thin filaments
I band
 
thin filament region; bisected by z disc protein connectin, anchoring elastic and thin filaments
Muscle cells shorten because their ____ shorten
 
individual sarcomeres; (pull z discs closer together)
Neither thick or thin filaments change in length during shortening T/F?
 
True
skeletal muscle must be stimulated by ___ or it won't contract
 
a nerve
cell bodies of somatic motor neurons are found _____
 
brainstem and spinal cord
somatic motor fibers
 
axons of somatic motor neurons; lead to skeletal muscles with each terminal branch supplying one muscle fiber
motor unit
 
each motor neuron and all the muscle fibers it innervates; dispersed throughout muscle causing weak contraction over wide area
postural control
 
ability to sustain long-term contraction as motor units take turns resting
Fine control
 
small motor units contain as few as 20 muscle fibers per nerve fiber (i.e. eye muscles)
strength control
 
gastrocnemius muscle has 1,000 fiber per nerve cell
neuromusclar junction (synapse)
 
functional connection between nerve fiber and muscle cell
synaptic cleft
 
tiny gap between nerve and muscle cells
acetycholine/ACh
 
neurotransmitter released from nerve fiber that stimulates muscle cell
synaptic knob
 
swollen end of nerve fiber; contains ACh in synaptic vesicles
junctional folds of sarcolemma
 
increase surface area for ACh receptors; contain acetycholinesterase that breaks down ACh and causes relaxation
basal lamina
 
thin layer of collagen and glycoprotein over all of muscle fiber
pesticides
 
cholinesterase inhibitors; binds to acetycolinesterase and prevents it from degrading ACh; spastic paralysis and possible suffocation
tetanus/lockjaw
 
spastic paralysis caused by toxin of Clostridium bacteria; blocks glycine release in the spinal cord and causes overstimulation of the muscles
Flaccid paralysis
 
limp muscles; due to curare that competes with ACh; respiratory arrest
resting membrane potential due to ___ outside of cell and ___ inside of cell
 
Na+ outside of cell; K+ (and other ions) inside the cell
resting membrane potential
 
difference in charge across the membrane (-90mV cell)
stimulation opens ion gates in membrane...
 
Na+ rushes into cell, K+ rushes out of cell
action potential
 
quick up-and-down voltage shift; (from negative RMP to a positive value and then back to negative)
4 actions involved in muscle contraction and relaxation
 
excitation, excitation-contraction coupling, contraction, relaxation
excitation
 
nerve action potentials lead to action potentials in muscle fiber
5 steps in excitation
 
nerve signal opens voltage-gated calcium channels; Calcium stimulate exocytosis of synaptic vesicles containing ACh and ACh release into synaptic cleft; ACh diffuses and binds to receptor proteins on sarcolemma; opening of Na+ and K+ channels resulting in jump in RMP from -90 to +75mV forming the end-plate potential (EPP); voltage change in EPP opens nearby voltage-gated channels producing an action potential
4 steps in excitation-contraction coupling
 
action potential spreading over sarcolema enters T tubules; voltage-gated channels open in T tubules causing calcium gates to open in SR; calcium released by SR binds to troponin; troponin-tropomyosin complex changes shape and exposes active sites on actin
4 steps in contraction
 
myosin ATPase in myosin head hydrolyzes and ATP molecule, activating the head and cocking it in a extended position; it bind to actin active site forming a cross bridge; myosin head releases ADP and phosphate as it flexes pulling the thin filament past the thick; with binding of new ATP, myosin head extends to attach to a new active site; thick and thin filaments slide past each other
5 steps of relaxation
 
nerve stimulation ceases and acetylcholinesterase remove ACh from receptors; stimulation of the muscle cell ceases; active transport needed to pump calcium back into SR to bind to calsequestrin (ATP needed for muscle relaxation as well as muscle contraction); loss of calcium from sarcoplasm moves tropnintropoyosin complex over active sites and stops the production or maintenance of tension; muscle fiber returns to its resting length due to recoil of series-elastic components and contraction of antagonistic muscles
rigor mortis
 
stiffening of the body 3-4 hours after death; deteriorating SR releases Ca; Ca activates myosin-actin cross bridge and muscle contracts but can't relax; muscle relaxation requires ATP and is no longer available after death; fibers remain contracted until myofilaments decay
length-tension relationship
 
amount of tension generated depends on length of muscle before it was stimulated
overly contracted
 
weak contraction results; thick filaments too close to Z discs and can't slide
too stretched
 
weak contraction results; little overlap of thin and thick filaments doesn't allow for very many cross bridges to form
optimum resting length
 
produces greatest force when muscles contract; CNS maintains optimal length producing muscle tone or partial contraction
threshold
 
voltage producing an action potential; a single brief stimulus at that voltage produces a quick cycle of contraction and relaxation called a twitch
3 phases of a twitch contraction
 
latent period, contraction phase, and relaxation phase
latent period
 
delay; only internal tension is generated; no visible contraction occurs since only elastic components are being stretched
contraction phase
 
