Principal signaling receptor is Frizzled (Fz), contains 

7 TM α helices.

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#Id: 4036

#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: 4037

#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: 4038

#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: 4039

#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 .

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#Id: 4040

#Unit 7. System Physiology – Animal

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#Id: 4041

#Unit 7. System Physiology – Animal