The Nervous System

In this episode, we learn about the Nervous System, focusing on the branches of the nervous system, the structure of neurons, supporting cells, and action potentials. If you have any questions, suggestions, or corrections, please email themcatquizshow@gmail.com

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SPEAKER_01 0:03

See what you've done. I don't know who you are. I don't know where you are, but you may want to start changing your ways or changing your name.

SPEAKER_03 0:30

Thanks for the intro, PatCovens. Welcome everyone to the MCAT Quiz Show. I'm Arnold Schwarzenegger. And joining me today, as always, is my favorite podcast host, Isaac. Let's not waste any time and get right into the episode. But first, if you haven't listened to the intro episode yet, make sure you do that first. So today's topic is the nervous system. Uh-huh. I'm actually quite nervous right now because I haven't hit my protein goals yet today. I still need to eat another six raw eggs. Anyways, Isa, are you ready to start with the first question?

SPEAKER_00 1:02

Yep. Thanks for the intro, Arnold. Let's get started.

SPEAKER_03 1:06

Round one. Fight.

SPEAKER_00 1:09

And like other episodes, we are now covering topics that we may have already discussed. So keep that in mind that you may see some overlap with other episodes. But this is a good opportunity for you to test if you actually remember what you learned in a previous episode and try to connect different topics because the MCAT is a connected test. They're not going to isolate questions saying, this is the nervous system question. It's all going to be in the bio-biochem section for these topics. And even across sections too. You may see some overlap with chemphys and with psychsoach. So keep that in mind. But let's get started with our first question. The sodium potassium pump is a primary active transporter that pumps how many sodium ions out of the cell for every how many potassium ions into the cell. And to answer this, I like the memory Q extra salty banana because we know that bananas are high in potassium. And salt is sodium, so extra salty. You can think of the salt on the outside of the banana, on the on the peel, maybe, just sprinkled outside. So you're gonna have that salt, extra salty because you're having three going out, because it's on the outside of the banana, and then two going in with that potassium. So three sodiums out, two potassiums in, extra salty banana. Okay. Next question. Which branch of the nervous system consists of the brain and spinal cord? This is the central nervous system. Which branch of the nervous system consists of the nerves outside of the brain and spinal cord? This is the peripheral nervous system. How about the branch that consists of sensory and motor neurons? And this is called the somatic nervous system. How about the branch that consists of nerves that control body parts that we do not control? And this is the autonomic nervous system. So somatic versus autonomic. Those are the two choices you're gonna have after you decide central or peripheral. Okay, after that, let's say for example we pick somatic, we're in the somatic branch still. The question is, which type of neurons transmit sensory information to the spinal cord? And these would be called afferent neurons. Afferent. And what are afferent neurons also known as? They are also known as sensory neurons because you are using them to sense information from your environment. What kind of neurons transmit motor information from the brain to the muscles for movement? So if it's not afferent, it is efferent, efferent neurons. And what are efferent neurons also known as? And they are also known as motor neurons because you're using them to transmit information to your muscles. So let's say, for example, I uh you know feel a feature on my sh shoulder. That would be afferent, right? I'm sensing information from my environment. And let's say my brain wants to tell me to fli to take that feather off of my arm because I'm maybe ticklish or something, then that would be the Eferent neurons. Those are your motor ones. Okay. And how about in your autonomic nervous system? Which branch of the nervous system is involved in the fight or flight response? And this is the sympathetic nervous system? And how about the branch that is involved in the rest and digest response? This is the parasympathetic nervous system. So how do we remember which is parasympathetic and which is sympathetic? Well, I've said it before, but I like to think of s snake. If you see a snake sympathetic, you are going to fight or flight. Uh I'd probably die, but those are your options. And if you are having a huge all-you-can-eat sushi meal, and you sit down on the couch, you probably feel pretty paralyzed. Your stomach's full, and that's when you want to rest and digest. So paralyzed and