Spinal Cord

Anatomy White Matter Tracts Gray Matter & Nuclei Blood Supply Cord Syndromes Board Pearls

🧵 Spinal Cord – Anatomy & Organization

Extent: Foramen magnum → ~L1–L2 vertebral level (adult)

Conus medullaris: Terminal cord → gives rise to cauda equina
Enlargements: Cervical (C5–T1, upper limb), Lumbar (L2–S3, lower limb)
Segments vs vertebrae: Cord segments end higher than same-numbered vertebrae (important for localizing lesions)

Region	Key Features	Clinical Relevance
Cervical	Large white matter, obvious anterior horns (C5–T1)	Common site for myelopathy (spondylosis)
Thoracic	Small anterior horns, intermediolateral cell column (T1–L2)	Horner syndrome with T1 involvement
Lumbar	Less white matter, large anterior horns	Polio, ALS, radiculopathies affect LMNs here
Sacral	Mostly gray matter, S2–S4 parasympathetic	Bladder, bowel, sexual dysfunction with conus/cauda lesions

📡 White Matter Tracts (High Yield)

Dorsal Columns (DCML) – Vibration & Proprioception ▼

Modality: Vibration, joint position, fine touch
Somatotopy (below T6): Gracilis (legs, medial); above T6 adds Cuneatus (arms, lateral)
Pathway: Dorsal root → dorsal columns → synapse in medulla (nuclei gracilis/cuneatus) → decussate in medulla → medial lemniscus → thalamus → cortex
Lesion in spinal cord: Ipsilateral loss of vibration/position sense below level

Clinical: B12 deficiency, tabes dorsalis, nitrous oxide toxicity → sensory ataxia, positive Romberg.

Spinothalamic Tract – Pain & Temperature ▼

Modality: Pain, temperature, crude touch
Pathway: Dorsal root → Lissauer’s tract → dorsal horn → decussate in anterior white commissure over 1–2 segments → ascend contralaterally
Lesion in cord: Contralateral loss of pain/temp starting ~1–2 levels below lesion

Clinical: Central cord/syrinx → bilateral cape-like loss of pain/temp (spinothalamic crossing fibers).

Corticospinal Tract (CST) – Voluntary Motor ▼

Origin: Primary motor cortex (area 4), premotor, SMA
Decussation: Pyramidal decussation in caudal medulla → lateral CST (contralateral)
Spinal lesion: Ipsilateral UMN signs below level (weakness, spasticity, hyperreflexia, Babinski)
At lesion level: LMN signs if anterior horn/root involved

Clinical: Myelopathy = UMN below (↑reflexes) + possible LMN at level (atrophy, fasciculations).

🌑 Gray Matter & Autonomic Nuclei

Horns & Columns ▼

Dorsal horn: Sensory processing
Ventral horn: LMNs to skeletal muscle
Intermediate zone: Autonomics & interneurons

Key Nuclei

Intermediolateral cell column (T1–L2): Sympathetic preganglionic neurons
S2–S4: Parasympathetic to bladder, bowel, sexual function
Clarke’s nucleus (T1–L2): Dorsal spinocerebellar tract (ipsilateral leg proprioception)

Clinical:

Horner syndrome: Lesion of T1 sympathetic outflow (Pancoast tumor, syrinx)
Conus medullaris: Early bladder/bowel/sexual dysfunction, saddle anesthesia

🩸 Blood Supply of the Spinal Cord

Anterior Spinal Artery (ASA) – 2/3 of Cord ▼

Supplies anterior 2/3 of cord: corticospinal tracts, spinothalamic tracts, ventral horns
Spares dorsal columns

ASA Syndrome:

Bilateral motor weakness below lesion
Bilateral pain & temperature loss
Preserved vibration & proprioception
Autonomic dysfunction (bladder, bowel)

Posterior Spinal Arteries (PSA) – Dorsal Columns ▼

Supply dorsal columns and posterior horns

PSA Syndrome:

Loss of vibration and position sense
Sensory ataxia, positive Romberg
Motor and pain/temp often preserved

Radicular Arteries & Adamkiewicz ▼

Radicular arteries: Segmental reinforcement of ASA/PSA
Artery of Adamkiewicz: Usually T9–L2, supplies lower thoracic/lumbosacral cord
Clinical: Aortic surgery or hypotension → infarct of lower cord, flaccid paraplegia → then spasticity

⚠️ Spinal Cord Syndromes

Brown-Séquard Syndrome – Hemicord Lesion ▼

Ipsilateral below lesion: UMN weakness (CST), loss of vibration/proprioception (DCML)
Contralateral below (starting ~1–2 levels down): Loss of pain & temperature (STT)
At lesion level: LMN signs, segmental sensory loss

Etiologies: Trauma, tumor, MS, penetrating injury.

Central Cord Syndrome – “Hands > Legs” ▼

Hyperextension injury in cervical spondylosis (elderly) or syringomyelia
Weakness: Arms > legs (cervical CST fibers for arms more central)
Sensation: Often bilateral cape-like pain/temp loss
Variable bladder involvement

Posterior Cord Syndrome ▼

Loss of vibration & proprioception, sensory ataxia, positive Romberg
Motor strength, pain & temperature largely preserved
Etiologies: B12 deficiency, tabes dorsalis, nitrous oxide, posterior spinal artery infarct

Anterior Cord Syndrome – ASA Infarct ▼

Bilateral motor paralysis below lesion (CST)
Bilateral pain/temp loss (STT)
Vibration/proprioception spared (dorsal columns)

Conus Medullaris vs Cauda Equina ▼

Feature	Conus Medullaris	Cauda Equina
Location	L1–L2 cord segment	Lumbar & sacral roots
Onset	Sudden	More gradual
Weakness	Symmetric; proximal & distal	Asymmetric, radicular, distal
Sensation	Saddle anesthesia	Asymmetric dermatomal loss
Bladder/Bowel	Early, prominent sphincter dysfunction	Late, less prominent early on
Reflexes	Ankle jerk ↓, bulbocavernosus ↓	Hyporeflexia in affected roots

💎 Spinal Cord – Board Pearls

Spinothalamic decussation occurs 1–2 levels above entry → explains contralateral pain/temp loss starting slightly below lesion.
Dorsal columns decussate in the medulla, not in the cord → spinal lesions give ipsilateral position/vibration loss.
Anterior spinal artery syndrome: motor + pain/temp loss, preserved vibration/proprioception.
Syringomyelia: bilateral cape-like pain/temp loss with preserved dorsal column function; think Chiari I.
B12 deficiency: combined degeneration of DCML + CST → sensory ataxia + UMN signs.
Horner syndrome with arm weakness = think lesion at C8–T2 (Pancoast, syrinx, lateral medullary/cord lesions).

💎 Quick Localization Trick

UMN signs below + LMN at the level = cord lesion. If legs are worse than arms with a sensory level, it’s almost never purely brain — think spinal cord.