external tension develops as muscle shortens
relaxation phase
 
loss of tension and return to resting length as calcium returns to SR
multiple motor unit summation
 
bringing more motor units into play/recruitment; i.e. lift a glass of milk versus a gallon of milk
twitch
 
low frequency (up to 10 stim./sec), produces an identical twitch response
treppe
 
moderate frequency (10-20 stim./sec); each twitch has time to recover but develops more tension than the one before as Ca not completely put back into SR and heat of tissue increases myosin ATPase efficiency
temporal or wave summation
 
higher frequency stimulation (20-40/sec) generates gradually more strength of contraction; each stimuli arrives before last one recovers; sustained fluttering contractions (incomplete tetanus); "piggy back"
complete tetanus
 
maximum frequency (40-50/sec); muscle has no time to relax at all; twitches fuse into smooth, prolonged contractions; rarely occurs in the body; no rest inbetween
isometric muscle contraction
 
develops tension without changing length; important in postural muscle function and antagonistic muscle joint stabilization
isotonic muscle contraction
 
contraction with a change in length but no change in contraction
concentric isotonic contraction
 
tension while shortening
eccentric isotonic contraction
 
tension while lengthening
pathways of ATP synthesis (2)
 
anaerobic fermentation and aerobic respiration
anaerobic fermentation
 
ATP production limited; without oxygen, produces toxic lactic acid
aerobic respiration
 
more ATP produced; requires continuous oxygen supply, produces H2O and CO2
immediate energy needs
 
short, intense exercise (i.e. 100 m dash); oxygen need is supplied by myoglobin
Phosphagen system
 
myokinase transfers Pi groups from ADP to make ATP; creatine kinase transfers Pi groups from creatine phosphate to make ATP
short term energy needs
 
glycogen-lactic acid system takes over; produces ATP for 30-40 seconds of maximum activity (i.e. playing basketball or running around diamonds); muscles obtain glucose from blood and stored glycogen
long term energy
 
aerobic respiration needed for prolonged exercise; produces 36 ATP/glucose molecules; after 40s, repsiratory and cardiovascular system must deliver enough oxygen for aerobic repsiration
fatigue
 
progressive weakness of muscles from prolonged use; ATP synthesis declines as glycogen is consumed; Na-K pump fails to maintain membrane potential and excitability; lactic acid inhibits enzyme function; accumulation of extracellular K+ hyperpolarizes the cell; motor nerve fivers use up their acetycholine
Endurance
 
ability to maintain high-intensity exercise >5 mins; determined by maximum oxygen uptake
maximum oxygen uptake (VO2 max)
 
proportional to body size, peaks at age 20, larger in trained athlete and males
carbohydrate loading
 
used by some athletes; packs glycogen into muscles; adds water at the same time (2.7g h20 with each g/glycogen); side effect of heaviness feeling
oxygen debt
 
heaving breathing after strenuous exercise;
4 purposes oxygen debt used for
 
replaces oxygen reserves; replenishes phosphagen system, reconverts lactic acid to glucose in kidneys and liver, serves the elevated metabolic rate that occurs as long as the body temp remains elevated by exercise
slow oxidative, slow twitch fibers
 
more mitochondria, myoglobin, and capillaries; adapted for aerobic respiration and resistance to fatigue; soleus and postural muscles of the back (100ms/twitch)
fast glycolytic, fast twitch fibers
 
rich in enzymes for phosphagen and glycogen-lactic acid system; SR releases calcium quickly so contractions are quicker (7.5 ms/twitch); extraocular eye muscles, biceps brachii; proportions genetically determined
resistance training
 
weight lifting; stimulates cell enlargement due to synthesis of more myfilaments
endurance training
 
aerobic training; produces an increase in mitochondria, glycogen, and density of capillaries
strength of contraction
 
muscle size and fascicle arrangement; 3-4 kg/cm2 of cross sectional area; size of motor units and motor unit recruitment; length of muscle at start of contraction
smooth muscle
 
fuisform cells with one nucleus; no striations, sarcomeres, or z discs; thin filaments attach to dense bodies scattered throughout sarcoplasm and on sarcolemma; SR scanty with no T tubules
Multiunit smooth muscle
 
largest arteries, iris, pulmonary air passages; terminal nerve branches synapse on myocytes; form a motor unit; independent contraction
single unit smooth muscle
 
most blood vessels and viscera as circular and longitudinal muscle layers; electrically coupled by gap junctions; large number of cels contract as a unit by stimulating each other
excitability
 
ability for cell to respond to a stimulus, especially the ability of nerve and muscle cells to produce membrane voltage changes in response to stimuli; irritibility
contractility
 
ability to shorten; amount of force that a contracting muscle fiber generates for a given stimulus
origin
 
where attached to bone, doesn't move
insertion
 
attached to joint, etc, and is moveable
prime mover
 
the muscle primarily responsible for a given joint action
antagonist
 
muscle that opposes the prime mover/agonist at a joint
fixator
 
holding base solid : ie moving shoulder, fixator muscles allow scapula to stay in place; hold the bone that the origin of the muscle attachs to
synergist
 
muscle that works with prime mover/agonist to assist

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