myeloencephalic

cerebrospinal [ser″ĕ-bro-spi´nal]

pertaining to the brain and spinal cord.

cerebrospinal fluid the fluid within the subarachnoid space, the central canal of the spinal cord, and the four ventricles of the brain. The fluid is formed continuously by the choroid plexus in the ventricles, and, so that there will not be an abnormal increase in amount and pressure, it is reabsorbed into the blood by the arachnoid villi at approximately the same rate at which it is produced.

The cerebrospinal fluid aids in the protection of the brain, spinal cord, and meninges by acting as a watery cushion surrounding them to absorb the shocks to which they are exposed. There is a blood-cerebrospinal fluid barrier that prevents harmful substances, such as metal poisons, some pathogenic organisms, and certain drugs from passing from the capillaries into the cerebrospinal fluid.

The normal cerebrospinal fluid pressure is 5 mm Hg (100 mm H₂O) when the individual is lying in a horizontal position on his side. Fluid pressure may be increased by a brain tumor or by hemorrhage or infection in the cranium. hydrocephalus, or excess fluid in the cranial cavity, can result from either excessive formation or poor absorption of cerebrospinal fluid. Blockage of the flow of fluid in the spinal canal may result from a tumor, blood clot, or severance of the spinal cord. The pressure remains normal or decreases below the point of obstruction but increases above that point.

Cell counts, bacterial smears, and cultures of samples of cerebrospinal fluid are done when an inflammatory process or infection of the meninges is suspected. Since the cerebrospinal fluid contains nutrient substances such as glucose, proteins, and sodium chloride, and also some waste products such as urea, it is believed to play a role in metabolism. The major constituents of cerebrospinal fluid are water, glucose, sodium chloride, and protein. Information about changes in their concentrations is helpful in diagnosis of brain diseases.

Samples of cerebrospinal fluid may be obtained by lumbar puncture, in which a hollow needle is inserted between two lumbar vertebrae (below the lower end of the spinal cord), or into the cisterna cerebellomedullaris just below the occipital bone of the skull (cisternal puncture). Pressure of the cerebrospinal fluid is measured by a manometer attached to the end of the needle after it has been inserted.

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myeloencephalic

pertaining to the spinal cord and brain.