Sinoatrial (SA) 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 muscarinic-cholinergic receptors.
c. exhibit spontaneous depolarization that is accelerated by way of 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 in-between atrial muscle cells and cells of the bundle of His.
Answer: c. exhibit spontaneous depolarization that is accelerated by way of activation of their beta-adrenergic receptors.
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