Spinal Cord Anatomy: Internal Structure and Tracts
Complete tutorial on spinal cord anatomy - white matter columns, gray matter nuclei, ascending (sensory) and descending (motor) tracts, blood supply, and segmental organization.
This content is for informational purposes only. Always consult a healthcare professional.
The spinal cord is the major neural pathway between the brain and the body. It extends from the foramen magnum to the L1-L2 vertebral level in adults.
Gross Anatomy
External Features
| Feature |
Description |
| Length |
~45 cm (adult) |
| Weight |
~30 g |
| Segments |
31 (8C, 12T, 5L, 5S, 1Co) |
| Enlargements |
Cervical (C4-T1), Lumbar (T9-T12) |
| Termination |
Conus medullaris (L1-L2 in adults, L3 in newborns) |
| Filum terminale |
Pial extension to coccyx |
| Cauda equina |
Lumbar/sacral nerve roots below conus |
Meninges
| Layer |
Description |
Spaces |
| Dura mater |
Thick fibrous tube |
Epidural space (fat, veins), Subdural space (potential) |
| Arachnoid mater |
Delicate avascular |
Subarachnoid space (CSF, vessels) |
| Pia mater |
Vascular, adherent to cord |
Denticulate ligaments (stabilize cord) |
Nerve Roots
- Ventral roots: Motor (efferent) - exit via anterior lateral sulcus
- Dorsal roots: Sensory (afferent) - enter via posterior lateral sulcus
- Dorsal root ganglion: Sensory neuron cell bodies
- Spinal nerve: Mixed (sensory + motor)
Internal Structure
Gray Matter
The gray matter is H-shaped or butterfly-shaped, divided into horns:
| Horn |
Location |
Contents |
Function |
| Dorsal (posterior) |
Dorsal |
Sensory neurons, substantia gelatinosa |
Sensory processing |
| Ventral (anterior) |
Ventral |
Motor neurons (alpha, gamma) |
Motor output |
| Lateral (intermediate) |
Between dorsal and ventral (T1-L2, S2-S4) |
Preganglionic autonomic neurons |
Autonomic output |
| Central gray |
Around central canal |
Interneurons |
Pain modulation, supraspinal connections |
Rexed Laminae
The spinal gray matter is organized into 10 laminae (I-X):
| Lamina |
Location |
Nucleus/Nuclei |
Function |
| I |
Dorsal horn (marginal zone) |
Posteromarginal nucleus |
Pain, temperature |
| II |
Dorsal horn (substantia gelatinosa) |
Substantia gelatinosa |
Pain modulation |
| III-IV |
Dorsal horn (nucleus proprius) |
Nucleus proprius |
Touch, pressure |
| V |
Dorsal horn (neck) |
Reticular formation |
Sensory processing |
| VI |
Dorsal horn (base) |
— |
Proprioception (cervical/lumbar only) |
| VII |
Intermediate zone |
Intermediolateral cell column (T1-L2), sacral autonomic, Clarke column (C8-L2), phrenic (C3-C5) |
Autonomic, proprioceptive relay |
| VIII |
Ventral horn (medial) |
Commissural interneurons |
Motor coordination |
| IX |
Ventral horn (lateral) |
Alpha and gamma motor neurons |
Motor output to skeletal muscle |
| X |
Around central canal |
— |
Pain modulation |
White Matter
The white matter is organized into three columns (funiculi):
| Column |
Location |
Major Tracts |
| Dorsal column |
Between dorsal horns |
Fasciculus gracilis, fasciculus cuneatus |
| Lateral column |
Between dorsal and ventral horns |
Corticospinal, spinothalamic, spinocerebellar |
| Ventral column |
Between ventral horns |
Corticospinal (anterior), vestibulospinal, tectospinal |
Ascending Tracts (Sensory)
Modality: Fine touch, vibration, proprioception (conscious)
| Component |
Location |
Description |
| First-order neuron |
Dorsal root ganglion |
Peripheral → spinal cord |
| Fasciculus gracilis |
Dorsal column (medial) |
Lower body (T7 and below) |
| Fasciculus cuneatus |
Dorsal column (lateral) |
Upper body (T6 and above) |
| Second-order neuron |
Nucleus gracilis/cuneatus (medulla) |
Decussates (internal arcuate fibers) |
| Medial lemniscus |
Medulla → pons → midbrain |
Crossed fibers to thalamus |
| Third-order neuron |
VPL nucleus (thalamus) |
Thalamus → primary somatosensory cortex |
Lesion: Ipsilateral loss of fine touch, vibration, and proprioception below the lesion
Spinothalamic Tract (Anterolateral System)
Modality: Pain, temperature, crude touch
| Component |
Location |
Description |
| First-order neuron |
Dorsal root ganglion |
Peripheral → spinal cord |
| Second-order neuron |
Substantia gelatinosa/nucleus proprius |
