Central and Peripheral Nervous System - Online Tutor, Practice Problems & Exam Prep

The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS). The CNS includes the brain and spinal cord, with gray matter on the outside and white matter inside in the brain, while the opposite is true in the spinal cord. The PNS relays information to and from the CNS, comprising the somatic and autonomic systems. Reflex arcs enable quick, involuntary responses to stimuli, bypassing the brain. Key brain regions include the forebrain, midbrain, and hindbrain, each responsible for various functions like sensory processing, motor control, and homeostasis.

Organization of the Nervous System

Hi. In this lesson, we'll talk about the structure and organization of the nervous system. The nervous system can be divided between the central nervous system and the peripheral nervous system. The central nervous system is composed of the brain and the spinal cord, and everything else is considered part of the peripheral nervous system. We often classify the tissue found here as either gray matter or white matter, and that distinction is based on whether the tissue mostly consists of neuron cell bodies or myelinated axons. Remember that myelin is a fatty substance coating the outside of axons. Just like fats appear to the naked eye, when you look at a bunch of myelinated axons, they just kind of look white from all the fat. Whereas the cell bodies take on that gray appearance. You can see that in the brain, the outside of the brain is mostly made up of gray matter. You can see it all along here, this darker stuff along the outside, that's all gray matter. However, there are some pockets within the brain as well. The general trend is that the gray matter is on the outside and the white matter is on the inside. All this business in here, that's all white matter. The organization in the spine is actually the opposite; in the brain, the gray matter is on the outside, and the white matter is on the inside; in the spine, which we're looking at here, this is the spine, you can see that the gray matter is actually found on the inside, right, and the white matter is on the outside. That's just a little pattern to take note of. It's not something you need to stress about, as being super important and related to a bunch of other stuff.

Within the central nervous system, we often find bundles of axons traveling together and we call these tracts. I make this distinction because when we talk about bundled axons outside of the peripheral nervous system, we call them nerves. For our purposes, tracts, nerves, same difference really, we don't need to care too much about those distinctions, but I want to point out the difference in terminology. The brain and the spine are not actually solid masses. The brain has these cavities called ventricles, where the cerebrospinal fluid is produced. That's the fluid that actually bathes the brain and the spine. The spine itself, although you can't see it in this picture, has a teeny little hole in it. This is called the central canal; it's just a hollow tube that runs through the spine. The central nervous system is an incredibly important structure. It is the command center of the body. As such, it needs to be isolated. You often get toxins, pathogens, all that bad stuff in your body. That's what your immune system is for, that's what your liver is for, that's what your kidneys are for, get that stuff out of there. However, the central nervous system is too important to be compromised. It's actually gated from the rest of the body by what's known as the blood-brain barrier. This is an endothelium barrier composed of astrocytes, which are a type of glial cell, and it separates the extracellular fluid of the central nervous system from the blood. You can see this right here. These cells are all astrocytes, and you can see that they are kind of wrapping around this blood vessel. You can see the red blood cells right there. They're wrapping around it to create a barrier. The blood-brain barrier isn't so much like one wall in one location, it's a structure that is very diffuse, but it's super important, and its importance comes from the fact that the central nervous system has to be very carefully regulated, and we don't want toxins, pathogens, any of that stuff getting in, if at all possible.

The peripheral nervous system extends throughout the body and it's made up of nerves, which remember are axon bundles, and ganglia, which are clusters of cell bodies outside of the brain and spinal cord. Similarly to how in the brain, the cell bodies of neurons group together in the gray matter, in the peripheral nervous system, you often see the cell bodies of neurons grouping together and sending their axons together as bundles. You can see here, everything in blue is part of the peripheral nervous system. The spine and the brain are kind of like a yellowish color, and all the other stuff is the peripheral nervous system. You can see it's a very diffuse network that goes all throughout the body. Now, the other thing I want to point out is here we're looking at a section of the spine very similar to this one right here, it's just not as good a picture. But what I want to point out to you is this ganglion; there are ganglia, which is the plural of ganglion, that run along the side of the spine. These are actually known as dorsal root ganglia. They're not the only ganglia of the peripheral nervous system but they're a very important one, and I want to just point them out. And over here, these are nerves that will connect to the spine, and you can see that there are a variety of ganglia there. So, with that, let's go ahead and flip the page.

