The Electrocardiogram And Excitation-Contraction Coupling

Front 1

The electrocardiogram (EKG or ECG) is

Back 1

a means of recording electrical activity of the heart from externally-applied electrodes.

Front 2

For ECG, the P-wave

Back 2

corresponds to depolarization of the atria

Front 3

For ECG, the ORS complex

Back 3

is the result of ventricular depolarization.

Front 4

For ECG, the T-wave

Back 4

is the result of ventricular repolarization

Front 5

The EKG can be used to detect

Back 5

abnormalities in electrical events

Front 6

The EKG cannot be used to detect

Back 6

abnormalities in mechanical activity unless it also causes electrical disturbance.

Front 7

Atrial depolarization occurs ________ ventricular depolarization.

Back 7

before and separated from.

Front 8

The role of the AV node is

Back 8

to delay transmission of AP from atria to ventricle.

Front 9

The pacemaker of the heart is

Back 9

SA node.

Front 10

SA node is the pacemaker of the heart because

Back 10

it drives AV node to threshold.

Front 11

A wave of depolarization coming towards a positive electrode will cause ________ on ECG.

Back 11

positive deflection

Front 12

A wave of depolarization going away from a positive electrode will cause ________ on ECG.

Back 12

negative deflection

Front 13

The ultimate stimulus for cardiac muscle contractions is

Back 13

the increase in cytosolic Ca2+ concentration

Front 14

For excitation-contraction coupling in the heart, AP induced on the plasma membrane are carried into the cell by

Back 14

T-tubules

Front 15

For excitation-contraction coupling in the heart, during the plateau phase of the cardiac AP

Back 15

calcium flows into the cells.

Front 16

For excitation-contraction coupling in the heart, extracellular calcium triggers

Back 16

release of Ca2+ from SR.

Front 17

For excitation-contraction coupling in the heart, extracellular calcium activates

Back 17

contraction process

Front 18

For excitation-contraction coupling in the heart, the increase in cytosolic Ca2+ concentration that initiates contraction is the result of

Back 18

Ca2+ being released from the SR and entering the cell from outside.

Front 19

For excitation-contraction coupling in the heart, during repolarization Ca2+ is removed from cytosol by

Back 19

1. Primary active Ca2++-ATPase pump into SR, and 2. Primary active Ca2+-ATPase pump and Ca2+/Na+ exchanger out of the cell.

Front 20

The amount of free Ca2+ that is available to trigger the process of cross-bridge formation is a direct determinant of

Back 20

the strength of cardiac contraction.

Front 21

Mechanisms for controlling the strength of contraction occur through

Back 21

factors that increase or decrease the amount of free Ca2+.

Front 22

The steps of excitation-contraction coupling in the heart are

Back 22

1. Depolarization of plasma membrane, 2. Opening of plasma membrane L-type Ca2+ channels in T-tubules, 3. Flow of Ca2+ into cytosol, 4. Ca2+ binds to Ca2+ (ryanodine) receptors on surface of SR and opens Ca2+ channels, 5. Cytosolic Ca2+ concentration increases, 6. Cross bridge cycling and contraction.

Front 23

Examples of control mechanisms to change free calcium concentrations are

Back 23

autonomic nervous system and drugs.

Front 24

The refractory period of cardiac muscle lasts

Back 24

almost as long as mechanical contraction

Front 25

During the refractory period of cardiac muscle, _______ can not be elicited.

Back 25

further muscle contractions

Front 26

The refractory period of cardiac muscle is due to

Back 26

long plateau phase seen in cardiac AP.

Front 27

Unlike skeletal muscle, is impossible to produce _______ in cardiac muscle.

Back 27

Tetanic contractions.