Point 3











Dorsal Spinocerebellar Tract at T1When the 1a, 1b, and II axons enter the spinal cord they dive into the grey matter of the dorsal horn until they reach its base. An investigator by the name of Rexed has divided the grey matter of the cord into layers or laminae, and the base of the dorsal horn is called lamina VII. Within this lamina at spinal segments C8-L3, AND ONLY AT THESE LEVELS, there is a very distinctive cell group called CLARKE'S NUCLEUS OR COLUMN. The 1a, 1b and II fibers terminate on cells in Clarke's nucleus. From there, cells in Clarke's nucleus send axons into the IPSILATERAL lateral funiculus where they are located dorsal and laterally. These axons comprise the DORSAL SPINOCEREBELLAR TRACT (DSCT). The cells of origin of this tract lie in the IPSILATERAL Clarke's nucleus. The pathway passes rostrally in the lateral funiculus and eventually terminates within the IPSILATERAL CEREBELLUM. As fibers from cells in Clarke's column enter the DSCT and ascend, they are organized such that the most caudal fibers lie laterally within the DSCT, while the most rostral (C8) lies medially in the DSCT. Compare this with the dorsal column system and ALS.

DSCTTo get into the cerebellum, the DSCT courses within (is a component of) the inferior cerebellar peduncle (L., a little foot) or restiform body. Think of a cerebellar peduncle as a bundle of axons connecting the spinal cord/brain stem and the overlying cerebellum. There are three of these peduncles. More on this later in the course!!

It's a crying shame that Clarke's nucleus is not present at every spinal cord level. As I mentioned earlier, it is only present at spinal cord segments C8-L3. So, if a 1a, 1b, or II axon comes into the spinal cord between C8-L3, fine!!! There is a Clarke's nucleus waiting for it and bingo, the fiber dives into the nucleus and the information that it is conveying is relayed to the cerebellum (via the DSCT). However, think about a 1a, 1b or II fiber coming in at spinal level L5. It looks around and there is no Clarke's nucleus to hitch a ride on. What would you do if you were a fiber who wanted to get your information to the cerebellum?? Personally, I would pass rostrally in the fasciculus gracilis (no fasc. cuneatus is here!!) until I got to L3, where there is a Clarke's column, and dive into the nucleus.

Accessory Cuneate NucleusStick DiagramWhat about 1a, 1b and II fibers associated with dorsal roots above C8? Well, they enter the cord, don't have a Clarke's nucleus , so they enter the fasciculus of the upper extremity (fasc. cuneatus) until they reach the caudal medulla, where they synapse in the ACCESSORY CUNEATE NUCLEUS. Cells in the accessory cuneate nucleus project to the IPSI cerebellum via the inferior cerebellar peduncle (just like cells in Clarke's column do).

I realize that this is a tremendous amount of information about the DSCT. Some instructors are fearless enough to talk about a ventral spinocerebellar tract. I am not fearless at this point! But you should know that you might hear the term SPINOCEREBELLAR PATHWAYS sometime in your career!