What is the refractory period in the cardiac cycle?
After an action potential initiates, the cardiac cell is unable to initiate another action potential for some duration of time (which is slightly shorter than the “true” action potential duration). This period of time is referred to as the refractory period, which is 250ms in duration and helps to protect the heart.
Why does cardiac muscle have a longer refractory period?
The refractory period of cardiac muscle is dramatically longer than that of skeletal muscle. This prevents tetanus from occurring and ensures that each contraction is followed by enough time to allow the heart chamber to refill with blood before the next contraction.
Which phase of the cardiac action potential is affected by calcium channel blockers?
Calcium-channel blockers reduce the slope of phase 4, thereby decreasing the rate of spontaneous depolarization, which reduces the rate of pacemaker firing. These drugs also decrease the slope of phase 0, which slows conduction velocity within the AV node.
What are the 5 phases of cardiac action potential?
Membrane currents that generate the a normal action potential. Resting (4), upstroke (0), early repolarization (1), plateau (2), and final repolarization are the 5 phases of the action potential.
What is the function of calcium in cardiac muscle fibers?
Calcium prolongs the duration of muscle cell depolarization before repolarization occurs. Contraction in cardiac muscle occurs due to the the binding of the myosin head to adenosine triphosphate ( ATP ), which then pulls the actin filaments to the center of the sarcomere, the mechanical force of contraction.
What does refractory mean in cardiology?
In electrocardiography, during a cardiac cycle, once an action potential is initiated, there is a period of time that a new action potential cannot be initiated. This is termed the effective refractory period (ERP) of the tissue.
How do calcium channel blockers prolong repolarization?
Calcium channel blockers block conduction cell phase zero. This makes the depolarization even less steep, and prolongs the whole action potential. This is how they slow conduction at the AV node.
What do calcium channel blockers do to muscles?
The calcium channel blockers act by blocking the influx of calcium ions into vascular smooth muscle and cardiac muscle cells during membrane depolarization. Because muscle contraction is largely dependent upon influx of calcium, its inhibition causes relaxation, particularly in arterial beds.
Does calcium cause action potential?
A critical component of the action potential is the rise in intracellular calcium that activates both small conductance potassium channels essential during membrane repolarization, and triggers transmitter release from the cell.
What is the function of calcium in cardiac muscle fibers quizlet?
Calcium is needed to detach the myosin from the actin. Calcium is needed to allow the muscle fiber to become depolarized. Calcium is needed to activate troponin so that tropomyosin can be moved to expose the myosin-binding sites on the actin filament.
What is the role of calcium in the cross bridge cycle?
What is the role of calcium in the cross bridge cycle? Calcium binds to troponin, altering its shape. The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.
What is the refractory period in cardiac action potentials?
The phenomenon of the refractory period prevents a cardiomyocyte from being restimulated by action potentials occurring in adjacent cells to which the action potential has just been spread. In the absence of a refractory period, the cardiac action potential could theoretically bounce back and forth between adjacent cardiomyocytes ad infinitum.
How long do calcium channels stay open after depolarization?
These calcium channels are slow to open following the rapid depolarization phase but remain open for a long time afterwards (i.e. several tenths of a second). Opening of the L-type calcium channel causes an influx of calcium into the cardiomyocyte which initiates Cardiac Excitation-Contraction Coupling.
What is the plateau phase of cardiac action potentials?
This plateau phase prolongs the action potential duration and distinguishes cardiac action potentials from the much shorter action potentials found in nerves and skeletal muscle. Repolarization ( phase 3 ) occurs when gK + (and therefore I Kr) increases, along with the inactivation of Ca ++ channels (decreased gCa ++ ).
What is the effective refractory period in biology?
Effective Refractory Period. The effective refractory period (ERP) is the amount of time in which the cell cannot respond to a new conducted stimulus.