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CHAPTER 7
The posterior roots conduct all afferent impulses to the spinal cord. These are trans–
mitted directly to the brain via the white posterior tracts or the afferent fibres, forming
connections with intercalated neurones of the posterior grey column cells, either synaptic-
ally with efferent cells of the anterior grey column (monosynaptic reflex arcs) or inter-
segmentally with intercalated neurones in segments above and below. Commissural
axons are those which cross to the opposite side of the cord. Fibres of the intersegmental
neurones may either remain in the grey matter or may travel in the white matter adjacent
to the grey and intermingle (reticular formation of the cord).
The cells of the lateral grey column form the intermediolateral group of cells and
their axons travel in the anterior roots as pre-ganglionic sympathetic fibres and through
the white rami communicanes into the ganglia of the sympathetic chain. In the sacral
section this cell group sends its axons to the anterior roots through the anterior rami of the
corresponding sacral nerves and thus represent a contribution to the para-sympathetic
system.
Electron-microscopy and the work of Eccles and his school has clarified to a great
deal the hitherto obscure physiology of the synapses (Eccles, 1963) and also helped in
solving the old controversy between the exponents of the neurone theory (His, 1886;
Forel, 1887; Cajal, 1888-1934) and those of the reticular theory (Gerlach, 1871; Golgi,
1885; Held, 1905,1929) in favour of the neurone theory.
The supporting tissue of the spinal cord consists of the three types of glia, macro,
micro and oligodendron glia. In addition there are the ependymal cells, forming the
central canal, furthermore, connective tissue in the form of collagen fibres and fibroblasts
accompanying the vascular endothelial cells of the blood vessels. The variety of all these
cells has its bearing on their reactions to injury of the cord.
The white matter
The anatomical arrangement of the white substance of the spinal cord consists of three
columns (funiculi): anterior, lateral and posterior. Within each of these funiculi there are
ascending and descending tracts conducting afferent and efferent impulses ofgreat variety.
ANTERIOR FUNICULUS
(a)
Ascending tract
Anterior spino-thalamic tract.
The anterior spino-thalamic tract is an additional pathway
for some touch and pressure sensibility. The afferent fibres after entering the cord ascend
two or three segments in the posterior funiculus before synapsing with cells of the posterior
grey column of the same side which sends their axons to the white commissure from
where they cross to the contralateral anterior funiculus and enter the anterior spino-
thalamic tract to ascend to the brain.
(b)
Descending tracts
(i) Anterior cortico-spinal tract.
This tract is situated alongside the anterior median
