BECOM 2 Exam 2 2019 – Membrane Potential Published on July 30, 2020 by David Leonard Membrane Potential, Synaptic Physiology, and Autonomic Physiology Which of the following combinations of membrane potential (Vm) and equilibrium potential (Eion) for either a cation or anion would result in an overall decrease in membrane potential if: The channel for the specific anion or cation was open and uninhibited. Concentration differences between the cytosol and EC anion/cation are negligible. Vm = -90, Eanion = 80 Vm = -90, Eanion = -100 Vm = -90, Ecation = -120 Vm = -70, Eanion = -100 Vm = -70, Ecation = -80Lethal injections contain potassium chloride which works to stop the heart. Why is this an effective method of euthinasia? It causes K gates to remain open which means it cannot return to resting membrane potential causing excessive action potentials which shock the heart until it stops working It causes Na gates to remain inactive which means it cannot return to resting membrane potential causing excessive action potentials which shock the heart until it stops working It causes Na gates to remain inactive which means it cannot return to resting membrane potential causing cessation of action potentials making the heart unable to pump It causes more potassium to be in the extracellular fluid making it harder for the cell to reach threshold so there is less action potentials being reached and thus the heart stops beating It causes K gates to remain open which means it cannot return to resting membrane potential causing cessation of action potentials making the heart unable to pumpPatent ductus arteriosus is a heart defect in the pulmonary artery that carries oxygen-poor blood to the lungs and the artery that carries oxygen-rich blood to the rest of your body. How would this condition affect the rest of the body in terms of membrane potential? It would not affect membrane potentials, it would have an effect on hemoglobin binding causing a shift to prefer myoglobin. It hyperpolarizes the membrane because there is an influx of K making it harder to reach threshold It repolarizes the membrane before there is an action potential, so the body cannot effectively carry oxygen throughout the body It depolarizes the membrane because there is no Na/K pump action because there is a lack of ATP It causes the threshold to increase meaning it takes a bigger stimulus and makes it harder for oxygen to be transported throughout the bodyCystic Fibrosis is a disease caused by a mutation in which of the following types of channels? Mechanically gated chloride channels Voltage gated calcium channels Ligand gated chloride channels Ligand gated calcium channels Voltage gated chloride channelsPotassium channels allow for potassium to leave the cell. What prevents sodium from using this channel? Potassium is much smaller than sodium so it is able to pass based on size. Sodiums waters of hydration do not align with the selectivity filter so they do not strip the waters off Sodium is negatively charged so it sticks to the positively charged sides of the channel. Sodium does not form waters of hydration so the selectivity filter does not recognize it. Sodium is too small to pass through the channel so it diffuses through without a channel.Which of the following is an example of a positive feedback mechanism? Stretch receptors in the cervix signal the pituitary to release oxytocin Pyruvate dehydrogenase is inhibited by acetyl-CoA Lactate is transported out of muscle tissue so that muscle lactate dehydrogenase can continue to recycle NAD+ against a low product concentration gradient Liver pyruvate kinase activity is up-regulated by fructose-1,6-bisphosphateGene was recently diagnosed with hypertension and put on enalapril, an ACE inhibitor. He wants to know how it works, so you tell him, in layman's terms: It blocks an enzyme that prevents a hormone that tells the body to not absorb water thus decreasing blood pressure It blocks the formation of Renin which then prevents the body from creating a hormone called aldosterone which thus decreases blood pressure It blocks a hormone that is secreted from the pituitary gland causing him to not absorb water thus decreasing blood pressure It blocks an enzyme that prevents a hormone that tells the body to absorb water thus decreasing blood pressure It blocks a hormone that is secreted from the pituitary gland causing him to absorb water thus decreasing blood pressureOrthostatic hypotension occurs when a person’s blood pressure falls when suddenly standing up from a lying or sitting position. