Spinal Nerve Anatomy

Most blogs that this author writes are oriented to the client. This blog ,however, is also for Chiropractors. At times, like this, there is a need to express with sheer amazement how wonderful it is to know and work with people’s spines.

Chiropractors love people and we love helping people. We also love spines and below you will be able to read about the spine and a good structural reason why we think and care so much to help people live with healthy spines.

The largest and most important structure to pass out of every intervertebral foramen is a nerve trunk which forms a spinal nerve. There are 31 pairs of spinal nerves. One for the right hand side of the body and one for the left hand side. The nerves are named from the vertebra they correspond to. For the most part, the spinal nerves exit the vertebral canal through the intervertebral foramen below their corresponding vertebra. 

The cervical spinal nerves differ from this pattern. C1-C7 spinal nerves emerge from the vertebral canal above the corresponding vertebra, with an eighth pair of cervical spinal nerves emerging below the C7 vertebra, meaning there are a total of 8 pairs of cervical spinal nerves despite that there are only 7 cervical vertebrae. There are 12 pairs of thoracic spinal nerves, 5 pairs of lumbar spinal nerves, 5 pairs of sacral spinal nerves, and a coccygeal nerve.

A nerve trunk is in fact a commingling of the anterior and posterior nerve roots before they divide into their respective branches. These branches of nerve comprise of afferent, efferent and autonomic fibres. According to Homeward, the sensory (afferent) fibres outnumber the motor (efferent) fibres 3-to-1.

A nerve trunk typically occupies the upper section of each vertebra. However, at some levels of the spine the nerve is small and its diameter will only take up a 1/12th of the space available. Larger diameter fibres can occupy up to 1/3rd of the upper intervertebral space. 

Most anterior nerves are involved with innervation of the limbs forming the cervical, brachial and lumbosacral nerve plexuses. Anterior nerves in the thoracic spine become intercostal and sub-costal nerves. Thus, anterior nerve fibres supply nerves to the anterior lateral body wall and trunk. 

The anterior nerve root contains efferent nerve fibres, which carry stimuli away from the central nerve system (CNS) towards their target structures. The cell bodies of the anterior root neurones are located in the central grey matter of the spinal cord. Motor neurones controlling skeletal muscle, as well as preganglionic autonomic neurones are located in the anterior nerve roots.

The posterior root contains afferent nerve fibres, which return sensory information from the trunk and limbs to the CNS. The cell bodies of the posterior root neurones are not located in the central grey matter in the spinal cord, but instead in a structure called the spinal root ganglion.

In some instances, found in within an intervertebral foreman can be the posterior nerve root ganglion. The posterior nerve root ganglion for the lower lumbar, sacral and coccygeal nerves and found within the spinal canal. Which makes good sense since the spinal cord ends at upper lumbar spine (L2 vertebral body).

The meningeal branch of spinal nerves, also known as recurrent meningeal nerves, or recurrent nerves of Luschka, are vital nerves. These nerves originate from an aspect of the nerve root within the intervertebral foremen. The meningeal nerves innervate: facet joints, the annulus fibrosis of the intervertebral disc, the posterior longitudinal ligament, the meninges and blood vessels. 

D.D. Palmer wrote this about the Meningeal nerve: 

“At its exit, the spinal nerve divides into two branches, and anterior and posterior somatic branches. Just before it divides, it gives off a small branch which returns inward. The anterior of the two divisions is joined by a branch from the sympathetic cord called ramus communicans. This latter gives to the recurrent branch a filament from the sympathetic. These two form one nerve which, returns through the intervertebral foreman, supplies innervation to the fibrous membrane which forms the outermost covering of the brain and spinal cord. It also, sends branches to the vertebrae and vertebral ligaments.”

D.D also says: “if the innervation of the recurrent nerve is interfered with by pressure, it becomes irritated, molecular action is increased, there is greater vibration, and the heat becomes intense.”

Now, Homeward also goes on to describe a few more interesting anatomical observations about the spine, spinal nerves and the meningeal nerve. 

As already stated, the spinal cord of an adult terminates at the 2nd lumbar spinal level. Interestingly, a spinal artery, with veins lying either side of the artery, accompany every spinal nerve through the intervertebral foramen. The artery and pair of veins are wrapped in one sheath, thus the pulsations of the artery promotes venous return (venal comitantes). There are 31 pairs of recurrent spinal nerves to supply the 31 spinal segments of the spinal cord and 31 pairs of spinal arteries. 

The anastomoses with the anterior and two posterior spinal arteries which run the full length of the spinal cord receive post-ganglionic sympathetic nerve fibres via each meningeal nerve.

This ends a short recap of spinal anatomy by a Chiropractor. Your spine is a wonderful area of the body and is a vital area for all people. Perhaps you can think through this exampe and better understand the role of Chiropractic.

When a tributary of a river becomes blocked, there is likely to be effects down steam. Water flow decreases and the river itself and the surrounding environment is deprived of vital nourishment. Likewise, the spinal column and nerves need no interference for optimal flow and this is the what Chiropractic seeks to understand and adjust. Take care of your whole-self and know that your spine needs care and attention each and every day. 


Homeward. A. E., 1977, The Neurodynamics of the vertebral subluxation, Valkyrie Press, inc.

Various anatomy books and websites.