Back and Spinal Cord - LO 6

6. Describe the meninges: their structure, distribution, specializations, functions, and relationships to osteological and neurological structures.

The central nervous system (CNS) is surrounded and protected by three layers of meninges. The meninges surrounding the brain are slightly more specialized than those surrounding the spinal cord, but the cranial and spinal meninges are contiguous. The meninges include:

• Pia mater ("delicate mother")

  • is a delicate investment that is closely applied to the brain and spinal cord

  • enmeshes blood vessels on the surface of the CNS.

  • Specializations:

    • Filum terminale internum: can be observed at the tip of the conus medullaris (~L2), traveling inferiorly through the dural sac

      • Enveloped by the filum terminale externum from ~S2 to the coccyx

      • Opaque white compared to the surrounding cauda equina

    • Denticulate ligaments: paired, extensions of pia mater

      • Located between the dorsal and ventral rootlets and roots of spinal nn.

      • ~20-22 denticulate ligaments

      • Opaque white compared to the rootlets and roots of spinal nn.

• Arachnoid mater ("spidery mother")

  • is a filmy, transparent, layer that is adhered to the dura mater and connected to the pia mater via trabeculae.

  • is separated from the pia mater by the subarachnoid space, which is filled with cerebrospinal fluid (CSF). 

• Dura mater ("tough mother")

  • outermost covering,

  • two layers in the cranium; one in the spinal canal

  • Specializations:

    • Dural sac: extension of dura past the termination of the spinal cord

      • The spinal cord ends at ~L2 at the conus medullaris but nerve roots continue inferiorly (cauda equina) and still protected by meninges and bathed in cerebrospinal fluid (CSF)

      • Dura (and the other meninges) continue inferiorly to ~S2 as the dural sac

    • Filum terminale externum: dural part of filum terminale

      • Often referred to as coccygeal ligament

      • After the dural sac terminates at S2, the externum envelops the internum to attach to the coccyx

      • Serve to anchor the dural sac to the coccyx

Spaces (actual & potential) - from superficial to deep:

• Epidural space - actual (in spine region); potential (in cranial region)

  • Between bone and dura mater

  • Filled with epidural fat in spine region

• Subdural space - potential

  • Between dura mater and arachnoid mater

• Subarachnoid space - actual

  • Between arachnoid mater and pia mater

  • Cerebrospinal fluid (CSF) flows within