Nerves of the Lumbar Spine

This article is still missing information.

The lumbar spinal nerves lie in the intervertebral foraminae, and are connected by spinal nerve roots to the spinal cord. The spinal nerves divide into the ventral and dorsal rami outside the vertebral column. The lumbar sympathetic trunks run along the anterolateral lumbar vertebral column, and they communicate with the ventral rami of the lumbar spinal nerves.

Lumbar Spinal Nerves

The lumbar spinal nerves are numbered according to the vertebra beneath which they lie; for instance, the L1 spinal nerve lies below the L1 vertebra in the L1/2 intervertebral foramen, and similarly for L2 and subsequent nerves. Each spinal nerve connects centrally to the spinal cord via a dorsal and a ventral root, with the joining of these roots to form the spinal nerve occurring within the intervertebral foramen.

Peripherally, the spinal nerve divides into a larger ventral ramus and a smaller dorsal ramus, a branching process that takes place outside the foramen. These spinal nerves are characterized by their short length, typically no longer than the width of their intervertebral foramen. Generally, they measure a few millimetres, although they can be less than 1mm in length if the roots branch directly into rami without the formation of a distinct spinal nerve.

Lumbar Nerve Roots

The spinal cord showing the meninges, its roots, spinal nerve, and branches (rami)University of Minnesota © 2006

The dorsal root is responsible for transmitting sensory fibres from the spinal nerve to the spinal cord, while the ventral root primarily transmits motor fibres from the spinal cord to the spinal nerve. However, the ventral root may also carry some sensory fibres (see Pain from Ventral Root Afferents), and notably, the L1 and L2 ventral roots additionally transmit preganglionic, sympathetic, efferent fibres.

The spinal cord itself typically terminates opposite the L1/2 intervertebral disc, although this can range from the T12/L1 to the L2/3 level. The lower lumbar and sacral nerve roots travel within the vertebral canal, largely enclosed in the dural sac. In contrast, within the cauda equina, the lumbar, sacral, and coccygeal nerve roots run freely. Each individual nerve root is covered by pia mater, which is continuous with the pia mater of the spinal cord. The roots forming the cauda equina are bathed in cerebrospinal fluid (CSF) that flows through the subarachnoid space. For most of their course, the nerve fibres within these nerve roots run together in a single trunk.

Near the spinal cord, these nerve roots separate into smaller bundles known as rootlets, which then attach to the spinal cord. Each root typically comprises between 2 to 12 rootlets, each 0.5-1mm in diameter. The rootlets of the ventral root attach to the ventrolateral aspect of the spinal cord, whereas the dorsal root rootlets attach to the dorsolateral sulcus. Along the ventral and dorsal surfaces of the cord, these rootlets form an uninterrupted series of attachments.

A dural sleeve is formed as a pair of spinal nerve roots leaves the dural sac, typically just above the level of their corresponding intervertebral foramen. These nerve roots penetrate the dural sac in an inferolateral direction, acquiring an extension of both dura mater and arachnoid mater, which constitutes the dural sleeve. This sleeve encloses the nerve roots and eventually merges with or becomes the epineurium of the spinal nerve. Within the dural sleeve, the nerve roots remain sheathed with pia mater, and CSF flows around them as far as the spinal nerve itself.

The dorsal root ganglion (DRG) is an enlargement of the dorsal root, formed immediately proximal to the junction of the dorsal root with the spinal nerve. It houses the cell bodies of the sensory fibres contained within the dorsal root. The DRG is situated within the dural sleeve of the nerve roots and typically occupies the upper, medial part of the intervertebral foramen, although it may lie further distally in the foramen in cases of short spinal nerves. Its location can be categorized into intraspinal, neuroforaminal, and extraforaminal regions. Notably, from L1 to L5, there is an increasing likelihood that the DRG will be found in the neuroforaminal region.

The angles at which each pair of nerve roots leaves the dural sac vary, becoming increasingly acute at more caudal levels. For example, the L1 nerve root exits at approximately 80°, L2 at about 70°, L3 and L4 at around 60°, and the L5 nerve root at about 45°. Regarding their vertebral body origins, the nerve root sleeves generally arise opposite the posterior aspect of their respective vertebral bodies, meaning the L1 sleeve arises behind the L1 body, and so on. However, for successively caudal sleeves, their point of origin shifts increasingly higher relative to their vertebral bodies. Consequently, the L5 nerve root sleeve arises behind the L4/5 intervertebral disc.

Relations of the Nerve Roots

Coronal cut away view of the lumbar transforaminal zone.

The nerve roots have an intimate relationship with the meninges. Specifically, the roots of the cauda equina are enclosed within the dural sac, and individual pairs of roots are further covered by pia mater, arachnoid mater, and dura mater within their respective nerve root sleeves. It is important to note that tumours or cysts originating from the dura or arachnoid can potentially compress these nerve roots. Radicular arteries and veins also course within these root sleeves. The dural sac itself has several key relations: anteriorly, it is related to the floor of the vertebral canal, which includes the vertebral bodies, intervertebral discs, the posterior longitudinal ligament (PLL), anterior spinal canal arteries, and sinuvertebral nerves; posteriorly, its relations include the roof of the vertebral canal, formed by the laminae and ligamenta flava.

