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RUSH – ADVANCED PHARMACOLOGY NSG 531 EXAM 3 QUESTIONS AND VERIFIED ANSWERS
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RUSH – ADVANCED PHARMACOLOGY NSG 531 EXAM 3 QUESTIONS AND VERIFIED ANSWERS...
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What is the distinction between the cardiac myocyte action potential and that ofthe CNS or ANS? - The nerve cell's action potential is quite brief.
The cardiac action potential is significantly longer.
They require more filling time to get a satisfactory contraction for a reasonable
bolus of blood.
This can only happen if the action potential is longer.
This also implies that the refractory period will be longer.
What are the five phases of the nonpacemaker action potential? - ANSWER 0:
Depolarization.
1 - Partial Repolarization
2 – plateau
3 - Repolarization.
4. Resting membrane potential.
What happens during phase 0 of the non-pacemaker action potential -
depolarization?
Voltage-gated sodium channels are opening up till we pass the threshold.
What happens during phase 1 of the non-pacemaker action potential - partial
repolarization?
What happens during phase 2 of the non-pacemaker action potential? ANSWER
plateau
Calcium channels open (L-type due to their length).
potassium is still open.
potassium out and calcium in - they oppose each other in voltage, resulting in
the plateau.
This is when the ventricles fill.
,What happens during phase 3 of the non-pacemaker action potential? ANSWER
repolarization.
Calcium channels are blocked.
Potassium channels are the sole thing open, carrying their positive charge with
them and making the interior more negative.
What happens during phase 4 of the non-pacemaker action potential? ANSWER
Resting membrane potential, where we are in between action potentials, there is
no net change in ovltage inside the cell.
When does the contraction take place? - ANSWER starts around the end of
repolarization and finishes at some point during it.
refractory period - ANSWER During phases 0, 1, 2, and a portion of phase 3,
the cell is resistant to the initiation of new action potentials.
Many antiarrhythmic medications prolong the refractory time, reducing
myocyte excitability.
What are the benefits of the refractory period? ANSWER reduces the frequency
of cardiac contractions.
provides for enough filling time.
Prevents sustained contractions.
How do pacemaker cells vary from non-pacemaker cells? ANSWER: There is
no resting membrane potential and no flat point.
There are extremely few sodium channels in the pacemaker; sodium channels
are not generating depolarization, rather calcium is.
Only three phases.
composed of cells within the SA node.
create regular and spontaneous action potentials.
What are the phases of pacemaker action potential? - ANSWER 0: fast
depolarization.
3 - Repolarization.
4. Slow depolarization.
What happens during phase 0 of the pacemaker action potential? ANSWER:
Rapid depolarization.
, When voltage-gated calcium channels (L-type) open, calcium rushes in.
What happens during phase 3 of the pacemaker action potential? ANSWER:
Repolarization.
Potassium channels now open, potassium rushes out and repolarizes.
What happens during phase 4 of the pacemaker action potential? - gradual
depolarization.
With potassium streaming out, we are all the way down to -60.
Funny sodium channels open up until the voltage reaches -50.
T-type (transient) calcium channels open until the voltage hits -40.
The L-type calcium channels then open back up.
Describe how non-pacemaker APs can mimic pacemaker APs: hypoxia and
ischemia.
When the resting membrane potential does not receive enough oxygen, it
becomes positive because oxygen is required to make ATP. If we are deficient
in ATP, the NA K ATPase pump won't function.
If someone is hypoxic in a specific location, say they have a resting membrane
potential of -45, the rapid sodium channels won't open; instead, they start
utilizing calcium to open, so they would change into action potentials that need
calcium.
Excitation-contraction coupling is the sequence of events from a 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 nonpacemakers, allowing
calcium to stream into myocytes, resulting in calcium in the cell and a
sarcoplasmic recticulum.
receptors termed RYR (ligand-gated calcium channels)
Calcium then pours out, arriving into the cell from the calcium channels and the
sarcoplasmic recticulum.
Describe how calcium binds to induce contraction. ANSWER: When there is an
influx of calcium in the cell, a myosin head is separated by troponin. Little
binding sites for myosin exist on aktin, however they cannot be accessed due to
troponin. Calcium then attaches to tropinin, generating a confirmational shift in
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