Human Anatomy
Spinal Cord
Spinal cord anatomy for MBBS: extent, grey and white matter, ascending and descending tracts, Brown-Sequard and syringomyelia, mapped to NMC codes AN57.1 to AN57.5.
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Spinal Cord
Spinal cord anatomy for MBBS: extent, grey and white matter, ascending and descending tracts, Brown-Sequard and syringomyelia, mapped to NMC codes AN57.1 to AN57.5.
This chapter describes the external form, internal grey and white matter and blood supply of the spinal cord. It builds the pathway knowledge needed to localise sensory and motor lesions and to understand syndromes such as syringomyelia and cord hemisection.
High-yield: Spinal Cord
- The spinal cord extends from the lower border of the medulla oblongata to the lower border of the first lumbar vertebra in the adult.
- In the newborn the cord ends at the third lumbar vertebra, and it appears to ascend with growth because the vertebral column grows faster.
- The cervical and lumbar enlargements give the nerves to the upper and lower limbs respectively.
- The cord tapers into the conus medullaris, from which the pia continues as the filum terminale.
- The lumbar and sacral nerve roots below the conus form the cauda equina within the lumbar cistern.
- Grey matter is central and butterfly-shaped, with dorsal, lateral and ventral horns; white matter surrounds it in three funiculi.
- The lateral corticospinal tract, a descending motor pathway, lies in the lateral funiculus and has already decussated in the medulla.
- The dorsal column carries fine touch, vibration and proprioception, and decussates in the medulla, not the cord.
- The lateral spinothalamic tract carries pain and temperature and decussates within one or two segments of the cord itself.
- Because of this, a cord hemisection gives ipsilateral loss of proprioception and contralateral loss of pain and temperature, the Brown-Sequard pattern.
- The lateral horn is present from the first thoracic to the second lumbar segment and contains preganglionic sympathetic neurons.
- Syringomyelia is a central cavitation that first interrupts the decussating spinothalamic fibres, giving a cape-like dissociated sensory loss.
- The anterior spinal artery supplies the anterior two-thirds of the cord, so its occlusion spares the dorsal columns.
- The subarachnoid space extends to the second sacral vertebra, giving a safe lumbar cistern for spinal puncture.
- The denticulate ligaments anchor the cord laterally to the dura between successive nerve roots.
Where do the main tracts decussate?
- **Dorsal column (fine touch, vibration, proprioception):** Decussates in the medulla. A cord lesion causes ipsilateral loss below the level.
- **Lateral spinothalamic (pain, temperature):** Decussates in the cord within one to two segments. A cord lesion causes contralateral loss a couple of levels below.
- **Lateral corticospinal (voluntary motor):** Already decussated in the medulla. A cord lesion causes ipsilateral upper motor neuron weakness.
- **Cord hemisection (Brown-Sequard):** Ipsilateral motor and proprioceptive loss, contralateral pain and temperature loss.
NMC competencies in this chapter
- **AN57.1:** External features of the spinal cord
- **AN57.2:** Extent of the spinal cord in the child and adult and its clinical implications
- **AN57.3:** Transverse section of the spinal cord at mid-cervical and mid-thoracic levels
- **AN57.4:** Ascending and descending tracts at the mid-thoracic level
- **AN57.5:** Anatomical basis of syringomyelia
Frequently Asked Questions
Where does the spinal cord end in an adult?
At the lower border of the first lumbar vertebra. In the newborn it reaches the third lumbar vertebra and appears to rise because the vertebral column grows more than the cord.
Why does a cord hemisection cause split sensory findings?
The dorsal columns ascend on the same side before crossing in the medulla, so proprioception is lost on the same side, while the spinothalamic fibres cross within the cord, so pain and temperature are lost on the opposite side. This is the Brown-Sequard syndrome.
What is the anatomical basis of syringomyelia?
A fluid-filled cavity expands in the central cord and first interrupts the spinothalamic fibres crossing in the anterior white commissure, producing a cape-like loss of pain and temperature with preserved touch.
What is the cauda equina?
It is the bundle of lumbar and sacral nerve roots that descend below the conus medullaris within the lumbar cistern before leaving the vertebral canal at their own levels.
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