Lecture 15 (Exam 3)
- University of Alabama - Birmingham
- Biology 409
- Lecture 15 (Exam 3)
Last Modified: 2010-11-11
the head acts as a bridge between myosin and actin
2. myosin ATPase site for binding and cleaving ATP
composed of actin molecules (which are globular
proteins) each molecule has a binding site for a myosin head
they wrap around the actin helix
i.e. the troponin-tropomyosin complex
so the troponin/tropomyosin complex covers binding sites on actin helix
prevents any "crossbridging" between actin and myosin
Attachment of myosin head triggers conformational change in myosinthat causes head to "tilt" (power stroke)
Tilting moves actin filament along myosin filament
thus shortening the sarcomere.
Tilting also releases ADP from myosin head
ATP binding causes head to detach from binding site on actin helix
ATP is then cleaved to ADP, causing the head to return to the non-tilted conformation.
stiffness of muscles occurring approximately 3 to 12 hours afterdeath
Existing ATP is utilized but without new ATP being generated, there is no way for the myosin to detach from the actin to relax the muscle
2. "Motor end plate" of muscle
Ca++ influx into axon terminal
release of acetylcholine to nicotinic receptors on motor end plate, opening ligand gated ion channels allowing large amounts of Na+ and small amounts of K+ in
generating an "end plate potential"
larger than EPSP of neuron (+50 to +75 mV)
this initiate action potentials in adjacent areas of cell membrane
ensures that a single action potential will cause a twitch in the muscle fiber
19,000 liters is enough to kill 3x the population of Earth
specific voice disorders
prevents excessive sweating
muscle spasms followed by fatigue
Alpha-bungarotoxin- venom in some poisonous snakes
extension of cell membrane, but they run perpendicular from
surface deep into the center of muscle fiber.They carry action potential which stimulates sarcoplasmic reticulum
Ca++ is pumped back into SR when at rest
forms ciliary and iris muscles of eye, piloerector muscles in skin, etc
each cell has a single nucleus
contains actin and myosin but not organized into myofibrils
Ca++ from the ECF binds to intracellular Ca++ receptor (the receptor is “calmodulin”)
Ca++/calmodulin complex activates the enzyme “myosin kinase”
that then activates myosin.Once activated, the myosin then binds to actin and undergoes a power stroke
uses less energy
forms an electrical “syncytium”
some is autorhythmic
Calcium channel blockers such as “verapamil” block the influx of Ca++ intosmooth muscle cells. Used for vasodilation, lowering blood pressure, and reducing angina
hybrid between skeletal and smooth muscle
It contains myofibrils (so it is striated).
Ca++ activates contraction by binding to troponin C.It has well-developed sarcoplasmic reticulum and t-tubules
quick powerful contractions
cells are connected via gap junctions, forming electrical syncytium
relatively short and branched muscle fibers (cells) which normally containone or two nuclei
Individual cells are connected to one another by “intercalated discs
display a "plateau" which allows for a prolonged muscle contraction (300 msec)
steady influx of Ca++ at peak of potential causes the plateau
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