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Anatomy of Spinal Cord

Gross Anatomy

  • A cylinder flattened from front to back that tapers into cone at lower end
  • In cross section has anterior fissure & posterior sulcus
  • Extends
    • Lower limit S2 in fetus
    • Level L3 at birth
    • Lower limit L1 by 20 years
  • Has two areas of discrete enlargement
    • Cervical area for Brachial plexus
    • Lumbosacral area for the Lumbar & Sacral plexuses
  • Cord fills
    • 1/3 of canal at atlas
    • 1/2 of canal at lower cervical spine
    • 1/2 of canal at thoracolumbar spine

Grey mater

  • Cell bodies
  • H-shaped
  • Has anterior & posterior horns & lateral horns
    • Anterior horn cells comprise the motor neurons
    • Lateral horns contain the preganglionic sympathetic cells from T1 to L2
    • Tip of the posterior horn contains the Substantia Gelatinosa responsible for pain transmission (Rexeds laminae)
  • Central canal is extension of 4th ventricle & lined by ependyma cells

White matter

  • Fibres arranged in columns/ tracts

Dorsal Columns

  • Lie between the posterior sulcus & the posterior horn
  • Ascending columns
  • Transmit sensation
    • Light touch & 2-point discrimination
    • Pressure
    • Vibration
    • Proprioception
  • Laminated with fibres from lower parts lie more medially
    • Gracile Nucleus – Lower limbs
    • Cuneate Nucleus – Upper limbs
  • Fibres cross in Medulla

Anterolateral Tract

  • AKA Spinothalamic Tract
    • Not broken into Anterior & Lateral Spinothalamic Tracts now
  • Lie anteriorly close to the anterior horn
    • Anterior to Lateral Corticospinal Tract
  • Ascending columns
  • Transmit sensation
    • Crude touch
    • Pain
    • Temperature
  • Laminated arrangement
    • Leg is lateral
    • Trunk is intermediate
    • Arm is medial
  • Fibres cross in Cord
    • Contralateral loss with unilateral cord or brainstem lesion

Lateral Corticospinal Tract

  • Large descending columns
  • Pyramidal supply to Motor
  • Transmit voluntary motor
  • Lie posteriorly close to posterior horn
  • Posterior to Spinothalamic Tract
  • Laminated arrangement
    • Leg is lateral
    • Trunk is intermediate
    • Arm is medial
  • Fibres cross in Medulla

Mixed in with the lateral tracts (Spinothalamic & Lat Corticospinal)

  • Lateral Reticulospinal Tract
  • Rubrospinal Tract

Anterior Corticospinal Tract

  • Small & unimportant descending columns
  • Pyramidal supply to Motor
  • Fibres cross in Cord

Anterior & Posterior Spinocerebellar Tracts

    • Lie on surface of cord between the anterior & posterior roots

Spinal Nerve Roots

  • Anterior & Posterior roots unite in the intervertebral foramina
  • Within the subarachnoid space the roots attached to spinal cord via series of rootlets
  • Dorsal Root Ganglion lies in the intervertebral foramen
  • Below L1 only anterior & posterior nerve roots present as the Cauda Equina
  • Filum Terminale (pia mater) passes from conus to the anterior periosteum of the coccyx

Blood Supply

  • Several basic principles
    • 1. Dependence on three longitudinal trunks
      • Anterior Median trunk
      • Paired posterolateral trunks
    • 2. Relative metabolic demands of the Grey matter greater than White
      • Thus the trunks are greatest in the Lumbar/ Cervical regions with the ganglionic enlargements
    • 3. Radicular vessels reinforce the longitudinal trunks at various levels
      • Average of 8 anterior & 12 posterior
        • Cervical region supplied by
          • Vertebral artery responsible for 80%
          • Other contributors
            • Deep cervical artery
            • Superior intercostal artery
            • Ascending pharangeal artery (in 60%)
        • Thoracic & lumbar areas supplied by
          • Aortic segmental vessels
          • Intercostal arteries
          • Lumbar arteries
        • Sacral area supplied by
          • Lateral sacral arteries
          • Middle sacral artery
          • Iliolumbar artery
          • Fifth lumbar artery (occasionally)

Single Anterior Spinal Artery

  • Largest
  • Midline
  • Supplies
    • Anterior 2/3 of cord (ie. not the posterior columns)
  • Formed at foramen magnum by union of the anterior spinal branches of vertebral artery
  • Runs in anterior fissure from medulla oblongata to cauda equina
  • Narrows & may become absent in thoracic cord
    • Watershed area
  • Receives feeders from segmental vessels

Double Posterior Spinal Arteries

  • Smaller than anterior spinal artery
  • Supplies the posterior columns of own side
  • Arise at foramen magnum from the PICA (posterior inferior cerebellar artery arising from vertebral artery) or vertebral arteries
  • Bilateral running in between & posterior to posterior spinal rootlets
  • Anastomosis with anterior spinal artery particularly at conus but very scanty at other levels

Segmental Arteries (Radicular arteries)

  • AKA Booster or Feeders
  • Highly variable
  • Embryologically each level had 2
  • Supply cord & roots via intervertebral foramen
  • Also contribute to ASA & PSA as Feeder artery
  • Summarise as
    • Upper C Spine
      • Branch of Vertebral Artery
    • Lower C Spine
      • Branch of Deep Cervical Artery, Superior Intercostal Artery
    • T Spine
      • Posterior Intercostal Arteries
    • L Spine
      • Lumbar Arteries
    • Sacrum
      • Lateral & Median Sacral Arteries, Iliolumbar Arteries

Artery of Adamkiewicz (Arteria Radicularis Magna)

  • Largest of radicular vessels
  • Lumbar cord feeder
  • Left side in 80% (aorta is on the left)
  • Can enter from T7 to L4
    • predilection for T10-T11
  • Critical Zone of Spinal Cord T4 to T9
    • Cord smallest & supply poorest
  • Injury to its parent blood vessel may damage cord
    • AAA repair etc

Pial Vessels

  • Small anastomotic blood vessels between ASA & PSA
  • Sit deep to Pia Mater
  • Give off central end arteries into cord via sulci
  • Supply Lateral Corticospinal tracts
  • Allows Sacral Sparing
    • Peripheral branches supply the cord periphery
    • Because sacral fibres are closest to the surface then they are often spared in ASA lesions

Venous Drainage

  • Anastomose freely without valves
    • Cf. Arteries are end arteries
  • External venous plexus anterior to bodies
  • Internal vertebral plexus in epidural space
  • Internal Vertebral Plexus
    • Loose knit plexuses anteriorly & posteriorly
      • Anterior Median Spinal Veins
        • Drain the anterior cord
      • Posterior Spinal Veins
        • Double & receive small radial veins from posterior columns
    • Communicate with
      • Anterior & Posterior Medullary Veins
      • Segmental Veins
    • That anastomose with
      • External Vertebral Plexus
  • Ultimate drainage into
    • Venacaval system
    • Azygos system
    • Vertebral
    • Lumbar
    • Sacral

Webpage Last Modified: 28 January, 2010