----start physio 1.9.97 b.---- note: exams 1991 to present are the same.... some concepts from last time: cardiac cells. same as other excitable tissue in that ions exist in concentration gradient across semipermeable membrane. potassium leak channels and sodium voltage gated channels are present. and also, different calcium voltage gated and potassium voltage gated channels. these channels have varying sensitivities and times of action. cardiac AP much longer 300 msec (nerve AP 3 msec). differences are related to how voltage and time regulate the different ion channels. at rest, K+ leak cahnnel gives rise to potential. Na+ channels cause depolarization, open Ca++ voltage gated channels, then K+ voltage gated channels cause recovery. don't consider the heart as a simple organ. atria: give rise to p wave ventricles: give rise to qrs SA node sets innate rate of heart, has intense symp and parasymp innervation AV node AV bundles purkinje fibers conducting system. purkinje fibers actually program sequence for ventricular activation. these fibers are all capable of automaticity. (eg, all conducting fibers) heart cells all act as if electrically interconnected. if you pace heart w/pacemaker, you only activate a few cells, but whole ventricle contracts. but anatomically they are separate. they are conencted by gap junctions in longitudinal and transverse directions. are a bit different between ligand gated and voltage gated channels. the connexons are made of connexin. voltage gated channels smallest pores, ligand gated larger pores, then gap junctions have even LARGER pore but are similar otherwise to ligand gated channels. the gap junctions are what allow this electrotonic spread. resistance and capicatance comes in and attenuates signals unless there is an amplification - eg repeated all or none response. when you depolarize the cell, the cell in front of it will also depolarize, see. ELECTROCARDIOGRAM will be on exam. first: p wave: atrial depolarization. small. then Q wave - dips down - also small - R wave = large hill, ventricular depolarization (QRS) - S wave, another dip down - T wave= ventricular repolarization dogs: no clavicle: if moves legs, heart moves a bit, so EKG different. so need to have dog stay still. /\ / \ ___ __/\____ / \ ____/ \____ \/ \/ p q r s t some cells have short activation times, other cells longer. the t wave has a longer duration because the first cells that recover initiate the t wave, then intermediate cells, then longer lasting cells. when ALL ventric cells depolarize, qrs is over. earliest recovery starts t wave. recovery of ALL indicates end of t wave. atrial depolarization: p wave. QRS: ventric depolarization. T wave: recovery P wave: there is an isoelectric period between atrial depolarization and ventricular depolarization. this is the PR (PQ) interval. in normal hearts, impulse is carried through AV node from atria to ventricles. while it is being conducted through AV node you have the PR interval. this delay is needed to ensure ventricular filling. AV node, bundle of His, bundle branches, purkinje fibers--isoelectric period. doesn't show up, really , on EKG< except as interval. can record from bundle directly using catheter threaded into heart but not easy in dogs as it is in humans. if you get a his contraction, you KNOW it's getting through the AV node. so you can isolate problems here. so looking at EKG you get heart rate, you see if conduction is normal, you look at QT interval to see if activation recovery process is ok. Heart activation sequence: same in cat, dog, man. different in ungulates. so at least in cats and dogs we can use this. first area of activation is in ventricular septum. shortest route is to left bundle. activates vent septum [don't need to know sequence. need to realize that there is a sequence, and that is why use different leads and stuff] first goes across septum then activates purkinje system then endocardium to epicardium then finally something he mumbled and i didn't hear :( the way we record these suckers is we actually record as a bipolar recording. put lead one on L and R arm. Lead 2 or legs. record how activation sequence gives rise to EKG. if you look at bipolar recording system, if activation goes from R to L, when it goes from R but hasn't reachd L you get upward deflection, then down when it reaches L. you also record chest leads. put alcohol on skin for good contact. put the clips on the chest itself. i can't duplicate what he's showing onthe slides here, but basically, as impulse travels toward electrode, you will see upward deflection, and when it recovers, it goes back to resting spot. by moving this around and looking for QRS you can find areas of infarct or myopathy. everyone's heart is positioned differently so EKGs are all kinda different. hopefully concept of bipolar recording and chest leads is understood by all (yeah right) amplitude and polarity: small outward vector toward electrode gives small deflection upward. larger gives larger. impulse AWAY from e-trode gives downward deflection. if impulse is toward e-trode is UPWARD, if away, is downward, size of deflection is relative to size of impulse. in dog, overall vector is caudoventral. you record with leads on LA RA and LL with grounding on RL. we're looking at the dog from the side. FRONTAL direction (this should be in handout) -this isn't making sense to me.- point: look at heart, look at vectors resulting from activation process; electrical activity seen by leads differs with direction from which you are looking. there may be an abnormality seen in only one direction. lead II: right arm left leg lead I LA RA lead III: LA LL I RA- --------- +LA \ / \ / \ / \ / \ / LL RA- --------- LA \ / \ / \ / II \ / \ / + LL KNOW LEADS for exam. EXAM: five things...choose the false statement. a question on each of these. Neuromuscular conduction EPSP and IPSP transfer of information # of receptors, etc Pacinian corpuscle squid axon action potential, resting potential, etc. go over back exams! will find the questions. ----end----