Which part of the disc is known as the annulus fibrosus?

The annulus fibrosus refers specifically to the outer layer of an intervertebral disc. This structure is composed of several concentric layers of collagen fibers that provide strength and support to the disc. The firm outer part plays a crucial role in containing the softer inner material, known as the nucleus pulposus, which is the core of the disc that absorbs compressive forces.

The annulus fibrosus is critical in maintaining the overall integrity of the disc and preventing herniation. Its design allows it to withstand the stresses placed on the spine during movement and weight-bearing activities. In contrast, the other parts mentioned, such as the nucleus pulposus or vertebral endplate, serve different functions within the anatomy of the spine and do not have the same structural characteristics or roles as the annulus fibrosus. Thus, identifying the annulus fibrosus as the firm outer part accurately reflects its anatomical and functional significance in the intervertebral disc.