Acetylcholine decrease hea rate by which of the following mechanisms?
In SA Node (SAN) and AV Node (AVN); the phase 4 of action potential is not straight as seen in action potential of non automatic myocardial fibres; hence the SAN and AVN depolarizes automatically. Sympathetic system ( beta receptors), increases the hea rate by increasing the slope of phase 4 of action potential curve of SAN and AVN. Parasympathetic stimulation (ACh) decreases the slope of phase 4 (known as diastolic depolarization) and hence causes bradycardia by action of ACh on M2 receptors (Gi GPCR) of mainly SA node. M2 receptors acts the following 3 mechanisms 1. opening of ACh sensitive potassium channels 2. inhibition of funny currents 3. inhibition of calcium channels.
By decreasing the rate of diastolic depolarization of SA node
By causing delay through AV node
By blocking calcium channels and prolonging the plateau phase
By reducing the rate of ventricular repolarization
Parasympathetic System & Glaucoma