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lecture_25 - Circulatory systems Pacemaker cells Control by...

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Circulatory systems Pacemaker cells Control by nervous and endocrine systems Spread of depolarization across heart Relaxation of heart
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Control of contraction Vertebrate heart muscle is myogenic Cardiomyocytes are electrically coupled with gap junctions Pacemaker cells are generally located in sinoatrial (SA) node
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Pacemaker cells Membrane potential (= pacemaker potential) is not stable In all cells, there are potassium leak channels, but in pacemaker cells, potassium permeability decreases over time There is also a slow inward movement of sodium (funny current) When pacemaker potential reaches threshold, voltage-gated Ca 2+ channels open (T-type Ca 2+ channels) Ca 2+ channels close and K + channels open, leading to repolarization Fig. 9.20/ 8.23
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Control of heart by nervous system and endocrine system Pacemaker potentials are affected by K + , Na + and Ca 2+ channels Nerves and hormones can affect these channels E.g., norepinephrine from sympathetic neurons and epinephrine from adrenal medulla (Fig. 9.21/ 8.24) E.g., acetylcholine from parasympathetic
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