Contents
What causes cardiac refractory period?
The refractory period in cardiac physiology is related to the ion currents that, in cardiac cells as in nerve cells, flow into and out of the cell freely. The flow of ions translates into a change in the voltage of the inside of the cell relative to the extracellular space.
What does it mean when a heart rhythm is refractory?
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.
What causes the long refractory period in cardiac muscle?
Calcium ions play two critical roles in the physiology of cardiac muscle. Their influx through slow calcium channels accounts for the prolonged plateau phase and absolute refractory period that enable cardiac muscle to function properly.
What determines effective refractory period?
During phases 0, 1, 2, and part of phase 3, the cell is refractory to the initiation of new action potentials. This is termed the effective refractory period (ERP). During the ERP, stimulation of the cell does not produce new, propagated action potentials.
What causes Autorhythmicity?
2. Automicity (Autorhythmicity) – some cardiac muscle cells are “self-excitable” allowing for rhythmic waves of contraction to adjacent cells throughout the heart. Skeletal muscle cells must be stimulated by independent motor neurons as part of a motor unit.
What causes depolarization of cardiac muscle?
In nerve and muscle cells, the depolarization phase of the action potential is caused by an opening of fast sodium channels. This also occurs in non-pacemaker cardiac cells; however, in cardiac pacemaker cells, calcium ions are involved in the initial depolarization phase of the action potential.
Why are refractory periods important?
The refractory period limits the rate at which action potentials can be generated, which is an important aspect of neuronal signaling. Additionally, the refractory period facilitates unidirectional propagation of the action potential along the axon.
What are the two types of refractory periods?
There are two types of refractory periods; the absolute refractory period, which corresponds to depolarization and repolarization, and the relative refractory period, which corresponds to hyperpolarization.
What causes hyperpolarization?
Hyperpolarization is often caused by efflux of K+ (a cation) through K+ channels, or influx of Cl– (an anion) through Cl– channels. While hyperpolarized, the neuron is in a refractory period that lasts roughly 2 milliseconds, during which the neuron is unable to generate subsequent action potentials.
What prolongs the refractory period?
Mechanism of action Procainamide blocks sodium channels and also has an effect on potassium channels and so prolongs the effective refractory period, decreases automaticity and slows conduction.
What increases refractory period?
An increased infusion of the hormone oxytocin during ejaculation is believed to be chiefly responsible for the male refractory period, and the amount by which oxytocin is increased may affect the length of each refractory period.
What is Autorhythmicity Why is the significance of this for heart function?
Heart is a hollow, muscular organ responsible for maintainance of blood flow. It accomplishes that function by being able not only to contract, but to do it without the need of any external stimulus- has autorhythmical capacity.
What causes tachycardia during the relative refractory period?
During the relative refractory period, a new action potential can be elicited under the correct circumstances. The cardiac refractory period can result in different forms of re-entry, which are a cause of tachycardia. Vortices of excitation in the myocardium ( autowave vortices) are a form of re-entry.
Is the cardiac refractory period a relative or absolute period?
In the classical sense, the cardiac refractory period is separated into an absolute refractory period and a relative refractory period. During the absolute refractory period, a new action potential cannot be elicited.
Can a new action potential be elicited during the refractory period?
During the absolute refractory period, a new action potential cannot be elicited. During the relative refractory period, a new action potential can be elicited under the correct circumstances.
When does Phase 1 of the refractory period begin?
Sodium ions enter the cell and cause the surrounding cells to begin to depolarize as well. This causes a wave of contraction to begin throughout the cardiac muscle cells. Phase 1: This phase begins once complete depolarization has occurred and the cell begins to return to its RMP. During Phase 1, calcium and potassium flow out of the cell.