White Matter

The tracts of nerve fibres in the white matter may be divided either: (1) anatomically - into short and long tracts, or (2) physiologically - into ascending and descending tracts. The short tracts lie immediately adjacent to the grey matter, along its outer side and round the anterior horn; they form the antero-lateral basis bundles.

The fibres which constitute them run for varying distances from one part of th cord to another, some connecting adjacent segments, others running comparatively long distances in the cord. Some of the fibres convey impulses upwards, others downwards (Fig. 37).

The long tracts extend between the brain and spinal cord. Those which convey impulses upwards towards the brain are termed ascending tracts - they are mainly sensory; conversely, the descending tracts carry impulses downwards in the cord and are largely motor. There are several minor tracts belonging to this series, but it will be sufficient to indicate the more important ones, viz. :

Descending -- Direct pyramidal tracts / Crossed pyramidal tracts.

Ascending -- Columns of Goll and of Burdach / Direct cerebellar tracts.