New Treatments for Movement Disorders. Part 5

So how do we understand these phenomena that we see? Now we can go to a review of the pathways. I actually like to draw it out, so I’m going to go to the overhead momentarily. But it begins with this concept. And that is, the connection between cortex and subcortical structures. It’s been known since the turn of the century. Kahal was writing about it, a lot of people writing about it. The cortex is associated or linked to other aspects of other subcortical structures in a rather paradigmatic way that we’ve known about for a long time. So by cortex here, I’ll refer to specific cortical areas, let’s say the motor strip and the supplementary motor area, going to the structures of the striatum. If you don’t know now, then let me tell you, that the striatum, the corpus striatum is comprised by four major structures that arise from the same embryologic restive tissue then migrate to different anatomic locales during development. These four locales are: the caudate, the putamen, and the structures of the ventral stratum, which include the nucleus secumbans (?) and the olfactory tubicle. All part of the striatum. The striatum sends its projections – that’s the major receiving port, if you will, for the basal ganglia – sends its projections to the globus pallidus and its homologous areas. Meaning, the globus pallidus pars interna is functionally homologous to – basically does the same thing as – the pars reticulata of the nigra. Not the compacta but the reticulata of the nigra. So when I say globus pallidus there, I’m talking about the globus pallidus and its homologous areas specifically. The globus pallidus sends its projections to specific nuclei of the thalamus in the motor system, particularly VA and VL. And the thalamus sends its projections back up to cortex in loops. Many different loops. Five different loops that have been identified to date. Now that’s the simple diagram. Let’s make it a little more complicated. I want to show you where I am going to go with this. This is the wiring diagram that you all see in the movement disorders things, but rather than just show it to you I want to draw it out for you to give it a little more sense. We are going to run through the list a little more quickly, so I am going to go over it.
Cheap Canada pharmacy levitra
Like I said, then … so we were talking about the cortex, right? And here I’m specifically talking about primary motor area and supplementary motor cortex, supplementary motor area. Sends its projections to stratum. Now there are two pathways from the stratum. The first one is the so-called direct pathway. The direct pathway is direct because it goes from the stratum, particularly the caudate and putamen and its homologous structures, substantia nigra pars reticulatum. From GPI to, and specifically, VA and VL nuclei in the thalamus motor system. Direct because there are only two arrows involved. Now the indirect pathway, so-called, makes a way-station stop at globus pallidus pars externa, externa to sub-thalamic nucleus of Lewy’s, subthalamic nucleus of Lewy’s to globus pallidus pars interna. From thence to thalamus. Thalamus completes its loop back upstairs. So the basic loop that I described to you before is still there, but now we’ve elaborated on it a little bit. The organizing principle behind this pathway is actually very simple. There are a lot of negatives in all of this. A lot of inhibition going on. In fact, most all of the arrows within subcortical structures are inhibitory and therefore GABA-ergic, with one exception which is the subthalamic nucleus projection to globus pallidus pars interna. The neurotransmitter therefore must be glutamate because it’s excitatory. Everything else is inhibitory within the structure because this projection pathway from thalamus going up to cortex also is excitatory and glutamate-ergic.

Leave a Reply

Your email address will not be published. Required fields are marked *