A treatise on the principles and practice of medicine . volving given neurones, non-system diseases. The functions of the cord are (1) conduction of motor impulses tothe muscles; (2) conduction of sensory impressions to the brain; (3)certain reflexes; (4) centres governing the bladder, rectum, etc., and(5) trophic influences. 1. The motor tract is composed of two sets of neurones or upper segment has its origin in the cells of the motor cortex (, A), runs through the corona radiata, internal capsule, cms, pons 820 DISEASES OF THE SPINAL CORD and anterior pyramids of the medu
A treatise on the principles and practice of medicine . volving given neurones, non-system diseases. The functions of the cord are (1) conduction of motor impulses tothe muscles; (2) conduction of sensory impressions to the brain; (3)certain reflexes; (4) centres governing the bladder, rectum, etc., and(5) trophic influences. 1. The motor tract is composed of two sets of neurones or upper segment has its origin in the cells of the motor cortex (, A), runs through the corona radiata, internal capsule, cms, pons 820 DISEASES OF THE SPINAL CORD and anterior pyramids of the medulla (whence the name pyramidaltracts), and crosses to the opposite side (Fig. 61, B), running down in thelateral columns of the cord (C) and giving off branches (D,D) to theanterior horns, where the tract ends infine terminal filaments, whichsurround the motor ganglion cells in the anterior horn. (See Fig. 56.)The lower segment begins with the motor cell in the anterior horn (E),the dendrites of which connect with the terminal ramifications of the FAC. ARM FACE Fig. 61.—Illustrating the course of the two motor neurones: A, cortical cell of origin ofmotor tract; B, decussation in medulla; C, course in lateral columns of cord: D,D, branchesto anterior horns in cord; in second (lower) neurone, E, cells of anterior horns, E, cellsin pons; F, nerve trunks; G, motor end plates; H, muscles. axis-cylinder of the upper segment by contact (Ramon y Cajal) or byconcrescence (Held); it extends along its own axis-cylinder into theanterior nerve roots and nerve (F)f and ends in terminal ramifications(G, motor end plates) in a muscle, e. g., of the arm or leg, which is on theside opposite to the origin of the cortical motor centre. From the cells ofboth segments the motor impulse travels downward (cellulifugal con-duction). About 75 per cent, of the upper motor neurones cross asabove described, are called the crossed pyramidal tracts (, in Figs. GENERAL ANATOMICAL CONSIDERATIONS 821 61
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