« PreviousContinue »
Unilateral destruction of this area results in hemianopsia, or blindness of the corresponding halves of the two retinæ. Destruction of both occipital lobes in man results in total blindness. Stimulation or irritation of the visual center causes photopsia, or hallucinations of sight, in corresponding halves of the retinæ. There have been instances of injury of these parts when sensations of color were abolished with preservation of those of space and light, thus showing a special localization of the color
Late experiments show that the centers of the two hemispheres are united, as ocular fatigue of a non-used eye was proportional to the fatigue of the exercised one.
The auditory centers are located in the temporo-sphenoidal lobes. Word deasness is associated with softening of these parts, and their complete removal results in deafness.
The gustatory and olfactory centers are located in the uncinate gyrus, on the inner side of the temporo-sphenoidal lobes. There does not seem to be any differentiation, up to this time, of these two centers.
The center for tactile impressions was located by Ferrier in the hippocampal region. Horsley and Schäfer found that destructive lesions of the gyrus fornicatus was followed by hemianesthesia of the opposite side of the body, which was more or less marked and persistent. These observers conclude that the limbic lobe“ is largely, if not exclusively, concerned in the appreciation of sensations painful and tactile.”
The superior and middle frontal convolutions appear to be the seat of the reason, intelligence, and will. Destruction of these parts is followed by proportional hebetude, without any impairment of sensation or motion.
SYMPATHETIC NERVOUS SYSTEM. The Sympathetic Nervous System consists of a chain of ganglia connected together by longitudinal nerve filaments, situated on each side of the spinal column, running from above downward. The two ganglionic: cords are connected together in the interior of the cranium by the ganglion of Ribes, on the anterior communicating artery, and terminate in the ganglion impar, situated at the top of the coccyx.
The chain of ganglia is divided into groups, and named according to the location in which they are found, viz., cranial, four in number; cervical, three; thoracic, twelve; lumbar, five; sacral, five; coccygeal, one.
Each ganglion consists of a collection of vesicular nervous matter, bundles of non-medullated nerve fibers, imbedded in a capsule of connective tissue.
The ganglia are reinforced by motor and sensory fibers from the cerebrospinal nervous system.
The Ganglia have distinet nerve fibers from which branches are distributed to the glands, arteries, muscles, and to the cerebral and spinal nerves; many pass, also, to the visceral ganglia, e.g., cardiac, semilunar, pelvic, etc.
1. The ophthalmic or ciliary ganglion is situated in the orbital cavity posterior to the eyeball; it is of small size and of a reddish-gray color ; receives filaments of communication from the motor oculi, ophthalmic branch of the fifth pair, and the carotid plexus. Its filaments of distribution are the ciliary nerves, which consist of
1. Motor fibers for the circular fibers of the iris and ciliary muscle.
retina. 4. Motor fibers for the dilator fibers of the iris. 2. The spheno-palatine, or Meckel's ganglion, triangular in shape, is situated in the spheno-maxillary fossa; receives filaments from the facial (Vidian nerve), and the superior maxillary branch of the fifth nerve. Its filaments of distribution pass to the gums, the soft palate, levator palati, and azygos uvulæ muscles.
3. The otic, or Arnold's ganglion, is of small size, oval in shape, and situated beneath the foramen ovale; receives a motor filament from the facial and sensory filaments from glosso-pharyngeal and fifth nerve; sends filaments to the mucous membrane of the tympanic cavity and to the tensor tympani muscle.
4. The submaxillary ganglion, situated in the submaxillary gland, receives filaments from the chorda tympani, sensory filaments from the lingual branch of the fifth nerve, and filaments from the sympathetic. The chorda tympani nerve supplies vaso-dilator and secretory fibers to the submaxillary and sub-lingual glands. The fifth nerve endows the glands with sensibility, while the sympathetic supplies secretory or tropic fibers.
The superior cervical ganglion is fusiform in shape, of a grayish-red color, and situate opposite the second and third cervical vertebræ ; it sends branches to form the carotid and cavernous plexuses which follow the course of the carotid arteries to their distribution; also sends branches to
join the glosso-pharyngeal and pneumogastric, to form the pharyngeal plexus.
The middle cervical ganglion, the smallest of the three, is occasionally wanting; it is situated opposite the fifth cervical vertebra; sends branches to the superior and inferior cervical ganglion and to the thyroid artery.
The inferior cervical ganglion, irregular in form, is situated opposite the last cervical vertebra; it is frequently fused with the first thoracic ganglion.
The superior, middle, and inferior cardiac nerves, arising from these cervical ganglia, pass downward and forward to form the deep and superficial cardiac plexuses located at the bifurcation of the trachea, from which branches are distributed to the heart, coronary arteries, etc.
The Thoracic Ganglia are usually twelve in number, placed against the heads of the ribs behind the pleura; they are small in size and gray in color; they communicate with the cerebro-spinal nerves by two filaments, one of which is white, the other gray.
The great splanchnic nerve is formed by the union of branches from the sixth, seventh, eight, and ninth ganglia; it passes through the diaphragm to the semilunar ganglion.
The lesser splanchnic nerve is formed by the union of filaments from the tenth and eleventh ganglia, and is distributed to the celiac plexus.
The renal splanchnic nerve arises from the last thoracic ganglion and terminates in the renal plexus.
The semilunar ganglia, the largest of the sympatbetic, are situated by the side of the celiac axis; they send radiating branches to form the solar plexus; from the various plexuses, nerves follow the gastric, splenic, hepatic, renal, etc., arteries, into the different abdominal viscera.
The Lumbar Ganglia, four in number, are placed upon the bodies of the vertebra; they give off branches which unite to form the aortic lumbar plexus and the hypogastric plexus, and follow the blood-vessels to their terminations.
The Sacral and Coccygeal Ganglia send filaments of distribution to all the blood vessels of the pelvic viscera.
Properties and Functions.—The sympathetic nerve possesses both sensibility and the power of exciting motion, but these properties are much less decided than in the cerebro-spinal system. Irritation of the ganglia does not produce any evidence of pain until some time has elapsed. If caustic soda be applied to the semilunar ganglia, or a galvanic current be passed through the splanchnic nerves, no instantaneous effect is noticed, as in the case of the cerebro-spinal nerves; but in the course of a few seconds