Question 1

Which of the following best describes the function of cardiac autorhythmic cells?

Accepted Answer

They generate the heart's action potentials and activate contractile cells.

Question 2

What is the primary ion responsible for the initial phase of depolarization in cardiac autorhythmic cells?

Accepted Answer

Na$$^+$$ influx through If (funny) channels

Question 3

During the pacemaker potential, which change in ion permeability contributes to the membrane's slow drift toward threshold?

Accepted Answer

Decrease in K$$^+$$ efflux

Question 4

Which equation best represents the net movement of ions during the Na$$^+-Ca$^{2+}$$ exchanger in the coupled-clock system?

Accepted Answer

$$\mathrm{Na^+_{out}} + \mathrm{Ca$$^{2+}$$_{in}} \rightarrow \mathrm{Na^+_{in}} + \mathrm{Ca$$^{2+}$$_{out}}$$

Question 5

Which phase of the cardiac contractile cell action potential is responsible for the long refractory period that prevents tetany?

Accepted Answer

Plateau phase maintained by slow Ca$$^{2+}$$ influx

Question 6

A patient is given a drug that blocks L-type Ca$$^{2+}$$ channels in cardiac contractile cells. What is the most likely effect on the cardiac action potential?

Accepted Answer

Shortened plateau phase and reduced contraction force

Question 7

Which of the following statements about the resting membrane potential (RMP) of cardiac contractile cells is correct?

Accepted Answer

The RMP is approximately $$-90 mV$$, more negative than skeletal muscle cells.

Question 8

According to the Frank-Starling Law, which equation best describes the relationship between stroke volume (SV) and end-diastolic volume (EDV)?

Accepted Answer

$$SV \propto EDV$$

Question 9

Which autonomic nervous system division decreases heart rate by increasing K$$^+$$ permeability in pacemaker cells?

Accepted Answer

Parasympathetic (via vagus nerve)

Question 10

A patient has a mutation that causes the If (funny) channels in SA node cells to be less permeable to Na$$^+. $$What is the most likely effect?

Accepted Answer

Slower pacemaker potential and decreased heart rate

Question 11

Which of the following best explains why cardiac muscle cannot undergo tetanic contractions?

Accepted Answer

The long refractory period overlaps with the contraction period, preventing summation.

Question 12

Which ion movement is primarily responsible for the rapid repolarization phase in cardiac contractile cells?

Accepted Answer

Outward K$$^+$$ flux through voltage-gated channels

Question 13

Which of the following is TRUE regarding the effect of sympathetic stimulation on the heart?

Accepted Answer

It increases heart rate and contractile strength by increasing Na$$^+$$ and Ca$$^{2+}$$ influx.

Question 14

Which process is described by 'calcium-induced calcium release' in cardiac contractile cells?

Accepted Answer

Extracellular Ca$$^{2+}$$ entry triggers release of more Ca$$^{2+}$$ from the sarcoplasmic reticulum.

Question 15

Which of the following would most likely result from increased stretch of ventricular muscle fibers at the end of diastole?

Accepted Answer

Increased force of contraction and greater stroke volume

Question 16

Which of the following best describes the role of the SA node in cardiac physiology?

Accepted Answer

It acts as the primary pacemaker, initiating action potentials that set the heart rate.

Question 17

Which equation best represents the relationship between force of contraction (F) and number of active cross-bridges (N) in cardiac muscle?

Accepted Answer

$$F \propto N$$

Question 18

Which of the following is a direct effect of parasympathetic stimulation on the SA node?

Accepted Answer

Hyperpolarization of pacemaker cells due to increased K$$^+$$ permeability

Question 19

Which of the following best explains why the heart can continue to beat even if all nervous connections are severed?

Accepted Answer

Autorhythmic cells generate action potentials independently of nervous input.

Cardiac Physiology: Cardiac Action Potentials & Contraction

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