Sinoatrial Node Cells

Sinoatrial node cells

A) reach threshold only when action potentials generated by the AV node arrive through gap junctions.
B) exhibit spontaneous depolarization that is speeded by activation of their cholinergic receptors.
C) exhibit spontaneous depolarization that is speeded by activation of their beta-adrenergic receptors.
D) exhibit a steep upstroke due to the presence of the same type of Na⁺ channels found in neuronal membranes. 
E) are between atrial muscle cells and cells of the bundle of His.