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 1 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 the 2 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 something to do with the ability to conserve water within the body So the sympathetic response would be to cause the mouth to become dry and thus cause thirst within the individual Another symptom is insomnia and this would have to