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain an adequate blood pressure when changing position to standing. As a result, blood pools in the blood vessels of the legs for a longer period and less is returned to the heart, thereby leading to a reduced cardiac output. This is an example of: Negative Feedback High Gain System None of the Above Positive Feedback Low Gain SystemJenna fell off her bike scraping her knee. This started a cascade of cellular processes: her knee started bleeding, turned red and was painful. Her broken endothelial cells release cytokines which signal thrombocytes to release more cytokines thus activating additional thrombocytes to clot and stop the bleeding. This is an example of: Anticoagulant response Returning to homeostasis Anti-inflammatory response Feedback inhibition Feed-forward activationOnce a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed. Blood clotting is an example of:Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed. Blood clotting is an example of which of the following? None of the Above Negative Feedback Positive Feedback Low Gain System High Gain SystemYour friend in medical school asks why depolarizing the membrane (such as in a state of acidemia), eventually leads to fewer action potentials. The best answer is: Depolarization has a boomerang effect and eventually leads to hyperpolarization. Depolarization causes degradation of K+ channel proteins Depolarization makes the cell more permeable to Cl-, which eventually hyperpolarizes the membrane. Did you hear the one about global warming? It depolarizes! Depolarization, if prolonged, leads to inactivated Na+ channels.A patient is diagnosed with hypoxia, which of the following is NOT true about the patient with regard to membrane potentials in B cells of the pancreas? Voltage sensitive Ca2+ channels are open The membrane is hyperpolarizing Vm is increasing ATP sensitive K+ channels are open Insulin is not being secretedWhich part of a K+ channel subunit is primarily responsible for K+ selectivity over Na+? S5 (outer helix) P segment S6 (inner helix) Alpha binder Hyrophospate endWhich of the following is true regarding the conductance velocity of an action potential? Myelin decreases conduction velocity by providing insulination for the axon Myelination decreases capacitance by allowing action potentials to “jump” from node to node, increasing conduction velocity Preganglionic fibers often have a slower conduction velocity as compared to postsynaptic fibers since they are unmyelinated Myelination creates a greater surface area to allow for ion exchange across membranes Axons with smaller diameters have increase conduction velocityA patient comes in with CO poisoning. What can be said about the likelihood (at first) of membrane threshold being reached compared to the normal? The cell is hyperpolarized, it is more likely to reach threshold. The cell is hyperpolarized, it is less likely to reach threshold. The cell is depolarized, it is less likely to reach threshold. The cell is depolarized, it is more likely to reach threshold.Which of the following is correct in regards to graded potentials and action potentials? GP only occur with voltage gated ion channels; AP can occur with any type of ion channel AP always have the same strength of signal and have a refractory period that must be obeyed; GP cannot have summation Graded potentials (GP) occur in the axon hillock; action potentials (AP) occur in the dendrites/cell bodies AP can be initiated with above threshold graded potentials at axon hillock; GP are initiated in ions through channels GP and AP can both only be depolarizedWhich of the following is occurring at the point in the graph depicted by the red arrow? Na+ inactivation gates are closed K+ activation gates are closing K+ inactivation gates are opening None of the above Na+ activation gates are openA neuron has a threshold of -45 mV. Resting membrane potential is -60 mV. A depolarization stimulus of 10 mV is applied. What is the effect? The neuron will depolarize however an action potential will not fire An action potential will fire The neuron will hyper-polarize Initially, the neuron will hyperpolarize but then it will depolarize There will be no effectIn the cold northern winters, you many times will see people out at bars not wearing jackets who claim that they are not cold, is this problematic? Why or Why not? Yes, because the only reason they don’t feel cold is because they are shivering which causes muscle contractions which will not regulate body temperature No because Northerners have excess brown fat reserves No, because hoes don’t get cold Yes because their parasympathetic nervous system becomes activated which shunts blood to their core causing them to feel warmer while causing frostbite Yes because they feel warm because their body is vasodialating causing heat to leave their skinTime is Up!