Localizations of Spinal Lesions.
Being at once a conductor between the brain and nerves, and a reflex nerve centre, we must consider both rôles in seeking to locate lesions from symptoms. In passing from the nerves to and from the sensorium both sensory and motor currents cross so that one side of the brain presides over the other side of trunk and limbs. This crossing of the motor fibres takes place in the medulla oblongata, while that of the sensory fibres occurs in the spinal cord close in front of the nerve from which they have entered.
Cross-Section of one lateral half of the spinal cord therefore causes motor paralysis and rise of temperature of the whole of that side of the body posterior to the lesion, while it induces sensory paralysis and cooling on the opposite side of the body up to the same point. A very limited sensory paralysis on the same side occurs corresponding to the few sensory fibres passing outward obliquely through the portion injured by the cross-section.
A vertical section of the cord separating the one lateral half from the other does not necessarily affect the motor currents, while it produces a limited anæsthesia on each side in the area of distribution of the nerves, the sensory fibres of which crossed in the seat of the lesion.
Transverse section of the superior columns causes hyperæsthesia and lack of coördination.
Transverse section of inferior columns, or of the inferior horn of gray matter, if close behind the medulla, causes no motor paralysis, but if farther back induces motor paralysis on the same side of the body.
Transverse section of the cervical lateral columns causes motor paralysis of the lateral walls of the chest (respiratory tract). If the section is made in the dorsal or lumbar region it is the same as lesion of the superior columns.
Among reflex centres in the cord the following may be named:
The Respiratory Tract in the cervical lateral columns just referred to.
A Glycogenic Centre in the anterior cervical section between the bulb and the fourth cervical nerve.
Centres which Dilate the Pupil between the fifth cervical and the sixth dorsal nerve.
Cardiac Accelerator Centres between the three last cervical and the five first dorsal nerves.
Vaso-Motor Sudoriparous Centres in the central gray matter.
Centre for Anal Sphincter between the sixth and seventh dorsal nerves.
Centre for Vesical Sphincter between the third and fifth lumbar nerves.
Genital Centre, opposite the first lumbar nerve.
Vaso-motor and Trophic Centres are found in the inferior horns of gray matter, and their degeneration causes progressive muscular atrophy.
The Muscular Sense Tract is located near the surface of the superior columns, so that a certain amount of incoördination and unsteadiness of progression follows its destruction.
The Deeper Part of the Superior Columns and the Column of Goll which bounds the superior median fissure control muscular sense and coördination, and their disease (posterior lateral sclerosis) entails locomotor ataxy.