Question

Can someone please explain to me why the medulla is smaller rostral to the spinal cord? The explanation given to me via my powerpoint & lecture is that majority of the tracts have already decussated to the opposite side and then descend as the lateral corticospinal tract. I feel silly, but I don't understand how changing sides somehow makes you no longer a part of the medulla. Can someone make this make sense because I feel like a crazy person trying to teach this to myself and my professor is literally no help at all.

Answer 1

Okay so here's the thing:

Medulla Oblongata is referred as simply Medulla.

And

Spinal cord is referred as Medulla spinalis.

Medulla oblongata is physically continuous with the spinal cord towards the back and official begining of the spinal cord is just a little bit below the lower medulla.

The connection between the medulla and the spinal cord occurs within an opening in the occipital bone called Foramen Mangnum.

With this overview, now let's come to your doubt:

Medulla is more of processing centre, it doesn't only have tracts, but also various centres like vasomotor centre, respiratory, cardiac, vomiting, etc. So it also regulates various processes in our body which are essential for life. Secondly, look at this:

Are you visualising those nucleus?

These nucleus can be of cranial nerve like hypoglossal nucleus or may belong to some tract like gracilis nucleus.

Nucleus are group of cell bodies. They not just carry the impulses like tracts do. They mediate those impulses.

What I am trying to convey is medulla is like a controlling centre of our body. It's not just a bundle of tract.

Now, Spinal Cord?

It is something of a structure which largely has tracts.

Though nucleus like nucleus proprius are there. But they are largely associated with peripheral actions. Spinal Cord is filled with tracts. It doesn't control any essential life features. That's why spinal injury doesn't take life, medullary injury does. Moreover, it is also located outside the skull.

All such differences make them different physiologically and anatomically.