The ratio VS/VM is referred to as the volumetric phase ratio, b. Hence:

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#Id: 5284

#Unit 7. System Physiology – Animal

The rate of spontaneous discharge increases Norepinephrine secreted by the sympathetic endings binds to β1 receptors

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#Unit 7. System Physiology – Animal

Increase in intracellular cAMP facilitates the opening of L channels, increasing ICa and the rapidity of the depolarization phase of the impulse.

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#Id: 5286

#Unit 7. System Physiology – Animal

When the cholinergic vagal fibers to nodal tissue are stimulated, the membrane becomes hyperpolarized and the slope of the prepotentials is decreased

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#Id: 5287

#Unit 7. System Physiology – Animal

Acetylcholine (ACh), released from parasympathetic nerve fibers, activates muscarinic (M2) receptors in the SA node.

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#Id: 5288

#Unit 7. System Physiology – Animal

Activation of the M2 receptors decreases cyclic adenosine 3′,5′-monophosphate (cAMP) in the cells, and this slows the opening of Ca 2+ channels.

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#Id: 5289

#Unit 7. System Physiology – Animal

βγ subunit of a G protein, open a special set of K + channels. The resulting IKAch slows the depolarizing effect of Ih .