![]() ![]() The refractory period of a cardiac fiber is longer than the contraction itself, as a result tetanus cannot occur.After the plateau phase the fiber repolarizes by allowing K +ions to flow out of the cytosol and at the same time the Ca ++channels close.The combined build up of Ca ++ and K + ions causes a delay of up to 250 milliseconds (.25 sec).in addition the fast potassium ion (K +) channels close reducing their effux. ![]() At +30 mV, the Na + channels close decreasing potential, however the membrane then enters a plateau by allowing calcium ion (Ca ++ ) channels to open causing a them to also flow inside the cytosol.An action potential stimulates the contractile fibers to depolarize - voltage gated channels in the membrane to open allowing sodium ions to flow back in the cytosol.The resting membrane potential is created by actively pumping sodium ions (Na +) out of the fiber.The resting membrane potential of the cardiac muscle fiber is -90 mV inside the cell.Rapid, partial early repolarization, prolonged period of slow repolarization which is plateau phaseĪ wave of depolarization that begins in the pacemaker and spreads over the heart (it precedes contraction).Repolarization due to normal K+ effluxĪction Potential of Contractile Cardiac Cells Falling phase at about +20 mV the Ca-L channels close, voltage-gated K channels openĩ. At threshold sharp depolarization due to activation of Ca2+ L channels allow large influx of Ca++Ĩ. Slow influx of Ca++ further depolarizes bringing to threshold (-40mV)ħ. As depolarization proceeds Ca++ channels (Ca2+ T) open before threshold is reachedĦ. Gradual depolarization because K+ builds up and Na+ flows inwardĥ. Constant influx of Na+, no voltage-gated Na + channelsĤ. Decreased efflux of K+, membrane permeability decreases between APs, they slowly close at negative potentialsģ. Membrane slowly depolarizes “drifts” to thresholdĢ.The animation is followed by practice questions. Initiates an action potential which travels throughout heart down to the atrioventricular (AV) node, which slows down the AP before traveling to the atrioventricular bundle (bundle of His) and splits into the R/L bundle branches which spread into conduction myofibers (Purkinje fibers).Ĭlick here for an animation on the conduction system of the heart.They act as a pacemaker and a conduction system.Allow the atria to contract first then the ventricles contract.Use calcium influx (rather than sodium) for rising phase of the action potentialĪutorhythmic cells depolarize spontaneously but at different rates:.membrane slowly depolarizes “drifts” to threshold, initiates action potential, membrane repolarizes to -60 mV.Have “drifting” resting potentials called pacemaker potentials.Intercalated discs allow branching of the myocardium.have a different looking action potential fro other nerve cells due to calcium channels.normally do not produce action potentials.Superior/Inferior vena cava and coronary sinusĬlick here for an animation that summarizes the flow of blood through the heart. Circuit of vessels carrying blood between heart and other body systemsġ.Closed loop of vessels carrying blood between heart and lungs.Regulating blood supply - changes in contraction rate and force match blood delivery to changing metabolic needs.Routing blood, ensuring one-way blood flow, separates pulmonary and systemic circulations.Generating blood pressure to produce a gradient that pushes blood through the vascular system.Transport medium within which materials being transported are dissolved or suspended.Passageways through which blood is distributed from heart to all parts of body and back to heart.Serves as pump that establishes the pressure gradient needed for blood to flow to tissues.The parts of the circulatory system include: ![]()
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