Cardiovascular Physiology n lecturer Dr Ahmed Badr n

Cardiovascular Physiology n lecturer: Dr. Ahmed Badr n Department Of Physiology

Sympathetic and parasympathetic innervation to the heart 2

PNS • SA node • AV node • To lesser extent to atria • Very little to vent SNS • All parts of the heart • Strong representation to the ventricular muscle 3

Effect of the sympathetic stimulation on the SA node Na NE B 1 receotor Ca Adenyl cyclase Na Ca f channel Ca channel Gs protean 4

Effect of the parasympathetic stimulation on the SA node Ach Ca Ca K channels M 2 receptor Gs protean Adenyl cyclase Ca channel Gi protean K K 5

Normal (resting) -40 -60 6

Sympathetic stimulation -40 -60 Reducd repolarization More rapid depolarization 7

Paraympathetic stimulation -40 -60 hyperpolarization slower depolarization 8

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l tia en ot ep pr l a i t ten o p e r p Symp. ↑ slope Parasymp. ↓ slope

About the prepotential, all the following are true except : a) the firing level occurs at a potential difference of about - 40 mv b) Its amplitude is about 80 mv c) its slope is decreased by increased permeability to K+ d) its slope is increased by increased permeability to Ca++.

Regarding the S-A node : a) sympathetic stimulation decreases the slope of the pacemaker potential. b) acetyl choline increases the slope of the pace maker potential. c) The membrane of cells within the S-A node depolarized spontaneously to threshold and initiate an action potential d) All of the above are true