Given that neurons are amitotic and therefore must have longevity, they must be well protected, optimized, and monitored. The provide significant cellular support to the neuron.

Oligodendrocytes

These glial cells produce a fatty protein called myelin that wraps around many neuronal axons. Myelin helps protect and insulate the axon, as well as plays a major role in managing nerve conduction velocity.


Astrocytes

These cells play a significant role in regulating diffusion of substances that may leave the general circulation and enter the CNS. They are a major component of the blood-brain barrier.

Microglia

These cells are macrophages. They play a critical role in maintaining and optimizing the neuronal extracellular space.

Ependymal Cells

These epithelial glial cells play a major role in the production and circulation of the protective cerebral spinal fluid (CSF) that embeds the CNS.






The CNS HAS Four Levels of Protection: Bone, Meninges, Cerebrospinal Fluid, and Blood-Brain Barrier





Bone

The CNS is encased in bone. They play a brain is protected by the skull and the spinal cord by the vertebral column.

Meninges

The meninges are three covering connective tissues. The most superficial is the fibrous dura mater, then the arachnoid mater, followed by the pia mater.

Cerbrospinal Fluid (CSF)

The CNS is immersed in this watery substance. The CSF cushions the brain and spinal cord from injury, provides nutrients, and removes waste products. It also helps the brain maintain neutral buoyancy, which allows it to function without being impaired by its own weight.


Blood-Brain Barrier (BBB)

The BBB protects tone CNS from the general circulation. The perivascular feet of astrocytes almost completely cover capillary walls inhibiting diffusion. The special epithelial lining is called endothelial. Its squamous cells are held together by tight junctions decreasing permeability. Further the basement membrane is continuous, further decreasing permeability.






The most superficial portion of the brain is the cerebral cortex. It is made up of two separate hemispheres, functionally connected to one another. The cortex is highly folded as seen by a series of bulges and grooves. The deepest groove is the longitudinal fissure where the hemispheres separate.



The cortex houses the “conscious mind.” It is responsible for responsible for the higher-level processes of the human brain, including language, sensorimotor processing, memory, reasoning, thought, learning, decision-making, emotion, intelligence and personality.







The brain is densely packed with neurons and neuroglia.



The right and left hemispheres have distinct functions. However they are functionally and physically interconnected by a large bundle of white matter called the corpus callosum. The corpus callosum ensures that, though two hemispheres, the brain acts as one collective organ.









The hemispheres are subdivided into four anatomical lobes.



The brain is subdivided into three anatomical/functional regions that organize and process neural information that enters and leaves the cortex. These regions are the forebrain, midbrain, and hindbrain.





The forebrain includes the cortex and diencephalon. The diencephalon includes the thalamus and hypothalamus.

The midbrain is just inferior to the diencephalon.

Hindbrain is just inferior to the midbrain and includes the pons and medulla (brain stem), and the cerebellum.







The spinal cord is the neural pathway to and from the brain.



The major sections of the grey matter of the spinal cord include the dorsal, lateral, and ventral horns.

Afferent information enters the spinal cord at the dorsal horn.

The lateral and ventral horns contain the cell bodies of efferent neurons.

The ventral horn contains the cell bodies of alpha motor neurons that innervate skeletal muscles.

The lateral horn contains cell bodies of neurons that innervate cardiac muscles, smooth muscles and glands.


The surrounding white matter contains myelinated ascending and descending neural tracts known as white columns.
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The hollow space in the center of the cord is called the central canal. The central canal contains cerebral spinal fluid (CSF).





Efferent information leaves the cord via the ventral root.

Afferent information enters the cord via the dorsal root.


A ganglion is a collection of cell bodies outside of the CNS.