We're starting this module with a focus on the physiology of the brain and nervous system. In this video, we will be taking a very broad look at what the various parts of the brain do and how they interact with the rest of the nervous system. The nervous system is separated into two structural parts, the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain and the spinal cord. The peripheral nervous system is made up of the nerves as they leave and return to the spinal cord. While we are talking about the nervous system as a whole, we should talk about one other way the nervous system is divided, and that is its functional division. Functionally, it separates into the voluntary and autonomic portions. The autonomic portions are all the things that happen without you having to think about them. We will talk more about this portion later, but the fact that your heart is beating without you thinking about it is an example. The voluntary nervous system refers to the portion of the system that we control, primarily, our muscles. Let's put this together with one example of how the nervous system works at a basic level. Imagine that it's a hot day and you are craving a cold glass of water. You reach out your hand to see if the glass is cold. Just in case the ice in the glasses isn't cool enough, it seems like you instantaneously know that it's cold, right? How does this happen? When your finger touches the cold glass, specialized nerves identify the surface is cooled. This message, is cold, is then carried up to what we call afferent nerves to the spinal cord and up the spinal cord to the brain. I've always remembered afferent because A is followed by B for the brain. So, afferent nerves send messages to the brain through the spinal cord. This message of it's cold arrives in the brain and is processed in a number of places in order for the brain to identify what part is affected and to put the impulse into motion to pick the glass up to take a drink. This message then leaves the brain through the spinal cord to the efferent nerves. The efferent nerves are the ones that carry the impulses from the brain. Efferent nerves typically attach to muscles and in this case, cause your hand to pick up the glass and raise it to your lips. I remember efferent nerves are the ones that take the message that are exiting the spinal cord. In summary, a movement of the voluntary nervous system is you reaching out to the glass. The afferent nerves, which are part of the peripheral nervous system, send the message it's cold to the spinal cord and the message travels through the spinal cord to the brain. The brain processes this information and decides to act on it by sending a message of drink up through the spinal cord to the efferent nerves for the muscles of that arm and to close your hand around the glass and raise it to your mouth. The cold glass example illustrates primarily how your central, which is your brain and spinal cord, interact with your peripheral nerves to achieve voluntary movement. We mentioned earlier that there is another portion of the nervous system, which is the autonomic nervous system. This system adds another layer of incredible complexity to the nervous system as a whole. Think of it as the automatic portion of the nervous system. You don't necessarily think about any of the processes that it controls. The autonomic nervous system controls a lot of the basic functions of the body through a very delicate balance of nerve impulses and receptors and is made up of the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system controls all the body responses associated with the fight or flight response. It is triggered by trauma, stress, or fear. The parasympathetic system controls the rest and digest responses. Review the autonomic nervous system resources page to see more details about this complex system. Have a headache yet? That concludes our review of the physiology of the nervous system. From here, we will move into the various neurologic conditions you will come across while taking care of patients.
