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.
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.
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.
The human brain has three major subdivisions--the brainstem, the cerebellum,
and the cerebrum.
a. The Brainstem. The brainstem (figure 2-1) is the basal portion of the brain.
It is continuous with the spinal cord. Exiting from the sides of the brainstem are 12 pairs
of nerves known as the cranial nerves. The brainstem is divided into 3 major portions.
Forebrainstem (diencephalon), consisting of:
(a) Thalamus--a sensory relay station for impulses conveyed upward
from the spinal cord.
(b) Hypothalamus--concerned with regulation of autonomic functions.
Midbrainstem (mesencephalon) consisting of:
Corpora quadrigemina--concerned with vision and hearing.