Spinal Cord Anatomy
Spinal Meninges & Blood Supply

Within the vertebral canal, both spinal cord (CNS) and spinal roots (PNS) are enveloped by meninges. (Each spinal root is enveloped by single or double meningeal sheaths.) Where spinal roots unite to form a spinal nerve, meninges are replace by connective tissue (epineurium, perineurium & endoneurium) enclosing the spinal nerve. Spinal dura mater is separated from periosteum lining the vertebral canal by an epidural space that contains a variable amount of fat (in the cranial cavity, dura mater and periosteum merge so an epidural space does not exist).

Three layers of meninges envelop the spinal cord and the roots of spinal nerves. The most superficial menix is dura mater. It is protective by virtue of its high collagen content. Layers of flattened fibrocytes line the inner surface of dura mater and blend with underlying arachnoid. The flattened fibrocytes that line the subarachnoid space are continuous with perineural epithelioid cells lining nerves fascicles.

Note: One way that cerebrospinal fluid is returned to the blood stream involves drainage from the subarachnoid space around spinal roots into lymphatics associated with spinal nerves. (Brain and spinal cord lack lymphatics but cerebrospinal fluid functions like lymphatic drainage.)

Arachnoid (arachnoid membrane) is thin and delicate, being composed of flattened fibrocytes and flimsy strands of collagen. In life, arachnoid contacts dura mater due to cerebrospinal fluid pressure within the subarachnoid space. Arachnoid trabeculae are delicate strands of arachnoid that traverse the subarachnoid space to join pia mater. They are more evident in cranial meninges than in spinal meninges.

Pia mater consists of flattened fibrocytes that line the subarachnoid space and collagen bundles in contact with glial cells at the surface of the spinal cord and spinal roots. Bilaterally, pia mater collagen is thickened to form denticulate ligaments. Processes of the ligaments periodically join dura mater and thus, within dura mater, the spinal cord is suspended by bilateral denticulate ligaments and thereby surrounded by protective cerebrospinal fluid within the subarachnoid space.

The arterial blood supply to the spinal cord comes from a ventral spinal artery and paired dorsal spinal arteries. The ventral spinal artery supplies most of the spinal cord. The artery is actually created by the sequence of cranial and caudal branches of radicular arteries that enter along ventral roots. Radicular arteries are branches of spinal arteries which, in turn, are branches of regional arteries (vertebral, costocervical, intercostal, and lumbar).

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