structure and function of exercising muscle Flashcards
what are the functions of skeletal muscle
- force generation for locomotion and breathing
- force generation for postural support
-heat production during cold stress
-communication
describe the 3 types of muscle
-smooth: involuntary, slow, spindle shaped and 1 nuclei
-cardiac: heart, involuntary, in between, branched, 1 or 2 nuclei, striated
-skeletal: attached to bone, voluntary, fast, straight, many nucleis, striated
what are the 4 properties of muscle
Excitability: Capacity to respond to a stimulus
* Contractility: ability to shorten and generate force
* Extensibility: ability to stretch
* Elasticity: ability to recoil to original resting
length after stretched
what surrounds the entire muscle
-epimysium
-consists of many bundles (fasciculi)
what is the fasciculi surrounded by
perimysium
it consists of individual muscle cells
what is the muscle fiber surrounded by and what does is consists of
surrounded by endomysium
consists of myofibrils divided into sacromeres
what is the function of the plasmalemma(cell membrane)
-fuses with tendon
-conducts action potential
-maintains pH, transports nutrients
what is the function of the sarcoplasm
– Cytoplasm of muscle cell
– Unique features: Glycogen storage, myoglobin
what is the function of the t tubules
– Extensions of plasmalemma
– Carry action potential deep into muscle fiber
what is the function of the sarcoplasmic reticulum
calcium (Ca2+) storage
what are the sarcomeres?
– Basic contractile element of skeletal muscle
– End to end for full myofibril length
what are the 4 different striped appearances of the sarcomeres?
– A-bands: dark/blue stripes (actin + myosin)
– I-bands: light/pink stripes (only actin)
– H-zone: middle of A-band (only myosin)
– M-line: middle of H-zone
* Common boundary structure: Z-disk (or Z-line)
what are the 3 proteins of actin
– Actin: contains myosin-binding site
– Tropomyosin: covers active site at rest
– Troponin: anchored to actin, moves tropomyosin
what is the structure of myosin
- Two intertwined filaments with globular heads
- Globular heads
– Protrude 360° from thick filament axis
– Will interact with actin filaments for contraction
what is the process of actin and myosin in a relaxed state ?
– No actin-myosin interaction at binding site
– Myofilaments overlap a little
what is the process of actin-myosin contraction in a contracted state ?
– Myosin head pulls actin toward sarcomere center (power stroke)
– Filaments slide past each other
– Sarcomeres, myofibrils, muscle fiber all shorten
what happens after the power stroke ?
– Myosin detaches from active site
– Myosin head rotates back to original position
– Myosin attaches to another active site farther down
the process continues until
– Z-disk reaches myosin filaments or
– AP stops, Ca2+ gets pumped back into SR
what happens when AP arrives at SR from T tubule
– SR sensitive to electrical charge
– Causes mass release of Ca2+ into sarcoplasm
what happens when Ca2+ binds to troponin on actin
– At rest, tropomyosin covers myosin-binding site
– Troponin-Ca2+ complex moves tropomyosin
– Myosin binds to actin, forming a cross-bridge, allowing a
contraction to occur
when ATP binds to myosin head, what does ATPase on myosin breaks ATP to?
– ATPase on myosin head
– ATP ADP + Pi + energy
what are the steps of excitation contraction coupling
- Action potential (AP) starts in brain
- AP arrives at axon terminal, releases acetylcholine (ACh)
- ACh crosses synapse, binds to ACh receptors on plasmalemma
- AP travels down plasmalemma, T-tubules
- Triggers Ca2+ release from sarcoplasmic reticulum (SR)
- Ca2+ enables actin-myosin contraction
what happens when the muscle relaxes
- AP ends, electrical stimulation of SR stops
where does the Ca2+ go when the muscle relaxes
- Ca2+ pumped back into SR
– Stored until next AP arrives
without___, troponin and tropomyosin return to resting conformation
Ca2+
what is the resting conformation of troponin and tropomyosin
– Covers myosin-binding site
– Prevents actin-myosin cross-bridging
