USMLE Forums - View Single Post - Spinal Nerve Root number and inter vertebral disc herniation
View Single Post
Old 09-15-2009
Sabio Sabio is offline
USMLE Forums Master
Steps History: 1+CK+CS+3
Posts: 3,316
Threads: 170
Thanked 5,036 Times in 1,820 Posts
Reputation: 5089
Anatomy Spinal Nerve Root number and inter vertebral disc herniation

The herniation of the nucleus pulposus is most commonly in the posterolateral direction as it is the weakest part of the surrounding annulus fibrosus.

So each inter vertebral disk (nucleus pulposus) will press on the corresponding spinal nerve causing specific anatomic (dermatomic distribution of the affected areas)

The question is what disc number corresponds to what spinal nerve number?

All the spinal nerves are named by the vertebra above it, so for example inter vertebral disc T11-T12 will press on the T11 nerve as it exits in the inter vertebral foramen right below T11 vertebra

There's an exception to this rule..

Because we have more cervical spinal roots (eight) than we have vertebra (seven), then the first seven spinal roots exit above the corresponding numbered vertebra.

So a C4-C5 disk herniation will press on C5 nerve.

Click on this thumbnail to view

Spinal Nerve Root number and inter vertebral disc herniation-cervical-root.jpg

Copyright notice: this image was modified from this image posted in Wikimedia Commons

It's also important not confuse the roots (ventral and dorsal contained within the meninges, see image) with the rami (ventral and dorsal, the dorsal ramus is usually not drawn in such an image because it sprouts immediately and loops back to the posterior body supplying the muscles of the back and zygahypophyseal joints)

Last edited by Sabio; 09-15-2009 at 09:57 PM. Reason: Adding copyright notice
Reply With Quote
The above post was thanked by:
anoop_1198 (06-23-2010), belai (10-16-2017), CHAKRAM (11-16-2011), DKAG (12-06-2015), Drbench (05-08-2012), drgabroomunda (09-30-2011), drortho (11-29-2011), gokulramani (01-06-2016), HBen2011 (11-16-2011), im99 (03-30-2011), Laurentiu (01-29-2010), navjotr (02-25-2014), pradeeprox (07-17-2012), rigbbm (04-05-2019), saadalobaysi (12-23-2015), Taiwan_Guy (08-17-2011), usluipek (08-13-2011), wahaha007 (01-10-2010), yarasara77 (08-22-2015), Zehra. (11-24-2011), zohra (11-16-2011)