Posterior spinocerebellar tract

At a glance

English

Posterior spinocerebellar tract

Latin (TA2)

Tractus spinocerebellaris posterior

System

Brain and spinal cord

Region

Whole body

Side

Single, on the midline

About the posterior spinocerebellar tract

The posterior (dorsal) spinocerebellar tract, also known as Flechsig's tract after the German anatomist Paul Flechsig, keeps the cerebellum informed about the length and tension of muscles in the lower half of the body. It runs up along the outer surface of the lateral funiculus, behind the anterior spinocerebellar tract and just in front of the dorsal root entry zone. Its signals never reach consciousness.

The information starts in muscle spindles, which sense stretch and send it in fast Ia and slower II fibres, and in Golgi tendon organs, which sense tension and use Ib fibres. These are large myelinated axons of first-order neurons in the dorsal root ganglia. Their central processes pass through the posterior horn and end on the cells of the posterior thoracic nucleus, Clarke's column, in lamina VII at the medial base of the horn. That nucleus exists only from about C8 or T1 to L2 or L3. Fibres from lower lumbar and sacral roots first climb in the gracile fasciculus until they reach it, which is why Clarke's column is largest at its lower end.

Axons from Clarke's column turn outwards to the lateral funiculus of the same side and ascend without crossing. In the medulla they enter the inferior cerebellar peduncle and end as mossy fibres in the anterior lobe cortex and the vermis, still on the same side as the limb. Only two neurons are involved and the pathway never changes sides.

The upper limb has its own equivalent, the cuneocerebellar tract, which relays in the accessory cuneate nucleus of the medulla and also enters the inferior peduncle. In walking animals the posterior tract falls silent if the dorsal roots are cut, showing that it reports actual movement of the limb. Degeneration of the tract, as in Friedreich ataxia, contributes to clumsy, unsteady gait.

Function and supply

Function

Carries unconscious proprioception from muscle spindles and tendon organs of the same-side trunk and lower limb to the cerebellum, which uses it to adjust posture and movement.

Blood supply

Mostly from the anterior spinal artery territory, with the surface of the lateral funiculus also reached by the arterial vasocorona and posterior spinal arteries.