parasympathetic. Okay, next question. In a neuron, the bulky part where the organelles are located is called what. And this is called the soma. The soma of a neuron is also known as what. It's known as the cell body. Because always remember the etymology, the origin of the word soma in Greek means body. So I'd encourage you to always take a look at the words, and it's going to help you in your future medical career. Next question. In a neuron, chemical signals are received from nearby cells by what? They are received by dendrites. And if these words are not making sense to you, never heard of a dendrite before, just look up a diagram of a neuron. Just Google it. Diagram of a neuron. And you always want to visualize things. So and anytime I mention a concept that you're not familiar with, look up a picture, it's going to help you visualize. So we went over the cell body. You should know where that is now. And we went over the dendrites. But the next question is in a neuron, signals from multiple dendrites meet up where? They're going to meet up at the axon hillic. In a neuron, the rod-like structure is what? It is the axon. And in a neuron, the axon is insulated by what? Insulated by myelin sheath. Which cells make the myelin sheath? These are called glial cells. And what are glial cells also known as? They are also known as neuroglia. Neuroglia. Okay, in the CNS or central nervous system, myelin is made by what? It's made by oligodendrocytes. Oligodendrocytes. Okay, how about the PNS or the peripheral nervous system? Myelin is made by what there? And the PNS, it is made by Schwann cells. So CNS, oligodendrocytes, PNS Schwann cells, and make a make a memory cue for that as well. Which cells form the blood brain barrier while nourishing neurons? These are called astrocytes because they look like a star, right? Astro meaning star. Which cells make cerebrospinal fluid? These are called ependemal cells or ependemal cells. Which cells are phagocytic and break down waste near nerve cells. These are called microglia. Between separate myelin sheaths are small areas of the axon that are exposed, known as what? These small areas that are exposed are called the nodes of Renvier. So you got all this myelin on your axon, but some parts are exposed, and those are the nodes of Renvier. Okay. What does the what do the nodes of Renvier do? What is the purpose? And their purpose is to help propagate the signal that's going down the axon. Uh it's through a complex process, and we might get to that later. Uh but definitely know that that's where that takes place. Okay, what is the space between the presynaptic and postsynaptic neurons called? This is the synaptic cleft. At the end of an axon, the signal reaches which membrane? It reaches the presynaptic membrane. And this is where the chemical signal will be sent out of what? It's going to be sent out of something called nerve terminals. Nerve terminals. Nerve terminals are also known as what they are known as synaptic boutons. After the nerve terminal, the neurotransmitters reach which membrane where the signal will continue to be propagated? So after the nerve terminal, the neurotransmitters reach the postsynaptic membrane. Postsynaptic. The chemical molecules that get transmitted between nerve cells are called what? These are called neurotransmitters. Easy one there, freebie. So when we look at this entire structure, right, of a neuron, if it helps try visualizing different parts, maybe as a human body, that's what I like to do. And obviously it looks like kind of a worm like street um creature, but the reason I like to visualize it like that is because I can understand how the signal moves through the neuron. So if we go back to our dendrites, our dendrites are gonna be like our hands. So imagine you were just lying down on the floor, and someone else is lying down just above you. They're also lying down, but not beside you, but above you. So your hands, your hands are reached above your head and they're touching the person's feet. And your feet are gonna be touching the other person's hands, uh, the next person. You have like a big chain of people, and they're all just lying on the ground in like a long line. Okay? So your hands that are reached up over your head are you gonna be your dendrites. And you're gonna wiggle around your fingers, maybe all the little dendrites, and you're gonna collect a piece of information from the person above you. Um and they're gonna transmit that information, kind of weird, but through their feet. And that information that you got from your hands is gonna go then to your body. Uh and your body in this case is gonna be your head. Because in the neuron, the the cell body, or um, you know, that kind of looks like a head, a little round head. So that's what I think of. I think the signal comes from my hands, then reaches my head. And from my head, I'm going to propagate