Term
| define equillibrium potential: |
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Definition
| - the electrical potential that directly balances an opposite concentration gradient |
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Term
| calcium and excitation contraction coupling: |
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Definition
| - voltage change> voltage gated calcium channels open> calcium rushes into cell> opens ryanodine receptor channels on SR, more calcium released into cell> contraction |
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Term
| 3 things that keep intracellular caclium low: |
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Definition
- calcium pump- uses ATP to expell calcium
- Na+ Ca++ exchanger- exchanges 1 calcium for 3 sodiums
- SR reuptake |
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Term
| importantance of normal, very negative resting potential (-70 to -90 mV): |
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Definition
- avoid spontaneous depolarization
- allows more Na+ channels to recover from inactivation
- faster depolarization
- greater amplitude of action potential
- more rapid propogation of action potential |
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Term
| Explain the "fast response" of cardiac action potentials: |
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Definition
- fast response: Na+ depolarization
- atrial and ventricular contractile cells
- rapidly conducting cells- Purkinje fibers |
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Term
| Explain cardiac action potentials "slow response" : |
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Definition
- slow response: Ca++ depolarization
- sinoatrial node- pacemaker cells
- atrioventricular node- slowly conducting cells, latent pace maker cells |
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Term
| what node has pace maker cells? |
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Definition
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Term
| what node has slowly conducting fibers aka latent pace makers? |
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Definition
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Term
| modulators with positive effects on calcium conductance: |
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Definition
- catecholamines: NE and Epinephrine
- Sympathicomimetic drugs |
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Term
| sympathicomemetic drugs are positive modulators of calcium conductance, how? |
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Definition
- enhance activation of L-type calcium channels
- enhance reuptake of calcium by SR |
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Term
| Modulators with negative effects on calcium conductance: |
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Definition
- Calcium channels antagonists
- acetylcholine |
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Term
| How is acetylcholine a negateive modulator for calcium conductance: |
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Definition
- parasympathetic neurotransmitter
- binds to muscarininc receptors> inhibits adenylyl cyclase> decreases cAMP> decreases activation of L-type calcium channels
- also causes NO release, which stimulates guanylate cyclase to increase cGMP. cGMP decreases activation of L-type calcium channels |
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Term
| calcium channel blockers block the voltage gated calcium channels so there is less intracellular calcium, this decrease force of contraction by decreasing ___. |
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Definition
- contractility
- used to decrease blood pressure |
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Term
| what are the two types of ligand-gated potassium channels in the heart? |
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Definition
- ATP-sensitive K+ channel
- Acetylcholine-activated K+ channel |
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Term
| The ATP- sensitive K+channel inhibits electrical activation of the heart by permitting ___ of___ when cytosolic ___ is low. This shortens the ___ phase of the cardiac action potential. Conserves limited myocyte energy during __. This channel is also opened by ___. |
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Definition
- outflux of potassium
- ATP is low
- plateau
- ischemia
- adenosine |
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Term
| The acetylcholine-activated K+ is opened by ___ stimulation and decreases what three things? |
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Definition
- vagal stimulation
- decreases resting diastolic potential
- decreases rate of rise of pacemaker potential
- decreases duration of action potential |
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Term
Slow Response:
If phase 4 of the cardiac action potential is not sufficiently negative, then the fast sodium channels remain closed and the rapid sodium influx cannot occur. Calcium channels are functional and at their threshold begin to open. A slowly deveolping inward calcium current produces a slowly raising phase 0. |
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Definition
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Term
| parasympathetic innervation on SA node causes what changes in the pace maker potential: |
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Definition
- slower rise from a more negative value
- affecting funny sodium channels and transient calcium channels? |
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Term
| sympathetic innervation causes a more rapid ___ depolarization. |
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Definition
| sympathatic innervation causes a more rapid diastolic depolarization |
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Term
| with parasymp on pacemaker potential you reach threshold ____. with sympathetics on pacemaker potential you reach threshold ____. |
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Definition
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Term
| Also parasymp decreases heart rate by making pacemaker potential reach maximal ___. |
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Definition
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Term
| The pace maker segment of membrane rises during ___ to reach threshold for sodium channels to open. Only one cell in the SA node has to reach threshold, and then from there on, excitation is conducted by action potentials. |
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Definition
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Term
| ___ not an ___ ___ is conducted. |
