Cardiac Action Potential

What are the three steps in the initiation of action potential in an autorhythmiccell?

1. Pacemaker Potential 2. Depolarization and Reversal of the Membrane Potential 3. Repolarization

Embedded in the plasma membrane of an autorhythmic cell are protein channels that allow sodium, calcium, and potassium to move into or out of the cell. In which direction do the ions move through these channels?

1. Sodium Channels - allow sodium ions to enter the cell 2. Fast Calcium Channels - allow calcium ions to enter the cell. 3. Potassium Channels - allow potassium ions to leave the cell.

What two cell types are involved in producing a coordinated heart contraction?

1. cardiac autorhythmic cells 2. contractile cells

What are the three steps in the action potential in a contractile cell?

1. depolarization 2. plateau 3. repolarization

11. (Pages 8-10.) What is the order of steps in an action potential within an autorhythmiccell. a. Fast calcium channels open and positively-charged calcium ions rush in. b. Depolarization peaks at about +10 mV. c. Autorhythmic cell starts out at resting membrane potential (~-60 mV), positive out,negative in. d. When the membrane potential gets to -40 millivolts, it has reached threshold forinitiating an action potential. e. Potassium channels open, resulting in potassium rapidly leaving the cell. f. Cell begins depolarizing due to a slow continuous influx of sodium. g. Calcium influx produces the rapidly rising phase of the action potential(depolarization), which results in the reversal of membrane potential from negativeto positive inside the cell. h. Membrane potential goes from +10 mV to resting membrane potential (-60 mV).

1.c, 2.f, 3.d, 4.a, 5.g, 6.b, 7.e, 8.h

19. (Pages 14-16.) What is the order of steps in an action potential within an contractilecell. a. Intracellular calcium initiates cell contraction. b. Neighboring cells (either autorhythmic or contractile cells) depolarize. c. Rapid influx of sodium results in depolarization, resulting in a reversal of charge(depolarization) (to about +25 mV) as sodium moves into the cell. d. Ionic pumps actively transport calcium ions out of the cell and back into thesarcoplasmic reticulum. Ionic pumps also pump sodium out and potassium in,restoring ion concentrations to their resting conditions. e. The calcium channels close while more potassium channels open, allowingpotassium to quickly leave the cell, resulting in repolarization. f. Gap junctions open and positive ions (Ca+2and Na+1) move in to the contractilecells through gap junctions. g. Depolarization also causes opening of slow calcium channels, allowing calcium entryfrom the extracellular space and SR. At the same time, potassium efflux beginsproducing a plateau in the action potential tracing. h. At rest, contractile cells have a resting membrane potential of about -90 mV. i. As the calcium is pumped out of the cell and back into the SR, the contractile cellrelaxes j. A small voltage change (of about 5 mV to about -85 mV) occurs, which initiatesdepolarization.

1.h, 2.b ,3.f, 4.j 5.c, 6.g, 7.a, 8.e, 9.d, 10.i

Match the following events in autorhythmic cells: A. Repolarization B. Pacemaker Potential C. Depolarization and reversal of the membranepotential x. due to influx of sodium y. due to efflux of potassium z. due to influx of calcium

A- y B-x C- z

How do the cardiac autorhythmic cells and cardiac contractile cells work together to produce a coordinated heart contraction?

Action potentials generated by autorhythmic cells create waves of depolarization thatspread to contractile cells via gap junctions.

What is responsible for the pacemaker potential?

Autorhythmic cells begin depolarizing due to a slow continuous influx of sodium, anda reduced efflux of potassium.

What is the function of gap junctions?

Gap Junction connects adjacent cardiac cells. This allows ions to pass between cells,allowing a ripple effect of initiating depolarization in one cell, and then another, andso on.

What is responsible for reestablishing ion levels in autorhythmic cells?

Ionic pumps actively transport calcium back to the extracellular space during repolarization. Na+/K+ pumps also pump sodium out and potassium in.

(Page 13. ) Are neurotransmitters involved in the transmission of depolarization fromone cardiac muscle cell to another?

No. Gap junctions are electrical synapses which do not depend on neurotransmitters.

When do cardiac contractile cells contract and relax with respect to depolarization and repolarization of the cell.

depolarization= contract repolarization= relax

15. (Page 11.) What allows depolarization to move from autorhythmic cells to the contractile cells?

gapjunctions

What allows depolarization to move from one contractile cell to anothercontractile cells?

gapjunctions

When cardiac autorhythmic and contractile cells depolarize, what happens to the charge inside and outside the cell.

outside - negative inside - positive

3. (Page 5.) Before cardiac autorhythmic and contractile cells depolarize, what is the charge inside and outside the cell.

outside - positive inside - negative

When cardiac autorhythmic and contractile cells repolarize, what happens tothe charge inside and outside the cell.

outside - positiveinside - negative

Where is calcium stored within contractile cells?

sarcoplasmic reticulum (SR)