that signal through the axon hillock. The axon hillock is basically like your neck. Okay? Yep, and then it's gonna go to the axon. And the axon is the rest of your body. It's like really long, right? So you can picture the rest of your body being really long. And then once you get to your feet, your feet are gonna be the end. And your feet in this case are gonna be the axon terminals, right? It's terminating the axon. And that's where you have your presynaptic membrane, your nerve terminals, your synaptic cleft, it's a space in between. So the space in between your toe, which is the nerve terminal, and in between the other person's hand, because they're actually not touching your hand. They're just really, really close. That space between someone else's finger that's laying beneath you, or not really beneath you, but just like, you know, next in line in this long chain. Their hands, their hand, the fingertip of their hand is gonna be the postsynaptic membrane, and the little edge of your toe is gonna be the presynaptic membrane, and the space in between is the synaptic cleft. So I don't know, it's kind of a weird example, but that's what makes sense to me. Just picture a whole bunch of people lying down in a long chain, and this message is getting passed along from person to person. Okay. But obviously at the end of the day, you know, use your own analogies and what makes sense to you. Okay, next question. Glutamic acid is an amino acid neurotransmitter that does what to nerve cells in the brain? Glutamic acid excites. Okay. How about um GABA and glycine? They are also amino acid transmitters. What do they do to signals? They inhibit signals. And which monoamine neurotransmitter regulates mood, eating, and sleeping? And this is uh this is one that you definitely should know. This is serotonin. Serotonin. And anytime you hear a name like that, it's an easy layup, easy allube to make a memory cue. So serotonin, I think of Sarah, just a girl named Sarah, and she's tonin. And make it more personal. Pick someone that in your life that you know that's named Sarah. I'm sure you know one at least. Pick someone the name is Sarah and just imagine them like toning, like they're working out, you know, they're getting toned. And somehow connect that, that your figure of Sarah getting toned, to regulating mood, eating, and sleeping. So you can think, oh no, she's happy while she's she's uh working out, then after she works out, she's gonna be eating a lot because she's gotta make up for all that energy she spent, and she wants to replenish her muscles, and she's gonna get such a good workout that she's gonna be so tired and she's gonna go to sleep. So just make a little make a little story for yourself, and that's a really easy way to memorize things. Okay. Which monoamine neurotransmitter makes people feel rewarded? This one you should know as well. It's dopamine. An easy story well, like I think of dope, you know. Not like that kind of dope, not like drugs, but dopamine, you know? Wow, what a dope feeling you get. People feel rewarded. You know, easy, easy. Which monoamine neurotransmitters make people more active and attentive? These are epinephrine and norepinephrine. And if you see the terminology adrenaline and noradrenaline, just know that those are the exact same thing. They're just uh, you know, UK English versus American English, but exactly the same thing. And epinephrine and norepinephrine, they can be subcategorized as what? Kind of a broad question, but they are catecholamines. Catecholamines. Which peptide hormones decrease pain and increase pleasure? And these are endorphins. So my memory cue there is I'd like to think endorphin and dolphin, you know, endolphin. And I think of a little dolphin swimming around and they are decreasing people's pain at whatever they are when you look at a dolphin, you feel really happy. So you're decreasing your pain and you're increasing your pleasure. Easy stuff. But you know, you should know what these I'm sure you know what these are already. But just in case, you don't know, I don't want to assume. Okay, next question: which neurotransmitter is involved in the autonomic nervous system and in making muscles contract? This is acetylcholine or acetylcholine. And you also should know generally how muscles contract. That's super important as well. So we're probably gonna get into that actually in our musculoskeletal episode that's coming up soon. At rest, a nerve cell is polarized to how many millivolts? It's polarized to minus 70. If a strong excitatory input is detected by dendrites of a neuron, what is triggered where electrical impulses are relayed through the axon to the synapse? What do you what gets triggered if you have a strong excitatory input? That would be an action potential. And this is super important. If you don't know what an action potential is, definitely look it up. Look