Anatomy and Physiology

• In the brain, there are channels within the dura mater, the dural sinuses, which contain venous blood returning from the brain to the jugular veins.

• In the spinal cord, the dura mater is often referred to as the dural sheath. A fat‐filled space between the dura mater and the vertebrae, the epidural space, acts as a protective cushion to the spinal cord.

The arachnoid (arachnoid mater) is the middle meninx. Projections from the arachnoid, called arachnoid villi, protrude through one layer of the dura mater into the dural sinuses. The arachnoid villi transport the CSF from the subarachnoid space to the dural sinuses. Two cavities border the arachnoid:

The subdural space occurs outside the arachnoid (between the arachnoid and the dura mater).

The subarachnoid space lies inside the arachnoid. This space contains blood vessels and circulates CSF. The fine threads of tissue that spread across this space resemble a spider web and give the arachnoid layer its name (arachnid means spider).

The pia mater is the innermost meninx layer. It tightly covers the brain (following its convolutions) and spinal cord and carries blood vessels that provide nourishment to these nervous tissues.