Functions of the nervous system

Voiceover: In this video, I'm going to talk about some of the functions of the nervous system and how I think about these functions and have organized them in my mind. The nervous system performs many functions that allow a person to experience their life and which create their behavior, as well as many necessary functions of the body, for which a person is usually unaware, and these functions can be categorized in different ways. The way I like to think about the functions of the nervous system is first to divide them into two big categories that I think of as the basic functions of the nervous system and the higher functions of the nervous system, and you could use whatever words you wanted here. You could say the lower functions and the higher functions or the basic functions and the complex functions, but the reasons I like to use these words is that the basic functions aren't really that simple. They're actually fairly complex when you start to get into them, and they're not really lower in any particular way either. Really, you need the basic functions and the higher functions. Now, dysfunction of different parts of the nervous system may cause different patterns of abnormalities of the functions of the nervous system, either the basic functions, the higher functions, or both, and patterns of abnormal functions we call syndromes. Let me just write that word down, syndromes, which means patterns of abnormalities, and certain syndromes involving abnormal functions of the nervous system are more common than others, because they're caused by neurological or psychiatric disorders that occur more frequently. The basic functions of the nervous system are performed by many parts of both the central nervous system, which is mainly the brain and the spinal cord, and the peripheral nervous system, which is mainly the nerves. When it comes to the nerves, the cranial nerves primarily perform the basic functions of the head and the neck, whereas the spinal nerves primarily perform the basic functions for the limbs and the trunk, because that's where those nerves generally go. Now, I like to divide up the basic functions of the nervous system into three big categories. The first category I would call motor, and the word motor, in this context, refers to control of skeletal muscle. So, skeletal muscle, the main muscle we have that's all over our body and attached to our skeleton, and by controlling skeletal muscle, the motor functions of the nervous system cause movement, tone, and posture, which are the end results of contraction of skeletal muscle. The next big category of basic functions of the nervous system I like to call sensory functions, and this involves all of the senses, basically anything that the nervous system can detect. And we're used to hearing about five senses, but it actually turns out that if you kind of split them up into finer categories, there's way more than five senses. There's vision, there's hearing, smell, taste. There's a sense from the inner ear, called vestibular sense, and there's multiple senses of the body, called somatosensation, and somatosensation includes the senses of touch, the position of body parts, vibration, pain, temperature, and several others. And for each of these categories, we'll get into a lot more detail on these in later videos, because there's really a lot going on within these categories. And the third big category I think of, when I think of the basic functions of the nervous system, I like to call automatic functions, automatic, and these are things that don't require conscious involvement, and that includes a lot of different things, like reflexes, like when your doctor taps on your knee at the clinic, and your leg kicks out without you telling it to, and there's all sorts of different reflexes of the nervous system, and we'll go over a few of them in later videos, but there's also all sorts of other kind of automatic functions the nervous system does without requiring the involvement of consciousness, including control of a number of the body systems involved and really important things like circulation, respiration, and digestion. So, more on that later too. But now, the higher functions of the nervous system are not performed by huge areas of both the central and the peripheral nervous system. The higher functions are performed by parts of the brain, and like the basic functions of the nervous system, I like to divide up the higher functions of the nervous system into three big categories. The first big category of the higher functions of the nervous system I like to call cognition, cognition, and people use this word in a number of different ways, so it can get confusing when you're reading about cognition, but I like to think of this as kind of the thinking functions of the brain, like thinking, but there's also a whole bunch of other things that we can often put under this term of cognition, including things like learning and memory and language and a group of things we call the executive functions, which involve creating goals and organizing behavior to achieve those goals. So, more on that later, because there's plenty going on there. The next big category of higher functions of the nervous system I call emotions, and emotions, of course, are our feelings, but it turns out there's a lot more to emotions than just kind of what we feel, because emotions play a major role in our experience of life and a lot of other functions of both the nervous system and the rest of the body. And the last category I like to think of under the higher functions of the nervous system is consciousness, and consciousness is a really tough word to define. I don't know that I have a great definition, because people have been trying to come up with a definition everyone can agree with for quite some time, although we all sort of know what consciousness is. The best I can probably come up with is that consciousness is related to the awareness of being a person, of experiencing one's life, and controlling one's actions, and while there's a lot we don't understand about how the nervous system does pretty much all of these functions or categories of functions that I've written out here, consciousness is the one we know the least about, where many many people are doing lots and lots of research to try to understand how this phenomenon of consciousness is created by the nervous system. So, this is how I like to think about the functions of the nervous system and how I like to break them up into some big categories, and like I said, we'll go into the details of lots of these categories in later videos, and if you look in different textbooks and things, you'll see people have organized the functions of the nervous system in lots of different ways, and in some ways, it doesn't really matter how you organize all the different functions of the nervous system, as long as you find some system that makes sense to you, to keep track of it all.