muscle Flashcards
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
botox
causes acetylcholine vesicles to not fuse to presynaptic membrane
- paralyzes muscles
duchenne muscular dystrophy
mutation of dystrophin gene
- muscle wasting, mental disability
- dystrophin is part of dystroglycan complex which links actin cytoskeleton to basal lamina
- CT and adipose tissue takes over muscles
cardiac muscle
forms thick layer in heart = myocardium
- rhythmic, involuntary
- short + branched striated fibers = cardiomyocytes
- one central nucleus per fiber
intercalated disks
Join cardiomyocytes together (junctional complex)
- step-like pattern
- transverse and lateral part
transverse part
runs across fibers
- zonula adherens: anchor actin of terminal arcomeres to plasma membr
- desmosomes: bind fibers tgt to prevent separation during contraction
lateral part
runs parallel to myofilaments
- gap junctions: flow of info between fibers
smooth muscle
involuntary + non-striated
- spindle-shaped fibers
- one central nucleus (corkscrew-shaped when contracted)
- No t-tubules
smooth muscle of arteries and veins
part of tunica media (smooth muscle + elastic tissue)
- thicker in arteries than veins
- control diameter
smooth muscle of intestine
longitudinal and circular layers
- peristalsis
- stomach also has oblique layer
smooth muscle fiber junctions
gap junctions
thin filaments of smooth muscle
arranged diagonally in cell
- attach to dense bodies in sarcoplasm or dense plaques on sarcolemma
contractile units of smooth muscle
myosin and actin filaments attached to dense bodies in sarcoplasm or dense plaques on sarcolemma
caveolae
flask-shaped invaginations of sarcolemma which are near peripheral SR
