Spinocerebellar tract

Brain: Spinocerebellar tract
Spinocerebellar tracts are labeled in blue at right.
Latin	Tractus spinocerebellaris
Gray's	p.761
NeuroNames	ancil-2137625602

The spinocerebellar tract is a set of axonal fibers originating in the spinal cord and terminating in the ipsilateral cerebellum. This tract conveys information to the cerebellum about limb and joint position (proprioception).

Origins of proprioceptive information

Proprioceptive information is obtained by Golgi tendon organs and muscle spindles.

• Golgi tendon organs consist of a fibrous capsule enclosing tendon fascicles and bare nerve endings that respond to tension in the tendon by causing action potentials in Ib afferent neurons (relatively large, myelinated, quickly conducting).

• Muscle spindles fibers are complicated systems of length monitoring within muscles which result in information being carried via Ia neurons (larger and faster than Ib) (from both nuclear bag fibers and nuclear chain fibers) and II neurons (solely from nuclear chain fibers).

All of these neurons are "first order" or "primary", are sensory (and thus have their cell bodies in the dorsal root ganglion) and pass through Rexed laminae layers I-VI of the dorsal horn, to form synapses with "second order" or "secondary" neurons in the layer just beneath the dorsal horn (layer VII)

Subdivisions of the tract

The tract is divided into:^[1]

Pathway for dorsal and spinocuneocerebellar tracts

The motor neurons synapse in an area known as Clarke's nucleus or "Clarke's column".

This is a column of relay neuron cell bodies within the medial gray matter within the spinal cord in layer VII (just beneath the dorsal horn), specifically between T1-L3. These neurons then send axons up the spinal cord, and project ipsilaterally to medial zones of the cerebellum through the inferior cerebellar peduncle.

Below L3, relevant neurons pass into the fasciculus gracilis (usually associated with the dorsal column-medial lemniscal system) until L3 where they synapse with Clarke's nucleus (leading to considerable caudal enlargement).

The neurons in the accessory cuneate nucleus have axons leading to the ipsilateral cerebellum via the inferior cerebellar peduncle.

Pathway for ventral and rostral spinocerebellar tracts

Some neurons of the ventral spinocerebellar tract instead form synapses with neurons in layer VII of L4-S3. Most of these fibers cross over to the contralateral lateral funiculus via the anterior white commissure and proceed up the spinal cord to synapse with neurons in the superior cerebellar peduncle. The fibers then often cross over again within the cerebellum to end on the ipsilateral side. For this reason the tract is sometimes termed the "double-crosser."

The Rostral Tract synapses at the dorsal horn lamina (intermediate gray zone) of the spinal cord and ascends ipsilaterally to the cerebellum through the inferior cerebellar peduncle.

References

External links

• http://www.anatomyatlases.org/MicroscopicAnatomy/Section17/Plate17327.shtml