36 PHYSIOLOGY [NERVOUS Columns of the Spinal Cord. Divided into Continued in Medulla Oblongata as Pass on to ( A. <!. Lateral, or crossed. Decussate in anterior pyra Cerebrum. Pyramidal fibres from the pos- mids. tract. terior part of the lateral column as low as the third or fourth sacral nerves. b. Anterior, or un Pass under " crossed, fibres from pyramid on the dorsal region same side, 1. Posterior Cerebrum. of the cord - col and form | longitudi- umns of Tiirck, or columns of Lock- longitndinal! nalbundle fibres of the ( in pons. hart Clarke. reticularisal- 2. Tract of Corpora _. ba in dorsal the fillet. quadri- 5 part of me gemina. = sial area. ) C B. c. Cerebellar tract, Restiform body. Cerebellum. 1 Cerebellar between lateral
tract. pyramidal tract and the outer sur i face of the cord as 7 low as the second C or third lumbar. All the d. Principal tract of antero- anterior column, lateral that is, the antero- columns lateral column less except the fibres in b. Not AandB. continued up probably commis- sural from one side of cord to the other. e. From anterior col Pass below olivary body to Cerebellum. umn. form part of restiform body. Sometimes called the "band of Solly "not always present. / o. Posterior white column, or Coil s tract, from middle of dorsal region. b. Posterior lateral Posterior median column, Cerebrum. column, between becoming the funiculus posterior median gracilis, which, with the Posterior column. > column and pos- tero-lateral groove. expansion called the clava, becomes the posterior py ramids. c. Funiculus of Ro Funipulus cuneatus, form Cerebellum. lando, between the ing, with cerebellar tract posterior lateral from antero-lateral column, column b and pos- the restiform body. tero-lateral groove
higher up. It is -important to note the fact that each column of the cord, through the medulla, is thus connected both with the cerebrum and with the cerebellum. Development has shown that the fibres of the bundles which are first formed develop a medullary sheath at a time when the fibres of the later-formed bundles are non-medullated. " When the cord of a human embryo is examined at the end of the fifth month it will be found that the pyramidal fibres of the lateral columns, the fibres of the columns of Tiirck, and of the columns of Goll are non-medullated; while the fibres of the anterior and pos terior root-zones and the cerebellar fibres of the lateral columns are medullated" (Ross). It would appear, therefore, that the latter are the more primitive structures, and that the former are super- added in the cords of the higher animals. The grey matter of the medulla is broken up by changes in the distribution of the white matter into nuclei or masses of nerve-cells, instead of having the crescentic form seen in the spinal cord. These nuclei are connected with the roots of important cranial nerves, and may be regarded as corresponding with the anterior horns of grey matter, with the posterior horns, and with the grey matter between these. The following nuclei can be found : (1) the hypoglossal nucleus, for the hypoglossal nerve, the motor nerve of the tongue; (2) a common nucleus, for a portion of the spinal accessory, vagus, and glosso-pharyngeal nerves; (3) the principal or lower auditory nucleus, for the auditory nerve; (4) nuclei for the sixth or abducent nerve, supplying the external rectus muscle of the eye; (5) nucleus for the fourth nerve, supplying the superior oblique muscle of the eye; (6) the facial nerve, the motor nerve of the face; (7) the cor- pus denUitum of the olivary body, not directly connected with the roots of nerves, but containing nerve-cells. * Some fibres, both of the sensory and motor roots of the fifth nerve, originate also as far back as the medulla. The third, fourth, sixth, and hypoglossal nerves belong to the system of anterior motor nerves, related to the anterior cornua, whilst the spinal accessory, vagus, glosso- pharyngeal, and fifth belong to the "mixed lateral system," that is, they are related to the posterior cornua and intermediate grey matter. Like the spinal cord, the medulla may be regarded as containing tracts for sensory and motor transmission, and as constituting a series of reflex centres for special movements. 