Spinal Cord Tracts
The spinal cord carries ascending (sensory) and descending (motor) tracts in a predictable somatotopic arrangement. Knowing which tract carries which modality explains Brown-Séquard syndrome and every level of cord lesion.
✦ The Mnemonic
"Dorsally Columns Stand, Spinothalamic Crosses, Corticospinal Descends"
Dorsal columns (ipsilateral fine touch) · Spinothalamic (contralateral pain/temp) · Corticospinal (ipsilateral motor)
Clinical Breakdown
The critical teaching point: dorsal columns carry fine touch and proprioception ipsilaterally (cross at medulla); the spinothalamic tract carries pain and temperature contralaterally (crosses at cord level). This explains Brown-Séquard syndrome — hemisection of the cord causes: ipsilateral UMN weakness + dorsal column loss below the lesion; contralateral pain/temperature loss 1–2 levels below.
Central cord syndrome: the most common incomplete spinal cord injury (usually cervical hyperextension in older patients with pre-existing stenosis). Motor loss greater in arms than legs; bladder dysfunction; preserved perianal sensation. Arms worse than legs because cervical motor fibres are somatotopically central within the corticospinal tract.
Anterior cord syndrome: anterior spinal artery infarction (aortic surgery, embolism). Loss of motor function and pain/temperature (spinothalamic) below the lesion, with preserved dorsal column function (proprioception and vibration — supplied by posterior spinal arteries). Worst prognosis of the incomplete cord syndromes.
⭐ Clinical Pearl
Subacute combined degeneration of the cord: vitamin B12 deficiency causes demyelination of the dorsal columns (fine touch/proprioception loss, positive Romberg) and lateral columns (corticospinal — UMN signs). The spinothalamic tract is relatively spared. B12 deficiency also causes a peripheral neuropathy — so the patient may have UMN signs (from cord) plus absent reflexes (from peripheral neuropathy) simultaneously.