Figure 1131

Schematic diagram of the cerebral meninges. The outer layer, the dura mater, is joined to adjacent bone of the cranial cavity (not shown). The inner layer, the pia mater, adheres to the brain surface and follows all its contours. Note that the pia mater follows the branches of the cerebral arteries as they enter cerebral cortex. The intervening layer, the arachnoid, is adjacent but not attached to the dura mater. The arachnoid sends numerous, web-like arachnoid trabeculae to the pia mater. Located between the arachnoid and the pia mater is the subarachnoid space; it contains cerebrospinal fluid. The space also contains the larger blood vessels (cerebral arteries) that send branches into the substance of the brain.

neuron cell body dura mater arachnoid subarachnoid space pia mater cerebral cortex neuron cell body

Blood-Brain Barrier

The blood-brain barrier restricts passage of certain substances from the bloodstream to tissues of the CNS

The observation over 100 years ago that vital dyes injected into the bloodstream can penetrate and stain nearly all organs except the brain provided the first description of the blood-brain barrier. More recently, advances in microscopy and molecular biology techniques have revealed the precise location of this unique barrier and the role of endothelial cells in transporting essential substances to the brain tissue.

The blood-brain barrier develops early in the embryo through an interaction between glial astrocytes and capillary endothelial cells. The barrier is created largely by the elaborate tight junctions between the endothelial cells, which form continuous-type capillaries. Studies with the TEM, using electron-opaque tracers, show complex tight junctions between the endothelial cells. Morphologically, these junctions are more similar to epithelial tight junctions than to those found in other endothelial cells. In addition, TEM studies reveal a close association of astrocytes and their end foot processes with the endothelial basal

0 0

Post a comment