Explain me bornes of spinal cord

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Here is a detailed explanation of the bornes (boundaries/extent) of the spinal cord, based on Gray's Anatomy for Students and Bradley and Daroff's Neurology in Clinical Practice:

Boundaries (Bornes) of the Spinal Cord

Spinal cord diagram showing conus medullaris, filum terminale, and lumbar enlargement

Upper Bound (Superior Limit)

The spinal cord begins at the foramen magnum, where it is continuous with the medulla oblongata (the lower part of the brainstem). This is the craniovertebral junction. The cord occupies the superior two-thirds of the vertebral canal.

Lower Bound (Inferior Limit) - The Conus Medullaris

The spinal cord tapers inferiorly into a cone-shaped tip called the conus medullaris. Its exact level varies:

Population	Normal Range	Typical Level
Adults	T12 - L2/L3 disc	L1-L2 disc
Neonates	Up to L4	L3

In adults, it most commonly ends at the level of the disc between L1 and L2, but can range from as high as T12 to as low as the L2-L3 disc.
In neonates, the cord extends further down to around L3 (and sometimes L4), because the vertebral column grows faster than the spinal cord after birth.

Gray's Anatomy for Students - p. 119

What Continues Below the Conus?

Once the spinal cord ends, two structures continue downward:

Filum terminale - A thin filament of connective tissue that extends from the apex of the conus medullaris. It has two parts:
- Pial part (filum terminale internum): extends from the conus through the subarachnoid space to S2.
- Dural part (filum terminale externum / coccygeal ligament): continues from S2 to the coccyx, anchoring the cord.
Cauda equina - The bundle of lumbar and sacral nerve roots that descend below the conus (since the spinal cord ends at L1-L2, but the spinal column extends to S5, the nerve roots travel a long distance within the subarachnoid space before exiting through their respective foramina).

The Subarachnoid Space

The subarachnoid space (which contains CSF) ends at approximately S2. This is clinically important - lumbar puncture is performed below L2 (usually at L3-L4 or L4-L5) to avoid injuring the spinal cord while still being within the subarachnoid space.

Length and Diameter

The spinal cord is not uniform in diameter. It has two fusiform swellings called enlargements:
- Cervical enlargement - at C5 to T1 level (for innervation of upper limbs)
- Lumbosacral enlargement - at L1 to S3 level (for innervation of lower limbs)

Clinical Relevance

Lumbar puncture is performed at L3-L4 or L4-L5 to avoid puncturing the cord.
Conus medullaris syndrome (injury at T12-L2): causes a mixed upper + lower motor neuron picture, saddle anesthesia, and bladder/bowel dysfunction.
Cauda equina syndrome (injury below conus): pure lower motor neuron syndrome with flaccid weakness, areflexia, and variable sensory loss. (Bradley and Daroff's Neurology, p. 485)

Summary Table:

Landmark	Level
Upper border	Foramen magnum (= medulla oblongata junction)
Lower border (adult)	L1-L2 disc (range: T12 to L2-L3)
Lower border (neonate)	L3 (range: up to L4)
End of subarachnoid space	S2
End of filum terminale	Coccyx

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