Question

Which are the outermost three layers which are called cranial meninges?

Answer 1

The meninges known as the membranous coverings of the brain and spinal cord. There are three layers, known as the dura mater, arachnoid mater, pia mater.

Complete answer:
Dura mater- The dura mater is called the outermost layer of the meninges, lying underneath the bones of the skull. It is thick, tough, inextensible. The dura contains two connective tissue sheets:
Periosteal layer – lines the inner surface of the bones of cranium.
Meningeal layer – present deep to the periosteal layer inside the cranial cavity.
Between these layers, dural venous sinuses are present. They carry out the venous vasculature of the cranium. The meningeal layer of the dura mater folds inwards as dural reflections. They partition the brain, and divide cranial cavity into different compartments. For eg, the tentorium cerebelli divides the cranial cavity into supratentorial, infratentorial compartments.

Arachnoid mater- Is the middle layer of the meninges, lying directly below the dura mater. It consists of layers - connective tissue, is avascular, and does not receive any innervation.
Below the arachnoid is a space called the subarachnoid space. It contains cerebrospinal fluid, which helps to cushion the brain. Small projections of arachnoid mater into the dura allow CSF to re-enter the circulation.

Pia mater- Is located under subarachnoid space. It is thin, and tightly adhered to the surface of the brain and spinal cord. It is a covering to follow the contours of the brain.
The dura mater is highly vascularised, with blood vessels perforating through the membrane which help to supply the underlying neural tissue.

Note: The function of the meninges is to protect brain and spinal cord from mechanical trauma and also to support the blood vessels and to form a continuous cavity which helps the cerebrospinal fluid (CSF) to pass.