Point 5 Intro Pathway Deficit Note Summary Overview Problems Contents Anatomy

You should recall from the spinal cord module that proprioceptive information from muscle spindles (Ia, II) and Golgi tendon organs (Ib) reaches the cerebellum via the dorsal spinocerebellar tract. The cells of origin of this tract lie in the ipsilateral Clarke's column. This column of cells is present only at spinal cord levels C8­L3. Central processes of dorsal root neurons that enter caudal to L3 have to ascend to reach L3. Consequently, Clarke's column is quite enlarged caudally. (Clarke's column neurons at L3 need to serve not only entering fibers at L3, but all of those entering below L3.) Ia, Ib and type II axons of the dorsal root ganglia rostral to Clarke's column (C8) pass rostrally to reach the ipsilateral caudal medulla, where they end within the ACCESSORY CUNEATE ("wedge­shaped") NUCLEUS. This nucleus, which is somewhat difficult to see, lies dorsal to the spinal tract and nucleus V and lateral to the most rostral pole of nucleus cuneatus. Cells in the accessory cuneate nucleus send their axons to the IPSILATERAL CEREBELLUM via a fiber bundle called the inferior cerebellar peduncle (together with the dorsal spinocerebellar fibers). This pathway is called the CUNEOCEREBELLAR TRACT. The accessory cuneate nucleus is concerned with relaying proprioceptive information from the arm (and neck) to the cerebellum, and the nucleus can be considered as the rostral equivalent of Clarke's column. REMEMBER: Accessory cuneate nucleus: lies in the medulla. receives UNCROSSED fibers from dorsal root ganglia above C8. receives the same kind of information that Clarke's column does. projects to the IPSILATERAL cerebellum via inferior cerebellar peduncle. is concerned with the arm, while Clarke's column is concerned with the forearm, trunk and lower extremity.