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.