The Size of the Gray Matter Varies

00:01 Now, just imagine that this butterfly or this area of gray matter is travelling all the way up and down the spinal cord, as is the white matter.

00:15 You are only looking at a single section or two in this image, a very thin section through the spinal cord. But as I said imagine this area of gray matter moving or being present all the way up and down the spinal cord, so you can then imagine the enormous numbers of ventral horn cells there may be and the enormous numbers of sensory neurons coming into the dorsal horn, all the way on the spinal cord, very fascinating concept. Of course you can see that the gray matter is different in both these images. And that is because the gray matter in the image on the left hand side is probably only housing motor neurons that might innervate muscles of the torso. So this is a section probably through the thoracic region of the spinal cord. Muscles of the torso are less in number than the muscles that we have that move our upper limb or our lower limb. And therefore we have the need for a lot more these ventral horn cells in the regions of the spinal cord where these ventral horn cells are going to exit and form peripheral nerves. So that is why you see the difference in the size of the gray matter as you move up and down the spinal cord. It is also pretty easy to understand or to identify what is a ventral horn and what is a dorsal horn because the ventral horn as you see on the right hand side is generally a lot larger, a lot more elongated as well, than the dorsal horn.

02:06 So in summary, you should understand the structure of the nerve cell. Remember, the cell body is called the soma. Lots of rough endoplasmic reticulum inside the cell is referred to as nissil substance. And the main processes of the nerve cell is the long axon.

02:29 The dendritic branches that receive information and the axons can be myelinated or unmyelinated.

02:37 And also between the myelin sheath and the myelin axon is the node of Ranvier, which enhances the transmission of the impulse along the axon. You should also understand the divisions of the nervous system, both anatomically and functionally. And finally you should know the structure of the spinal cord and the different functional components within that spinal cord, because that is going to be the subject of a later lecture. So thank you very much for listening to this lecture. I hope you have enjoyed learning about the neuron, the structure of the spinal cord and the general organization of the nervous system.