Learn · Structure
Meninges and cerebrospinal fluid
The three membranes around the brain and cord and the fluid between them. What dura, arachnoid and pia are, where cerebrospinal fluid is made and where it goes, and why a lumbar puncture is done low in the back.
Updated 2026-10-022 sources
Why it matters
The cord is soft tissue inside a bony canal. It is wrapped in membranes, the meninges, which protect it, and it floats in cerebrospinal fluid, which provides a liquid cushion [1].
What it is
The meninges are three layers of connective tissue membrane covering the outer surface of the central nervous system [1]:
- The dura mater, a thick fibrous layer and a strong protective sheath over the entire brain and spinal cord [1].
- The arachnoid mater, a thin fibrous membrane that forms a loose sac around the central nervous system; beneath it a filamentous mesh, the arachnoid trabeculae, looks like a spider web [1].
- The pia mater, a thin fibrous membrane directly on the surface of the brain and cord [1].
The trabeculae lie in the subarachnoid space, which is filled with circulating cerebrospinal fluid (CSF) [1].
What it does
CSF circulates throughout and around the central nervous system [1]. It cushions the brain and cord, and it circulates to remove metabolic wastes from the fluid around nervous tissue and return them to the bloodstream [1].
How it works
In the brain, CSF is produced in special structures: in some of the ventricles, a specialised membrane called the choroid plexus makes it by filtering the blood [1]. It flows through the ventricles into the subarachnoid space, and the arachnoid granulations, which reach into the dural sinuses, filter it back into the blood for drainage [1].
Blood vessels nourishing the central nervous tissue lie between the pia mater and the nervous tissue [1]. Below the end of the cord the dural sac continues; in an MRI study of 200 adults its lower end was most often at S2 [2].
When it does not behave
Meningitis is inflammation of the meninges, which can be caused by bacteria or viruses; bacterial meningitis tends to be more severe [1]. The primary test for it is a lumbar puncture [1]. This site describes it for learning only and gives no advice about anyone's illness.
In theatre and clinic
Because the spinal cord does not extend through the lower lumbar region, a needle can be inserted there through the dura and arachnoid to withdraw CSF: a lumbar puncture [1]. A sample of CSF can show chemical evidence of disease, as blood tests do [1].
Common misconceptions
Misconception: Cerebrospinal fluid just sits still around the brain.
It circulates: it is made in the ventricles, flows through the subarachnoid space and is filtered back into the blood at the arachnoid granulations [1].
Check yourself
Which space holds the cerebrospinal fluid?
The subarachnoid space, between the arachnoid and the pia mater [1].
Why is a lumbar puncture done in the lower lumbar region?
The spinal cord does not extend that far down, so the needle can reach the fluid without the cord [1].
Read next
References
- Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, et al.. 13.3 Circulation and the Central Nervous System. Anatomy and Physiology 2e. OpenStax. 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/13-3-circulation-and-the-central-nervous-system
- AL Jawad MS, Alhomoud MA, Alfaraj FM, Almuhaimeed FN, AlDawsari FA, AL-Jubran SA, et al.. Evaluation of the Level of Dural Sac Tip in Saudi Population: A Magnetic Resonance Imaging Study. Cureus. 2022. doi:10.7759/cureus.32533
For learning only. This page does not diagnose, predict outcomes or recommend treatment. Corrections are welcome: how to suggest one.