Here are the lab objectives for the Synaptic Integration, Synaptic Transmission lab. By the end of the lab and by the end of the post-lab questions, you should be able to do all these objectives. Last lab, we focused on the Acts Potentials or the events that happen at the axon headlock up through the axon or the propagation of action potentials. This lab we are going to be focusing on the events that happen at the synapse of two neurons.
Right, so before we move on talk about the lab let's review some concepts right so when that exponential spreads down the axon it arrives at the exon terminal and when it arrives at the exon terminal it's going to open in voltage-gated calcium channels When we open a voltage-gated calcium channels, we're going to get calcium influx. Remembering back to our intracellular communication lab, we learned that calcium can have its own cell response. The cell response that calcium is going to have at the exoterminal is it's going to cause the exocytosis.
neurotransmitter. That neurotransmitter right is then going to bind to ligand gated channels on the dendrites and cell body or soma. the post-synaptic neuron or cell.
When that neurotransmitter binds to the ligand-gated channels on the post-synaptic cell, that neurotransmitter will then cause a post- synaptic potential or a PSP. PSPs are a type of graded potential. So let's spend some time and talk about and compare contrast graded potentials and ax potentials. Graded potentials have summation right so they can sum together.
Ax potentials cannot summate because of the absolute absolute refractory period. Ax potentials can travel through saltatory conduction. Action potentials are going to be all or none. We are either going to have them or not. There's not any like half action potentials.
Grade potentials can be excitatory or inhibitory. Grade potentials are decremental or they lose strength as they travel away from the stimulus gray potentials involve ligand gated channels on sub body dendrites. Axial potentials involves voltage gated channels on the axon hillock.
axon and grade potential strength related to strength of the stimulus so stronger stimulus means a stronger grade of potentials well axon potentials they're all or none so it doesn't matter if it meets that threshold it doesn't matter how strong the stimulus is they're all going to be the same let's talk about spatial versus temporal summation right remember that gravity is looking some right so they can add together or subtract from each other right temporal summation is when the stimulus comes from one pre-symmetric neurons that fires repeatedly over time. let's say it says stimulus stimuli right multiple stimulus stimuli right so it's like think of this like a person's thing at your front doorbell regular doorbell just repeatedly over time over time that sound will build and make a larger stim make a larger um sound within the house spatial summation comes from when the stimuli comes from multiple pre-symmetric neurons. Think someone at your front door, someone at your back door, ringing the doorbell at the front door and the back door at the same time. In that case, the sound will get louder, but it's coming from two different areas, right?
It's going from the back door and the front door. Well, temporal summation is only coming from the front door. but both of these have to occur pretty close at the same time. All right so let's figure out net electrochemical gradients. All right this practice problem we're using potassium.
All right and remember how we set these up in lecture. First we kind of draw out where the concentration of these ions are. potassium is higher inside the cell than outside the cell our next thing is to determine the charge of the cell by that we look at the membrane potential of the cell since this is positive 25 that tells you that the the cell is more positive in the icf than the ecf now we can answer actually answer these questions. So chemically it goes from high to low so therefore it's going to go from the cell out into the ECF. All right electrically it's going to go towards its opposite charge since we're dealing with potassium with a positive charge it's going to be attracted to the negative ECF.
And then finally to figure out electrochemical direction, electrochemical gradient, which way is that, does that ion have to move to get the membrane potential of the cell equal to the equilibrium potential of the ion. Since we're going to go from positive 25 down to negative 90 and we're doing the positive ion, that means that that ion will have to leave the cell and enter the ECF. Another practice problem here, we have higher concentration of ions inside the cell in comparison to outside the cell. The charge of the cell is positive 30 millivolts, so that tells you that the charge of the ICF is positive, the charge of the ECF is negative. Chemically, this ion will want to leave the cell because it's going to travel from high to low.
Electrically, since we're dealing with an anion, it has a negative charge, so this is going to be attracted to the ICF, which is positive, because opposites attract. And then finally, this ion will have to go from, to move the member potential of the cell closer to the equaler potential of the ion, means that that negative ion will have to enter the cell. and we want to bring that member potential closer to its equal potential of negative 20. So this one we have a cation. It's higher outside the cell than inside the cell. The member potential of the cell is positive five so that means that the ICF is going to be positive and the ECF is going to be negative.
So chemically this ion will move into the cell because it's going from high to low. Electrically it's going to move out of the cell because the positive ion is going to be attracted to the negative ECF and to move the member potential closer to the equivalent pictures of ion it's already there so that means that there will be no net movement of ions because it's already at its equilibrium potential. So that way we label a double-headed arrow in and out.
And finally, we have another practice problem here. We have a cation, which is higher outside the cell than inside the cell. We have the membrane potential of the cell being positive 30. So that means that the ICF is going to be positive.
the ecf is going to be negative chemically this ion will flow into the cell because going from high to low electrically it's going to leave leave the cell because it can be attracted to the negative ecf and for electrochemical this ion will have to go from positive 30 to positive 5 milivolts So since we're dealing with a positive ion, in order to get that member potential more negative or less positive, that positive ion will have to leave the cell. When your TA asks you to fill this out in lab for your quiz, as you see, I drew the arrows into the cell, right? I've seen in the past where students have dealt, dropped tall or dry arrows beneath the cell.
And that doesn't work. I've seen problems with students do this where a TA might ask for multiple cells and student will just do one cell, electrical, chemical, and electrochemical for each cell. So each cell, so always have three and draw the arrows on the cell not below or above or above, below, to the side. Draw it on the cell. This week in lab, the second exercise or third exercise, we're dealing with synapses.
It's a good idea to try to figure out a way how this actually works. So we'll be changing the number of synapses and changing the conductance, changing the current, changing the equilibrium potential of these ions that are flowing. So before we start, let's define these terms.
Conductance is simply the number open channels current is the number of ions that are moving and the equal impotential is the membrane potential where the electrical and chemical forces equal and opposite and whenever an ion moves it will move the member potential closer to the equilibrium potential. So for example for this scenario right we have one presumptive neuron right we'll call this syn0 that's just terminology this program uses it releases a neurotransmitter right which will then influence the number of how many open channels there are right and when that neurotransmitter opens that channel it's then going to allow ions to move And then it will move the ion, when the ion moves, it will move the member potential of the cell closer to the equal potential of the ion. So here's an example of single synapse.