SCI-01 · Spinal Cord Anatomy and Neuroanatomy

Spinal Cord Anatomy and Neuroanatomy. Part of the Spinal Cord Injury series of the Reflex PM&R Board Review podcast. Audio corrections: (1) In the audio: It provides roughly 50% of cervical movement, specifically the flexion and extension. That belongs to the joint right above it, the atlantooccipital joint. — Correct: The atlanto-occipital joint is the nod joint, but it does not supply half of the cervical flexion-extension arc. Measured in-vivo contributions cluster around 15 to 20 percent of the whole-neck arc, and the joint is strongly extension-biased. There is no 50/50 split to memorise here: the rotation half of the pair, about 50% of cervical rotation at the atlantoaxial joint, is correct, but the flexion-extension half is not. (2) In the audio: We also absolutely must highlight the mid-thoracic region, specifically the T4 to T8 vascular segment. This is a critical watershed zone where the upward and downward arterial feeds meet. It is highly vulnerable to global systemic hypotension, meaning a severe drop in blood pressure will selectively infarct the T4 to T8 cord first. — Correct: Two things to unlearn here. T4 to T8 is a commonly taught approximation of the mid-thoracic watershed, not an established boundary; and no first-to-infarct ranking is established at all, so the claim that hypotension selectively infarcts that segment first goes past the evidence, which shows variable origins, variable segmental reinforcement and variable collateral adequacy between individuals. What survives is that the mid-thoracic cord is the conventional watershed, lying between the upper territory reinforced by the vertebral arteries and the lower territory reinforced by Adamkiewicz and receiving the fewest segmental reinforcements, that it is the region to suspect when an aortic cross-clamp case develops new paraplegia, and that a sensory level alone cannot identify the culprit vessel. The closing recap restates the same T4-to-T8 span. The written chapter is correct. Full correction register: https://www.reflexpmr.com/errata. The full companion chapter and a linked board-style Q-bank set for this topic are at https://www.reflexpmr.com/read/SCI-01.