A ring of concentric collagen layers around a gelatinous centre, sandwiched between two vertebral bodies
Intervertebral disc — anulus fibrosus and nucleus pulposus.
Anatomy · Joints & cartilage
Intervertebral disc
23 in the human spine
Vertebral column · between vertebral bodies
An intervertebral disc is a pad of fibrocartilage between the bodies of adjacent vertebrae. A tough outer ring, the anulus fibrosus, surrounds a soft gelatinous core, the nucleus pulposus. Together they act as shock absorbers and allow the spine to bend and twist, and as a whole they make up about a quarter of the length of the column between the pelvis and the skull.
How to spot them
- ▸A flattened round or kidney-shaped pad sitting between two vertebral bodies
- ▸Concentric collagen layers (anulus fibrosus) around a soft, wet centre (nucleus pulposus)
- ▸There is none between the atlas and axis, and none between the fused sacral and coccygeal vertebrae
- ▸Thickest in the lumbar region, where the load is greatest
What to know
Twenty-three of these separate the movable vertebrae; none lies between the first two cervical vertebrae
Intervertebral disc — no disc between atlas and axis.
Together they make up about a quarter of the length of the column between pelvis and skull, and squash a little each day
Intervertebral disc — you are slightly taller in the morning.
The soft core is a remnant of the notochord
Intervertebral disc — the nucleus pulposus.
A 'slip' is a misnomer: the soft core bulges or ruptures through the outer ring, most often in the lower lumbar spine, pressing on a nerve root and causing sciatica
Intervertebral disc — herniation at L4/L5 or L5/S1.
Key ideas
- A disc is a secondary cartilaginous joint (a symphysis): fibrocartilage between two bone surfaces coated in hyaline cartilage.
- Water content of the nucleus falls with age, so discs lose height and spinal flexibility.
Quick-fire facts
- •There are 23 intervertebral discs in the spine: none between C1 and C2, and none between fused sacral or coccygeal segments.
- •OpenStax: the discs account for approximately 25 per cent of body height between the top of the pelvis and the base of the skull.
- •Outer ring: anulus fibrosus; core: nucleus pulposus, which derives from the notochord.
- •Adult discs are largely avascular and are nourished by diffusion through the vertebral end plates.
- •Most disc herniations occur in the lower lumbar spine, where the load is greatest, commonly at L4/L5 and L5/S1.
- •A 'slipped disc' is a misleading term: the disc does not slip, it prolapses.
- •Sciatica is pain from irritation of the sciatic nerve roots, often from a prolapsed disc.
- •You are a little taller in the morning than at night because discs lose fluid under load and rehydrate when lying down.
Drill it — 7 cards
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Sources
- OpenStax — The vertebral column (Anatomy and Physiology 2e)
- NHS — Slipped disc