muscle Flashcards
(37 cards)
skeletal muscle function (striated)
- body movement
- posture
- respiration
smooth muscle function
- peristalsis
- constriction of blood vessels
cardiac muscle function (striated)
heart beat
organization of skeletal muscle
one myofibril (cell)-> one muscle fiber -> a fascicle of muscle fibers -> a muscle
epimysium
dense collagen CT surrounding entire muscle
perimysium
collagen CT surrounding a fascicle
endomysium
fine reticular fiber CT that surrounds ind muscle fibers
myotendinous junction
finger-like extensions of muscle fibers that extend into tendon CT
basal lamina of muscle fibers
external, contains glycoproteins and collagen
- binds to myofiber via dystrophin-containing
myofibril organization
long, cylindrical, striated
- multinucleated, nuclei at periphery
- aligned in parallel
- separated by mitochondria and SR
- composed of myofilaments
sarcoplasmic reticulum
smooth ER of muscle
- interconnected tubules surrounding each myofibril
- store Ca2+ when muscle is at rest
- release Ca2+ into sarcoplasm when muscle is stimulated
T-tubule
invaginations of sarcolemma (membr)
- perpendicular to length of myofiber
triad junction
single T tubule and two terminal cisternae of the SR on either side
- ryanodine receptor on terminal cisternae, attached to
- dihydropyridine receptor (voltage-gated) on T-tubule
- Ca2+ passes through
sarcomeres
contractile unit of myofibrils
- from Z disc to Z disc
- actin filaments on the outside
- myosin on the inside
- elastic titin filaments on edges of myosin
myosin filament
thick myofilament
- monomer: long tail with two heads; actin and myosin ATPase binding sites
actin filament
think myofilament
- two tropomyosin filament helix, with actin balls attached through troponin complex
- troponin complex: 3 types of troponin, each one binding to actin, tropomyosin, or calcium
binding of myosin head to actin
Low Ca2+: myosin binding sites on actin are blocked by tropomyosin
High Ca2+: calcium binds to troponin complex, induces conformational change, and unmasks myosin binding sites on actin
electrical stimulation ->
SR releases Ca2+ into sarcoplasm ->
Ca2+ binds troponin ->
conformational change uncovers myosin binding site ->
myosin head binds to actin
skeletal muscle contraction
- myosin attaches to actin, ADP and Pi released
- myosin head bends and pulls actin filament towards the center of the sarcomere
- new ATP binds to myosin head, myosin unbends and detaches from actin
- ATP hydrolysis occurs, myosin attaches again
sliding filament model
actin and myosin filaments overlap slightly
- actin filaments slide along myosin -> greater overlap -> sarcomere shortening
skeletal muscle
- voluntary
- controlled by motor neurons
motor unit
motor neuron and all the muscle fibers it innervates
motor endplate
domain of sarcolemma responsible for initiating action potential
- AP propagates along myofiber, causing muscle contraction
neuromuscular junction
junction of the axon terminal of MN and motor end plate of muscle
excitation-contraction coupling
- ACh released and binds to nicotinic acetylcholine receptors
- Na+ gated channels open, intiating AP
- AP propagates along sarcolemma and into t tubules
- AP triggers dihydropyridine receptors to trigger release of Ca2+ into sarcoplasm from ryanodine receptors
- Ca2+ binds to troponin; troponin changes shape and uncovers myosin binding site
- myosin cross bridges attach to actin, bend when ATP is hydrolyzed, pulling actin filaments toward center of sarcomere; cyclic process powered by ATP hydrolysis
- Ca2+ actively transported into SR after AP
- low Ca2+ in sarcoplasm so tropomyosin blocks myosin binding site again