up a diagram as well. You want to be familiar with the graph of how the different millivolts work. In neuron depolarization, what kind of summation occurs when multiple signals are sent out in a short period of time? This is called temporal summation. Temporal summation. And what about when multiple neurons send a signal at the same time? This is called spatial summation. So what's the difference? Temporal is when multiple signals are sent out in a short period of time, but spatial is when you have multiple neurons sending a signal at the same time. So let's say, for example, you're lying down in that same scenario, you have your hands outstretched, all your fingers outstretched, and you have like ten people's, this is kind of weird, but you have like ten people's toes right connected to your fingertips. That would be spatial summation, because you have multiple neurons sending a signal at the same time. But temporal is different. Temporal is when you just have the one person connected to you, but it's gonna be multiple signals sent out in a short period of time. They're gonna keep sending signals super frequently. What is the threshold for an action potential? If we talk to both an action potential, what it is. How many millivolts does it take? It's gonna be minus 55, right? So at rest we said it was minus 70. And the threshold we need for an action potential or an AP is minus 55. So we have to go from 70, sorry, minus 70 to minus 55. We need to increase ourselves by plus 15. During an action potential, a neuron will reach a maximum charge of what? What's the highest it can get? It can get to plus 35 millivolts. That's gonna be the peak. During an action potential, the cell is depolarized when which kind of channels open? And remember, depolarized means you're we're becoming less negative, aka more positive. We're going up on our diagram. And the cell is depolarized when sodium channels open. And during an AP, not an afterparty, but an action potential, the cell is repolarized when which channels open? So repolarized is going the other way. We're going down our diagram, now we're becoming more negative. And this happens when potassium channels open. After neuron repolarization, no amount of stimulation can cause another action potential during which period? This is called the absolute refractory period. And not that kind of refractory period. Yes, I know what you guys are thinking. No. This is slightly different. But same concept. Refractory period means you can't do something during that time. So no amount of stimulation, no matter how much you stimulate, whatever you're thinking about, an action potential can't happen. That's called the absolute refractory period. No matter what you do, it can't happen. But how about after neuron repolarization, greater than normal stimulation would be needed to send out another action potential during which period? So now it's not impossible, but we need greater than normal stimulation. And that's called the relative refractory period. Okay. The impulse of a neuron is propagated through what kind of conduction? Where the do depolarization travels from one node of Ron VA to the next. So remember those nodes of Rom VA, those are just little gaps in our axon. How is this uh neuron propagated through. It's a process called saltatory conduction. And this process is basically those gaps where there's no myelin sheath, a lot of ions can flow in and out. So think about it that way, you know, you have a chance to reset, recharge, kind of. So there's a lot of flow during the spots, but there's no flow of those ions in the myelin sheath. That's the protected areas. Okay. During an action potential, when the signal reaches the tip of the axon, which kind of channels open? These are calcium channels. And the whole process of you know action potentials is very important. It's a very high yield topic in the MCAT, so definitely look up a video explaining this process. You gotta have the whole thing memorized and understood because they can change any little portion you need to know how that affects the whole chain. Okay, well that is the last question. So that's all for me. I hope you enjoyed and I hope you learned something new or refreshed your current understanding. Once again if you have any questions corrections or suggestions please feel free to email me. And with that I will pass the mic back to Arnold for a final message.

SPEAKER_03 23:16

Thanks, Isa I learned a lot from this episode. If you guys also benefited from this podcast please feel free to leave us a review as it helps us reach more students. And for all the listeners out there you got this but hold on I just need to answer this little kid's question first.

SPEAKER_01 23:31

What's the matter?

SPEAKER_03 23:32

I have a headache it might be a tumor it's not a tumor it's not a tumor at all baby I'll be back in the middle of the