What is meant by the absolute refractory period?
: the period immediately following the firing of a nerve fiber when it cannot be stimulated no matter how great a stimulus is applied. — called also absolute refractory phase. — compare relative refractory period.
How long is the absolute refractory period?
about 0.4 ms
Why is it harder to fire a second action potential in the relative refractory period?
The time when no action potential can be generated, no matter the strength of the stimulus. Why is it harder to generate a second action potential during the relative refractory period? Voltage gated K+ channels that oppose depolarization are open during this time, this opposition requires a stronger stimulus.
Do muscle fibers have a refractory period?
Skeletal muscle fibers transmit action potentials in a way very similar to those seen in neurons. Because of that inactivation, there is technically a refractory period in muscle.
How does the threshold change during the refractory period?
How does the threshold change during the relative refractory period? The threshold that must be achieved is higher than the original stimulus intensity during the relative refractory period.
How does Mg2+ block the effect?
When a small amount of calcium is added back, a small amount of synaptic vesicles are released. How does Mg2+ block the effect of extracellular calcium on neurotransmitter release? When magnesium is added to the extracellular fluid it blocks the calcium channels and inhibits the release of neurotransmitter.
Why is it called relative refractory period?
The cell membrane cannot immediately produce a second AP. As voltage-gated Na+ channels transition from the inactivated to the closed state (i.e., they become capable of being activated), the membrane becomes capable of supporting a 2nd action potential – this period is called the RELATIVE REFRACTORY PERIOD.
What are the three periods of the refractory phase?
The total refractory period is comprised of the (1) absolute refractory period (ARP) or effective refractory period (ERP), which is the period during which an electrical stimulus will not elicit an AP because the membrane is not sufficiently repolarized and sodium channels have not completely recovered; (2) relative …
What is the absolute refractory period of cardiac muscle?
The absolute refractory period for cardiac contractile muscle lasts approximately 200 ms, and the relative refractory period lasts approximately 50 ms, for a total of 250 ms.
What is action potential duration?
One major difference is in the duration of the action potentials. In a typical nerve, the action potential duration is about 1 ms. In skeletal muscle cells, the action potential duration is approximately 2-5 ms. In contrast, the duration of cardiac action potentials ranges from 200 to 400 ms.
What are the 4 classes of antiarrhythmic drugs?
Antiarrhythmic drug classes:
- Class I – Sodium-channel blockers.
- Class II – Beta-blockers.
- Class III – Potassium-channel blockers.
- Class IV – Calcium-channel blockers.
- Miscellaneous – adenosine. – electrolyte supplement (magnesium and potassium salts) – digitalis compounds (cardiac glycosides)
What happens if you block sodium channels?
Complete block of sodium channels would be lethal. However, these drugs selectively block sodium channels in depolarized and/or rapidly firing cells, such as axons carrying high-intensity pain information and rapidly firing nerve and cardiac muscle cells that drive epileptic seizures or cardiac arrhythmias.
What is a Class 5 antiarrhythmic?
Class V / other agents Adenosine is used intravenously for terminating supraventricular tachycardias. Magnesium sulfate, an antiarrhythmic drug, but only against very specific arrhythmias which has been used for torsades de pointes.