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Portrait of Meninges

Anatomy · Brain & nerves

Meninges

Three protective membranes

Central nervous system · coverings

The three membranes that wrap the brain and spinal cord: the tough outer dura mater, the delicate web-like arachnoid mater and the thin inner pia mater, which clings to the surface of the nervous tissue. Between the arachnoid and pia lies the subarachnoid space, filled with cerebrospinal fluid. Together they protect and cushion the central nervous system and carry its blood supply and venous drainage.

How to spot them

  • ▸Three layers, outermost to innermost: dura, arachnoid, pia — often remembered as 'DAP' in, or 'PAD' out
  • ▸The outer layer is thick and leathery and forms folds that partition the skull, such as the falx cerebri
  • ▸The middle layer is a spider-web mesh, with fluid-filled space beneath it
  • ▸The inner layer follows every fold of the brain's surface closely

What to know

Three membranes surrounding the brain and spinal cord, outermost to innermost: dura, arachnoid and pia

Meninges — the coverings of the central nervous system.

Its outermost layer is called 'tough mother' in Latin, and its innermost 'tender mother'

Meninges — dura mater and pia mater, a translation from Arabic.

The middle layer is named for its resemblance to a spider's web

Meninges — the arachnoid mater.

The space beneath its middle layer is filled with cerebrospinal fluid and crossed by blood vessels

Meninges — the subarachnoid space.

Infection of them by bacteria or viruses causes neck stiffness, headache, fever and a non-blanching rash

Meninges — meningitis.

A blow to the side of the head tearing an artery beneath the pterion can produce a lens-shaped collection of blood between skull and dura

Meninges — extradural haematoma from the middle meningeal artery.

Its sickle-shaped fold dips into the midline fissure between the hemispheres, and a tent-like fold separates the cerebrum from the cerebellum

Meninges — falx cerebri and tentorium cerebelli, folds of dura.

Small projections from the middle layer into the venous sinuses return cerebrospinal fluid to the blood

Meninges — arachnoid granulations.

Key ideas

  • The dura has two layers in the skull, periosteal and meningeal, which split to enclose the venous sinuses.
  • An extradural haematoma bleeds from an artery under high pressure; a subdural bleeds from bridging veins, more slowly.

Quick-fire facts

  • •The names dura mater, pia mater and arachnoid mater are Latin, dura mater meaning 'tough mother' and pia mater 'tender mother', translated from Arabic terms used by medieval scholars
  • •The arachnoid is named after the Greek for spider, arachne, for its web-like trabeculae
  • •The subarachnoid space is filled with cerebrospinal fluid (about 150 mL in total, shared with the ventricles) and holds the large cerebral arteries and veins
  • •The middle meningeal artery runs under the pterion, the thin region of skull where four bones meet, which is why a blow there can cause an extradural bleed
  • •The falx cerebri, tentorium cerebelli and falx cerebelli are folds of dura
  • •The spinal dura ends at about S2, but the pia continues as the filum terminale
  • •The epidural space of the spine, used for pain relief in labour, lies outside the dura
  • •Meningitis can be caused by bacteria, viruses or fungi; bacterial meningitis is a medical emergency

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Sources