[MUSIC] Okay so, we have three types of movements. Reflexes, stereotyped automatic type movements, and movements of self expression. And so, let's imagine what those three types are. So, reflex as you know, one of them is the one of doctor office fame, where you're sitting on a table and the doctor does this, and you do that. There are other reflexes, such as if you put your hand on a hot stove, you don't think about it, you don't intend to do it, you just withdraw. That's a reflex, that withdrawal reflex. Stumbling elicits a reflex, a recovery from stumbling reflex, that hopefully works so you don't fall down. These are all reflexes. Your brain is not required. These can take place very low in the motor hierarchy. So when we talk about the motor hierarchy, it all boils down to skeletal muscle. And skeletal muscle is not going to contract without input from the motor neurons. This is very different from the cardiac muscle. The heart contracts on its own. You could put it in a dish and it would contract. But that it not true for the skeletal muscle. It has to have this input from the motor neuron. So this is the final common pathway of [INAUDIBLE]. The motor neuron to the skeletal muscle. These motor interneurons collect groups of motor neurons into basic movements, and it's this area, this group right here that is involved in reflexes. So that is what's involved in reflexes. The next type of movement are stereotyped movements. Movements that we do all the time. Chewing, walking, running, standing. And also movements that we don't do very often but they are still stereotypes. And one example which I think is illustrative is vomiting. Vomiting is so stereotyped, that what filmmakers do is they really don't wanna show you the disgusting part of vomiting. So all they show you is the thorax, the abdomen and thorax and just the movement of somebody vomiting. Going through that motion, you know exactly what's going on. So, it's a very stereotype movement and it's produced, not by a lot of brain power up in the neocortex, but it's produced by these entities called, these circuits called central pattern generators. And central pattern generators are a very interesting and important concept that we'll spend some time looking at. And finally, there are intentional movements. Movements that we make for either deliberate reasons or for emotional reasons, and these come from the cortical motor control centers. The brain stem motor control centers are involved in things like engaging walking, postural control, and orienting movements. But the cortical motor control centers are involved in things like reaching, talking, getting a little piece of food out of your teeth [SOUND], writing, and doing things with your dancing, doing the jig, all of those things require or the cortical motor control centers. So what you get as you go up this motor hierarchy, as you involve more and more pieces of the brain up the motor hierarchy. If you just had motor neuron excitation, you'd have a twitch. And down here, with the central pattern generator, you'd have simple movement. And if you get into the brain stem motor control center, you get some complex movements. Once you get to the motor, to the cortex, now the movement is imbued with meaning. It is imbued with meaning and intention and that all of a sudden movement becomes an action. Things are not actions unless the neocortex is involved. It has no context. It has no meaning and no self value of self expression. [MUSIC]
