Rush - Advanced Pharmacology - NSG 531 - Exam 3 Questions with Complete Solutions what is the difference between cardiac myocyte action potential and that of the CNS or ANS? - Correct Answer nerve cell action potential is very short cardiac action potential is much longer they are longer to have adequate filling time in order to get a good contraction for a reasonable bolus of blood the only way this can happen is if the action potential is longer this will also mean that the refractory period will be longer What are the 5 phases of the non-pacemaker action potential? - Correct Answer 0 - depolarization
- - partial repolarization
- - plateau
- - repolarization
- - resting membrane potential
what happens during phase 0 of the non-pacemaker action potential - Correct Answer depolarization voltage gated sodium channels are opening up until we get past threshold what happens during phase 1 of the non-pacemaker action potential - Correct Answer partial repolarization what happens during phase 2 of the non-pacemaker action potential - Correct Answer plateau calcium channels open (L-type because they are long) potassium is still open potassium out and calcium in - they are opposing each other in voltage giving the plateau this is when the ventricles are filling what happens during phase 3 of the non-pacemaker action potential - Correct Answer repolarization calcium channels are closed 1 / 3
potassium channels are the only thing open taking their positive charge with them making the interior more negative what happens during phase 4 of the non-pacemaker action potential - Correct Answer resting membrane potential where we are in between action potentials there is no net change in ovltage inside the cell When does contraction take place? - Correct Answer begins towards the end of repolarization and ends at some point during repolarization refractory period - Correct Answer during phase 0, 1, 2, and part of phase 3 the cell is refractory to the initiation of new action potentials many antiarrhythmic drugs increase the Refractory period which reduces myocyte excitability what are the benefits of the refractory period - Correct Answer limits frequency of cardiac contractions allows for adequate filling time prevents sustained contractions how are pacemaker cells different from non-pacemaker cell - Correct Answer no resting membrane potential - no point where it is flat there are very few sodium channels in pacemaker - sodium channels are not driving depolarization - calcium is only 3 phases comprised of cells within the SA node generate regular, spontaneous action potentials what are the phases of pacemaker action potential - Correct Answer 0 - rapid depolarization
- - repolarization
- - slow depolarization
what happens during phase 0 of the pacemaker action potential - Correct Answer Rapid depolarization 2 / 3
something is coming to open voltage gated calcium channels (L-type) calcium comes rushing in what happens during phase 3 of the pacemaker action potential - Correct Answer repolarization potassium channels now open up, potassium rushes out, repolarizes what happens during phase 4 of the pacemaker action potential - Correct Answer slow depolarization with potassium rushing out we are all the way down at -60 funny sodium channels open up until voltage reaches -50 T-type (transient) calcium channels open up until voltage reaches -40 L-type calcium channels then open back up Describe how non-pacemaker APs can mimic pacemkaer APs - Correct Answer Hypoxia and ischemia when the resting membrane potential is not getting enough oxygen it is going to become more positive because you need oxygen to produce ATP. If we are deficient in ATP then the NA K ATPase pump wont be functioning if someone is hypoxic in a focal area - say they have a resting membrane potential at -45 - the fast sodium channels won't open - they start using calcium to open - so they would convert into action potentials that use calcium (hence how they mimic pacemaker APs) excitation-contraction coupling - Correct Answer sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber's sarcomeres conversion of depolarizing currents into contractile force L-type calcium channels open up in phase 2 in nonpacemaker - calcium comes flooding into myocytes, so we now have calcium in the cell and a sarcoplasmic recticulum (a resovior for calcium) receptors called RYR (ligand gated calcium channels) calcium then comes out - coming int the cell from the calcium channels and the sarcoplasmic recticulum describe how calcium binds to cause contraction - Correct Answer when there is an influx of calcium in the cell there is a myosin head separated by troponin. little binding sites for the myosin exist on the aktin but it can't get to it because of the troponin. calcium therefore binds to the tropinin causing a
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