Structures · Coverings
Dural sac (dura and arachnoid)
The outer coverings of the cord. The dura is a tough sheath; the arachnoid forms a loose sac inside it, and the space under the arachnoid holds cerebrospinal fluid.
At a glance
- In this model
- Lower end drawn at S2 (vertebral level)Schematic placement at the most common level found on MRI. AL Jawad et al. 2022
Drawn as one surface for dura and arachnoid together, offset from the cord. Its lower end is placed at S2, the most common level in an MRI study of 200 adults (AL Jawad et al. 2022); it was not measured on this model.
What the sources say
“The dura mater is a thick fibrous layer and a strong protective sheath over the entire brain and spinal cord.” Betts et al. 2022, §13.3
“The arachnoid mater is a membrane of thin fibrous tissue that forms a loose sac around the CNS.” Betts et al. 2022, §13.3
“The trabeculae are found in the subarachnoid space , which is filled with circulating CSF.” Betts et al. 2022, §13.3
“This procedure is called a lumbar puncture and avoids the risk of damaging the central tissue of the spinal cord.” Betts et al. 2022, §13.3
“Frequency distribution for the level of DS termination was mostly located in S2 (71.50%).” AL Jawad et al. 2022
Read more
- Conus medullaris and cauda equina
Where the spinal cord ends and what fills the canal below it. Why the cord stops near L1, how much that varies, and how the lower nerve roots travel down as the cauda equina.
- 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.
For learning only. Levels and sizes vary between people; nothing here describes a particular person or gives medical advice. Sources: Betts et al. 2022, §13.3; AL Jawad et al. 2022.