BMS 300 1st Edition Lecture 20 Outline of Last Lecture I. Membrane potential to action potential and propagation-role of K+, A-, & K+ leak channels in Restin’s membrane potential -role of Na+ channels to switch polarity -concept of ion permeability 1. membrane potential seeks the equilibrium potential of the ion whose permeability is dominant II. The Action Potential -sequential openings and closing of ion channels 1. V-gated Na2. V-gated K+ III. Na+ channel properties -voltage/charge sensitive -inactivates-closes IV. Propagating potentials -in membrane lacking v-gated channels -unmyelinated conductile regions -myelinated conductile regions 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.Outline of Current Lecture V. Action Potential Propagation -in membrane lacking v-gated channels 1. concept of decrementing potential -in membrane with v-gated channels but no myelination 1. concept of the regenerating potential-in membrane with v-gated channels clustered at nodes of ranvier 1. concept of conduction VI. From generation potential to action potential in a sensory neuron -DNA as molecules of life 1. stores information about RNA structures 2. RNA structure stores information about protein structure VII. The generation potential -opening stretch-activated channels -amplitude of the potential is proportional to the strength of the stimulus-reaching threshold -propagating the potential Current LectureRecap from last lecture: -cylinder membrane with an outside and an inside -the outside concentration of Na is 120-130 mmol -the Na concentration on the inside is 10 mmol -the K concentration on the outside is 4-5 mmol -the K concentration on the inside is 110 mmol -the way we set up the thought experiment is to only put v-gated channels on one end-when we add positive charge the gates swing open and allow sodium to get in-there is a membrane potential which means there has to be leak channels -the leak channels are selective for potassium -if we put electrodes along the length of the cylinder, what happens? >what the fate of the depolarization? >the leak channels are taking the positive charge out of the membrane **the positive charge is leaking out of the membrane and because of this it gets smaller and smaller because of the distance **by the time it gets all the way down the membrane it gets less and less **imagine this is a garden hose with faucets that can open and let water in as the leak channels ***this is propagation of decrementing potential (smaller and smaller with distance) Propagating a regenerating action potential in an unmyelinated neuron -same drawing as the last one -the only difference is that instead of having the v-gated channels on one end of the membrane they will now be at regular small intervals all the way down the membrane -the same thought experiment as above -we have positive charge that opens gates and it’s a chain reaction -the positive charge goes down the membrane in a rolling fashion -the action potential at each end is identical to the beginning of the membrane and at the end of the membrane-propagation velocity is about 1 meter/second **the concentrations inside and outside **when these channels open the concentration won’t change on the inside and the outside, thepositive charge changes the membrane potential **action potential hardly changes the membrane potential at all Myelination of a conductive region -we have an axon with concentric rings of myelin around and around the axon -the myelin achieving the conductile region **reminder of what the myelin looks like Rules for propagating potential in a myelinated axon -very close to above >instead we will add layers and layers of insulation and -same image with a cylinder but have an onion wrap arrangement around each side -nodes of ranvier >uncovered/naked regions of the conductive plasma membrane >there are no v-gated channels in these regions>v-gated potassium channels are right under the nodes-the regions in between the nodes are the intermodal regions -we still need v-gated channels that are responsible for the action potentials -the v-gated sodium channels are clustered at the nodes -if we add positive charge the delivery of positive charge causes channels to open and then sodium is let into the sites -its not the movement itself, the sodium has an electromagnetic field -aka it only cares if it sees the effect of the ion not necessarily making direct contact -the effect of the electromagnetic field can only manage to go down a couple nodes >this is called sulcatory conduction (to hop)-the more myelin the faster the conduction***use this image to understand all three of the topics
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