You briefly apply acetylcholine (ACH) directly to the motor end plate and observ

Question

You briefly apply acetylcholine (ACH) directly to the motor end plate and observe the results. After ACH is applied to the muscle fiber, there is an AP generated on the sarcolemma of both the normal and dysgenic muscle fibers. 5. Which of the following is NOT PROVEN by the above result? a) ACH receptors are present in the membrane of the motor end plate b) ACH binds to receptors c) Sodium permeability of the end plate membrane is increased d) Acetylcholinesterase breaks down ACH. Part II The normal mouse fiber contracts after the ACH application but the dysgenic mouse fiber does not. 6. Do you suspect that the motor neurons are working normally? Why or Why not? Does this test whether the defect seen in dysgeny is in the motor neuron or the muscle fiber. Briefly discuss how you came to your conclusion. 7. Draw and label a sarcomere: Include all bands and zones and indicate where the thick and thin filaments are located. List the proteins that make up the thick filament and the thin filament. List the binding sites found on each. 8. Place the following steps in a muscle contraction in the correct order: 1. AP spreads down sarcolemma and t-tubules 2. AP on t-tubules opens voltage gated Ca++ channels on the sarcoplasmic reticulum 3. Ca++ leaves sarcoplasmic reticulum and binds to troponin 4. End-plate potential triggers an action potential on the sarcolemma 5. ATP is split and energy released is used to re-cock the myosin heads 6. Action is repeated over and over until AP ends and Ca++ is returned to sarcoplasmic reticulum 7. Troponin changes shape and pulls tropomyosin off the myosin binding sites on actin 8. Myosin heads bind to actin 9. ACH binds to chemical gated Na+/K+ channels 10. Na+ enters and K+ leaves resulting in an end-plate potential 11. Myosin heads rotate toward center of sarcomere pulling thin filament 12. Sarcomere shortens 13. ATP binds to myosin heads and myosin-actin bond is broken a. 9,10,4,1,8,7,11,13,5,6,2,3,12 b. 9,10,4,1,8,7,11,13,2,3,5,6,12 c. 9,10,4,1,8,7,2,3,11,13,5,6,12 d. 9,10,4,1,2,3,7,8,11,12,13,5,6 e. 9,10,4,1,2,3,7,8,11,5,6,12,13 9. Draw and label the expected graph of a muscle twitch of a normal fiber (time = 60 ms, force = 3 gms). Label and briefly describe the activities in the muscle during the: latent period contraction period relaxation period 10. Draw a muscle twitch (max force muscle can produce is 3 gms) with a 2.5 gm weight attached and with a 5gm weight attached. Include the length of the muscle as well as the tension produced. Label as to whether the graph shows an isotonic or isometric contraction Part III 11. You artificially raise the calcium concentration inside the myofibrils and observe that both the normal and dysgenic fibers contract. From this observation, where would you conclude that the defect occurs in the steps of muscle contraction? Briefly explain how you came to this conclusion. a. Exposure of the active sites on actin b. Binding of the calcium to troponin c. Release of the calcium ions from the sarcoplasmic reticulum into the myofibril d. The repeated cycles of cross-bridge formation, myosin power strokes, and detachment 12. Where in the muscle fiber do you suspect that the normal protein made by the mdg gene functions in normal mice? 13. What causes the mice to die shortly after birth (i.e. What do they die from?) 14. Is this spastic paralysis or flaccid paralysis? Which of the following would have the same effect (same type of paralysis)--on the muscles of the mouse? Briefly discuss your reasoning. a. Botulism toxin b. Poisoning with atropine c. Poisoning with military nerve gas d. Tetanus toxin

Explanation / Answer

5. For the first question-, option d is the right choice. From the given experiment, we cannot find how ACH activates by Acetylcholinesterase. This will require ligand study.

6. Dysgenic mouse are paralyze in muscles. It affects excitation-contraction coupling in skeletal muscle. Hence, they would not show any reflex. Therefore, sarcolemmas instead of neurons are not working properly.

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