Cardiac Muscle TIssue

Question 1

What do valves do?

Answer 1

prevent blood from flowing in the wrong direction.

Question 2

What does the right heart do?

Answer 2

pumps blood to the lungs

Question 3

What does the left heart do?

Answer 3

pumps blood through circulation to various parts of the body.

Question 4

What does the atrium do?

Answer 4

It is a primer pump for a ventricle and moves blood to it.

Question 5

What is a cardiac muscle referred to as?

Answer 5

syncytium

Question 6

What are features of cardiac muscle tissue?

Answer 6

it is striated, mononucleated, has discs and branching cells.

Question 7

What is the plateau?

Answer 7

Region of the cardiac action potential that stays flat for a period of time before repolarization occurs. It allows contraction to last 15 times longer in cardiac tissue.

Question 8

What is a purkinje fiber?

Answer 8

A fiber that conducts an AP in the ventricular wall. It is a modified cardiac muscle cell.

Question 9

How are the T-tubules and SER different in cardiac muscle fibers?

Answer 9

The t-tubules are larger and the SER is not as extensive.

Question 10

Where are fast cardiac action potentials found?

Answer 10

in the atria, ventricles and conduction system. They are rapidly conducting and contractile with a high amplitude.

Question 11

Where are slow cardiac action potentials found?

Answer 11

the SA and AV nodal tissues; they automatically depolarize during resting phase and have a low amplitude.

Question 12

How many phases are in the fast action potentials?

Answer 12

4

Question 13

What is the resting potential of a fast action potential?

Answer 13

-90 mV

Question 14

What phase is the resting potential?

Answer 14

4

Question 15

What phase does depolarization occur

Answer 15

0; Fast Na channels open and depolarize to +20 mV.

Question 16

What phase does incomplete repolarization occur?

Answer 16

1; Na closes and K opens

Question 17

What phase does the plateau occur, and why does it occur?

Answer 17

2; Ca channels open and K close; increased Ca and decreased K causes plateau

Question 18

What phase does repolarization occur?

Answer 18

3; Ca closes, slow K opens, K rapidly enter and resting potential is restored.

Question 19

What causes fast action potentials?

Answer 19

changes in conductance of K, Na and Ca ions. The conductance pattern is due to voltage dependent gates.

Question 20

What results in a greater conduction velocity?

Answer 20

greater AP amplitude, more rapid rate of rise of phase 0, larger cell diameter.

Question 21

What are features of slow action potentials?

Answer 21

no fast sodium ion gates, smaller change in potential

Question 22

What is the resting phase potential of of a slow action potential?

Answer 22

-60 mV

Question 23

What are characteristics of fast type contractile myocytes?

Answer 23

large diameter, high amplitude and rapid onset of potential.

Question 24

What are characteristics of fast type non-contractile muscles?

Answer 24

large diameter and rapid upstroke

Question 25

What are characteristics of slow type non-contractile myocytes?

Answer 25

small diameter, low amplitdue and slow rate of depolarization.

Question 26

What causes an action potential in a ventricular fiber?

Answer 26

the opening of fast sodium channels and slow calcium-sodium channels.

Question 27

Where does the calcium come for the electrical-mechanical coupling?

Answer 27

from the T tubues via diffusion through voltage-gated calcium channels.

Question 28

What cannot be generated during an absolute refractory period?

Answer 28

another action potential

Question 29

What determines the length of the refractory period?

Answer 29

the ability of ion channels and gates to return to phase 4 (resting membrane) state.

Question 30

What determines the rhythmicity of the cell?

Answer 30

the rate of depolarization; gradual depolarization is caused by special Na channels that open during phase 4

Question 31

What tissues gradually depolarize during phase 4?

Answer 31

SA and AV nodes, purkinje fibers.

Question 32

Which node usually reaches threshold first and becomes the normal pacemaker of the heart's rhythmicity?

Answer 32

SA node

Question 33

What allows fine control over sarcoplasmic calcium concentration and contractility?

Answer 33

fewer calcium induced calcium release channels.

Question 34

What results in relaxation of cardiac muscle fibers?

Answer 34

SERCA and sodium-calcium exchanger in the sarcolemma