Peripheral Nervous System

The purpose of the peripheral nervous system is to gather information and relay commands from the central nervous system. So it's going to bring information to the CNS and bring commands from the CNS out to the body. Now, the peripheral nervous system is often divided into a bunch of different categories. One of the major divisions is between what's called the somatic nervous system and the autonomic nervous system. Now the somatic nervous system is usually frequently referred to as the motor system because it controls voluntary movements. It has 2 divisions, the afferent division and the efferent division. F as in 2, ef as in away. So afferent nerves carry sensory information from sensory receptors to the central nervous system. Whereas, efferent nerves carry signals from the central nervous system out to the body. And here, you can see the skin has these nerves connected to it, those are part of the afferent division. They'll go to the spine, which is part of the CNS, and there they might connect with an efferent nerve that's going to go and form a neuromuscular junction on muscle. So, it doesn't always work out this way. The point is there are 2 divisions, some afferent nerves are going to have their signals go all the way to the brain, others will simply stop in the spinal cord. Here, I just want to point out the, this is the primary somatosensory cortex. Basically, that's where all the sensory information from the body is going to come in. And just want to show that this is connected to a particular pathway in the spine, and that will go radiate down and, of course, nerves will exit through the body. So just want to show you that, these efferent and afferent nerves, they're all over the body. It's not just a small little loop like this image implies.

Now, the autonomic nervous system regulates unconscious functions. So the motor system is voluntary muscle movements. Right? The autonomic nervous system can result in muscle movements. However, these are not conscious functions, they are involuntary and unconscious functions. And the autonomic nervous system is really going to control organs of the endocrine system, the cardiovascular system, digestive system, and excretory system. All the systems that we don't really have conscious control over. Right? Now, in and of itself, the autonomic nervous system can be broken between 2 divisions. The sympathetic division and the parasympathetic division. Actually, there's another division too, the enteric division. You don't need to worry about memorizing this, but it is becoming a hotter subject of research now that we are understanding the importance of our guts, and this enteric division is going to control the organs of the digestive tract, as well as the pancreas and gallbladder. I only bring it up again because, you know, you know me, I love gut bacteria, I think the whole enteric system is super cool, and cutting edge research. Right? So, let's get to the stuff that you need to make sure you know, and that is the sympathetic and parasympathetic division. These are often simplified as the fight or flight division and the rest and digest division. Now, this simplification is pretty much good enough for our purposes, however, when you try to delve, or if you I should say delve into greater detail in these matters you'll see why it's not a perfect definition. For our purposes, it's good enough. So the sympathetic division is going to have neurons that release norepinephrine, and remember that's going to trigger that fight or flight response. That's why this is the fight or flight division. And you can see what happens in the sympathetic nervous system down here, you know, dilation of pupils, dry mouth inhibiting saliva production, increasing heart rate, and all that stuff that gets your body ready to either run away or fight, you know, a tiger or whatever it is. Now, the parasympathetic division releases acetylcholine. And this is going to be the rest and digest division, and it's going to have some effects that are opposite, but not always. I don't want you to try to think of these two things as, sympathetic does this and parasympathetic does the opposite because they don't really line up quite so perfectly. So there are some contrasts, for example, parasympathetic division constricts the pupils, as opposed to the sympathetic dilating them, but and, you know, likewise, it reduces heart rate as opposed to raising heart rate. Of course, it has other kind of unrelated things, and, you know, you can see all of its activities here. And, the reason, you know, just to give a little preview, the reason we sort of say it's not a great, you know, the rest digest, fight or flight division isn't perfect. You know, for example, when you look at reproductive functions, rest and digest, well, stimulating the genitals just doesn't really sound like rest. But that's a parasympathetic function. So, you know, these aren't perfect definitions, but for our purposes it's a good enough generalization.

