The relaxation is essential so the heart can fill with blood for the next cycle. The refractory period is very long to prevent the possibility of tetany, a condition in which muscle remains involuntarily contracted. In the heart, tetany is not compatible with life, since it would prevent the heart from pumping blood.
What is the absolute refractory period of cardiac muscle?
The absolute refractory period of the cardiac muscle action potential refers to the time interval when the voltage gated sodium channels are inactivated. The absolute refractory period lasts ~180 msec.
Why is the plateau phase of the cardiac contractile cells so important?
Phase 2 is the plateau phase of the cardiac action potential. Membrane permeability to calcium increases during this phase, maintaining depolarization and prolonging the action potential.
Why is it important for all the cells in cardiac muscle to be totally linked?
Because they are connected with gap junctions to surrounding muscle fibers and the specialized fibers of the heart’s conduction system, the pacemaker cells are able to transfer the depolarization to the other cardiac muscle fibers in a manner that allows the heart to contract in a coordinated manner.
What is the refractory period of muscle contraction?
refractory period – The time interval, after a muscle fiber has been stimulated and a contraction has been achieved, which has to pass before the muscle cell can be stimulated to contract again; it is prolonged in cardiac muscle.
How long is a refractory period?
The length of the refractory period varies greatly from person to person, from a few minutes to 24 hours, or longer.
What happens during the refractory period in the heart?
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.
Why is there a plateau phase in cardiac muscle?
Phase 2. This phase is also known as the “plateau” phase due to the membrane potential remaining almost constant, as the membrane slowly begins to repolarize. … This phase is responsible for the large duration of the action potential and is important in preventing irregular heartbeat (cardiac arrhythmia).
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.
Which of the following is unique to cardiac muscle?
One feature unique to cardiac muscle is the presence of intercalated discs. These were originally believed to be another type of striation or stripe. From studies of these bands with the electron microscope it can be seen that these discs represent the end-to-end junction of adjacent cardiac muscle cells.
Why is heart Autorhythmic?
The heartbeats of the heart are autorhythmic, which means the heart produces its own pulses through electrochemical stimuli originating from a small group of cells in the wall of the right atrium, known as the sinoatrial node (or SA node).
What are the two types of cardiac muscle cells?
Structure. There are two types of cells within the heart: the cardiomyocytes and the cardiac pacemaker cells. Cardiomyocytes make up the atria (the chambers in which blood enters the heart) and the ventricles (the chambers where blood is collected and pumped out of the heart).
Is cardiac muscle striated?
Cardiac muscle cells are located in the walls of the heart, appear striated, and are under involuntary control.
What is the refractory period and why is it important?
The refractory period is important because it allows us to adjust briefly to a stimulus and limits the amount of action potentials sent per minute.
What happens during muscle contraction?
During muscle contraction, the heads of myosin myofilaments quickly bind and release in a ratcheting fashion, pulling themselves along the actin myofilament. At the level of the sliding filament model, expansion and contraction only occurs within the I and H-bands.
What is depolarization in muscle contraction?
Skeletal muscle contraction and changes with exercise. (A) Neurotransmitter (acetylcholine, ACh) released from nerve endings binds to receptors (AChRs) on the muscle surface. The ensuing depolarization causes sodium channels to open, which elicits an action potential that propagates along the cell.