The denticulate ligaments, also known as the ligamentum denticulatum, are connective tissues attached to the spinal cord within the vertebral column, which is the bony structure surrounding and protecting the spinal cord. One denticulate ligament runs lengthwise along both sides of the spinal cord, making a total of two denticulate ligaments. The function of the denticulate ligaments is the suspension of the spinal cord inside the vertebral column. They are also thought to serve as stabilizers during bodily movements. Denticulate refers to their tooth-like appearance.
Inside the vertebral column is a membrane called the dural sac. It's the outermost layer of tissue that surrounds the spinal cord. This sac is also part of the meninges, which is a collective term for the three membranes of tissue that cover both the spinal cord and the brain.
The outermost and strongest meningeal layer, called the dura mater, forms the dural sac. The middle membrane is called the arachnoid because of its resemblance to a spider web. The thinnest and innermost layer of meningeal tissue is called the pia mater, and it attaches directly to the surface of the spinal cord. The denticulate ligaments are extensions of the pia mater's inner surface. There are 21 attachment points on the denticulate ligaments connecting them to both the arachnoid and dura mater's inner surface, providing stability to the spinal cord.
The first pair of denticulate ligaments attach to the foramen magnum, which is the opening at the base of the skull. The brainstem and spinal cord pass through this cranial opening. The last pair of denticulate ligaments are attached to the the end of the spinal cord, which is called the conus medullaris.
The conus medullaris is found in the lumbar region, which is located in the lower back above the buttocks. The first lumbar vertebra is called L1, which is the terminal point for the spinal cord. After the spinal cord ends, the filum terminale, or terminal thread, which is a thin strand of tissue, continues downward to sacral region, located between the hip bones. The filum terminale begins at the conus medullaris and ends at the coccyx, commonly called the tailbone.
The filum terminale is composed of two parts. The first is called the filum terminale internum, which ends at the second sacral vertebra. The second lower part of the filum terminale is called the filum terminale externum, and it ends at its attachment point on the first segment of the coccyx.