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Solns prob set #6

Solns prob set #6 - BIPN 108 Physiology of...

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BIPN 108, Physiology of Exercise--Solutions to Problem Set #6 Page 1 1.a. Flexeril is a common treatment for muscle spasms. Muscle contraction is driven by activity in α -motor neurons, so inhibiting their activity will reduce contraction of muscles (notice that the activity is turned down , not off ). In addition, reducing activity in γ -motor neurons will reduce contraction of intrafusal fibers, thus decreasing activity in the muscle spindle organs and making them less sensitive to stretch. The net effect will be reduced tension in skeletal muscles, which would make walking a mile feel a lot more difficult. b. By decreasing the likelihood that ryanodine receptors will open, Dantrolene keeps the [Ca 2+ ] of the cytoplasm from rising as high as it normally would in response to an action potential traveling along the plasma membrane of muscle fibers. Lower [Ca 2+ ] cytoplasm will mean less Ca 2+ bound to troponin, fewer myosin-binding sites revealed on actin in the thin filaments, fewer myosin heads bound to actin, and thus less force applied by myosin to the actin fibers. The net effect will be less tension produced by muscle fibers, and the muscles will feel weak. Walking a mile would feel difficult. c. By blocking nicotinic ACh receptors, d-tubocurarine will reduce the size of the post-synaptic potentials at the neuromuscular junction. If enough ACh receptors are blocked, synaptic transmission at the neuromuscular junction will be blocked, which would produce paralysis. Walking a mile would be impossible (but so would breathing). d. Glycinergic synapses are the most abundant inhibitory synapses in the spinal cord. If these synapses are blocked, as they are by strychnine, the balance between excitation and inhibition onto spinal α -motor neurons is disturbed and the α -motor neurons are much more active than they otherwise would be. In particular, the motor pools of antagonistic muscles will be excited simultaneously, and the result will be rigid paralysis.
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