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