Infections of the Central Nervous System
The brain and spinal cord are protected by the skull and spinal column. Three connective tissue layers, the pia mater, arachnoid mater and dura mater, separate the nervous tissue from bone ( Figure 14.1 ). Between the first two layers in the subarachnoid space is the cerebrospinal fluid (CSF), which acts as a shock absorber. It is produced by the choroid plexus of the ventricles, exiting by the foramina of Luschka and Magendie, and then circulates around the brain and spinal cord. CSF is reabsorbed by the arachnoid granulations, which extend into the superior sagittal sinus, one of the great vessels draining the brain. The blood–CSF barrier consists of capillary endothelial cells resting on a basement membrane. The tight junction between these cells is such that constituents of the plasma, such as albumin, are unable to cross into the CSF under normal circumstances. The blood–brain barrier is the boundary between the vasculature and the brain tissue.