39. In experimental preparations, activation of the corticospinal tract can result in excitation of both a- and y-motoneurons. The co-activation of a- and y-motoneurons confers which of the following advantages compared with activation of only a-motoneurons? A) Decreased tension in the intrafusal muscle fibers increases the force of muscle contraction. B) Inhibition of y-motoneurons is overcome by activity in recurrent collaterals of a-motor axons C) y-Motoneuron axon collaterals excite a-motoneurons, increasing their total activity D) Muscle spindles shorten, preventing an unloading effect on muscle spindle sensory endings
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- 4) You set up an experiment using an isolated mouse muscle-nerve preparation.a. Draw the force traces (used to measure the force of contraction using a force transducer) you wouldexpect to get if you stimulated the nerve at 3 different lengths: 1) slack, 2) the normal length of the musclein the body, and 3) stretched past a length the muscle could ever experience in a mouse. If the force tracesare different explain why. (Hint: refer back to the length-tension relationship)b. Draw the nerve signals you would record from a Group Ia muscle spindle afferent at each of those 3lengths. If the 3 conditions are different explain why. (Hint: refer back to the function of the musclespindleCardiac and skeletal muscle are both “striated” types of muscle and yet they have very distinct functional characteristics. a) Skeletal muscle functions as discrete motor units and the cardiac muscle works as a functional syncytium. Define the italicized terms in the previous sentence, explain their importance, and describe the cellular features that underlie these functional differences. b) Cardiac muscle exhibits automaticity, while excitation of skeletal muscle is neurogenic. Define the italicized terms and provide a brief explanation of mechanisms underlying each.Botox has become popular for reducing wrinkles. It is a dilute solution of a toxin which inhibits muscle contraction by working at the presynaptic portion of the NMJ. Which of the following could be a possible mechanism for Botox wrinkle-reducing action? a.) Increase Calcium influx b.) Cleave (degrade) syntaxin c.) Increase sensitivity of synaptotagmin to Ca d.) Decrease synthesis of nSec1
- 34. in an experimental study of skeletal muscle function, an isolated muscle strip is electrically stimulated from various initial lengths, and tension is recorded in the graph shown. Compared with initial length A, the greater tension generated at initial length B is the result of which of the following? A) Decrease in intracellular calcium concentration B) Decrease in shortening velocity C) Increase in load D) Increase in numbers of active cross-bridges E) Increase in rate of cross-bridge cycling Maximal tension 8 Skeletal muscle length9. Which of the following correctly describes the end plate potential (EPP)? A)It is primarily mediated by Na+ influx B)It is both a local potential in the end plate area of the muscle cell that allows the muscle cell to depolarize and it is primarily mediated by Na+ influx C)It is both a local potential in the alpha motor neuron that allows a cell to depolarize and it is primarily mediated by Na+ influx D)It is a local potential in the end plate area of the muscle cell that allows the muscle cell to depolarize E)It is a local potential in the alpha motor neuron that allows the muscle cell to depolarizeExplain the intracellular mechansim of smooth muscle relaxation of agaonist such as mepyrimine and atropine.
- Succinylcholine act as adepolarising agent that prevents repolarization of the somatic motor neuron. Thus, no further ACh is released until drug is cleared. Name another site within the MNJ we could target to prevent muscle contraction, and explain why this would work.3. The calcium that permits neurotrasmitter release from the alpha motor neuron is recycled and used as calcium that becomes available for the muscle contraction. A)False B)True147 An investigator is examining the effects of various manipulations on the electrical activity in intestinal smooth muscle. The resting changes in membrane potential are shown between points W and X in the figure shown The observed changes in membrane potential are most likely due to which of the following manipulations occurring at points X and Y, respectively? Point X Point Y B) Acetylcholine administration Epinephrine administration Norepinephrine administration Stretching the smooth muscle C) stretching the smooth muscle acetylcholine administration stretching the smooth muscle sympathetic stimulation vagal afferent stimulation E) Sympathetic stimulation. OOOO Membrane potential (mv) -20- -30- -40- -50- -60- -70- 0 in vrr t 10 15 20 Time (sec) 25 30
- Explain the intracellular mechansim of smooth muscle relaxation of agaonist such as mepyrimine and atropine. Give diagram for each.34. A 32-year-old woman has had progressive intermittent double vision for the past 6 weeks and weakness in her legs for the past 2 weeks. Physical examination shows bilateral ptosis and normal sensory function in her legs. The most likely mechanism of these findings is antibody to which of the following? OA) Acetylcholine receptor B) Cholinesterase C) Motor end-plate membrane D) Myosin E) Postsynaptic membraneDiscuss the following statement: “The basal lam-ina of muscle fibers serves as a molecular bulletin board,in which adjoining cells can post messages that direct thedifferentiation and function of the underlying cells.”