C4–C5 nucleus !
The nucleus pulposus is the soft, gel-like centre of the C4-C5 disc in the neck; it works like a water cushion that spreads the load.
Official name: C4-C5
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What it is
The soft, gel-like centre (nucleus pulposus) of the C4–C5 disc.
What it does
Works like a water cushion: it turns pressure from above into outward push on the fibre ring, spreading the load. It is under the most pressure when you bend forward and lift.
Key facts
- Where
- Centre of the C4–C5 disc, slightly toward the back, inside the annulus fibrosus
- Function
- Notochord-derived gel (about 70–90% water, proteoglycans); turns axial load into annulus tension; herniates posterolaterally toward the C5 root
Relations
- Behind
- Annulus fibrosus and posterior longitudinal ligament, then the spinal cord
- Lateral
- Uncovertebral joints of C5, the C5 root entering its foramen, and the vertebral artery beyond
How to find it
From the front, behind the thyroid cartilage (about C4–C5); from behind, about two spinous processes above the vertebra prominens.
Examination
- C5 root: weak shoulder abduction (deltoid) and elbow flexion, a numb patch over the outer upper arm, and a reduced biceps reflex (C5–C6)
- Spurling test: the neck is extended and turned toward the painful side with gentle downward pressure on the head; reproduced arm pain suggests root compression in the foramen
On imaging
Axial T2 MRI shows where the C4–C5 fragment sits: centrally against the cord, or posterolaterally at the entrance of the C5 foramen.
Common problems
- Squeezes out through a tear in the ring (herniation), usually backward and to one side, toward a nerve root.
- Loses water with age, so the disc gets thinner and stiffer.
How it is diagnosed
On MRI a healthy nucleus is bright on T2 images; a worn one turns dark ('black disc').
Treatment
- In a microdiscectomy only the loose piece that has pushed out is removed; most of the disc stays.
Clinical notes
- The adult nucleus has no blood vessels and is fed by diffusion through the endplates, so a torn annulus heals poorly and the nucleus slowly loses water
- An extruded or sequestered fragment more often shrinks on its own than a protrusion does
Development
In infancy the nucleus is rich in large notochordal cells and water. During childhood these cells are replaced by smaller cartilage-like cells, and the water content keeps falling with age, the first step of disc degeneration.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
How are protrusion, extrusion and sequestration of the C4–C5 nucleus defined?
Protrusion: the base of the displaced nucleus is wider than its tip. Extrusion: the tip is wider than the base, or the material has migrated. Sequestration: a free fragment.
What makes a herniation of the C4–C5 nucleus «contained»?
It stays under the outer annulus fibrosus and the posterior longitudinal ligament; an uncontained one breaks through them.
Why does a torn annulus around the C4–C5 nucleus heal poorly?
The adult nucleus has no blood vessels and is fed by diffusion through the endplates, so it slowly loses water.
Which type of C4–C5 nucleus herniation more often shrinks on its own?
An extruded or sequestered fragment, more often than a protrusion.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- nucleus pulposus C4-C5 TA2 1686
- Official Spanish (DeCS)
- Núcleo pulposo C4-C5 DeCS D000070614
- English (TA2)
- C4-C5
Related
Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Back, Nucleus Pulposus; Anatomy, Back, Intervertebral Discs; 7.3 The Vertebral Column (OpenStax (Rice University), 2022) · adapted, CC BY 4.0; 7.5 Embryonic Development of the Axial Skeleton (OpenStax (Rice University), 2022) · adapted, CC BY 4.0.
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Representative model, for educational purposes only.
