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Lecture 12 FA2017 Cardiovascular Physiology Continued Ch.14 Last time: ECG and the conduction pathway through the heart http://commons.wikimedia.org/wiki/File:ECG_principle_slow.gif Name: Eddy Age: Newborn Tetanus caused by bacteria Clos. tetani Bacteria blocks inhibitory neurotransmitter (e.g. GABA) signaling from CNS Prevalent in developing world, without immuniz. practices, hospital standards Easily preventable with vaccination But Eddy’s heart was still contracting AND relaxing Heart generates high pressure by contracting. Must go through highly coordinated contraction: Heart generates high pressure by contracting. Must go through highly coordinated contraction: How do the heart generate contraction?? How does it differ from skeletal muscle? Heart generates high pressure in arteries by contracting. So what kind of cells in the heart generate contraction? Cardiac contractile cells vs. Skeletal Muscle Cells • Smaller than skeletal fibers and have single nucleus • Cardiac cells branch and join neighboring cells through intercalated disks – Desmosomes allow force to be transferred – Gap junctions provide electrical connection “Pacemaker” cells spontaneously generate APs https://www.youtube.com/watch?v=rpHg6Kpe76A How do cardiac muscle cells contract? Here’s where stuff starts to get reeeeal interesting First step: need to be “excited” Figure 14.12 ACTION POTENTIALS IN CARDIAC AUTORHYTHMIC CELLS Autorhythmic cells have unstable membrane potentials called pacemaker potentials. The pacemaker potential Ion movements during an State of various ion channels gradually becomes less negative action and pacemaker until it reaches threshold, potential triggering an action potential. 20 Ca2+ channels close, K+ channels open 0 Ca2+ in K+ out Lots of Ca2+ channels open −20 Threshold −40 2 Ca2+ in Some Ca + channels open, If channels close −60 If channels Membrane potential (mV) Membrane potential + Net Na in If channels open Pacemaker Action open potential potential K+ channels close Time Time Time “Funny”GRAPH QUESTIONS voltage gated Na+ channels automatically re- 1. Match the appropriate phases 2. Which of the following would speed up the of the myocardialopen contractile once depolarization cell repolarizes rate of the pacemaker potential?to -60 mV. cell action potential (Fig. 14.10) (a) increase in Ca2+ influx to the pacemaker action (b) increase in K+ efflux potential above. (c) increase in Na+ influx An unstable resting(d) none membrane of these potential leads to spontaneous action potentials in pacemaker cells Network of autorhythmic cells coordinates heart’s electrical activity ~70 bpm ~50 bpm }~25-40 bpm The yellow cells in the conduction system above are all autorhythmic cells Figure 14.12 ACTION POTENTIALS IN CARDIAC AUTORHYTHMIC CELLS Autorhythmic cells have UNSTABLE membrane potentials called pacemaker potentials. The pacemaker potential Ion movements during an State of various ion channels gradually becomes less negative action and pacemaker until it reaches threshold, potential triggering an action potential. 20 Ca2+ channels close, K+ channels open 0 Ca2+ in K+ out Lots of Ca2+ channels open −20 Threshold −40 2 Ca2+ in Some Ca + channels open, If channels close −60 If channels Membrane potential (mV) Membrane potential + Net Na in If channels open Pacemaker Action open potential potential K+ channels close Time Time Time GRAPH QUESTIONS 1. Match the appropriate phases 2. Which of the following would speed up the of the myocardial contractile depolarization rate of the pacemaker potential? cell action potential (Fig. 14.10) (a) increase in Ca2+ influx to the pacemaker action (b) increase in K+ efflux potential above. (c) increase in Na+ influx (d) none of these Figure 14.12 ACTION POTENTIALS IN CARDIAC AUTORHYTHMIC CELLS Autorhythmic cells have UNSTABLE membrane potentials called pacemaker potentials. The pacemaker potential Ion movements during an State of various ion channels gradually becomes less negative action and pacemaker until it reaches threshold, potential triggering an action potential. 20 Ca2+ channels close, K+ channels open 0 Okay, so this is the Ca2+ in K+ out Lots of Ca2+ channels open autorhythmic−20 AP. We then need Thresholdto excite the actual −40 2 contractile cells before Ca2+ in Some Ca + channels open, If channels close −60 If channels Membrane potential (mV) Membrane potential they contract. + Net Na in If channels open Pacemaker Action open potential potential K+ channels close Time Time Time GRAPH QUESTIONS 1. Match the appropriate phases 2. Which of the following would speed up the of the myocardial contractile depolarization rate of the pacemaker potential? cell action potential (Fig. 14.10) (a) increase in Ca2+ influx to the pacemaker action (b) increase in K+ efflux potential above. (c) increase in Na+ influx (d) none of these Figure 14.12 ACTION POTENTIALS IN CARDIAC AUTORHYTHMICThe AP CELLS in autorhythmic cells in the Autorhythmic cells have UNSTABLE membraneheart potentials is most