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BIO2A03-2011-L12-template - Biology 2A03 Lecture 12...

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1 Biology 2A03 Lecture 12 Circulation VI
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2 Heart affected by changes in rates of AP generated by pacemaker Regulation of heart rate (hr) (both rate & force are regulated) Pacemakers get direct input by autonomic nervous system SNS NE Acts on SA and AV nodes via β 1 adrenergic receptors to increase hr PSNS ACh Acts on SA and AV nodes via M 2 muscarinic receptors to decrease hr Vegus nerve Cardiac nerve (acetylcholine) Predominant factor in setting resting heart rate of 70 bpm (rate without any inputs = 100bpm) SNS and PSNS have opposite effects NOTE : SNS has more connections to myocardium (more effects on force than PSNS)
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3 Hormones (e.g. epinephrine) can affect heart rate Increases hr via same mechanisms as SNS Temperature: directly alters the intrinsic rate of the SA node Changes hr by 15bpm / ˚ C, e.g. 1 deg fever hr is ~85 bpm Regulation of heart rate (hr)-cont…. Molecular Mechanism (neuro- and hormonal): Receptor binding alters ion movements and changes rate of spontaneous AP e.g. Norepi (or Epi) binding to a G-coupled receptor alters Na + and Ca + movement into pacemaker cell (for faster depolarization) Fig 14-23A Shorter time btw AP = faster hr Fig 14-24
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4 Sequence of electrical events that triggers a heartbeat 1 AP initialed in SA node AV node Internodal & interatrial pathway Spreads through atrial muscle 2 Transmission slows down at the AV node by ~0.15sec 3 AP transmitted through the AV node to the Bundle of His
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