So with that let's go ahead and flip the page.

Reflex Arc

We've all experienced that moment at the doctor's office where they tap our knee and our leg just shoots out completely involuntarily. This is an example of a reflex. These are neural pathways that control involuntary instantaneous movements in response to some type of stimulus. Often, you'll hear this referred to as a reflex arc. Now, the sensory neurons will actually carry information from the stimulus into the dorsal side of the spine. So here we have the dorsal side, this is the ventral side. Let me pop my head out of the way so you can see what I've written. Ventral, dorsal, basically, think dorsal like the fin which is on the back of dolphins. So, the sensory neuron is going to carry information towards the spine and it's going to enter the dorsal side, and its cell body will be part of that dorsal root ganglion we talked about a little while ago. And it's either going to synapse directly on a motor neuron or an interneuron that will, in turn, synapse on a motor neuron. So basically, some type of stimulus is going to signal it and it's going to in turn signal either the interneuron or motor neuron. In this case, we have an interneuron right here before the motor neuron, and it's essentially going to result downstream in the motor neuron sending a signal to a muscle and causing some type of movement in response. Motor neurons will leave the ventral side of the spine, as you can see, and they'll synapse on a muscle, right, neuromuscular junction to create some type of movement. The basic outcome of all this is a very fast response to a potentially damaging stimulus. This is your body's way of protecting itself, and what's important to note is that none of this involves the brain. It does go into the spine, so it does involve the central nervous system, but no processing occurs in the brain with these reflex arcs. So here in our example, you can see this guy is touching a hot flame, which is not a good idea, I don't recommend it, and that's going to cause a reflex arc which will result in him pulling his hand away from the flame very quickly. You know, this is like if you step on a sharp object, you just shoot your foot up before you even have a chance to realize what happened. And again, these reflex arcs are just very simple neural pathways that allow for a quick response to some type of stimulus, generally a stimulus that signals some type of potential damage or injury. So with that, let's flip the page.

Cerebrum and Cerebral Cortex

Hello, everyone. In this lesson, we are going to be going over the major parts of the brain. Okay. So the brain is going to be in the Central Nervous System. Remember, the Central Nervous System is going to be the brain and the spinal cord. The Peripheral Nervous System is everything else that's not the brain or the spinal cord, but it's still part of the nervous system. So things like spinal nerves, and the nerves in your hands, and things like that. But we're talking about the central nervous system, so we're talking about the brain and the spinal cord. And specifically, we're going to go over the different regions of the brain that you are going to need to know. So obviously, the brain is the most famous organ in the human body, and you've probably seen diagrams like this before, but you may have not known exactly which portions of the brain you were looking at. So we're going to talk about the forebrain, the midbrain, and the hindbrain.

Now, the Forebrain is going to include things like the Cerebrum, the Hypothalamus, olfactory bulb. It's going to include some other things as well, which are a little bit more detailed that you'll learn more about later. Now, the forebrain is going to be this region that you see here in orange. And fore means in front, and brain obviously means brain. And you may be thinking, but wait, that orange part isn't in the front of the brain, is it? Because this would be the front, or the Anterior side, and this would be the posterior, or backside. So, if we cut the Brain in half, this is what it would look like from the side view, the lateral view. And this should be the front, this portion of your brain here. But, you can see that the forebrain wraps all the way around to the posterior side. So you might be saying, why is it called the forebrain if it's not in just the front? That is because the forebrain, whenever it was developing inside of the fetus, was actually in the front. And whenever you're developing as a fetus your forebrain is going to be called your Prosencephalon. Which I know sounds like a lot, and you guys probably don't have to know this information. I just wanted to let you know, why it's called the forebrain. That's because in the fetus, that particular region, the prosencephalon that becomes the forebrain is in the front of your head. And just for, just so you guys know, cephalon or cephalic means brain. So whenever you see something like this, cephalic, or you see that particular cephalon, cephalic, those particular, letters in a word. It's generally going to be dealing with the brain.

