The ventricles of the brain are interconnected hollow spaces filled with CSF. The
right and left lateral ventricles are found in the cerebral hemispheres. The lateral
ventricles are connected to the third ventricle by the interventricular foramen. The
third ventricle is located in the forebrainstem. The third and fourth ventricles are
connected by the cerebral aqueduct. The fourth ventricle is located in the
hindbrainstem. The fourth ventricle is continuous with the part of the spinal cord
The spinal cord, located within the spinal canal, is continuous with the brainstem.
The spinal cord has two enlargements. One, associated with nerves for the upper
members, is called the cervical enlargement. The other, associated with nerves
for the lower members, is called the lumbosacral enlargement. Nerves arising
from the spinal cord are called spinal nerves. There are 31 pairs of spinal nerves.
In the cross section of the spinal cord, one can see a central region of gray matter
shaped like an H. Each arm of this figure is called a horn. The connecting link is
called the gray commissure. These horns are actually sections of the gray
columns. Since a column of white matter is a large bundle of processes, it is
The skeletal covering for the brain is provided by bones of the cranium.
overall skeletal structure covering the spinal cord is the vertebral column (spine).
The brain and spinal cord have three different membranes surrounding them
called meninges. The tough outer covering for the CNS is the dura mater.
Beneath it is the subdural space. The fine second membrane is called the
arachnoid mater. Beneath it is the subarachnoid space, which is filled with CSF.
The delicate membrane applied directly to the surface of the brain and spinal cord
The two main pairs of arteries supplying oxygenated blood to the brain are the
internal carotid and the vertebral arteries. Beneath the brain, branches of these
arteries join to form a circle, called the cerebral circle (of Willis). The main pair of
veins carrying blood back toward the heart is the internal jugular veins. The blood
supply of the spinal cord is by way of a combination of three longitudinal arteries
running along its length and reinforced by segmental arteries from the sides.
Found in the cavities of the CNS is a clear fluid called cerebrospinal fluid (CSF).
This fluid is found in the ventricles of the brain, the subarachnoid space, and the
spinal cord's central canal. Special collections of arterial capillaries found in the
roofs of the third and fourth ventricles are called choroid plexuses. These
structures continuously produce CSF from the plasma of the blood. (para 11-13)