BIOL 3800 1st Edition Lecture 8 Outline of Current Lecture I. Compound Action PotentialA. What it means?B. History of fibersC. StimulationII. SynapsesA. SynapsesIII.What Happens in Chemical Synapse?A.Steps In Chemical SynapseB.Review of StepsIV. Synaptic PotentialsA. How Do You Create a Depolarization B. How do you get inhibitory potentials?Current LectureMore on Membrane Potentials Chapter 6I. Compound Action PotentialA. What it means?1. Word compound means a bundle of axons (750,000) in olfactory nerve it may be (2,000,000) (olfactory nerve pure C fibers) but a nerve is a bundle and compound actionpotential looks at whole nerve 2. different groups of fibers will have different conduction velocities you do see a separation B. History of fibers1. Because people didn’t know what was going on a long time ago they just called it A, B, C and to see the B and C fibers was really tough. 2. You stimulate in one place and you have to have long fiber before you see that separation because different groups of fibers will conduct at different speedsC. Stimulation1. We say that our action potential in the single axons always the same size except for relative refractory period which is special case, but you can have it at a relatively slow Hz(meaning frequency) of firing when the action potential is the same size. 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. (Fig 6.7) This one here you can change with the strength of the stimulus because you are looking at 750,000 fibers and the fibers that are closest to the electrode are the onesthat will be stimulated first. So, if you’ve got a certain stimulus current you get a small response the response is a summation of the action potentials that you’re triggering 3. increase the stimulus and you recruit more fibers further away from the electrode. And then a. at some point you pretty much stimulate everybody in that nerve, (That’s alive)… and you get the max compound action potential and after that if you increase the current or voltage you see little smoke and your frying it, then you’ve killed the fibers. 4. So the compound action potential becomes a summation of many individual action potentials. a. It can have different sizes, amplitudes because of the phenomenon of recruitment. That means if you are at low voltage you only get the fibers close to the electrodes. b. Nerve is pretty large structure. So don’t mix up compound action potential andthe individual single action potential. One is a summation the other is a single fiber with action potential propagation. II. SynapsesA. Synapses 1. may be the most complex area in nerve cell. Because not only do you have mitochondria in there but you have all the exocytosis mechanisms and other mechanisms.2. The colorful picture above is an example of chemical synapse not an electrical synapse. a. Electrical synapses are simpler. Electrical synapses in the nervous system are not specialized they just are gap junctions; they serve as electrical synapses in excitatory tissue.III. What Happens in Chemical Synapse?A. Steps in Chemical Synapse1. We have 2 regions the synapse is the whole thing. a. presynaptic bouton or region b. postsynaptic region. i. postsynaptic region could be another nerve cell, muscle cell, or gland cell. It does not have to be the cell body you can make many synapses on dendrites.2. Then we have a sequence of events of what happens we have all these channels and alot of vesicles (could be 700 vesicles in there or (7,000) depending on the size of the synapse. 3. the vesicle inside which have the same kind of membrane structure very similar to theplasma membrane fuse with the plasma membrane and pop open. a. They do not come out; they do not go to the postsynaptic membrane. They stay and become part of the plasma membrane. 4. The vesicles are filled with smaller molecules that we call transmitter. For example, serotonin happens to be a transmitter; glutamate is the primary excitatory transmitter. 5. Whatever is inside diffuses across to special regions that have receptors. a. Synaptic channels are ligand gated channels that means they bind something that’s what a ligand is. So, they are activated by binding of a transmitter. b. Action potential channels are voltage gated channels and are activated by sudden depolarization so those are two different things. c. There is something about specificity you may read in Eckert about reversal potential but skip that.6. Once the transmitters in the gap (the picture exaggerates relative size of gap is for clarity) but transmitter goes everywhere some of it will attach itself to receptor sites andit’s that transmitter interaction with the receptor which opens up the channel 7. Then ions move according to their electrochemical potential, meaning its electrical force but also a chemical potential which is diffusion.a. Transmitter does not get into postsynaptic membrane or across postsynaptic membrane. b. Transmitter dissipates; it’s either hydrolyzed or taken up depending on the transmitter and the type of neuron so you have to get rid of this transmitter. (In fact you have too much transmitter in that synapse and you cannot get rid of it this is exactly how nerve gas works. Nerve gas doesn’t kill cells it simply interferes with that breakdown process and then there is overstimulation and you get spastic paralysis.) 8. After the transmitter is removed or below certain concentration level the channels close most of them and what happens is there is reuptake and this happens mostly at the neck region of the membrane 9. There is a recycling of vesicles they do not have to go all the way up the road to cell body to say they need vesicles. They are reprocessed in the presynaptic bouton .a. Are we making Action potentials at this point? Not yet. 10. This Is a fast synapse and it only has one type of transmitter only has enzymes that’s connected determined to make a certain transmitter like acetylcholine and so that’s all that’s in there. a. You have to know the steps. B. Review of Steps 1. There is an arrival of action potentials at the presynaptic bouton 2. action potential dies out in the presynaptic bouton. a. It will not be transferred to the postsynaptic membrane unless you have an electrical synapse there; we are talking about chemical synapse. b. There is depolarization obviously that’s