The epidural space is situated between the dural sac and the osseoligamentous boundaries of the vertebral canal. It is a narrow, almost potential space, filled by a thin layer of areolar connective tissue, sometimes referred to as the epidural membrane, which surrounds the dural sac. Dorsally, this membrane lines the deep surface of the laminae and pedicles. Ventrally, it lines the vertebral bodies, passes medially deep to the posterior longitudinal ligament, and attaches to the anterior surface of the deep portion of this ligament; it does not cover the anulus fibrosus (AF) but instead blends with the upper and lower borders of the AF just anterior to the posterior longitudinal ligament. Laterally, opposite the intervertebral foramen, the epidural membrane extends laterally to form a circum-neural sheath around the dural sleeve of the nerve roots and the spinal nerve. The anterior and posterior internal vertebral venous plexuses are located within the areolar tissue of this epidural membrane. Additionally, epidural fat is characteristically concentrated around the nerve roots within the intervertebral foramina.

Individual pairs of nerve roots, enclosed in their dural sleeves, course towards the intervertebral foramina along structures known as radicular canals. Within these canals, the nerve roots are related laterally to a pedicle. They pass the posterior aspect of their respective vertebral body, run downwards, and then enter the upper portion of their intervertebral foramen. Dorsal to the radicular canal are a lamina and the ligamenta flava, which serve to separate the root sleeve from the overlying facet joints.

Dural ligaments, also known as meningovertebral ligaments or ligaments of Hofmann, are condensations of the epidural fascia that tether the nerve root sleeves to the vertebral column. The term "dural ligament" is not strictly anatomically correct, as these structures represent connections between the meninges and the vertebral column. Their development is variable at the L1-L4 levels but they are typically well developed at L5. Ventrally, these ligaments pass from the ventral surface of the dura to the posterior longitudinal ligament. Laterally, they extend from the lateral surface of the dural sac to the periosteum of the pedicles and the capsule of the facet joint. Posteriorly, the dural sac is attached to the roof of the vertebral canal by occasional weak, pseudo-ligamentous connections.

Nerve root sleeves are tethered both within the vertebral canal and in the intervertebral foramen. Within the vertebral canal, this tethering is achieved by the meningovertebral ligaments, which connect the dura to the posterior longitudinal ligament and the periosteum of the adjacent pedicle. In the intervertebral foramen, the root sleeve is enveloped by the circum-neural sheath. This sheath indirectly binds the nerve roots and the spinal nerve primarily to the facet joint capsule dorsally, as well as to the margins of the foramen. At the outer end of the foramen, a transforaminal ligament may be present; the spinal nerve typically lies below most varieties of these ligaments but above the inferior type.

Regarding the size of the spinal nerves and their roots relative to the foramina, the intervertebral foramen generally increases in size from L1/2 down to L4/5. However, the L5/S1 foramen is notably smaller than the others, despite the L5 spinal nerve being the largest. The L5 spinal nerve occupies approximately 25-30% of its foramen, whereas the other lumbar nerves occupy between 7-22% of theirs. Consequently, the L5 nerve is the most susceptible to foraminal stenosis.

Anomalies of the Nerve Roots

The clinically most significant anomalies of the lumbar nerve roots are aberrant courses and anastomoses between nerve roots. See Trimba et al for a comprehensive review of the topic.

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  Classification of conjoined nerve roots.

Type	General Anomaly	Subtype A	Subtype B
Type 1	Roots arise from a common dural sheath	Roots exit through a common foramen	Roots exit through separate foramina
Type 2	Roots arise from separate dural sheaths	Roots exit through a common foramen	Roots exit through separate foramina (this is normal anatomy, but described in some classifications of anomalies when discussing adjacent root origins)
Type 3	Anastomosis between roots	Intrathecal	Extrathecal

Classification of conjoined nerve roots.Morishita et al.. Intra-operative identification of conjoined lumbosacral nerve roots: a report of three cases. Journal of orthopaedic surgery (Hong Kong) 2012. 20:90-3. PMID: 22535819. DOI.

The incidence of such anomalies is approximately 8.5%. These anomalies do not invariably produce symptoms. However, doubled nerve roots, for example, occupy more of the available space in the radicular canal or intervertebral foramen than a single root. Therefore, any space-occupying lesion is more likely to compress a double nerve root, leading to symptoms occurring sooner than they would for a single nerve root compression. While disorders of the lumbar spine are not inherently more common in individuals with these anomalies, symptom development is more frequent when a space-occupying lesion is also present.