1. As a Conductor of Motor and Sensory Impressions. Inasmuch Motor also, as such movements as those of the circulation, respiration, and and vaso -motor action are necessary to life, destruction of the sensory medulla causes almost instant death. Motor fibres coming from trnnsmi> the brain above decussate in the anterior pyramids and then run sion of down the lateral columns of the cord, issuing to the muscles by medulla the anterior roots of the spinal nerves. Hence, whilst section of an antero-lateral column of the cord will cause paralysis of motion on the same side, section of an anterior pyramid above the decus sation causes paralysis of motion on the opposite side. But fibres carrying sensory impressions also decussate in the grey matter at the bottom of the posterior median fissure of the cord. It follows, therefore, that disease, such as rupture of a vessel causing a clot in the brain, say in the left corpus striatum and left optic thalamus, causes paralysis both of motion and of sensation on the opposite side, that is, in the case supposed, there would be right hemiplegia. The path of sensory impressions is probably in the grey matter but the precise course of sensory fibres has not been traced. 2. As a Reflex Centre. Numerous special centres have been re- Medulla ferred to the medulla oblongata. as refles (1) Respiratory centres, two in number, expiratory and inspiratory, connected centre, with the roots of the pneumogastric nerves. Destruction at once causes cessa tion of respiratory movements. (2) 1 aso-motor centre, regulating the calibre of the smaller blood-vessels throughout the body (see p. 30). (3) Cardiac centres, probably two in number one accelerating, associated with the sympathetic; the other inhibitory, connected with the pneumogastric (see "p- - ) (*) Centres for deglutition, associated with the sensory and motor nerves involved in this process (see NUTRITION, vol. xvii. p. 670). (5) Centre for voice, regu lating to some extent, through the sterno-cleido-mastoid muscle, the emission of air through the glottis in expiration and phonation. (li) Centre influencing f/lycogenesis, probably by the action of the vaso -motor centre on the blood vessels of the liver (see NUTRITION, vol. xvii. p. 082). (7) Centre directly in fluencing salivary secretion, from which originate those fibres of the facial, forming the chorda tympani and lesser superficial petrosal, distributed to the salivary glands (see NUTRITION, vol. xvii. p. 672). (8) Centre for the motur fibres supplying the face and muscles of mastication. These exist in the facial for the muscles of the face and in the motor portion of the fifth for the muscles of mastication. Further, the medulla receives nervous influences from the higher centres, by which all the centres above enumerated may be more or less influenced. Pons Varolii. The pons Yarolii is above and in front of the Pons medulla oblongata, and between the hemispheres of the cerebellum. Varolii. It consists of fibres passing in two directions, viz., longitudinally, connecting the brain above with the medulla and cord below; and transversely, connecting the lateral hemispheres of the cerebellum, thus forming the middle peduncles of that organ. Its general position and appear ance are seen in fig. 23. Mixed up with these fibres are various nuclei of grey matter connected with the roots of cranial nerves. The most important of these nuclei are (1) the nucleus of the facial nerve; (2) the motor nucleus of the fifth nerve; (3) the upper sensory nucleus of the fifth nerve; (4) the inner or chief nucleus of the auditory nerve; (o) the outer or superior nucleus of the auditory nerve; (6) the accessory nucleus of the auditory nerve; (7) the nu cleus of the sixth nerve. It will be observed that several of these nerves are also con nected with nuclei in the Fio. 23. Section of medulla oblongata and medulla oblongata. Like P<>ns to show the course of fibres. , super- t 1 io flclal, and a , deep transverse fibres of pons; b, b, anterior pyramids ascending at b the cord and medulla, the pons is to be regarded as a conductor of impressions and probably also as a reflex centre. Motor transmission occurs chiefly in the an terior part. As the fibres of the facial nerve decussate in the pons, and then carry in fluences outwards, unilateral through pons; c, c, olivary bodies; c , oli vary fasciculus in pons; d,d, anterior columns of cord; e, inner part of right column .joining anterior pyramid; /, outer part going to olivary fasciculus; g, lateral column of cord; It, the part which decus sates at k, the decussation of the pyramids; I, the part which joins the restiform body; TO, that which forms the fasciculus teres; H, arciform fibres. 1 and 2, sensory and motor roots of the fifth nerve; 3, sixth 1 " rvn; 4> l )0rtio (lura I 5 > l "i tio inter- iniurv or di ISP of the IK uijuiy 01 ase or the poi ) lnedia . 0> portio mo]lis of the scvcnt h may cause paralysis of the nerve; 7, glosso-pharyngeal; s, pneumo- face on the same side as the gastric; 0, spinal accessory; 10, hypo- disease, and paralysis of the K lossal nerve. limbs on the opposite side if the disease has affected the facial before its decussation in the pons. Usually in cases of paralysis of one side (hemiplegia) from a clot or disorganization in one corpus striatum the paralysis of the face is on the same side as that of the
limbs. In diseases of the pons loss of sensibility is a much moro