Now, we're going to talk about the midbrain. This is going to be a portion of the brain stem, kind of like the upper portion of the brain stem that connects the forebrain to the hindbrain, which you can see here in green. So, there's going to be some very interesting structures in here, which we will talk about a little bit later, but basically it's connecting the Brainstem to the forebrain. And it is going to be used for a whole bunch of different things. It's going to be utilized for eye movement. It's going to be utilized for processing visual information before it's sent to the Occipital Lobe. It's going to be utilized for coordination and your alertness. And your Midbrain is also going to have a particular name in development, and this is going to be the Mesencephalon. Which I do not believe you need to know this, but I just wanted to let you know that that is what it is called in the developing fetus. And again, you can see that cephalon, that cephalic word in there meaning brain, so your middle brain.

Now, I forgot to tell you, all the different crazy functions that your forebrain can do. Your forebrain is gigantic. It is going to do so many different things. It is obviously the majority of your brain, as you can see there in orange. It's going to control your sleep. It's going to control your reproduction, your eating, your body temperature. It's going to control your motor functions, your emotional functions, and it's going to do a lot of your interpretation and thinking. Okay? Alright.

So, now let's move on to the Hindbrain which is going to be more composed of the Brainstem, but it's going to include the Medulla Oblongata, Pons, and Cerebellum. And it's going to be the lower portion of the Brainstem. This is a very important portion of your brain because it connects your brain to the rest of your body. This is going to connect your brain to your spinal cord, and you can see your hindbrain is here in pink. And it's going to connect to the spinal cord, which is going to be more inferior, so more below the brain. Now, your hindbrain also has a particular name during development. Its name is kind of funky. Its name is rhombo, or rhombencephalon. And, again, you can see the cephalic word in there meaning brain. Okay? Now it's going to do a whole bunch of things. Most of your cranial nerves are going to come off of your hindbrain. It's going to control some eye movement as well, your facial sensations, your balance. A lot of your voluntary movement is going to be, controlled through your hindbrain. It's also going to control your heart rate, your blood pressure, your reflexes, your breathing, things like that. Okay.

So now, let's go down and let's talk about a more specific region of the brain called the cerebrum. Your cerebrum is going to be in your forebrain. This is the largest portion of your brain, and probably the most famous portion of your brain. Now, this is the large outer part of the brain that is going to include the cortex. The cortex is going to surround the cerebrum and other subcortical structures like the hippocampi. So your cerebrum, whenever you think of what a brain looks like, you're looking at the cerebrum. This is going to be 85% of your brain. And it is divided into 2 hemispheres, a left and a right Hemisphere. And, it's going to have all sorts of different things inside of it that are going to do different functions. Your cerebrum is very famous for your thinking, your planning, your reasoning skills, your interpretation of information and senses, and it's also very important for language. So this portion of your brain is basically what makes you intelligent for the most part. It's the thinking part of your brain. Okay. So, like I already said, it is going to be divided into 2 hemispheres, a left and a right, but it's going to be connected. We can't have those 2 hemispheres not talk to each other. They need to communicate with one another, and they're going to utilize the Corpus Callosum. This is going to be a bundle of nerve fibers called axons that transmit information between the hemispheres. This is very important. This allows the left side of your brain to talk to the right side of your brain. And, in fact, the left and right sides of your brain do have slightly different functions, so they do need to communicate with one another. So it's very, very important. Now, the Cerebral Cortex is going to be the outer layer of the cerebrum composed of gray matter. This is going to be the outermost layer of the brain that most likely you're going to see whenever you think of a brain.

