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Lesson 2. The Central Nervous System


The CNS consists of the brain and the spinal cord, which share a continuous, protective, fibrous membrane cover called the meninges. The meninges consist of three separate membranes, which are separated by spaces.

a. Dura Mater.

(1) The dura mater is a tough fibrous layer that serves as the outer layer of meninges and the inner lining of the cranial bones.
(2) Between the dura mater and the next layer of meninges is a potential space called the subdural space.

 b.     Arachnoid Mater.

(1) The arachnoid mater is a fine, membranous layer of spider-web-like threads that extend from the dura mater, through the subarachnoid space, to the innermost layer of meninges.
(2) The subarachnoid space is filled with cerebrospinal fluid (CSF).

c.      Pia Mater.

(1) The pia mater is the delicate, transparent membrane that directly covers the surface of the brain and spinal cord.
(2) The pia mater contains a network of blood vessels.

d.     Cerebrospinal Fluid

(1) Cerebrospinal fluid, circulating within the network of the subarachnoid space, provides the brain and spinal cord with protection. It acts as a cushion, or shock-absorber, against injury.
(2) CSF is manufactured from blood in networks of capillaries called choroid plexuses. It circulates through the ventricles (cavities inside the brain) and subarachnoid space of the meninges.


David L. Heiserman, Editor

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Revised: June 06, 2015