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 CEREBELLAR
HEMISPHERE 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.