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Introduction to the nervous system
Published on August 29, 2019 41 min
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Hello. My name is Melissa Andrews and I'm a lecturer in Systems Physiology at the University of Southampton School of Biological Sciences. Today, I'm going to talk to you about the basics of the nervous system, specifically the structure and function of the nervous system.
In terms of functions of the nervous system, the nervous system serves to control and coordinate a wide range of functions throughout the body. It allows our bodies to respond to internal and external stimuli. So, we will have to discuss sensory functions and motor functions which will allow us to receive that information, as well as to drive the input or whatever response is necessary. Specifically, in terms of these functions, we can detect changes within and around the body through, for example, whatever sensory information is coming our way. We can respond to external changes by changing the movement of our body; we can receive and interpret sensory information which allows us to adapt to changes. We can also stimulate muscles and glands in our bodies. and in terms of muscles, those might be voluntary or involuntary. and this is all to maintain homeostasis.
In order to understand the nervous system, we must first draw back to the cellular level and look at the basic building blocks of the nervous system. In this basic cartoon drawing that you see here, you can see a multipolar neuron. But, in essence, it's a neuron with different shapes and structures associated with it. On the left-hand side, you can see a large cell body in red. From that cell body, you can see several dendritic processes, or dendrites, emanating from the cell body. You can also see a nucleus in the cell body as it's a standard cell line or standard cell in the body. So, it has to have a nucleus. Emanating from the right-hand side of the cell body is what's called an axon; it's quite long in its shape and structure. and what you can see in comparison between the dendrites and the axon is that you have several dendrites which helps to receive information and collect signals from other cells and then you have one single axon to take information from that particular neuron and send the signals elsewhere likely on to other neurons or onto muscles. This is a very important part in the structure of a neuron in that you have one single axon but the ability to receive numerous signals via several dendrites. As I mentioned here, neurons have several functions. They receive stimuli, they transmit nerve impulses or action potentials, and they also activate muscles. Whether a neuron has a sensory function or a motor function will depend on what its action and function turns out to be. So, as I said, we have to have dendrites to collect signals and axons to transmit those signals. We have a couple more component parts that we have to be aware of. What we can see right next to the cell body as we go into the axon is an axon hillock. This structure is rich in voltage-gated sodium channels. and as I'll talk about later on in our discussion on the nervous system, this is a very important part of how we start what's known as an action potential. The axon initial segment, very nearby to the axonal hillock, is associated with the start of the axon as well as an enrichment of the voltage-gated sodium channels. As the name suggests, it is the start of the axon. and what we also see in the axon are these bead-like structures shown in black color going along the length of the axon and what these structures represent are myelin. Myelin is a lipid-rich structure that we'll discuss in more detail in the next slide.