called pacemaker like: potentials. The pacemaker potential Ion movements during an State of various ion channels gradually becomes less negative action and pacemaker until it reaches threshold, potential triggering an action potential. A.) AP in the somatic motor neuron 20 B.) AP in a muscle fiber Ca2+ channels close, C.) Ca2+ release in the muscleK+ channels fiber open 0 Okay, so this is the Ca2+ in K+ out Lots of Ca2+ D.) Mannnn I don’tchannels know! open autorhythmic−20 AP. We then need Thresholdto excite the actual −40 2 contractile cells before Ca2+ in Some Ca + channels open, If channels close −60 If channels Membrane potential (mV) Membrane potential they contract. + Net Na in If channels open Pacemaker Action open potential potential K+ channels close Time Time Time GRAPH QUESTIONS 1. Match the appropriate phases 2. Which of the following would speed up the of the myocardial contractile depolarization rate of the pacemaker potential? cell action potential (Fig. 14.10) (a) increase in Ca2+ influx to the pacemaker action (b) increase in K+ efflux potential above. (c) increase in Na+ influx (d) none of these Now let’s look at the AP in cardiac contractile cells Name: Eddy Age: Newborn Tetanus diagnosis. But Eddy’s heart was still contracting AND relaxing Turns out the AP in cardiac contractile cells have unique property that prevents tetanus Review: AP in neuronal/skeletal muscle cell More Positive Charge Inside I II 0 Time More Potential Difference Potential Negative Across Cell Membrane Charge Inside III AP in cardiac contractile cell Figure 14.10 Slide 1 PX = Permeability to ion X +20 0 -20 -40 Depolarization spreads from autorhythmic cells via gap PNa -60 junctions. -80 Takes cell to threshold. Membrane potential (mV) Membrane potential Just like a graded potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Na+ channels open *The phase numbers are a convention. Figure 14.10 AP in cardiac contractile cell Slide 1 PX = Permeability to ion X +20 0 -20 -40 -60 PNa -80 Membrane potential (mV) Membrane potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Resting membrane potential of contractile cells in the heart is -90 mV. Compare this to the RMPNa + ofchannels skeletal open muscle fibers (-70 mV). What might explain this difference for cells at “rest”? A.) Contractile cells are more permeable to calcium B.) Skeletal muscle fibers have greater permeability to K+ C.) Contractile cells are relatively impermeable to ions other than K+ *The phase numbers are a convention. © 2013 Pearson Education, Inc. Figure 14.10 AP in cardiac contractile cell Slide 2 PX = Permeability to ion X PNa +20 0 -20 -40 -60 PNa -80 Membrane potential (mV) Membrane potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Na+ channels open Na+ channels close *The phase numbers are a convention. © 2013 Pearson Education, Inc. Figure 14.10 AP in cardiac contractile cell Slide 3 PX = Permeability to ion X PNa +20 PK and PCa 0 -20 -40 -60 PNa -80 Membrane potential (mV) Membrane potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Na+ channels open Na+ channels close Ca2+ channels open; fast K+ channels close *The phase numbers are a convention. © 2013 Pearson Education, Inc. Figure 14.10 AP in cardiac contractile cell Slide 4 PX = Permeability to ion X PNa +20 PK and PCa 0 -20 P and -40 K PCa -60 PNa -80 Membrane potential (mV) Membrane potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Na+ channels open Na+ channels close Ca2+ channels open; 1st set of “fast” K+ channels close Ca2+ channels close; 2nd set of “slow” K+ channels open *The phase numbers are a convention. © 2013 Pearson Education, Inc. Figure 14.10 AP in cardiac contractile cell Slide 5 PX = Permeability to ion X PNa +20 PK and PCa 0 -20 P and -40 K PCa -60 PNa -80 Membrane potential (mV) Membrane potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Na+ channels open Na+ channels close Ca2+ channels open; 1st set of “fast” K+ channels close Ca2+ channels close; 2nd set of “slow” K+ channels open Resting membrane potential (-90mV) *The phase numbers are a convention. What are two thingsFIGURE that QUESTION look different about this AP compared to Compare ion movement during this action potential to ion the onemovement that of aoccurs neuron’s action in potential skeletal [Fig. 8.9, muscle p. 256]. fibers? © 2013 Pearson Education, Inc. Figure 14.10 AP in cardiac contractile cell Slide 5 PX = Permeability to ion X PNa +20 PK and PCa 0 -20 P and -40 K PCa -60 PNa -80 Membrane potential (mV) Membrane potential -100 0 100 200 300 Time (msec) Phase* Membrane channels Na+ channels open Na+ channels close Ca2+ channels open; 1st set of “fast” K+ channels close Ca2+ channels close; 2nd set of “slow” K+ channels open Resting membrane potential (-90mV) *The phase numbers are a convention. Where do you thinkFIGURE the QUESTION inactivation gate closes? Where do you think Compare ion movement during this action potential to ion movement of a neuron’sit action opens? potential [Fig.
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