Central Nervous System (CNS)

In the Spinal Cord, each segment is connected to a pair of spinal nerves. Each spinal nerve is joined to its segment of cord by a number of roots or rootlets grouped as dorsal (posterior) roots and ventral (anterior) roots. In a transverse section, there is partial division into left and right halves by the dorsal (posterior) median septum and the ventral (anterior) median fissure. The butterfly-shaped inner substance is called the gray matter. The white matter surrounds the gray matter.

Thoracolumnar region (T1-L2) has small lateral horns. This is the site of motor neurons of the sympathetic division of the autonomic nervous system.

In the Brain:

Neurons of the cerebrum gray matter are arranged into SIX layers of neurons. Each layer houses neurons with a particular characteristic. H&E staining does not demonstrate the architecture of the gray matter. The cerebral cortex, part of the outer cerebrum, can be divided into three layers:

There are three sequential CNS connective tissue membranes (aka the meninges, which cover the brain and spinal cord):

The Blood-Brain Barrier (BBB) segregates the neurons of the CNS from the blood-borne molecules that can act as neurotransmitters. It provides protection against harmful substances (i.e toxic drugs, bacterial toxins, etc.). This is accomplished by tight junctions between endothelial cells of the capillaries (the morphological bases of the BBB). Substances must pass through (not between) the endothelial cells. Notably, few endocytotic vesicles are seen in brain endothelium (i.e. restriction of transendothelial transport). There is a relatively thick basement membrane around the capillaries. The BBB is maintained by astrocyte feet.

Response to Injury is a complex sequence of two events: