Vertebral Column and Spinal Cord

Prepared and reviewed by the PrepElephant Academic Review Team

First published 2 Oct 2026 · Spot an error?

On this page

Direct answer
What you must remember
Performing a safe lumbar puncture
Levels the exam loves
Frequently asked questions
Related topics

Direct answer

Thirty-three vertebrae make up the column — seven cervical, twelve thoracic, five lumbar, five fused sacral and four coccygeal — and the spinal cord it protects ends at the conus medullaris around the lower border of L1 in adults (L3 in the newborn), a fact that makes lumbar puncture at L3–L4 or L4–L5 safe below the cord. Regional identification is exam currency: cervical vertebrae carry foramina transversaria for the vertebral artery, thoracic vertebrae carry costal facets on heart-shaped bodies, and lumbar vertebrae are massive and kidney-shaped. The primary thoracic and sacrococcygeal curves are present in the fetus; the secondary cervical and lumbar lordoses develop after birth with head control at about three months and walking at about one year.

What you must remember

Typical vertebra: a body anteriorly, two pedicles and two laminae forming the vertebral arch, and seven processes — one spinous, two transverse and four articular; adjacent vertebrae bound the intervertebral foramen for the spinal nerve.
Special vertebrae: the atlas has no body or spine; the axis carries the dens (the body of the atlas fused); C7 is the vertebra prominens with a long, palpable spine; the sacral hiatus, capped by the coccyx, is the landmark for caudal epidural block.
Ligaments: the anterior longitudinal ligament is strong and resists hyperextension; the posterior longitudinal ligament is weaker and narrower laterally, which is why disc prolapse is posterolateral; the ligamentum flavum, rich in elastic fibres, links adjacent laminae and gives the epidural needle its characteristic resistance.
Intervertebral disc: annulus fibrosus with a nucleus pulposus — the notochordal remnant; L4–L5 and L5–S1 are the commonest prolapse sites, compressing the traversing L5 and S1 roots respectively.
Cord endings and coverings: conus medullaris at L1–L2, filum terminale to the coccyx, denticulate ligaments suspending the cord; the dural sac ends at S2, so below L1–L2 the theca contains only the cauda equina.
Blood supply: the anterior spinal artery supplies the anterior two-thirds (corticospinal and spinothalamic tracts); paired posterior spinal arteries supply the dorsal columns; the artery of Adamkiewicz, a large segmental feeder usually entering on the left between T9 and L2, makes the lower cord vulnerable in aortic surgery.
Landmark levels: C4 — carotid bifurcation; C6 — cricoid cartilage and entry of the vertebral artery into its foramen transversarium; T4 — sternal angle; L1 — transpyloric plane; L4 — aortic bifurcation and the intercristal (Tuffier) line joining the iliac crests.

Performing a safe lumbar puncture

Position the patient in the left lateral decubitus, fully flexed — neck and knees drawn in to open the interspinous spaces. Palpate the iliac crests: a line joining their highest points, the intercristal line of Tuffier, crosses roughly the L4 spine or L4–L5 interspace, so the needle is aimed at L3–L4 or L4–L5, one space at or just below the landmark. In the midline, bevel parallel to the longitudinally running dural fibres to reduce CSF leak, advance through skin, supraspinous and interspinous ligaments; a distinct increase in resistance announces the ligamentum flavum, and crossing it with the stylet in place enters the epidural space — beyond that, a pop signals the dura and arachnoid, and CSF drips with the stylet removed. Before the tap, exclude raised intracranial pressure — papilloedema or focal signs demand imaging first, because decompressing a tense posterior fossa or supratentorial mass can herniate the brainstem.

Levels the exam loves

Screening papers convert this region into level-matching exercises, and two skills cover them. First, know why the tap is safe — cord at L1–L2, dural sac at S2 — and children get the higher space because their cord ends lower. Second, hold the arterial map steady: anterior spinal artery occlusion spares the dorsal columns while striking motor and pain pathways, a dissociation NBE turns into a clinical stem, and the artery of Adamkiewicz explains the anterior cord syndrome occasionally seen after thoracoabdominal aortic repair.

Frequently asked questions

At what level does the spinal cord end in adults, and why is lumbar puncture performed below it?

The conus medullaris ends at L1–L2 in adults (about L3 in newborns); puncture at L3–L4 or L4–L5 encounters only the cauda equina roots, which are pushed aside by the needle.

Which ligament produces the resistance felt during lumbar puncture?

The ligamentum flavum, the elastic ligament connecting adjacent laminae; beyond it lies the epidural space and then the dura.

What is the arterial supply of the spinal cord?

One anterior spinal artery to the anterior two-thirds, and paired posterior spinal arteries to the posterior one-third including the dorsal columns, reinforced segmentally with the large artery of Adamkiewicz.

What occupies the intervertebral disc and which is the commonest level of prolapse?

The nucleus pulposus, a notochordal remnant, within the annulus fibrosus; prolapse is commonest at L4–L5 and L5–S1, and it is directed posterolaterally by the strong midline posterior longitudinal ligament.

Which line is used to identify the L4 vertebral level at the bedside?

The intercristal (Tuffier) line joining the highest points of the iliac crests crosses approximately at the L4 spine or L4–L5 interspace.