Cardiovascular System notes - Cardiovascular System...

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Cardiovascular System Conduction System 1) Cells: a. Autorhythmic fibers- pace setters (conduction system) b. Contractile fibers- contract ventricles 2) Pathway: a. SA Node (pace makers)- initiates action potential (FAST 100 beats/minute); communicates AV Node around atrium i. Can be replaced by artificial pace maker b. AV Node (SLOW 40-50 beats/minute), fibers are smaller & slows down action potential/beat to give time for the atrium to dump the blood into ventricles or contract fully, then sends message to Bundle of His c. Bundle of His d. Bundle Branches, then goes around ventricles through e. Purkinje fibers- larger fibers so message will go faster f. Contractile fibers, then it will contract 3) Influences: a. Autorhythmic fibers set pace b. Nervous system **Does NOT set pace i. Sympathetic- increase heart rate ii. Parasympathetic- decrease heart rate c. Endocrine system **Does NOT set pace i. Hormones- increase heart rate ii. Neurotransmitters- decrease heart rate Action Potential in Ventricular Fiber (Response to autorhythmic cells) [skeletal muscle system has no plateau phase; only present in heart] - depolarization (excitation)- change of inside membrane potential from negative to positive via pumping in Na+ ** Depolarization leads to contraction - repolarization - back to resting by pushing K+ outside so that inside membrane potential goes from positive to negative -contractile fibers in the heart have a resting membrane potential (-90 mV) because if they didn’t it would cause them to be in a permanent state of contraction which would prevent blood from pumping in & out **Your heart is a PUMP, so it contracts & relaxes 1) Rapid Depolarization a. Opening of FAST voltage gated Na+ channels at sarcolemma Autorhythmic fibers initiate action potential, once they get to contractile fibers via gap channels they just excite voltage gated channels 2) +20 mV (max) Na+ becomes inactive —activation gate closes because no more Na+ needs to come in 3) Plateau a. opening of SLOW voltage gated Ca+ channels at sarcolemma Difference between cardiac and skeletal muscle is small SR, which means less Ca+ ions. The extra Ca+ has to come from ECF **Ca+ is needed for muscle contraction (review chapter 10) b. opening of some voltage gated K+ channels —this balances it so that membrane potential does not go back up (maintains plateau) 4) Repolarization a. Closing of SLOW voltage gated Ca+ channels b. Opening of additional voltage gated K+ channels to get back to resting Refractory Period -Absolute—no signal can re-excite system
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-Relative—only strong signal can re-excite system -Contractile fibers in heart have a LONG absolute refractory period to maintain O2 supply for protection so that it does not go through tetany (permanent contraction) -fuzed tetanus- permanent contraction (no relaxation) -unfuzed tetanus- contract in spasms and increase in intensity Cellular Respiration Cardiac muscles make ATP in two ways: 1) Aerobic cellular respiration- produces a bunch of ATP 2) Creatine Phosphate- recharges ATP in a 1:1 ratio EKG (ECG) 1)
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