Now, I want to show you a picture. Let me get out of the way here. I'm going to scroll down a little bit. Do you see this arrow right here? It's going to be pointing to the Corpus Callosum, which is going to be kind of right here, which is going to allow those 2 hemispheres of your brain, your left and right hemispheres of your brain, to connect with one another, and to communicate with one another, so that they can share information. So that's a good visual representation of your corpus callosum. Okay. So now the cerebrum is quite large. Right? It's 85% of your brain. It's going to be chopped up into 4 different lobes. So each side, the left and the right, are going to have a frontal lobe, a parietal lobe, a temporal lobe, and an Occipital Lobe that are all going to have unique functions. The Frontal Lobe contains areas involved in decision making and your Primary Motor Cortex. So this is going to be the cognizant part of your brain that's actively making those decisions. The Parietal Lobe is involved in sensory information processing and it contains the Primary Somatosensory Cortex. Okay. So the Parietal Lobe, whenever you touch something, it is actually looking through all this sensory information and processing the sensory information. Whether that's sight, taste, smell, touch, anything like that, your Parietal Lobe is taking care of that. Okay. Then we have our temporal lobe which is going to contain the regions involved in hearing and language and visual processing. So whenever you're listening to language or you're speaking, your temporal lobe is going to be involved in that process. Now, finally, we have the occipital lobe, which is the visual cortex. This is where the majority of your visual information is going to be processed and understood. So it's utilized in processing visual information. Now, if I scroll down, you can actua Sessions are attended by a faculty of international experts and industry leaders who engage with attendees, offering insights and guidance for future endeavors.

Motor, Sensory, and Association Areas

With the lobes of the brain, we saw that different cognitive processes are located in different areas. However, sometimes, there are differences in cognitive processes across the hemispheres. For example, language tends to be left hemisphere dominant. Most of the areas involved in language processing will be found in the left hemisphere, and there are very few in the right. These differences between the hemispheres we refer to as lateralization. And just as an example, we're going to look at two areas in the brain: Broca's area and Wernicke's area. Broca's area is involved in speech production and is found in the frontal lobe, whereas Wernicke's area, part of the temporal lobe, is involved in language comprehension. These black lines are trying to indicate that these two areas are intimately connected. I'm sure you can imagine, the production of speech and the ability to understand what's being spoken to you are going to be linked processes.

However, the takeaway I want you to get here is just that different functions are localized to specialized areas of the brain, and there is not always going to be balance between the right and left hemispheres. However, I will dispel the whole right-left hemisphere nonsense that you find in pop science right now. That's all garbage. Don't listen to any of that. Just know that there are differences in the cognitive processes between the hemispheres. However, they are not nearly as pronounced as pop science would have you believe. Another way to look at the cerebral cortex is to divide it into sensory, motor, and association areas. Essentially, in this model, we think of sensory areas as receiving and processing sensory information. These will be areas like the visual, auditory, and somatosensory cortices, that's the plural of cortex. And you will find them, you know, in and around these regions of the brain here in pink.

Now, the motor areas process voluntary motor movements, and these are going to be processed in the primary motor cortex, which you can see has been highlighted in green for us right here. Notice that it's parallel to the primary somatosensory cortex, right here in dark pink. Hopefully, it comes as no surprise that the area that receives information from the body would need to be intimately connected with the area that sends signals back to the body for movements. Basically, the rest of the brain that is not a sensory area or a motor area is considered an association area. These association areas are basically there to extract meaning from the sensory information we receive. To some of you, this might come as no surprise. To others, this will be kind of a groundbreaking idea, but what you perceive as the world is not real. It's just a construct in your brain. So, things you are seeing, you're not really seeing, your brain is interpreting the signals from photons bouncing off of it to construct an image of it. Essentially, these association areas are there to take what comes from the sensory areas and make sense of it and generate your reality. Now, with that, let's flip the page.

Limbic System

The diencephalon is the part of the forebrain worth noting because it contains the thalamus and the hypothalamus. These structures are super important, and they're actually kind of small when you look at them in the grand scheme of the brain. Here we have a zoomed-in picture, and you can see the thalamus sits above the hypothalamus, and that's where it gets its name. Hypo means, you know, like lower, so it's just below the thalamus. Now the thalamus basically acts as a relay center for the brain. I like to think of it as a telephone operator in a way. Information sent in and then it routes it to the appropriate area of the cortex. It's going to play an especially important role in visual processing, routing the different types of visual information to their appropriate areas for processing. The hypothalamus is important because it's going to serve as the link between the nervous system and the endocrine system. And it's going to do this by interacting with the pituitary gland, which is an endocrine gland that is going to have very high-level effects in the endocrine system, high-level signaling. The hypothalamus is also going to be involved in homeostasis, which is why it makes sense that it will serve as a bridge between the two major communication systems in the body, as homeostasis requires lots and lots of really good communication.

