6. In cases where there is no ATP and the calcium concentration is high in the m

Question

6. In cases where there is no ATP and the calcium concentration is high in the myofibrils, the muscle cell would be rigid, unable to either relax or contract because:

a. troponin would be unable to bind calcium.
b. myosin heads would be unable to bind ATP and become unbound from the actin.

c. tropomyosin would unable calcium.
d. myosin heads would be unable to bind calcium.
e. myosin heads would be unable to bind to the actin filaments.

3. At the junction between the T-tubule and the sarcoplasmic reticulum in skeletal muscle, Ca2+ enters the cytoplasm of the muscle cell from the _____ through ________.

a. T-tubule, ryanodine receptors.
b. sarcoplasmic reticulum, DHP receptors
c. sarcoplasmic reticulum, ryanodine receptors

d. extracellular space, ryanodine receptors.
e. a and d are correct.

4. For skeletal muscle, the movement of the myosin head occurs when:

a. the myosin head binds ATP.
b. the myosin head binds actin
c. ADP and inorganic phosphate ion leave the myosin head.

d. the myosin head cleaves ATP to ADP and inorganic phosphate ion.

e. the myosin head forms ADP and inorganic phosphate ion.

22. In both the dorsal column system and in the anterolateral system, the role of the second order neuron is to:

a. deliver sensory information to the thalamus.
b. send a process across the midline of the body.
c. deliver sensory information in the dorsal column nuclei.

d. form synapses in the spinal cord.

e. a and b are correct.

Explanation / Answer

6) When there is high concentration of calcium and no ATP in myofibrils, the muscle cell would be rigid unable to either contract or relax because myosin heads would be unable to bind to ATP and become unbound from the actin (option b). This is because myosin requires energy from ATP hydrolysis to get released from binding with actin. Since ATP is absent, this process cannot occur and muscle cell remains in rigid state.

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