Need help answering questions 8 and 10 Need well explained answers step by step

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Need help answering questions 8 and 10 Need well explained answers step by step please include theories.. A little more then just an answer Iam trying to understand whats going on... Thanks again

6. Compare Icontrast an action potential and a synapse. Why alAl potential travel from nerve to nerve. . 7. How is a muscle able to achieve a graded contraction? What is the between a motor end plate and a NMJ? 8. Describe how a spike results in a muscular contraction? 9. Compare and contrast skeletal, smooth and cardiac muscle? 10. Explain the role of ATP in the sarcomere.

Explanation / Answer

8. Although muscle contraction can be initiated by direct electrical stimulation of the muscle, it usually results from activity in the motoneurons innervating the muscle. An action potential initiated in an alpha-motoneuron propagates into the motoneuron terminals and releases acetylcholine into the synaptic cleft. The acetylcholine induces an end-plate potential in the muscle which, in normal muscle, always leads to an action potential in the muscle. The muscle spike is very much like the nerve spike but longer in duration and with a hypopolarizing tail on the falling phase that prolongs the spike by 3-4 msec.The long (4-5 msec) hypopolarizing tail of the muscle action potential is probably the electrotonic reflection of the action potential as it conducts into the T tubules. At least, the tail disappears from the spike when the muscle is treated with glycerol and then returned to Ringer's solution, a treatment that more or less specifically ruptures T tubules, leaving the surface membrane and resting potential intact. The muscle still generates a spike but does not contract. Conduction of the spike into the T tubules is probably an active process as elsewhere on the membrane, and it is the hypopolarization of the T tubule that leads to contraction.

10.

In a rested, non-contracting muscle, myosin binding sites on actin are obscured and myosin exists a in high-energy conformational state (M*), poised to carry out a contractile cycle. The energy of ATP hydrolysis is used to drive myosin from a low-energy conformational state (M) to the high-energy state, as depicted in the following equation:

(M-ATP) <——> (M*-ADP-Pi)

When cytosolic calcium increases and myosin binding sites on actin become available, an actomyosin complex is formed, followed by the sequential dissociation of Pi and ADP with conversion of myosin to its low-energy conformational state. These events are accompanied by simultaneous translocation of the attached thin filament toward the M line of the sarcomere. The latter events, summarized in the following 2 equations, comprise the power stroke of the contractile cycle. Note that the energy of the power stroke is derived from ATP, via ATP-driven conversion of a low-energy myosin conformational state to a high-energy conformational state. A useful analogy is that ATP cocks the myosin trigger and the formation of an actomyosin complex pulls the trigger, releasing the energy stored in cocking the trigger.

(M*-ADP-Pi) + A <——> (M*-ADP-A) + Pi

(M*-ADP-A) <——> (M-A) + ADP

At the end of the power stroke the actomyosin complex is remains intact until ATP becomes available. ATP binding to myosin is a very exergonic reaction, with the result that ATP displaces actin from the myosin head as indicated by the equation below. Thus, it is often said that ATP is required for muscle relaxation. It is important to note that in relaxed muscle, myosin is in its high-energy conformational state. Note that the final product (M-ATP) is also the first reactant shown in the first equation above, completing the reactions of the contractile cycle.

(MA) + ATP <——> (M-ATP) + A

Energy for contraction

(Muscle contraction uses up a lot of ATP.)

1. Creatine phosphate dephosphorylation = Fast regeneration of ATP from ADP and Pi
2. Glycogen --> glucose. Aerobic respiration provides most of the ATP needed during moderate exercise.
3. Blood glucose and fatty acids --> Fuel for aerobic respiration when muscle glycogen exhausted.
4. Fermentation (anaerobic metabolism) --> When respiratory and circulatory systems cannot deliver enough oxygen to sustain muscle contraction during vigorous exercise, glycolysis supplies ATP and produces lactic acid (lactate) from the breakdown of glucose. Recall that the net yield is 2 ATP per glucose molecule instead of 34-36. Lactic acid rapidly builds up in cell.

Muscle tension, strength, fatigue

1. Muscle tension = total force developed by cross-bridge activation. Isometric contraction occurs when the muscle is stimulated but not allowed to shorten (constant length).
2. Strength of contraction

(depends on muscle size, how many muscle cells in the muscle are contracting (of motor units active), how rapidly the nervous system is stimulating them; motor unit = single motor neuron and all the muscle fibers (cells) that it forms juctions with.

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