BIOL 460 1st Edition Lecture 20Outline of Last Lecture I. Cardiac Cycle ContinuedII. Valve sounds III. Electrical Activity of the Heart IV. Electrical Activity of cells of SA nodea. Pacemaker potential Outline of Current Lecture Current Lecture1. Electrical activity of myocardial cells a. Graph in notes.(ventricular)b. We have atrial myocardium and ventricular c. Myocardial cells do have resting membrane potential of about -90d. SA node generates AP, which are spread though heart, eventually they encountermyocardial cells in ventriclei. When they do the AP which is depolarization, the AP depolarizes myocardial cells to threshold and you get sudden depolarization.ii. Caused by opening of Na voltage gated channelsiii. Opened in response to action potential generated by SA node that are spread out throughout heart.iv. Followed by a phase called plateau phase (last 300ms)v. Plateau phase is where membrane potential becomes more negative and levels out at about -10. vi. Caused by two types of channels:1. Open Ca voltage gated channels- Ca into cells, inside more positive. 2. Open K voltage gated channels, slow, K out, makes inside more negative3. Cancel each other out so membrane pot doesn’t change much These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.vii. Followed by repolarization, K voltage gated channels, faster, K out, Ca close at end of plateau phase and more K open. 2. Conducting tissues of the heart or Cardiac conduction system a. The SA node (pacemaker)i. Initiates action potential1. Spread out over two atria at a speed of about 90 cm/sa. Through atria myocardia, atria contract forcing blood into ventriclesb. Ventricular myocardia is electronically isolated by fibrous skeleton of hearti. Need way to spread from atria to ventricular myocardiaii. We use AV node, slows the pace of action potentials to about 4 cm/second iii. This to allow the atria to pump blood into ventriclesbefore ventricles contractiv. This delay is about .12-.2 seconds 2. AP go from Av node into the bundle of His (AV bundle). Bundle pierces fibrous skeleton of heart and goes into ventricles of heart. Branches into right and left bundle branches. These bundle branches branch into perkenji fibers. Perkinji fibers terminate in papillary muscles. 3. Once AP leaves AV node they get faster and faster. Once in perkenji fibers they are going 500 cm/s3. Excitation contraction couplinga. AP spread into myocardial cells from SA nodeb. Spreads over sarcolemma and down to T-tubulesc. This opens the usual Ca voltage gated channels d. Ca voltage gated channels and a little bit(puff) of Ca goes into cells down electrochemical gradient e. Most Ca comes from SR.f. Release channels in SRi. Ca ligand gated release channels ii. Called Ca induced/Ca release mechanism g. Steep concentration gradient allowing Ca to flow into sarcoplasm from SRh. Ca binds to troponin C of troponin C/tropomyosin complexi. No Ca mechanically coupled release channels i. This causes systole j. To cause diastole i. At end of systole AP stop and Ca voltage gated channels closeii. Ca ATPase pumps (primary active transport) pump majority of Ca in sarcoplasm back to SRk. On pm of cardiac cells are Ca/Na exchangersi. Couple downhill movement of Na into cell with uphill movement of Ca out of the cell. ii. This is secondary active transport. Anti-port iii. Called cotransport proteins 4. Unlike skeletal muscle heart cannot sustain contraction a. Skeletal muscles can by asynchronous activation of motor units i. Also show summationb. Cardiac muscle is organized into myocardium, can’t sustain contraction because of different motor units c. Can;t sustain or undergo summation because they have long refractory period. i. Refractory period is almost same length as systole (300ms) ii. Necessary to fill up with blood. 5. Electrocardiograma. Visual image of electrical image of heartb. machine called electrocardiograph c. DOES NOT look like APi. Bc leads are on skin and heart’s ap cause ion currents are picked up via electrocardiogram d. Most important lead is between right arm and left leg, across hearti. Unipolar-arm and ground ii. Different leads to let you see different conditions e. Electrocardiogram partsi. P-wave= Caused by Atrial depolarizationii. QRS complex= caused by ventricular depolarization 1. When cells of ventricles 2. Occurs when half of ventricular myocardium is depolarized and half is not. iii. Between QRS and T-wave is st-segment= corresponds to plateau phase of action potential, which is duration of ventricular systole iv. T-wave=ventricular repolarization, max amplitude when half atria are depolarized and half are polarized. v. No atrial repolarization, because mass of ventricles is enormous so QRS mask atrial repolarization. f. PR-interval-time between atrial systole and ventricular systole. (.1-.2 s)g. Can detect Cardiac arrhythmias i. Bradycardia- less than 60bpm1. Induced by SA node=sinus bradycardia 2. Normal in athletes ii. Tachycardia- more than 100 bpm at resting 1. At rest is abnormal 2. Caused by drugs or abnormally fast ectopic pacemaker iii. Flutter-extremely rapid rates 200-300 bpm1. Does pump blood but not much a. because not much time to fill with bloodb. Can degenerate into fibrillation- some groups of myocardial cells are generating action potentials and contracting while others aren’t. i. heart doesn’t pump blood just quivers c. Can have atrial flutter—usually degenerates into atrial fibrillation. Can live for years like this, because ventricles are already 80% full of blood without atria pumping d. Ventricular flutter- life threatening, purpose of defibrillator.Parts of myocardium contracting, where as other parts aren’t (circus rhythm) i. Normally when ap is sent up heart it doesn’t turn around and come back due to long refractory period, but scar tissue (non-conductive) slows progression of AP through myocardium, once wave spreads across myocardium some have left , so continuous circling, quivers ii. Also from enlarged heart due to large ventricles cancause it to take long time for AP to cross it, and some cells may be non-refractory causing flutter. iv. AV node block-AV blocked1. Av node has to pass the two atria into the ventricular myocardium. If Av node is damaged it can’t pass wave of AP from atrial myocardium to ventricular. 2. There are three levels of AV node block:a. 1 degree-if