Elements of human physiology (1907) Elements of human physiology elementsofhumanp05star Year: 1907 THE SPINAL CORD 599 anterior and postero-lateral columns is produced. These are the anterior or direct and the crossed pyramidal tracts. The fibres composing these tracts are derived from the pyramidal cells in the motor area of the cerebral cortex, and are there- fore found degenerated if the motor area of the cortex is destroyed. The crossed pyramidal tracts are derived from the other side of the cerebral cortex and have crossed the middle line at the lower part of the medulla, at the pyramida
Elements of human physiology (1907) Elements of human physiology elementsofhumanp05star Year: 1907 THE SPINAL CORD 599 anterior and postero-lateral columns is produced. These are the anterior or direct and the crossed pyramidal tracts. The fibres composing these tracts are derived from the pyramidal cells in the motor area of the cerebral cortex, and are there- fore found degenerated if the motor area of the cortex is destroyed. The crossed pyramidal tracts are derived from the other side of the cerebral cortex and have crossed the middle line at the lower part of the medulla, at the pyramidal decussation. The anterior tracts contmue the course of the pyramids in the medulla for a time, but cross gradually by the anterior commissure on their way down the cord. Fmally, Diagram of spinal cord. Anterior spinal nerve-roots, Posterior root. Anterior pyi-amidal tract, Lateral pyramidal tract, Direct cerebellar tract, Posterior median cokimn. Posterior external column, Antero-lateral ascending tract. therefore, all the fibres reach the crossed pyramidal tracts. They end in the spinal cord by turning into the grey matter, where they break up into a fine bunch of fibrils in close connection with the motor cells of the anterior cornua (or, according to SchJifer, with the cells of the posterior cornua). On their way down the cord they give oii' fine side branches or ' collaterals,' which run into the anterior cornu and there terminate, thus establishing connections between one cortical cell and the anterior cornual cells of several diflerent seg- ments of the spinal cord. It is therefore concluded that they carry motor impulses from the cerebral cortex to the ganglion cells of the cord. Destruction of these columns by disease or otherwise causes the abolition of voluntary control over the muscles.
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