Introduction to the Autonomic Nervous System

00:01 In this lecture, I am going to describe the sensory and motor pathways in the spinal cord.

00:09 At the end of this lecture, I want you to be able to describe both the motor pathways and the sensory pathways, so you have a very good understanding of these pathways.

00:21 I also would like you to know the difference between the various ganglia in the body and be able to tell the difference histologically, when you see images of the structures.

00:36 Well, let's just make sure that we are aware of the autonomic nervous system again before we then try to put all these together and try to describe the structure of the spinal cord in more detail and show the pathways of all the sensory and motor neurons, somatic motor and also visceral motor neurons. Well, just to recall that there are a number of functional divisions of the autonomic nervous system. There is the efferent innervation to smooth muscle, we're unaware of. Efferent innervation means it is exiting the spinal cord or the brain. They are visceral motor neurons, they are causing contraction of smooth muscle, components of cardiac muscle and also the contraction of muscle around glands to increase or decrease secretion. They are going to be divided into two components, the sympathetic components and the parasympathetic components. And as I mentioned earlier, they have opposite effects, but it is worth remembering also that when we see these neurons travelling to their destinations, they are also accompanied by sensory neurons that are taking information back from the viscera. Now, it is important also to understand that when I describe the ventral horn neuron, that was stimulated by that pyramidal cell very early on the lecture, that ventral horn cell was only the one cell needed to innervate skeletal muscle.

02:31 The axon of that ventral horn cell travelled all the way out of the ventral horn, all the way down to innervate the skeletal muscle that is designed and joined on to innervate. It could be all the way down to the muscles in your toe. In the case of the autonomic nervous system, in the case of the need to innervate the smooth muscle and glands etc. that I have mentioned, there are two neurons involved. Neurons we called preganglionic and neurons we called postganglionic. And I will describe that in more detail as we go through. But it is an important point. Somatic motor neurons are only one neuron, whereas the autonomic neurons require two neurons.