Meninges

The meninges (from the Greek μῆνιγξ mēninx, 'membrane') are the connective tissue membranes that cover the entire central nervous system, adding a soft protection that complements the the dura of bone structures. In mammals there are three layers with two intermediate spaces, from the inside out:

• Piamadre is a thin layer, very vascularized and in close contact with the brain, following the contour of the brain tissue. It contains fibroblasts similar to those of the aracnoid trays.
• Subaracnoid spacewhich contains cerebrospinal fluid and damp shocks, reducing the possibility of trauma.
• Aracnoids It is a vascular layer, though crossed by blood vessels to the flame. It is called leptomeninge to the set of piamadre and aracnoids.
• Subdural space It is very narrow and with some cerebrospinal fluid.
• Duramadre is the outer layer.

Illustration for the Review of the Work of Antonio Pacchioni Disquisitio anatomicae de durae meningis... published in Acta Eruditorum, 1703

The outer region borders the periosteum in the brain and the epidural space in the neural tube. Despite being in close contact, a layer of glial processes is always interposed.

Function

The meninges act as a selective barrier:

• Chemical attack: prevents, as a filter, the entry of substances and microparticles harmful to our nervous system, which protects us from infections such as encephalitis or meningitis and the neurological damage generated by some substances.
• Mechanical protection: the cerebrospinal fluid (CSF) is a transparent liquid that circulates in the subaracnoid space, damping blows, lubricating and nourishing the myelin beams that coat the CNS. It plays a very important role in allowing small blows to the head not to pose a serious danger to the life of the human or animal.

Medical relevance

When the meninges or cephalomedullary fluid are attacked by cells (bacteria, viruses, etc.) or chemical substances (usually by inoculations after serious accidents), damage occurs, which can be inflammatory or infectious. This can cause meningitis, which requires a quick and accurate diagnosis to act accordingly, otherwise the subject's life can be seriously compromised.

Additional images

Transverse section of the spinal cord and its membranes. Schematic representation of a section of the upper part of the skull, showing the membranes of the brain, etc.