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Ex Phys ch 8

Skeletal Muscle: Structure and Function

QuestionAnswer
Human body contains how many skeletal muscles? over 400; which constitute 40-50% of total body weight
3 Functions that Skeletal Muscle perform: 1) Force generation for locomotion and breathing 2) force generation for postural support 3) heat production during periods of cold stress
Muscles attach to bone via... tendons!
origin of muscle- one end of muscle attached to bone that does not move
insertion point of muscle- opposite muscle fixed to a bone that moves during muscle contraction
muscles that decrease joint angle are flexors
muscles that increase joint angle are extensors
epimysium surrounds entire muscle
perimysium surrounds individual bundles of muscle fibers
endomysium connective tissue around each individual muscle fiber
basement membrane just below endomysium, surrounding each muscle fiber- extra layer of protective tissue
sarcolemma cell membrane surrounding muscle fiber cell
satellite cells play role in muscle growth and repair, contribute to muscle growth during strength training
myonuclear division cytoplasm surrounding each nucleus
more nuclei allow for.. greater protein synthesis
myofibrils contain contractile proteins actin (thin) and myosin (thick)
a sarcomere includes.. Z line, M line, H zone, A band, I band
Sarcoplasmic reticulum (SR) storage sites for calcium
transverse tubules extend from sarcolemma ---> SR
motor unit- the motor unit and the muscle fibers it innervates
neuromuscular junction junction between motor neuron and muscle fiber
motor end plate pocket formed around motor neuron by sarcolemma
neuromuscular cleft- short gap between neuron and muscle fiber
acetylcholine being released from a motor neuron causes what.. EPP- End Plate Potential
EPP is ALWAYS.. large enough to exceed threshold and is signal to begin contractile process
The Sliding Filament Model best explains the process of muscular contraction; andrew huxley and colleagues, actin and myosin interaction
First step of The General Process of Muscular Contraction Myofilaments actin and myosin do not change length during muscle contraction
Second step of Muscular contraction during contraction, actin myofilaments at each end of the sarcomere slide past the myosin filaments toward each other. Z discs become closer together as the sarcomere shortens.
Third step of Muscular contraction As actin myofilaments slide over the myosin myofilaments, the H zones and I bands narrow. The A bands stay the same, they do NOT narrow.
Fourth step of muscular contraction In a fully contracted muscle, the ends of the actin myofilaments overlap and the H zone disappears.
3 Sources of ATP production in muscle contraction: 1) phosphocreatine 2) glycolysis 3) oxidative phosphorylation
Excitation-Contracting coupling sequence of events in which a nerve impulse (AP) reaches the muscle membrane and leads to shortening by cross-bridge activity
breakdown of ATP for contraction energy is by what enzyme?? myosin ATPase (located of head of myosin cross-bridges)
power stroke a single contraction cycle
when muscles are relaxed... actin and myosin have a weak binding state
The 2 Regulatory Proteins which Control Muscular contraction (regulate interaction between actin and myosin) troponin and tropomyosin
where are troponin and tropomyosin located? on the actin molecule
in relaxed muscle, which protein blocks the active sites on actin molecules where myosin cross-bridges must attach? tropomyosin
what is released from the SR that diffuses into muscles to bind to troponin? Calcium
What is the trigger step in the detailed outline of muscular contraction? When the AP reaches the SR and calcium is released and diffuses into the muscle to bind to the protein troponin.
The trigger for contraction to occur is linked to release of stored Ca++ from where? lateral sac aka terminal cisternae of SR
In a resting (relaxed) muscle, the concentration of Ca++ is .. very low
The contraction cycle can be repeated as long as... there is free Ca++ available to bind to troponin and ATP can be hydrolized to provide the energy
what is muscle fatigue? decline in muscle power output, decrease in force generation, decrease in shortening velocity
what causes muscle fatigue? build up of hydrogen, lactic acid, high intensity, accumulation of ADP + Pi and free radicals, long duration exercises (2-4 hrs), disturbances in muscle/ extracellular electrolyte homeostasis
what are muscle cramps? spasmodic, involuntary muscle contraction
what causes muscle cramps? electrolyte depletion and dehydration theory
Created by: sbush0804