A limbic system is kind of a loose definition, that more or less encompasses a bunch of different structures, mostly in the forebrain. There are some structures in the midbrain that are referred to as limbic midbrain structures. We don't really need to worry too much about these. For the most part, the structures of the limbic system are in the forebrain, and the only ones that we need to actually know about are all located in the forebrain. These are structures that are going to be kind of deeper in the brain, so they're not at the surface, they're below the cortex, and these structures are the hippocampus and the amygdala. The hippocampus is going to be involved in learning and memory, and it's actually especially important for the formation of long-term memory and spatial memory. Long-term memories are memories that you can, you know, recall for a long time. For example, what your home when you were a child looked like, or something to that effect. Without the hippocampus, people are actually completely incapable of forming these types of long-term memories. So, there's a famous example of a person who had both of their hippocampi removed, and they were completely unable to form memories for the rest of their life. People that they met after this operation, they were never able to recognize, no matter how much time they spent with them. It's also involved in spatial memory formation, and this is sort of like your ability to construct mental maps. So, for example, when you go to a new part of a city or something and you don't know your way around, you actually have to build a mental map of the layout of the area you're in, and it's going to be the hippocampus that's responsible for that process. So, generally speaking, learning and memory, specifically long-term memory and this type of spatial memory.

The amygdala is involved in emotional processing and it's actually going to kind of sit right on the end of the hippocampus. So we have the amygdala here, and this structure is the hippocampus. So it sits right at the end of the hippocampus, and it's going to be linked in some ways to the hippocampus because emotions can create very powerful memories. There's a strong link there. I don't want to make too many wild assertions, but there's certainly a link between the emotional processing of the amygdala and long term memory formation.

Now with that, let's actually go ahead and turn the page.

Cerebellum and Brainstem

The cerebellum, or "little brain" as its name suggests, sits at the back of the brainstem underneath the cerebrum. As you can see, it really does look like a smaller version of the cerebrum, hence its name. Its main job is integrating motor functions. It does not initiate any motor movement on its own, but rather coordinates those signals and integrates the output. For example, when you stand up straight, you must coordinate many different muscles across your body to maintain your posture. Without the cerebellum, you would simply face plant, unable to maintain balance. It also plays a role in fine motor movements, such as performing delicate tasks with your fingers.

Moving on, the brain stem contains the pons and the medulla oblongata, which are located right next to the cerebellum. However, our image here lacks a cerebellum. I don't know why. Perhaps there is a bias, maybe emphasizing the brain stem. The pons and the medulla oblongata have roles in unconscious types of functions that are necessary for life. These structures are often considered as parts of the "lizard brain," responsible for very basal functions that are absolutely essential for sustaining life. These areas are crucial; for instance, the pons is involved in swallowing, breathing, eye movements, posture, and notably, in dream production, which is not well understood at all. Sleep and dreaming remain significant mysteries in science, but it is known that the pons plays an important role in producing dreams.

The medulla oblongata also manages many passive unconscious functions necessary for life, including maintaining heart rate. It also plays roles in breathing, alongside the pons, and in regulating blood pressure. Therefore, these structures are often thought of as more basal because they handle those unconscious functions. So with that, let's actually go ahead and flip the page.

