Human Anatomy and Physiology (with age-related features of the child's body) - Sapin M.R., Sivoglazov V.I. 2002

Nervous system
Brain
Meninges of the spinal cord and brain

The Brain AND SPINAL cord are enveloped by three Meninges: the outer dura mater, the middle arachnoid mater, and the inner pia mater. At the level of the foramen magnum, the meninges of the Spinal Cord are continuous with the corresponding meninges of the brain.

Directly adjacent to the outer surface of the brain and spinal cord is the pia mater {vascular membrane), which extends into all fissures and sulci. The pia mater is extremely thin, composed of loose Connective Tissue rich in fine elastic fibers and Blood Vessels. Connective tissue fibers arise from it, penetrating into the brain substance along with the blood vessels.

External to the vascular membrane lies the arachnoid mater. Between the brain substance covered by the pia mater and the arachnoid mater is the subarachnoid space, filled with 120—140 ml of CEREBROSPINAL FLUID. In the lower part of the spinal canal, within the subarachnoid space, the nerve roots of the lower (sacral) Spinal Nerves float freely. Within the cranial cavity, over large fissures and sulci, the subarachnoid space widens to form reservoirs called cisterns. The most extensive of these is the cerebellomedullary cistern (cisterna magna), located between the Cerebellum and the Medulla Oblongata; the cistern of the lateral fossa lies within the corresponding sulcus. The chiasmatic cistern is situated anterior to the optic chiasm, and the interpeduncular cistern lies between the cerebral peduncles. The subarachnoid spaces of the brain and spinal cord communicate with each other where the spinal cord transitions into the brain.

Cerebrospinal fluid, produced in the ventricles of the brain, drains into the subarachnoid space. The lateral (I and II), third (III), and fourth (IV) ventricles contain choroid plexuses that secrete cerebrospinal fluid. These choroid plexuses consist of loose Fibrous connective tissue with a rich network of blood vessels (capillaries), covered on the ventricular side by cuboidal epithelium.

From the Lateral ventricles, the fluid drains through the interventricular foramina into the Third ventricle, from the third ventricle via the cerebral aqueduct into the fourth, and from the Fourth ventricle through three apertures (the lateral and median apertures) into the cerebellomedullary cistern of the subarachnoid space. The outflow of cerebrospinal fluid from the subarachnoid space into the bloodstream occurs through projections {granulations) of the arachnoid mater that project into the lumen of the Dural Venous Sinuses, as well as into blood capillaries where the cranial and spinal nerve roots exit the cranial cavity and spinal canal. Due to this mechanism, cerebrospinal fluid is continuously produced in the ventricles and reabsorbed into the bloodstream at an equal rate.

External to the arachnoid mater lies the dura mater, which is composed of Dense Fibrous Connective tissue and is remarkably strong. Within the spinal canal, the spinal dura mater forms a long sac containing the spinal cord with its spinal nerve roots, spinal ganglia, the pia and arachnoid maters, and cerebrospinal fluid. The outer surface of the spinal dura mater is separated from the periosteum lining the spinal canal by the epidural space, which is filled with adipose tissue and a venous plexus. Superiorly, the spinal dura mater is continuous with the cranial dura mater.

The cranial dura mater fuses with the periosteum, thereby directly lining the inner surface of the Skull bones. It is firmly attached to the BONES OF THE cranial base, but loosely attached to the bones of the cranial vault. Between the dura mater and the arachnoid mater lies a narrow space containing a small amount of fluid.

In certain areas, the cranial dura mater forms folds (septa) consisting of two layers that project deeply into the fissures separating the PARTS OF THE brain. At the origins of these folds, the dural layers separate to form triangular channels—the dural venous sinuses, which are lined with endothelium. The layers forming the walls of the sinuses are tightly stretched and do not collapse. Venous blood from the brain drains into these sinuses via cerebral Veins and then flows into the internal jugular veins.

The largest fold of the dura mater, situated in the sagittal plane, is the falx cerebri. The falx separates the cerebral hemispheres from each other. At the Base of the falx cerebri, its layers separate to form the superior sagittal sinus. Within the free lower margin of the falx lies the inferior sagittal sinus.

Another large fold, the tentorium cerebelli, projects from behind into the transverse cerebral fissure and separates the occipital lobes of the cerebral hemispheres from the cerebellum. The tentorium cerebelli is attached anteriorly to the superior borders of the temporal bones, and posteriorly to the Occipital bone along the margins of the groove for the transverse sinus. Along the line of attachment of the tentorium cerebelli to the occipital bone, the transverse sinus is formed between its layers, continuing laterally into the paired sigmoid sinus. On each side, the sigmoid sinus, lying in the sigmoid sulcus, transitions into the Internal jugular vein.

Between the cerebellar hemispheres, in the sagittal plane, lies the falx cerebelli, which is attached posteriorly to the internal occipital crest. Along the line of attachment of the falx cerebelli to the occipital bone, the occipital sinus is located within its separated layers.

Above the Pituitary Gland, the dura mater forms the diaphragma sellae, which separates the hypophyseal fossa from the cranial cavity.

On either side of the sella turcica lies the cavernous sinus. Passing through this sinus are the Internal Carotid Artery, as well as the oculomotor, trochlear, and abducens Cranial Nerves, and the ophthalmic branch of the Trigeminal nerve.

The two cavernous sinuses communicate with each other via the transverse intercavernous sinuses. The paired superior and inferior petrosal sinuses, which run along the corresponding margins of the petrous part of the Temporal bone, connect anteriorly with the respective cavernous sinus, and posteriorly and laterally with the transverse and sigmoid sinuses.

On each side, the sigmoid sinus, lying in the sigmoid sulcus, transitions into the internal jugular vein.