BIOL 1119 Lecture Notes - Lecture 10: Cardiac Output, Vagus Nerve, Tachycardia

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Karina Da Rosa
1. Cardiac Output
a. Sympathetic Nervous System
i. Secrete norepinephrine
1. Binds to beta adrenergic receptors in the heart
2. Activates cAMP 2nd messenger in nodal cells and cardiocytes
ii. cAMP activates a kinase
1. Activates enzymes or proteins
a. Activated enzyme opens more Na+ channels in the plasma
membrane of nodal cells
2. Activates L type channels
a. Open L type calcium channels in plasma membrane of
cardiocytes more quickly : speed control
3. Activates receptors on calcium channels in the SR
a. Open calcium channels on the SR in order to open the
channels of cardiomyocytes more quickly
iii. In the SA node
1. Opening of special Na+ channels leads to increased influx of
sodium input : brings nodal cell back up to threshold quicker
a. Depolarization occurs quicker, heart rate increases
iv. In cardiocytes
1. More Ca+ channels open on the surface of cells and on the SR
a. More calcium both on the inside and outside
b. Positive membrane potential more quickly
i. Increases the speed of depolarization more quickly :
heart rate deceases
2. Cytosolic calcium concentration
a. Raises more quickly : increases contraction speed
i. Raising heart rate
ii. Pumps Ca+ back into the SR
1. Cardiocytes can repolarize and relax more
quickly
b. More calcium = more troponin = more actin sites = more
crossbridges form = better contraction strength
b. Parasympathetic Output
i. Cardioinhibitory center sends out signals via the vagus nerve
1. Innervate SA and AV nodes
a. Cholinergic and inhibitory effects
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