Neuroplasticity, Learning, and Memory

Our brains have an amazing ability to reorganize themselves. We call this ability neuroplasticity, and this is when our neurons reorganize themselves by modifying and forming new connections. Now this is related to synaptic plasticity, which is the ability of neurons to strengthen or weaken their connections based on various activity patterns. And you can see a very simplified version of that here, where we have one neuron that receives stimulation that's going to have some change occur in its synapse, and another neuron that does not receive stimulation and does not change its synapse. So synaptic plasticity is sort of a mechanism that contributes to neuroplasticity. Now one amazing example of neuroplasticity can be seen here, with something known as phantom limb syndrome. With phantom limb syndrome, basically, people who have lost a limb will still experience the presence of the limb there, and that's because even though they've lost the limb very suddenly, their neural networks haven't adapted yet to that change. So one amazing way that people deal with phantom limb syndrome is by using something called a mirror box. It's very common for people with phantom limb syndrome to feel as though the limb they've lost is tensed up and uncomfortable. So, one way they deal with this is by using a mirror box, and they'll have the person, you know, essentially use the hand or, you know, the limb that they still have in the mirror box, and it will appear to them as if it's the limb that they're missing, the phantom limb. And so they can take that limb in the mirror box and they can tense it up, and then ease the tension, and relax it, and it will appear like it's the phantom limb doing that, and that will actually help change their neural networks to get rid of that discomfort. So pretty amazing stuff, neuroplasticity. Also, people with traumatic brain injuries are capable of recovering lost functions due to brain damage by reorganizing other parts of their brain to pick up the slack and carry out those functions that they aren't even supposed to do technically. It's pretty incredible. And, this capacity is much greater when we're younger, and we sort of lose it as we get older, which is why children are so much better able to recover from brain injuries, for example, and also better able to learn things. Now neurogenesis is the growth of new nervous tissue, and this occurs mostly when we're developing embryos. As adults, we really can't produce new nervous tissue; however, there are some small exceptions. Now all of this neuroplasticity, synaptic plasticity is highly related to learning and memory. Now learning is going to be technically acquiring, modifying, or reinforcing some type of knowledge, behavior, or skill. So, you know, you can, for example, learn a new skill, and then you're going to be adapting your brain to that new skill, or you can have a neural network that's already in place for some particular behavior, for example, and reinforce that, make it stronger, strengthen that behavior, so to speak. Memory, on the other hand, is going to be the encoding, storage, and retrieval of information. There are actually different types of memory. We actually have what's known as sensory memory, and this is a very transient type of memory. It's basically, the ability to hold sensory information for just like a second after you perceive it. So for example, if you look at something and then very quickly close your eyes, for a second you hold that image in your mind as if you're still looking at it. That’s sensory memory of what you were just experiencing, the perception that you just had. Now there's also short-term memory, which is the ability to recall a small number of items without actually having to, sort of, rehearse it. Technically, rehearsal is a jargony term, and is, you know, when, for example, if you're trying to memorize something, you repeat it over and over to yourself to just kind of strengthen it in your mind. So, short-term memory is our ability to, you know, kind of, without having to really try to remember things hold just a few limited pieces of information in our mind. In fact, it's thought to be about 7 pieces of information, and that's why telephone numbers are 7 digits long. So, there you go. Now long-term memory is going to be information and knowledge that's stored and recalled for a very long time. In fact, it could be potentially your entire life that you can retrieve this information. And the mechanism behind this long-term formation of memory is thought to be something called long-term potentiation. And this is the long-term strengthening of a synapse based on activity patterns. And it’s extrapolated to be involved in the cellular mechanisms behind learning and memory. Essentially, we're not trying to sit here and tell you that all memory comes from long-term potentiation, but there's definitely some involvement of this process in long-term memory. So what happens with long-term potentiation? Well, essentially,Synapse due to some type of activity pattern, this connection is going to be strengthened. And one of the ways it'll be strengthened is by adding new receptors to the postsynaptic, postsynaptic side of the synapse. And you can see that, here we only had 2 receptors, whereas over on this side here we now have 4 receptors. So that's going to strengthen that synapse. Right? Another thing that can happen is by releasing more neurotransmitter, we will strengthen that connection. See here, we're only releasing a little bit of neurotransmitter. Here, we're releasing a lot more neurotransmitter. So these two effects are gonna add together and result in a much stronger connection at this synapse by a combination of added receptors and added neurotransmitter. So those two facets are going to combine together and produce a much stronger overall response. With that, let's go ahead and turn the page.