Spinal Cord Pathways — INBDE Review
Lateral corticospinal tract, dorsal columns, and spinothalamic tract — where each one decussates and what its lesions look like (Brown-Séquard, ASA infarct). 11 board-style MCQs.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. Mnemonics in amber, clinical pearls in blue.
Spinal cord pathway questions on the INBDE come down to three things per tract: what it carries, where it crosses, and what a lesion looks like ipsilateral vs contralateral to the level. Get those three facts straight for the corticospinal tract, dorsal columns, and spinothalamic tract, and the syndrome questions become straightforward.
| Tract | Function | Crossing point | Lesion below crossing |
|---|---|---|---|
| Lateral corticospinal | Voluntary motor (limb) | Medullary pyramids (decussation of pyramids) | Ipsilateral weakness below lesion |
| Dorsal columns | Vibration, proprioception, fine touch, two-point discrimination | Medulla (gracile/cuneate nuclei → medial lemniscus) | Ipsilateral loss below lesion |
| Spinothalamic (anterolateral) | Pain, temperature, crude touch | Within 1–2 levels of entry, via anterior white commissure | Contralateral loss starting 1–2 levels below |
| Syndrome | Pattern | Cause |
|---|---|---|
| Brown-Séquard (hemicord) | Ipsilateral motor + vibration loss; contralateral pain/temp loss | Penetrating trauma, tumor, MS plaque |
| Anterior spinal artery (ASA) infarct | Bilateral motor + pain/temp loss; vibration/proprioception SPARED | Aortic surgery, severe hypotension |
| Posterior spinal artery (PSA) infarct | Bilateral vibration/proprioception loss only | Rare; isolated dorsal column deficit |
| Central cord syndrome | Bilateral pain/temp loss; motor + vibration spared | Syringomyelia, hyperextension injury |
Lateral corticospinal tract (LCST) — voluntary motor
- Origin: motor cortex → internal capsule → cerebral peduncle → medullary pyramids (decussation) → descends contralaterally → synapses on lower motor neurons in the anterior horn.
- Above the decussation (e.g., cortical or capsular stroke): contralateral weakness.
- Below the decussation (cord lesion): ipsilateral weakness below the level.
Dorsal columns — fine touch, vibration, proprioception
- Origin: peripheral receptor → dorsal root ganglion → ascends ipsilaterally in the dorsal columns.
- Decussation in the medulla: gracile nucleus (lower body, medial) and cuneate nucleus (upper body, lateral) → medial lemniscus → thalamus → cortex.
- Cord lesion → ipsilateral loss of vibration and proprioception below the level.
- Romberg test: positive (falls when eyes close) confirms a dorsal column deficit.
Spinothalamic tract — pain, temperature, crude touch
- Origin: nociceptor → dorsal root → synapses in the dorsal horn.
- Decussates within 1–2 levels via the anterior white commissure → ascends contralaterally.
- Cord lesion → contralateral pain/temperature loss starting 1–2 levels below the lesion (because the fibers ascend a couple of segments before crossing).
Vascular supply
- Anterior spinal artery: anterior two-thirds of the cord (motor + spinothalamic). Infarct → bilateral motor + pain/temperature loss; vibration spared.
- Posterior spinal arteries: posterior third (dorsal columns). Infarct → isolated vibration/proprioception loss.
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong — that's where the learning compounds.
The MCQs above are Core Recall — testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- Question 1EasyWhich spinal cord tract carries voluntary motor commands for limb movement?
- Question 2EasyWhere do fibers of the corticospinal tract decussate?
- Question 3ModerateA lesion of the right lateral corticospinal tract at C6 produces weakness on which side?
- Question 4EasyWhich tract carries vibration and proprioception?
- Question 5ModerateWhere do dorsal column fibers cross to the opposite side?
- Question 6EasyThe spinothalamic tract primarily carries:
- Question 7ModerateWhere do spinothalamic tract fibers cross to the opposite side?
- Question 8HardBrown-Séquard syndrome (hemicord lesion) classically produces:
- Question 9EasyWhich artery supplies the anterior two-thirds of the spinal cord?
- Question 10ModerateAnterior spinal artery infarct typically spares which function?
- Question 11ModerateA patient with chronic alcoholism stumbles when his eyes are closed during a Romberg test. Which spinal pathway is most likely impaired?
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.