Cells and general organization of the Central Nervous System (CNS)

First, review gross and microscopic features of CNS tissue: cerebrum, cerebellum, spinal cord, and meninges. This will help orient you to what you will be looking for on the slides in this unit. We’ll start with the cerebrum.

Examine the images below and sections of cerebral cortex with low power, noting the differences between white and gray matter. Gray matter, the thick surface layer where most synapses occur (see TEM image below), is composed of the cell bodies of six types of neurons, dendrites, and glial cells such as astrocytes and microglial cells (study the table below for more information about glial cells). The most recognizable of the neurons are the pyramidal neurons with their large, distinctive pyramid-shaped cell bodies. Cerebral cortex neurons integrate sensory information and stimulate voluntary motor functions. In contrast, the white matter consists mainly of myelinated axons and glial cells, such as the oligodendrocytes that produce myelin, as well as astrocytes and microglia. Few neuronal cell bodies are present in the white matter.

Under higher power, examine this section of the cerebral cortex and identify: neuronal cell bodies, neuropil (Np, axons and dendrites of neurons), and glial cells (oligodendrocytes and astrocytes).

On the slide of cerebral cortex and in the images below, identify structural features of neurons that are visible in the light microscope, including their prominent nucleoli and chromatophilic Nissl substance (RER). These features are typical of metabolically active cells that are producing abundant proteins.

The meninges include three connective tissue layers (pia, dura, and arachnoid mater) that surround and protect the CNS. On the cerebral cortex section, examine the edge showing remnants of the innermost meningial layer, the pia mater, and note the intracerebral penetration of blood vessels from this surface. Pia mater covers arteries and veins in the brain.

Clinical note: The meninges are the site of various medical problems, such as meningitis, subdural hematomas, subarachnoid hemorrhage, and meningiomas.
 

Cerebellum and spinal cord.