Cardiac Muscle TIssue Flashcards
What do valves do?
prevent blood from flowing in the wrong direction.
What does the right heart do?
pumps blood to the lungs
What does the left heart do?
pumps blood through circulation to various parts of the body.
What does the atrium do?
It is a primer pump for a ventricle and moves blood to it.
What is a cardiac muscle referred to as?
syncytium
What are features of cardiac muscle tissue?
it is striated, mononucleated, has discs and branching cells.
What is the plateau?
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.
What is a purkinje fiber?
A fiber that conducts an AP in the ventricular wall. It is a modified cardiac muscle cell.
How are the T-tubules and SER different in cardiac muscle fibers?
The t-tubules are larger and the SER is not as extensive.
Where are fast cardiac action potentials found?
in the atria, ventricles and conduction system. They are rapidly conducting and contractile with a high amplitude.
Where are slow cardiac action potentials found?
the SA and AV nodal tissues; they automatically depolarize during resting phase and have a low amplitude.
How many phases are in the fast action potentials?
4
What is the resting potential of a fast action potential?
-90 mV
What phase is the resting potential?
4
What phase does depolarization occur
0; Fast Na channels open and depolarize to +20 mV.
What phase does incomplete repolarization occur?
1; Na closes and K opens
What phase does the plateau occur, and why does it occur?
2; Ca channels open and K close; increased Ca and decreased K causes plateau
What phase does repolarization occur?
3; Ca closes, slow K opens, K rapidly enter and resting potential is restored.
What causes fast action potentials?
changes in conductance of K, Na and Ca ions. The conductance pattern is due to voltage dependent gates.
What results in a greater conduction velocity?
greater AP amplitude, more rapid rate of rise of phase 0, larger cell diameter.
What are features of slow action potentials?
no fast sodium ion gates, smaller change in potential
What is the resting phase potential of of a slow action potential?
-60 mV
What are characteristics of fast type contractile myocytes?
large diameter, high amplitude and rapid onset of potential.
What are characteristics of fast type non-contractile muscles?
large diameter and rapid upstroke
What are characteristics of slow type non-contractile myocytes?
small diameter, low amplitdue and slow rate of depolarization.
What causes an action potential in a ventricular fiber?
the opening of fast sodium channels and slow calcium-sodium channels.
Where does the calcium come for the electrical-mechanical coupling?
from the T tubues via diffusion through voltage-gated calcium channels.
What cannot be generated during an absolute refractory period?
another action potential
What determines the length of the refractory period?
the ability of ion channels and gates to return to phase 4 (resting membrane) state.
What determines the rhythmicity of the cell?
the rate of depolarization; gradual depolarization is caused by special Na channels that open during phase 4
What tissues gradually depolarize during phase 4?
SA and AV nodes, purkinje fibers.
Which node usually reaches threshold first and becomes the normal pacemaker of the heart’s rhythmicity?
SA node
What allows fine control over sarcoplasmic calcium concentration and contractility?
fewer calcium induced calcium release channels.
What results in relaxation of cardiac muscle fibers?
SERCA and sodium-calcium exchanger in the sarcolemma
