The filum terminale ('terminal thread') is a delicate strand of
fibrous tissue
Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesode ...
, about 20 cm in length, extending inferiorly from the apex of the
conus medullaris to attach onto the coccyx.
The filum terminale acts to anchor the spinal cord and spinal meninges inferiorly.
The upper portion of the filum terminale is formed by spinal pia mater within a dilated
dural sac, while the lower portion is formed by both pia and dura mater (with the outer dural layer closely adhering to the inner pial component).
Anatomy
The proximal/superior partthe filum terminale internum or pial part of terminal filum
measures 15 cm in length and extends as far as the inferior border
of the second
sacral vertebra (S2) (the inferior limit
sacral canal). It is composed of the vestiges of neural tissue, connective tissue, and neuroglial tissue lined by pia mater.
It is contained within a tubular sheath of the
dura mater and is surrounded by the nerves of the
cauda equina (from which it can be easily recognized by its blueish-white color).
The inferior/distal partthe filum terminale externum, dural part of terminal filum, or coccygeal ligament - is formed as the filum terminale internum reaches the inferior extremity of the dural sac; henceforth, the filum terminale becomes invested by a layer of dura mater.
The filum terminale ultimately terminates inferiorly by attaching to the dorsum of the
coccyx
The coccyx (: coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horse anatomy, horses. In tailless primates (e.g. hum ...
at the first coccygeal segment,
flaring out
to blend with the coccygeal
periosteum
The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartila ...
.
Relations
The filum terminale is situated centrally
amid the spinal nerve roots of the
cauda equina (but is not itself a part of the cauda equina
).
The
inferior-most spinal nerve, the
coccygeal nerve, leaves the spinal cord at the level of the conus medullaris via respective vertebrae through their intervertebral foramina,
superior to the filum terminale. However, adhering to the outer surface of the filum terminale are a few strands of
nerve fibres which probably represent rudimentary second and third coccygeal nerves.
The
central canal
The central canal (also known as spinal foramen or ependymal canal) is the cerebrospinal fluid-filled space that runs through the spinal cord. The central canal lies below and is connected to the ventricular system of the brain, from which it r ...
of the spinal cord extends inferiorly into the superior part of the filum terminale.
Development
The filum terminale is the vestigial remnant of the caudal portion of the spinal cord which forms a tail-like caudal eminence in the embryo.
Additional images
File:Slide3dsdd.GIF, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
File:Slide5sese.GIF, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
File:Slide6drdr.GIF, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
File:Slide4rer.JPG, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
File:Slide5rer.JPG, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
File:Slide6rer.JPG, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
File:Slide7feer.JPG, Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
References
* Martini, F. Timmons, M. and Tallitsch, R. ''Human Anatomy''. 5th ed. San Francisco: Pearson/Benjamin Cummings, 2006.
External links
*
*
* - "Vertebral Canal and Spinal Cord: Regions of the Spinal Cord"
*
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Meninges