Читать книгу Special Report on Diseases of the Horse - Charles B. Michener - Страница 16

The great brain, or cerebrum, is the seat of intelligence, and it contains the centers that control motion in many parts of the body. The front portion of the brain is believed to be the region that is most important in governing the intelligence. The central and posterior portions of the cerebrum contain the centers for the voluntary motions of the face and of the front and hind legs. The growth of a tumor or an inflammatory change in the region of a center governing the motion of a certain part of the body has the effect of disturbing motion in that part by causing excessive contraction known as cramps, or inability of the muscles to contract, constituting the condition known as paralysis. The nerve paths from the cerebrum, and hence from these centers to the spinal cord and thence to the muscles, pass beneath the small brain, or the cerebellum, and through the medulla oblongata to the spinal cord. Interference with these paths has the effect of disturbing motion of the parts reached by them. If all of the paths on one side are interfered with, the result is paralysis of one side of the body.

The small brain, or cerebellum, governs the regularity, or coordination, of movements. Disturbances of the cerebellum cause a tottering, uncertain gait. In the medulla oblongata, which lies between the spinal cord and the cerebellum, are the centers governing the circulation and breathing.

The spinal cord carries sensory messages to the brain and motor impressions from the brain. The anterior portions of the cord contain the motor paths, and the posterior portions of the cord contain the sensory paths.

Paralysis of a single member or a single group of muscles is known as monoplegia and results from injury to the motor center or to a nerve trunk leading to the part that is involved. Paralysis of one-half of the body is known as hemiplegia and results from destruction or severe disturbances of the cerebral hemisphere of the opposite side of the body or from interference with nerve paths between the cerebellum, or small brain, and the spinal cord. Paralysis of the posterior half of the body is known as paraplegia and results from derangement of the spinal cord. If the cord is pressed upon, cut, or injured, messages can not be transmitted beyond that point, and so the posterior part becomes paralyzed. This is seen when the back is fractured.

Abnormal mental excitement may be due to congestion of the brain or to inflammation. The animal so afflicted becomes vicious, pays no attention to commands, cries, runs about in a circle, stamps with the feet, strikes, kicks, etc. This condition is usually followed by a dull, stupid state, in which the animal stands with his head down, dull and irresponsive to external stimuli. Cerebral depression also occurs in the severe febrile infectious diseases, in chronic hydrocephalus, in chronic diseases of the liver, in poisoning with a narcotic substance, and with chronic catarrh of the stomach and intestines.

Fainting is a symptom that is not often seen in horses. When it occurs it is shown by unsteadiness of gait, tottering, and, finally, inability to stand. The cause usually lies in a defect of the small brain, or cerebellum. This defect may be merely in respect of the blood supply, to congestion, or to anemia, and in this case it is likely to pass away and may never return, or it may be due to some permanent cause, as a tumor or an abscess, or it may result from a hemorrhage, from a defect of the valves of the heart, or from poisoning.

Loss of consciousness is known as coma. It is caused by hemorrhage in the brain, by profound exhaustion, or may result from a saturation of the system with the poison of some disease. Coma may follow upon cerebral depression, which occurs as a secondary state of inflammation of the brain.

Where the sensibility of a part is increased the condition is known as hyperesthesia, and where it is lost—that is, where there is no feeling or knowledge of pain—the condition is known as anesthesia. The former usually accompanies some chronic disease of the spinal cord or the earlier stages of irritation of a nerve trunk. Hyperesthesia is difficult to detect in a nervous, irritable animal, and sometimes even in a horse of less sensitive temperament. An irritable, sensitive spot may be found surrounded by skin that is not sensitive to pressure. This is sometimes a symptom of beginning of inflammation of the brain. Anesthesia occurs in connection with cerebral and spinal paralysis, section of a nerve trunk leading to a part, in severe mental depression, and in narcotic poisoning.