Decussates within 1-2 segments via anterior commissure |
| Lateral spinothalamic |
Lateral column |
Pain and temperature |
| Anterior spinothalamic |
Ventral column |
Crude touch (controversial) |
| Third-order neuron |
VPL nucleus (thalamus) |
Thalamus → primary somatosensory cortex |
Lesion: Contralateral loss of pain and temperature 1-2 segments below the lesion
Spinocerebellar Tracts
Modality: Unconscious proprioception (for coordination)
| Tract |
Location |
Origin |
Termination |
| Dorsal spinocerebellar |
Lateral column (posterior) |
Clarke column (C8-L2) |
Cerebellum (ipsilateral, via ICP) |
| Ventral spinocerebellar |
Lateral column (anterior) |
Lamina VII (lumbar) |
Cerebellum (contralateral, via SCP) |
| Cuneocerebellar |
Lateral cuneate nucleus (medulla) |
Fasciculus cuneatus (upper body) |
Cerebellum (ipsilateral) |
| Rostral spinocerebellar |
Lateral column |
Cervical cord |
Cerebellum |
Descending Tracts (Motor)
Corticospinal Tract (Pyramidal Tract)
Function: Voluntary fine motor control
| Component |
Location |
Description |
| Origin |
Primary motor cortex (BA 4), premotor (BA 6) |
Upper motor neuron (UMN) |
| Corona radiata |
Cerebral white matter |
Converging fibers |
| Internal capsule |
Posterior limb |
Between caudate and putamen/thalamus |
| Cerebral peduncle |
Midbrain |
Middle 3/5 of crus cerebri |
| Pyramid |
Medulla |
Visible ventral ridge |
| Decussation |
Caudal medulla |
85-90% of fibers cross |
| Lateral corticospinal |
Lateral column (crossed) |
To all spinal levels |
| Anterior corticospinal |
Ventral column (uncrossed) |
To cervical/upper thoracic |
| Termination |
Lamina IX (anterior horn) |
Synapse on lower motor neuron |
Lesion: Contralateral spastic paralysis, hyperreflexia, Babinski sign (UMN signs)
| Tract |
Origin |
Function |
Location in Cord |
| Rubrospinal |
Red nucleus (midbrain) |
Flexor tone |
Lateral column (anterior to corticospinal) |
| Vestibulospinal (lateral) |
Lateral vestibular nucleus |
Extensor tone, balance |
Ventral column |
| Vestibulospinal (medial) |
Medial vestibular nucleus |
Head position |
Ventral column |
| Reticulospinal (pontine) |
Pontine RF |
Facilitates motor activity |
Ventral column |
| Reticulospinal (medullary) |
Medullary RF |
Inhibits motor activity |
Lateral column |
| Tectospinal |
Superior colliculus |
Head/eye reflexes |
Ventral column |
Blood Supply
Arterial Supply
| Artery |
Origin |
Territory |
| Anterior spinal artery |
Vertebral arteries (intracranial) |
Anterior 2/3 of spinal cord |
| Posterior spinal arteries (2) |
Vertebral or PICA |
Posterior 1/3 (dorsal columns) |
| Radicular arteries |
Segmental arteries (vertebral, intercostal, lumbar, sacral) |
Supplement spinal arteries |
| Artery of Adamkiewicz (great anterior radicular) |
Intercostal or lumbar (left, T8-L2) |
Lower 2/3 of spinal cord |
Vulnerable zones:
- Watershed zone T3-T4 (between cervical and thoracic radicular supply)
- Artery of Adamkiewicz territory (critical for lower cord)
Venous Drainage
| Vein |
Description |
| Anterior spinal vein |
Along anterior median fissure |
| Posterior spinal veins |
Along posterior lateral sulci |
| Radicular veins |
Drain to internal vertebral venous plexus |
| Internal vertebral venous plexus (Batson plexus) |
Valveless, connects pelvic to spinal veins |
Spinal Cord Syndromes
| Syndrome |
Lesion |
Findings |
| Brown-Sequard (hemisection) |
Half of cord |
Ipsilateral UMN weakness, loss of vibration/proprioception; contralateral loss of pain/temperature |
| Anterior cord |
Anterior spinal artery occlusion |
Bilateral UMN weakness, loss of pain/temperature; preserved vibration/proprioception |
| Central cord |
Syringomyelia, trauma |
Bilateral loss of pain/temperature in upper extremities (suspended sensory level); variable motor |
| Posterior cord |
Tabes dorsalis |
Loss of vibration and proprioception; sensory ataxia; positive Romberg |
| Complete cord transection |
All tracts |
Bilateral UMN weakness below level, loss of all sensation, autonomic dysfunction |
| Cauda equina |
Below conus (lumbar nerve roots) |
Lower motor neuron signs, radicular pain, bladder/bowel dysfunction |
| Conus medullaris |
S2-S4 level |
Early bladder/bowel dysfunction, saddle anesthesia; LMN signs |