Assume that an EPSP is being generated on the dendritic membrane. Which will occur? a. specific Na⁺ channels will open, b. specific K⁺ channels will open, c. a single type of channel will open, permitting simultaneous flow of Na⁺ and K⁺ , d. Na⁺ channels will open first and then close as K⁺ channels open.

Video transcript

Welcome back everyone. Our next question says, the excitatory postsynaptic potential epsp refers to a small depolarization of the postsynaptic membrane potential that occurs when an excitatory neurotransmitter binds to its receptor on the post synaptic neuron. What happens when the espiepsp is strong enough to reach the threshold? A an action potential will be generated b the action potential will be lost c the production of neurotransmitters will be blocked or d the transfer of information between the neurons is hindered. So let's think about the situation that's going on here. We have a synapse. So let's draw and excuse my for drawing. This is the end of the axon that's transmitting the electrical signal. So I've drawn a sort of, I don't know, tentacle looking shape here and underneath it, I'll have a sort of sine wave shaped wiggle which is going to be the junctional folds of our post synaptic neuron. So we have a gap between them. That's the synapse. Just our basic um junction diagram here. And we have a release of excitatory neurotransmitters from that axon to the post synaptic neuron. And those neurotransmitters bind to receptors on the junctional folds. So, neurotransmitters, there's not much room on my drawing. So I've drawn an arrow on the outside showing excitatory neurotransmitters moving across the synapse to bind to receptors on the junctional folds. I'll put little dots on there for receptors. So our question is telling us that when these excitatory neurotransmitters bind to these receptors. So when the excitatory neurotransmitters bind to the receptors, the result is a small depolarization of the post synaptic membrane. So in our postsynaptic cell, we have this small depolarization. So some uh positively charged ions migrating out of the cell changing that membrane potential. And let's recall that in general, you have a signal continuing, you have an action potential when there's enough of a depolarization of that membrane that it triggers depolarizations in neighboring cells. So we're saying that we have this little small depolarization. So what we can kind of imagine is maybe uh something teetering on the edge of a cliff and you're giving it a little nudge and you're getting it closer to the edge. So it takes less force to tip it all the way over. And that's essentially what's happening here. This small depolarization brings the post synaptic neuron closer to the firing threshold for that action potential. So you're not actually causing um the electrical signal to continue directly with those excitatory neurotransmitters, but you're bringing it closer to the point at which that will happen. So making it more likely that an action potential will be generated. So again, the question says what happens when the EPSP is strong enough to reach the threshold. When you reach that tipping point, that threshold you have choice A, an action potential will be generated. So just looking briefly over our other answer, choices, choice B says the action potential will be lost. Well, that's the exact opposite of what's going to happen. Choice C, the production of neurotransmitters will be blocked. Well, that would be the action of an inhibitory neurotransmitter, not an excitatory neurotransmitter. So that's not our correct answer. And choice. D the transfer of information between the neurons is hindered. Again, that's the opposite of what will happen. We're increasing the chances that that transfer of information will take place. So again, our answer to what will happen when this Epsp ha is strong enough to cause a post synaptic neuron to reach the threshold choice A and action potential will be generated. See you in the next video.