Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Central Nervous System
Meninges of the Brain and Spinal Cord

There are three distinct meningeal layers surrounding the Brain AND SPINAL cord: the outer, middle, and inner membranes. The first is called the dura mater, the second is the arachnoid mater, and the third is the pia mater. Together, the arachnoid and pia mater form the leptomeninges (or soft Meninges), which fuse closely with one another in numerous areas.

At the Base of the Skull, the dura mater is firmly fused with the bone, whereas in the cranial vault it is only loosely connected to it. The cranial dura mater forms several folds and projections, including the falx cerebri, which extends between the right and left cerebral hemispheres, and the falx cerebelli, which separates the cerebellar hemispheres. The tentorium cerebelli is situated between the occipital lobes of the cerebrum and the superior surface of the Cerebellum. Additionally, the dura mater forms projections in the region of the body of the Sphenoid bone, creating the Structure known as the diaphragma sellae, beneath which the Pituitary Gland (hypophysis) lies. In certain areas, the cranial dura mater splits to form endothelial-lined channels called venous sinuses, through which venous Blood flows.

The pia mater closely follows the contours of the brain, dipping into all of its sulci and fissures. The arachnoid mater is an extremely thin, avascular membrane. It covers the brain without extending into its sulci, bridging across them instead. Between the pia mater and the arachnoid mater lies the subarachnoid space, which is filled with CEREBROSPINAL FLUID. In several areas, the subarachnoid space of the brain expands significantly to form cisterns, which also contain cerebrospinal fluid. The largest cisterns are located between the cerebellum and the Medulla Oblongata, between the cerebral peduncles, and in the region of the lateral sulcus.

The potential space between the dura mater and the arachnoid mater is known as the subdural space, which contains a small amount of fluid.

The cerebrospinal fluid located within the subarachnoid space and the cerebral ventricles serves as both a nutritive and metabolic medium for the brain, as well as a pathway for the removal of Metabolic waste products. Circulating outward from the ventricles, this fluid drains into the subarachnoid space. Accumulations of cerebrospinal fluid are also found along the Spinal Cord, where the subarachnoid space is more pronounced than in the cranial cavity.

The spinal cord is likewise enclosed by all three meningeal layers: the dura mater, arachnoid mater, and pia mater. Because of the substantial accumulation of cerebrospinal fluid surrounding the spinal cord, it is effectively suspended and cushioned within this fluid.

Between the spinal dura mater and the periosteum of the vertebrae lies the epidural space, which is filled with adipose tissue and Blood Vessels. This space plays a vital role in protecting the spinal cord from mechanical Shock and impact. A comparable space does not exist in the cranial cavity, because the cranial dura mater is tightly fused with the BONES OF THE skull.