MS - Anat & Phys (Muscle) Flashcards
Pg. 417-418 in First Aid 2014 Sections include: -Muscle conduction to contraction -Types of muscle fibers -Smooth muscle contraction
What are the 6 major steps in muscle contraction?
(1) Action potential depolarization opens presynaptic voltage-gated Ca2+ channels, inducing neurotransmitter release (2) Postsynaptic ligand binding leads to muscle cell depolarization in the motor end plate (3) Depolarization travels along muscle cell and down T tubule (4) Depolarization of the voltage-sensitive dihydropyridine receptor, mechanically coupled to the ryanodine receptor on the sarcoplasmic reticulum, induces a conformational change, causing Ca2+ release from sarcoplasmic reticulum. (5) Released Ca2+ binds troponin C, causing a conformational change that moves tropomyosin out of the myosin-binding groove on acting filaments (6) Myosin releases bound ADP and subsequently, inorganic (PO4)3- => displacement of myosin on the actin filament (power stroke). Contraction results in shortening of H and I bands and between Z lines (HIZ shrinkage), but the A band remains the same length (Think: “A bands is Always the same length”).
Draw a muscle unit, including and labeling the following: (1) A band (2) Actin (3) H band (4) I band (5) Mitochondrion (6) Myosin (7) Myofibril (8) M line (9) Sarcomere (10) Sarcoplasm (11) Sarcoplasmic reticulum (12) T tubule (13) Z line.
See p. 417 in First Aid 2014 for visual at top right of page
Draw a visual depicting sarcoplasmic reticulum release in the normal versus depolarized setting, including and labeling the following: (1) Ca2+ (2) Cytosol (3) Dihydropyridine receptor (4) Exterior (5) Ryanodine receptor (6) Sarcoplasmic reticulum (7) T-tubule membrane.
See p. 417 in First Aid 2014 for visual at top left of page
Which bands in the sarcomere are shortened due to muscle contractions?
Contraction results in shortening of H and I bands and between Z lines (HIZ shrinkage), but the A band remains the same length (Think: “A bands is Always the same length”).
What causes the sarcomere to release its Ca2+? What effect does this Ca2+ release have?
Depolarization of the voltage-sensitive dihydropyridine receptor, mechanically coupled to the ryanodine receptor on the sarcoplasmic reticulum, induces a conformational change, causing Ca2+ release from sarcoplasmic reticulum. Released Ca2+ binds troponin C, causing a conformational change that moves tropomyosin out of the myosin-binding groove on acting filaments
What causes the “power stroke”? What does it entail?
Myosin releases bound ADP and subsequently, inorganic (PO4)3- => displacement of myosin on the actin filament (power stroke)
What kind of twitch do Type 1 versus Type 2 muscle fibers have?
Type 1 muscle - Slow twitch; Type 2 muscle - Fast twitch
What color fibers do Type 1 (slow-twitch) muscles have, and why? What is an effect of this?
Red fibers resulting from increased mitochondria and myoglobin concentration (increased oxidative phosphorylation) => sustained contraction; Think: “1 slow red ox”
What color fibers do Type 2 (fast-twitch) muscles have, and why? What is an effect of this?
White fibers resulting from decreased mitochondria and myoglobin concentration (increased anaerobic glycolysis)
What effect does weight training have on muscle fibers?
Weight training results in hypertrophy of fast-twitch (type 2) muscle fibers
What ultimate effect does Ca2+ increase have on smooth muscle contraction?
Increase Ca2+ => Contraction; Think: “C’s”
What ultimate effect does Nitric oxide have on smooth muscle contraction?
Nitric oXide => RelaXation; Think: “X’s”
List the major cellular steps that lead to smooth muscle contraction.
(1) Action potential => Membrane depolarization (2) Depolarization activates L-type voltage gated Ca2+ channel => Ca2+ influx (3) Ca2+ influx increases Ca2+-calmodulin complex (4) Ca2+-calmodulin complex stimulates Myosin-light chain kinase (MLCK) (5) MLCK converts Myosin + actin to Myosin-phosphorylated + actin (i.e., phosphorylates myosin) (6) Contraction (via cross-bridging); See p. 418 in First Aid 2014 for visual
List the major cellular steps that lead to smooth muscle relaxation.
(1) Nitric oxide enters cell (2) Nitric oxide stimulates Guanylate cyclase (3) Guanylate cyclase converts GTP to cGMP (4) cGMP activates Myosin-light chain phosphatase (MLCP) (5) MLCP converts Myosin-phosphorylated + actin to Myosin + actin (i.e., cleaves phosphate from myosin) (6) Relaxation
What is MLCK, and what is its function?
Myosin-light chain kinase (MLCK); MLCK converts Myosin + actin to Myosin-phosphorylated + actin (i.e., phosphorylates myosin) => smooth muscle Contraction
