The spinal cord in the vertebral canal is surrounded by the following connective tissue membranes: the tough spinal meninx (pachymeninx), or spinal dura mater (A1), and the soft spinal meninx (leptomeninx) consisting of the spinal arachnoidea (A2) and the spinal pia mater (A3).
The spinal dura mater forms the outermost sheath which is separated from the perios-teum-like lining of the vertebral canal, the endorhachis (A4), by the epidural space (A5).The space is filled with adipose tissue and contains an extensive venous plexus, the in-ternal vertebral venous plexus (see vol. 2).The dura mater forms caudally the dural sac (B6), enveloping the cauda equina (B7), and finally extends together with the terminal filament as a thin cord up to the periosteum of the coccyx (dural terminal filament) (B8). Only at the oral end at the foramen magnum (occipital bone) is the dural sac attached to bone. The epidural space forms a resilient cushion for the dural sac, which moves to-gether with the vertebral column and the head. Bending the head pulls the dural sac upward, causing mechanical stress on the spinal cord; when bending the head for-ward, roots and blood vessels are stretched (D9), when bending the head backward, they are compressed (D10).
The arachnoidea borders closely onto the inner surface of the dura mater. It forms the boundary of the subarachnoidal space (AC11), which is filled with cerebrospinal fluid (CSF). Between the inner surface of the dura and the arachnoidea lies a capillary cleft, the subdural space, which widens into a realspace only under pathological conditions (subdural bleeding). Dura and arachnoidea accompany the spinal roots (AC12), pass with them through the intervertebral foramina, and also envelope the spinal gan-glia (AC13). The funnel-like root sleeves contain CSF in their proximal portions. The dura then turns into the epineurium (A14), and the arachnoidea into the perineurium (A15) of the spinal nerves. The part of the root leaving the vertebral canal, the radicu-lar nerve (A16), runs obliquely downward inthe cervical and lumbosacral regions and obliquely upward in the midthoracic region (C).
The spinal pia mater borders directly onto the marginal glial layer of the spinal cord. This represents the boundary between me-sodermal envelopes and ectodermal nerve tissue. The pia mater contains numerous small blood vessels that penetrate from the surface into the spinal cord. A connective tissue plate, the denticulate ligament (A17), extends on both sides of the spinal cord from the pia to the dura and is attached to the latter by individual pointed processes. The ligament extends from the cervical spi-nal cord to the midlumbar spinal cord, thus keeping the spinal cord, which floats in the CSF, in position.
Clinical Note: Under sterile conditions, cere-brospinal fluid may be safely withdrawn for ex-amination from the lower segment of the dural sac that contains only the fibers of the cauda equina. For this purpose, with the patient bending over, a needle is deeply inserted between the processes of the second to fifth lumbar vertebrae until CSF begins to drop (lumbar puncture) (E).
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