What are the membranes that cover the brain

Meninges

What are the meninges?

The three meninges are layers of connective tissue that enclose the brain. They develop from the embryonic neural tube. The meninges are called from the outside in:

  • Dura mater (hard meninges)
  • Spider web skin (arachnoidea)
  • Pia mater (soft meninges)

Dura mater

The dura mater is the outermost of the three meninges and is quite tight. It lines the cranial cavity and consists of two layers: connective tissue and a low, inner epithelial layer. The outer layer, in which the vessels that supply the skull bone run, is also the periosteum of the skull bone.

This periosteum is still firmly attached to the skull bone into adolescence. This ensures that the child's skull, whose individual bones are still separated by soft sutures, cannot deform. In adults, the periosteum can then be easily detached from the bone - only at the base of the skull does it always remain firmly attached to the bone.

The dura mater also forms duplicates that project between the two halves of the cerebrum and between the cerebrum and cerebellum: the cerebral sickle (Falx cerebri), the cerebellar sickle (Falx cerebelli) and the cerebellar tent (tentorium cerebelli).

The two cerebral sickles separate the two cerebral hemispheres deeply from each other in the middle of the skull, down to the bar.

The cerebellar tent (tentorium cerebelli), on the other hand, is positioned transversely and separates the cerebral and cerebellar hemispheres. This dura mater duplication merges into the part of the dura mater that lines the inner skull bone. The cerebellum lies beneath the tentorium cerebelli in the posterior fossa; the brain stem passes through a small section.

The dura mater divides into two sheets in three places: At the petrous pyramid (in which the inner ear is located) it encloses the trigeminal ganglion (a knot of nerve cells and fibers of the trigeminal nerve); At the top of the petrous pyramid, it encloses the endolymphatic sac (sensory cells for the organ of equilibrium); in the area of ​​the sella turcica (Turkish saddle) it includes the pituitary gland (pituitary gland).

Under the dura mater there is a narrow space, the subdural space, which separates the dura mater from the middle of the three meninges, the arachnoid.

Arachnoid

The arachnoid consists of connective tissue, is vascular and connects on the inside via small trabeculae and membranes with the underlying, inner meninges, the soft pia mater. To the outside, to the dura mater, the arachnoid forms a closing membrane for the liquor, which cannot pass this border.

The arachnoid rests smoothly on the surface of the brain, it passes over the furrows and depressions of the brain in the area of ​​the entire domed skull. Cistern-like enlargements are only formed at the base of the brain, due to bony elevations and depressions.

The arachnoid forms villi-like connective tissue, vascularless outgrowths (arachnoid villi) that extend into the dura mater, veins and also into the cranial bones. The liquor is absorbed from the subarachnoid space via these arachnoid villi and released into the blood.

Pia mater

The third layer of the meninges, the pia mater, rests directly on the brain, follows the furrows and depressions of the cerebrum and cerebellum and guides the vessels and nerves that lead into the brain. The pia mater also extends into the chambers of the brain.