BMS 300 1st edition Lecture 31 Outline of Last Lecture I. Cardiomyocyte structure and function -cardiomyocyte type 1. conductile >deliver electric signal to contractile cells >set rate and rhythm 2. contractile >generate force >sarcomere shorteningII. Structure of cardiomyocytes -intercalated disks -gap junctions III. Electrical signaling -conductile1. HCN channels (generator potential) 2. v-gated Ca2+ channels 3. v-gated K+ channels -contractile 1. v-gated Na+ 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.2. v-gated Ca2+3. v-gated K+-membrane structure of contractile cells 1. T-SR junction 2. Ca2+ induced Ca2+ releaseOutline of Current Lecture IV. Interface between conductile and contractile-action potential in contractile cells 1. the channels (v-gated Na, Ca2+, K+)2. the effect >ca2+ induced calcium release >anatomy of the T-SA junction 3. the electrocardiogram >electrical currents in contractile myocardiumV. Autonomic modulation of the heart -anatomy of autonomic systems 1. CNS 2. PNS ganglia 3. target VI. Parasympathetic innervation -vagus-cardiac ganglion-g-protein coupled receptor VII. Sympathetic innervationCurrent LectureTo recap last lecture-we recall the interface between a conductile cell and a contractile cell -by the time the action potential has propagated through the conductile system to the parkinje fibers we are no longer dealing with the pacemaker action potential -we have conductile action potentials that are passing electromagnetic fields from one cell to the next through gap junctions **the distribution of channels is extremely important -in the contractile cells we see many channels >v-gated Na+ channels >v-gated Ca2+ channels dihydropurine receptors >v-gated K+ channels -all of these channels are working in concert to generate the cardiac contractile action potential -they all work at the T-SR junction to release Ca2+ from the sarcoplasmic reticulum -in the contractile cells there are Z-lines >have the attachment of actin thin filaments >these are characterized by having filamentous actin, trophin complexs (trophin C), and tropomyosin -all of the rules of muscle contraction apply here as well -there is an extension of the sarcolemma called the transverse tubule -there are regions with sarcoplasmic reticulum and just about touches the t-tubule membrane -when we look at what happens at the interface: >sarcoplasmic reticulum: ca2+ storage > along the sarcolemma there are v-gated sodium channels -when the gate on the sodium channel swings open there is now an influx of sodium ions which causes us to reach threshold -and we get the influx of sodium to produce depolarization >not much over 0mm-the v-gated sodium channels inactivate -there’s a very long plateau that is produced from the influx of Ca2+ through v-gated Ca2+ channels (dihydropyrine receptors)-their function is to allow calcium into the cell from the extracellular environment -in the sarcoplasmic reticulum is the rhymaine receptor which is opened by the Ca2+ influx-this process is calcium induced calcium release -that calcium rains down on to the sarcomeres, which binds to the trophonin C -aka classic muscle contraction -after all this occurs there is the opening of the v-gated potassium channels which then closes the ca2+ channels and stops the release of calcium -this makes contraction stop -then there’s a period of diastolic filling when the blood is flowing into the ventricles -we are then resetting the sarcomeres, waiting for the action potential from the conductile system to arrive **this pattern happens throughout life, when it stops so do we -the nervous system is not telling the heart to beat every time it has its own generators Autonomic nervous system -affects cardiac muscle, smooth muscle, and glands -recognize that there are a number of roles -its role on cardiac muscle is the conductile and contractile cardiomyocytes -sympathetic branch: fight or flight-parasympathetic branch: rest and digest Central nervous system:-there will always be a neuronal cell body -sends a process out into the periphery -which is the autonomic ganglion in the PNS -sends a process out and innervates a target-one issue we will always see is the neuron with a cell body in the CNS (preganglionic autonomic neuron) -in the periphery it synapses onto the postganglionic autonomic neuron -in all cases the neurotransmitter released from the 1st cell releases astrochyline -the input region contains nicoytinc acetylcholine -the “target” is the heart-here we release neurotransmitter -postganglionic synapse onto the target releases acetylcholine for the parasympathic branch but for the sympathetic branch it releases norepipherine -in both cases the neurotransmitter released binds to a G-protein coupled receptor **G-protein coupled receptor leads to activation or inhibition of adenocyclase (converts adenicinetriphosphate into cyclic
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