BION 3202

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BION 3202

• Lecture 5. Whole-heart Electrophysiology

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Where does the first impulse come from and why?
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Figure 14-8 - Overview
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Figure 14-17
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Figure 14-18
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Electrical Heterogeneity
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Youre in the laboratory looking at a heart
beating in ringers solution. Normally, the
ringers solution has 12 mM Nai, 145 Nao, 155 Ki
and 4 Ko. You raise the extracellular K to 30 mM.
What happens to the ventricular rhythm and why?
Using the goldman equation, you raise the resting
membrane potential to -42 mV, which inactivates
the sodium channels because its above -60mV the
point for Na to activate. This means no INa is
available for depolarization and the ventricles
cant initiate an action potential and therefore
beat. PNa/PK0.013
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Put these autorhythmic cells into the correct
order for conveying electrical signals through a
normal heart. 1. bundle of His 2. internodal
pathway 3. Purkinje fibers 4.
atrioventricular node 5. sinoatrial nodes 6.
left and right bundle branches A) 5, 2, 1, 6,
4, 3 B) 5, 2, 4, 1, 6, 3 C) 4, 2, 5, 1, 6, 3
D) 3, 6, 1, 4, 2, 5 E) 5, 4, 1, 6, 2, 3
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Which event happens at the start of a cardiac
cycle? A) Blood is ejected from the atrium.
B) The SA node fires. C) The P wave develops.
D) Ventricular systole occurs. E) Atrial
systole occurs.
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In cardiac muscle tissue, A) Ca2 releases from
the sarcoplasmic reticulum and initiates
contraction. B) Ca2 enters the cell from the
extracellular fluid, directly initiating
contraction. C) Ca2 enters the cell from the
extracellular fluid, which causes more Ca2 to be
released from the sarcoplasmic reticulum. D)
Both A and C are correct.
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Drugs known as calcium channel blockers can be
used A) decrease the force of cardiac
contraction. B) increase blood pressure. C)
constrict the coronary arteries. D) increase
sympathetic stimulation of the myocardium. E)
increase stroke volume.
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If the membranes of the cardiac muscle cells in
the SA node become more permeable to potassium
ion, A) the heart rate will increase. B) the
heart rate will decrease. C) the membrane will
depolarize. D) the stroke volume will increase.
E) the intracellular concentration of calcium
ion will increase.
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Calculate the Nernst potential for K and then
answer why increasing K permeability decreases
the pacing rate. Ko 155 mM Ki 4 mM
-98mV which means that increasing potassium
permeability should bring resting membrane
potential closer to potassiums reversal
potential.
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In which graph is the K permeability during the
pacemaker potential increased?

• A
• B

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If a myocardial infarction results in the
formation of scar tissue along the pathway of the
left bundle branch, A) cardiac arrhythmias may
occur. B) blood flow to the lungs will decrease.
C) the ventricle will contract more forcefully.
D) conduction through the left ventricle would
remain normal. E) the right ventricle will fail
to contract.
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Student Presentations
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Next Class The ECG

• Chapter 14, pages 480-484
• ECG, EKG
• Dipole