1 Quiz 05 Results Question 1: Multiple Choice Average Score 0.40068 points The type of skeletal muscle fiber we usually discuss in class is called a twitch fiber. Motor axons that innervate twitch fibers generate large endplate potentials (EPSPs) that always trigger a postsynaptic action potential. The action potential rapidly conducts along the entire length of the fiber, and a single all-or-none twitch results. However, there is another type of skeletal muscle fiber in some vertebrates, called a tonic fiber. Tonic fibers do not generate action potentials. Despite the absence of action potentials, activity in the motor axon does cause tonic fibers to contract along their entire length. Which one of the following would you not expect to be a characteristic of tonic muscle fibers? Correct Percent Answered A lower density of voltage-gated Na+ channels in the plasma membrane compared to twitch fibers. 8.219% Graded contractions, the amplitude of which depends on the frequency of motor nerve firing. 6.849% A single neuromuscular junction near the middle of the length of each fiber. 80.137% Myosin-containing thick filaments and actin-containing thin filaments. 4.795% Unanswered 0% Question 2: Multiple Choice Average Score 0.35274 points Imagine that you standing on a platform that is about 18 inches high, and then you decide to hop off the platform onto the ground, landing such that your toes contact the ground first, and both feet land simultaneously. (If you try this at home, please don’t hurt yourself.) A few tens of milliseconds after your toes contact the ground, which one of the 5 labeled points in the attached diagram (Quiz05 Q2 Fig.jpg) best describes the state of your gastrocnemius muscle? Correct Percent Answered Point a. 4.11% Point b. 10.959% Point c. 8.904% Point d. 70.548% Point e. 5.479% Unanswered 0% Question 3: Multiple Choice Average Score 0.45205 points Why are pharmacological inhibitors of adrenergic beta receptors (beta blockers) used for the treatment of high blood pressure? Correct Percent Answered Beta blockers reduce transmitter release at synapses in sympathetic ganglia. 2.74% Beta blockers block the action of epinephrine and norepinephrine on heart muscle cells. 90.411%2 Beta blockers stimulate contraction of blood vessels (vasoconstriction), which lowers blood pressure. 2.74% Beta blockers interfere with the action of acetylcholine on heart muscle cells, preventing the normal effect of ACh to raise heart rate and blood pressure. 4.11% Unanswered 0% Question 4: Essay Average Score 0 points Phenelzine is a common inhibitor of monoamine oxidase (MAO) that has been used to treat depression. However, it is not prescribed as often as other antidepressants due to its effects on the autonomic nervous system. Describe two (only 2) autonomic side effects that may result from taking phenelzine and briefly explain why they might occur. Example Answer [None Given] Unanswered Responses 0 Given Answers One of the side effects that may result from taking phenelzine is high blood pressure. This is because monoamine oxidase speeds up the process of the degradation of norepinephrine. Thus, as an inhibitor of monoamine oxidase, the effect of norepinephrine on its target is enhanced, as the mechanism to remove it are removed. Norepinephrine is released by postganglionic sympathetic neurons onto targets, and the sympathetic nervous system is responsible for increasing blood pressure. Thus, it follows that enabling an enhanced effect of norepinephrine onto targets would increase blood pressure to unhealthy proportions, which is what is seen by taking this medication. Another side effect associated with this medication is difficulty in digestion. This side effect too can be explained by the drug's effect as an inhibitor of monoamine oxidase. Again, as an inhibitor of monoamine oxidase, this drug increases the effect of the sympathetic nervous system on the body, and one of its functions is vasoconstriction in viscera. This means that the sympathetic nervous system decreases digestion and makes digestion difficult. Because Phenelzine enhances the effect of norepinephrine in the target cells, digestion is inhibited and the user experiences difficulties. Generally, MAO is responsible for removing norepinephrine, dopamine, and seritonin from the brain. Because norepinephrine is responsible for stimulating the sympathetic nervous system, it may cause side effects such as increased heart rate and blood pressure. However, since MAO is responsible for removing norepinephrine, it would inhibit the sympathetic nervous system, which would decrease heart rate and blood pressure. However, since phenelzine inhibits MAO, it inhibits this inhibition and therefore stimulates the sympathetic nervous system, which could, for example, lead to the following effects: 1) increased heart rate & 2) increased blood pressure. Because MAO breaks down norepinephrine intracellulary from being repackaged and released again as a neurotransmitter, prescription of phenlzine allows norepinephrine to continue to be used and the pathway to be continuously stimulated. This could cause sympathetic side effects that include continous increased heart rate and increasd respiratory rate. MAO is an enzyme that breaks down dopamine, serotonin, noradrenaline, and adrenaline; so phenelzine (an inhibitor of MAO) allows these excitatory neurotransmitters to hang around longer in the synaptic cleft (inhibits reuptake), so it is used to treat depression. However, this drug can cause some effects on the3 autonomic nervous system, including hypertensive crisis (extremely high blood pressure, which can be fatal) and withdrawal syndrome. Hypertensive crisis can occur because compounds like tyramine (from food) will not be broken down when phenelzine is taken. This extra tyramine can cause adrenaline to be displaced from storage vesicles, leading to excess adrenaline in the system and rapid overexcitation, causing hypertensive crisis. Withdrawal syndrome can occur if drug use is halted abruptly because the system will be used to high levels of adrenaline and noradrenaline and not know how to cope when levels suddenly drop. One effect that it has on the autonomic nervous system is in the gastrointestinal tract, where dry mouth is caused. This would be caused by the sympathetic response of decreasing secretion in the mouth. The drug could be affecting