DISEASES OF THE NERVOUS SYSTEM (CONTINUED). III. DISEASES OF THE MEDULLA OBLONGATA. PRELIMINARY DIAGNOSTIC CONSIDERATIONS. THE medulla oblongata is known also as the spinal bulb, and its diseases and also its distinctive symptoms are therefore designated bulbar. As the motor and sensory tracts between the brain and the spinal cord traverse the medulla oblongata, it is not surprising that in the presence of bulbar disease motor and sensory disturbances are not rarely encountered. It is worthy of especial consideration that the motor tracts from the brain largely cross over within the pyramidal decussation to the lateral pyramidal tract of the opposite half of the spinal cord, for it follows that if the motor tract is interrupted before decussation has taken place the paralysis will occur upon the opposite side of the body, whereas lesions below this point (toward the spinal cord), therefore after decussation has taken place, give rise to paralysis upon the same side of the body. At times lesions are so situated as to involve a portion of the motor path above and another portion below the decussation, and as a result of which it is possible that perhaps the arm upon the side of the lesion (below the decussation) and the leg upon the opposite side of the body (above the decussation) are paralyzed-so-called crossed hemiplegia. Smaller lesions give rise at times to bulbar monoplegia of the arm or the leg, and it may also happen that the paralysis occurs upon the same side as the lesion or upon the opposite side accordingly as the lesion is seated above or below the decussation of the motor paths. Motor and sensory disturbances are in nowise characteristic of bulbar disease. The bulbar symptoms proper result from involvement of the nuclei of individual cerebral nerves, particularly the hypoglossal, the glossopharyngeal, and the vago-accessory, which are situated at the lowermost extremity of the fourth ventricle. As is well known, groups of ganglion-cells are found upon the floor of the fourth ventricle, from which arise nerve-fibers for the individual cerebral nerves, whence the designation nuclei of cerebral nerves. These nerve-fibers first pass through the medulla oblon 2-II. 17 gata (and the pons) before they appear at the surface as cerebral nerve-roots, and they thus pursue an intramedullary (bulbar, pontine) course. Between the nuclei and the brain the nerve-fibers undergo decussation, so that, for example, the fibers of the right facial nerve above the facial nucleus pass over to the tracts from the left cerebral hemisphere. From these relations it will be FIG. 1.-Medulla oblongata and adjacent portion of the brain, with the nerves arising therefrom after Schwalbe): of, olfactory nerve; op, optic nerve; orm, oculomotor nerve: troch, trochlear nerve; trg, trigeminal nerve; ab, abducens nerve; fe, facial nerve; ac, auditory nerve; gl, glossopharyngeal nerve: rg, vagus: ace, accessory nerve: hp, hypoglossal nerve; py, pyramid; or, olive; th, optic thalamus; gm, q, internal and external geniculate bodies, h, hypophysis: c, c, mammillary bodies; JR, island of Reil. clear that lesions in the nerve-nuclei or within the medullary path up to the point of exit of the cerebral nerve-trunk will give rise to paralysis upon the same side, while disease above the nuclei for the cerebral nerves will be attended with paralysis upon the opposite side of the body. The principal bulbar symptoms consist in derangement of articulation, paralysis of swallowing, and disturbance in breathing and in cardiac action. Articulatory disturbances (anarthria, dysarthria) result from paralysis of the hypoglossal nerve and the attendant paralysis of the tongue (bulbar glossoplegia). In severe cases the tongue lies in the mouth like an immovable mass of flesh, and the formation of a bolus is therefore impossible. Should the disease pursue a chronic course, degenerative atrophy of the tongue takes place, and the organ exhibits fibrillary muscular contractions and degenerative electric reaction. The symptoms are entirely analogous to those of anterior poliomyelitis, as the ganglion-cells of the nuclei of the cerebral nerves also are largely endowed with trophic-motor functions. Disorders in swallowing FIG. 2.-Medulla oblongata seen from its posterior aspect, with a view of the fourth ventricle and the nerve-nuclei upon its floor: le, locus coeruleus (nucleus of the trigeminus); fa, fovea anterior (nucleus of the facial nerve); et, eminentia teres (knee of the facial nerve); hk, nucleus of the hypoglossal nerve; ak, median nucleus of the posterior root of the auditory nerve; vk, nucleus of the vagus (ala cinerea); acck, nucleus of the accessory nerve; cq, corpora quadrigemina; cccq, crura cerebelli ad corpora quadrigemina; cap, crura cerebelli ad pontem: pc, pedunculus cerebelli: stm, medullary or auditory striæ; ob, obex; fg, funiculus gracilis; je, funiculus cuneiformis. depend upon paralytic conditions involving the glossopharyngeal and vago-accessory nerves, which supply the muscles of deglutition with motor fibers. Vago-accessory paralysis may be attended also with paralysis of the laryngeal muscles, derangement in respiratory activity (Cheyne-Stokes breathing), and acceleration of the action of the heart. Naturally, not all bulbar diseases give rise to the bulbar symptoms just described. These occur only when the bulbar nuclei of the cerebral nerves or the intrabulbar nerve-fibers originating from them are involved in the morbid process. For the better comprehension of what has preceded, a few anatomic remarks and illustrations may be appropriate. Upon the anterior (ventral) |