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151.L1.Lect5_6.Cardiovasc.11.18_20.13.Stu (1)

Stimulation sympathetic nervous system sns increases

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Unformatted text preview: SA node myocardial cells SA 1. Stimulation: Sympathetic nervous system (SNS) - increases heart rate a. Nerve terminal of SNS neuron releases norepinephrine (NE) on to SA node cells (β-adrenergic receptors) b. NE decreases intervals between openings of Na+ channels: a. by increasing activity of Na+/K+ pumps, gets to -90mV faster b. increasing number of Na+ channels opened so that less time to Ca++ channels opening because cytoplasm goes +ve faster, and c. increasing # of Ca++ channels opened So: - increases # beats/min, - increases force of contraction, - so increases systolic blood pressure NE contracts artery smooth muscle, increases blood pressure Opposing Systems Regulate Heart Rate at SA node myocardial cells SA 2. Inhibition: Parasympathetic nervous system (PNS) - decreases heart rate a.Nerve terminal of PNS neuron releases acetylcholine (ACh) on to SA node cells (...
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