The Synapse

[Music] hi it's Paul Andersen and in this video I'm going to talk about the synapse which is a connection between adjacent neurons that's a pretty strict definition remember neurons can also be connected to effector cells in our body but if we look at this and are on here in this neuron the information has to get from this axon to this cell body or to this dendrite and then the same thing down here and we use synapses to do that we're mostly going to be talking about chemical synapses in this video in a chemical synapse you have an action potential move down an axon it triggers the release of neurotransmitters into this gap or this cleft right here they're going to dock with chemically gated channels on the other side and that can lead to an action potential on the other side some of the early work done with neurotransmitters was done by Otto LOI he had this dream of a wonderful experiment in the middle of the night dealing with the heart of a frog he wrote it down but when he woke up in the morning he couldn't read his handwriting thankfully he had that same dream again and this is how the experiment that led to a Nobel Prize win he had the heart of a frog that was beating and then he would stimulate the vagus nerve on the surface of the heart and what that does is slow the beating of the heart so we're sending a message to the heart he then took another heart from a different frog but he removed the vagus nerve so there's no neuron there he got it beating but he moved some of the liquid from the stimulated heart to the non stimulated heart and it slowed down as well what did that mean there was something in the liquid he discovered these neurotransmitters and he discovered a chemical synapse in a chemical synapse a action potential moves down a nerve down a neuron it triggers the release of neurotransmitters into the gap that are going to dock with receptors on the other side now that's only one type of synapse we also have electrical synapses and an electrical synapse and action potential is going to move down and again that's triggered by these voltage-gated channels once it gets to that synapse it's going to open up more voltage-gated channels and the message is going to go and electrical synapse if you have an action potential in the neuron before the synapse you're going to have an action potential in the one after what's great about electrical synapses is that they're very very fast what's bad about them is that there's no control so let's talk about chemical synapses identify the different parts of it so this would be where the information is coming in so on this neuron and this would be the cell body of the the adjacent neuron so we have a presynaptic side and a postsynaptic neuron and then this little gap in the middle is going to be synaptic cleft now there are structures that hold this in place is not just floating there on the inside of that terminal bud we have synaptic vesicles and those are filled with neurotransmitters those are different chemicals chemical messages that can be sent across that synaptic cleft there's some other anatomy that we should cover there are going to be voltage-gated channels on the terminal but those are going to be calcium ion channels we also have docking proteins for vesicles on the presynaptic side and then we're going to have receptors on the postsynaptic side and so if we remove all of those terms let's see what happens so first thing that happens is we have an action potential that's moving down this neuron here if you don't understand what an action potential is I'll put a link to a video that I made on those so the action potential comes down and what that's going to do is the depolarization of that neuron is going to open up these calcium voltage-gated channels now the electrochemical gradient for that those calcium ions is into the neuron itself and so they're going to moved in and they'll dock with chemicals on the surface of those vesicles they're going to activate proteins on those surfaces and what allows those to do is to connect with other docking proteins on the surface of the presynaptic side and allows those vesicle membranes to merge they then dumped their neurotransmitters out into the gap where they can dock with these chemically gated channels on the other side so they're sending a message through those neurotransmitters now the neurotransmitters will quickly then break apart some are broken down some are recycled back into those synaptic vesicles but let's see what's going on so there are a number of different channels in every neuron they're going to be leak channels for sodium and potassium what those do is establish this resting potential we also have voltage-gated channels those are important in the transmission of that action potential but here we're talking about receptors these are chemically gated channels so when the neurotransmitters gap with it they can open it up what does that do well it can move us towards or away from an action potential so in action potential is when we hit this threshold of negative 85 millivolts that's determined by these voltage-gated channels but what can happen in an excitatory neurotransmitter and it a neurotransmitter that's pushing us towards the threshold is that it is increasing the voltage it's moving it closer to that threshold what's a quick way to do that if we have a receptor on the postsynaptic side that allows the flow of sodium into the neuron that sodium is quickly going to depolarize the neuron and move us closer to the action potential now some of those neurotransmitters may be inhibitory what they're doing is they're allowing the flow of ions but these are ions that are moving us away from that action potential what's a quick way to do that we could release a bunch of potassium or Lord allow chloride to come into the cell itself but if you think about it a neuron is then receiving information from all the the neurons that are connected to it that are telling it to either fire an action potential or not what are they really doing they're sending either excitatory those are depolarizing messages the influx of sodium that is starting to trigger an action potential or inhibitory those are ones that are allowing potassium out or chloride in and they're stopping that message from from being sent and so we really have an analogue side to a neuron and a digital side the summation of all of those signals all those neurotransmitters either tell that action potential to fire or not it's going to move down that axon now remember when we get to the end they're going to be terminal buds here again calcium gates are going to open up and we're going to have those new neurotransmitters that are Center across now when you remember things so if you can remember things early from this video a lot of that has to do with connections in neural pathways in your brain and what we're starting to find is that when you really remember something that as we fire action potentials as we have more of these synapses being activated what we have is long term potentiation and so if we look at what's going on here if we keep firing this neuron we've done this in the lab we keep firing and releasing neurotransmitters on the postsynaptic side the cell will actually develop and build more of these receptors so it's more susceptible to that and so we're building pathways of memory over time and that's really what memory is it's a set of neural pathways that are firing inside your brain so that's the chemical synapse and if you can remember a lot of the parts on this pre and postsynaptic side you're well on your way to improving your memory and I hope that was helpful [Music]

Channel: Bozeman Science

Views: 382,146

Rating: 4.9525537 out of 5

Keywords: educational videos, science videos, high school science, synapse, neuron, chemical synapse, electrical synapse, neurotransmitter, calcium channel, synaptic vesicles, presynaptic neuron, Otto Loewi, post synaptic neuron, long term potentiation, nervous system, action potential

Id: L41TYxYUqqs

Length: 7min 8sec (428 seconds)

Published: Mon Feb 06 2017