THE SPINAL CORD AS A CONDUCTOR 



353 



carrying motor impulses involving 

 maintenance of posture, and are the 



On their way down the cord they give off fine side branches or collaterals, which 

 run into the grey matter, thus establishing connections between one cortical cell and the 

 anterior cornual cells of several different segments of the spinal cord. These fibres 

 carry voluntary motor impulses from the cerebral cortex to the reflex motor mechan- 

 isms of the cord. Their destruction by disease, or otherwise, causes the abolition 

 of voluntary control over the muscles, without however interfering with the reflex 

 motor functions of the cord which, 

 as a matter of fact, are increased in 

 cases where these tracts have under- 

 gone degeneration. 



(2) RUBRO-SPINAL OR PRE- 

 PYRAMIDAL TRACT (also called 

 Monakow's Bundle). This is a fairly 

 compact group of fibres which degene- 

 rate down wards after section of the 

 cord. It is situated, in cross-section, 

 ventral to the pyramidal tracts. Its 

 fibres can be traced up to the cells in 

 the red nucleus, a mass of grey matter 

 in the mid-brain lying ventrally to 

 the nucleus of the third nerve. They 

 are probably chiefly concerned with ^.174. Diagram j/rom SCHAFEB) showing the 



ascending (right side) and the descending (left 

 side) tracts in the spinal cord. 

 1, crossed pyramidal ; 2, direct pyramidal ; 



main efferent channels of the cere- 3 antero-lateral descending; 3a, spino-olivary 

 bellum red nucleus co-ordinating Descending (bundle of Helweg); 4, pre-pyramidal 



> (rubro-spinal) ; 5, comma ; 6, postero -mesial ; 

 mechanism. 7> pos tero-lateral ; 8, Lissauer's tract ; 9, dorsal 



(3)VESTIBULO-SPINALTRACT. (ascending) cerebellar; 10, antero-lateral ascend- 

 This consists of scattered fibres in the ing ; sm, septo-marginal ; spl, dorsal root zone ; 

 antero-lateral column, which degene- a ' anterior horn-cells ;i, intermedio-lateral horn; 



p, cells of postenor horn ; d. Clarke s column. 



rate in the downward direction. They The fine dots represent the situation of the 

 were formerly supposed to be derived ' internnncial ' or ' endogenous ' fibres of the spinal 

 from the cerebellum of the same side, cord, 

 but it has been shown that they are 



,in all probability derived from Deiters' nucleus in the medulla an important trans- 

 mitting station between the cerebellum and cord. 



(4) OLIVO-SPINAL AND THALAMICO-SPINAL TRACTS (Bundle of Helweg). 

 This tract is also situated in the antero-lateral column, opposite the head of the anterior 

 horn. It consists mainly of fibres which pass from the thalamus (the fore brain) through 

 the inferior olive of the medulla downwards in the cord as far as the lower cervical 

 region. 



(5) COMMA TRACT. This tract lies in the posterior columns at the junction of 

 the postero-median and postero-lateral portions. It consists for the most part of the 

 descending branches of the afferent dorsal nerve roots. These divide as they enter 

 the cord, and their descending branches pass down for two or three segments in the 

 comma tract before turning into the grey matter. The tract, however, contains fibres 

 of other origin, some of which begin and end in the spinal cord itself. 



(6) TRACT OF MARIE. This, also in the anterior column, contains both descend- 

 ing and ascending fibres and is largely a continuation of the posterior longitudinal bundle, 

 the connections of which we shall have to study later on. A small tract of fibres, which 

 degenerate in the descending direction, is also found in the posterior part of the cord 

 adjoining the posterior longitudinal fissure. 



(7) SEPTO-MARGINAL BUNDLE. This is largely proprio -spinal, but may 

 contain fibres coming from the mid-brain. 



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