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Definition
| Excitation not an action potential is conducted. |
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Term
| put heart tissues in order from fastest conducting to slowest conducting: |
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Definition
| purkinje fibers> atrial and ventricular contractile cells> AV node |
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Term
| factors that influence velocity of conduction: |
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Definition
1. fast or slow response action potentials
2. negativity of resting potential
3. rate of rise of phase 0
4. degree of depolarization |
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Term
| parasympathetic stimulation slows ___ conduction by opening ___ sensitive ___ channels and by stimulating the release of ___ ____which promotes the formation of ___ which tends to close ___ __ ___. |
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Definition
- AV
- acetylcholine sensitive K+ channels
- nitric oxide
- cGMP
- cGNP closes L-type calcium channels |
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Term
| sympathetic stimulation increases AV conduction by increasing the ___ ___ ___. |
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Definition
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Term
| calcium channel antagonists decease the ___ ___ ___ ___ and thus slow __ conduction. |
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Definition
- L-type calcium current
- AV |
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Term
| Adenosine blocks ___ conduction by inhibiting the ___ ___ ___and by opening ___ ___ ___ ___ causing hyperpolarization. |
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Definition
- AV
- L-type calcium current
- adenosine sensitive K+channels |
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Term
| Ischemia and other conditions can slow the rate of rise of the ___ ___ action potentials and convert fast response action potentials to slow response action potentials. This occurs when the sodium channels remain ___ and the membrane is depolarized by influx of ___ through___ ___ ___ ___. |
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Definition
- fast response
- unactivated
- calcium
- slowly opening calcium channels |
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Term
| ischemia alters myocardial _____ of ___ ___ and can decrease efficiency of ___. |
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Definition
conduction of action potentials
ejection |
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Term
| Ischemia slows the rate of rise of fast response action potentials b/c it stops the ___ ___ which is essential for membrane potential. |
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Definition
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Term
| ischemia causes especially slow conduction in the ___. |
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Definition
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Term
| Ischemia causes loss of intracellular ___ and an elevation of extracelluar ___. This elevates diastolic ___, and thus, the rate of rise and amplitude of action potential ____ and the conduction velocity ___. The duration of action potential is also ___. |
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Definition
- potassium
- potassium
- diastolic potential
- decrease
- decreases
- decreased |
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Term
| Since sodium channels remain unactivated if the membrane is not polarized, ischemia can make fast action potentials in the slow ones. |
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Definition
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Term
| parasympathetic stimulation slows or blocks ___ Conduction. |
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Definition
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Term
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Definition
| SA node> right atrium> atrial fibers> AV node > AV bundle branches > purkinje cells> around ventricular chambers> contracile cells> contraction |
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Term
| intial wave on an electrocardiogram is the __ wave and is caused by spread of electrical activity in the ___. |
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Definition
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Term
| the QRS complex on an electrocardiogram represents: |
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Definition
| - spread of electrical activity to depolarize left and right ventricles |
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Term
| The electrocardiogram: As the cardiac mass depolarizes time varying differences in ___ ___exist on the body surface. The EKG is a recording of these ___ ____. The electrocardiogram is produced by a ___ of ___ ___ __ (exciation, and then repolarization at different times and places). The EKG is NOT a recording of one action potential. |
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Definition
- electrical potential
- potential differences
- series of cardiac action potentials |
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Term
| A wave of depolarization APPROACHING a positive electrode will always give a ___ deflection on the EKG. Remember a deflection can positive but descending. |
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Definition
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Term
| A wave of depolarization MOVING AWAY from a positive electrode will give a ___ delfection. Remember a deflection can be negative and still ascending. |
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Definition
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Term
| The entire surface of a strip of RESTING myocardium is ___charged (relative to the interior of the cells of the fiber) so that no potential difference exists between electrodes A and B. A strip chart recording of this ECG (right) records zero potential difference and so remains at its baseline. |
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Definition
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Term
| look at slides 36-41 of this lecture and be able to interpret EKG. |
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Definition
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Term
| events during cardiac action potential during conduction of excitation: |
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Definition
| Ions move parallel to the membrane; Na+ channels open; Ca++ channels open; K+ channels open. |
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