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Lesson 2. The Central Nervous System
2-2. 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.
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