Clinically, an examination might reveal signs of nerve root compression, but if that root has an anomalous course, the causative lesion will not be at the typically expected location. Furthermore, in the case of a double nerve root, a single compressive lesion could produce clinical signs suggestive of two distinct lesions. Any unusual clinical signs should prompt consideration of a possible nerve root anomaly.

Intrathecal anastomoses are more common, with an incidence of 11-30%; however, these occur proximal to the standard locations of compression and are therefore not usually of diagnostic significance for common compressive syndromes, though they may be important in the context of proximal nerve root surgery.

Dorsal Rami

Axial view of L4 vertebra showing spinal nerve, ventral ramus passing anteriorly and dorsal ramus passing posteriorly

The dorsal rami of L1-L4 are short, approximately 5mm in length, and arise at almost right angles from their respective lumbar spinal nerves. They are directed backwards, coursing towards the upper border of the subjacent transverse process. As they approach these transverse processes, each divides into two or three branches: a medial branch and a lateral branch are consistently present, while an intermediate branch may arise either from the dorsal ramus itself or as a branch off the lateral branch. In contrast, the L5 dorsal ramus is longer and travels over the top of the ala of the sacrum. It typically forms only a medial branch and a branch that is equivalent to the intermediate branches of the other lumbar dorsal rami.

The lateral branches of the dorsal rami are principally distributed to the iliocostalis lumborum muscle. Notably, the lateral branches of L1-L3 can emerge from the dorsolateral border of the iliocostalis lumborum and become cutaneous. These cutaneous branches pierce the thoracolumbar fascia and descend inferolaterally across the iliac crest to innervate the skin of the buttock, covering an area that extends from the iliac crest to the greater trochanter. As these nerves cross the iliac crest, they run parallel to one another, with those from lower segmental levels positioned most medially (see article on cluneal nerve pain). The lowest and most medial of these nerves typically crosses the iliac crest approximately 7-8cm from the midline. There is variability in which of these lateral branches become cutaneous. In embryos and fetuses, the L1 lateral branch is always cutaneous, L2 in 90% of cases, L3 in 70%, and L4 in 40%. In adults, the pattern is similar, though L4 cutaneous branches are uncommon. Specifically, L1 provides exclusive cutaneous innervation in 60% of adults, L1 and L2 contribute in 27%, and L1-L3 together in 13%.

The intermediate branches have an exclusively muscular distribution, supplying the lumbar fibres of the longissimus muscle, within which they form an intersegmental plexus. The L5 intermediate branch specifically supplies the lowest fibres of the longissimus muscle, which arise from the L5 transverse process and attach to the medial aspect of the iliac crest.

The medial branches of the dorsal rami are distributed to the facet joints, the interspinous ligaments and muscles, and the multifidus muscle. The L1-L4 medial branches travel across the superior aspect of their respective transverse processes and then pierce the dorsal leaf of the intertransverse ligament at the base of the transverse process. The nerve subsequently runs along the bone at the junction of the root of the transverse process with the root of the superior articular process. Each such nerve hooks medially around the base of the superior articular process, where it is covered by the mamillo-accessory ligament. After this point, it crosses the vertebral lamina and divides into multiple branches that supply the multifidus muscle, the interspinous muscle and ligament, and two facet (zygapophysial) joints – specifically, the joint above and the joint below its course. An ascending articular branch arises from the nerve just beyond the mamillo-accessory ligament, at the point where the nerve begins to cross the lamina. A descending articular branch arises slightly more distally and travels downwards to the subjacent joint. The L5 medial branch of the dorsal ramus follows a course similar to those of L1-L4, with the key difference being that it crosses the ala of the sacrum instead of a transverse process. It runs in the groove formed by the junction of the ala and the root of the superior articular process of the sacrum. It then hooks medially around the base of the lumbosacral facet joint. An articular branch supplies this lumbosacral facet joint, and the nerve also ramifies in the multifidus muscle.

Regarding the muscular and interspinous ligament innervation by the medial branches of the dorsal rami, the muscles that move a particular segment are innervated by the nerve of that segment; for example, the L1 medial branch supplies only those muscle fibres related to the L1 vertebra. Furthermore, muscles arising from the spinous process and lamina of a lumbar vertebra are innervated by the medial branch of the dorsal ramus located immediately below that vertebra.

Histology

Histologically, lumbar facet joint capsules are richly innervated, featuring encapsulated, unencapsulated, and free nerve endings. These capsules are capable of transmitting both proprioceptive and nociceptive information. Nerves containing neuropeptide Y are more commonly found than those containing substance P or calcitonin gene-related peptide (CGRP). Nerve fibres and nerve endings are also present in the subchondral bone of the facet joints, making the subchondral bone another potential location for nociception. Intra-articular inclusions within the facet joints contain nerve fibres with substance P, though it is unclear whether these are primarily nociceptive or vasoregulatory. The interspinous ligaments also possess plentiful nerve fibres. These nerves give rise to Ruffini endings, pacini-form endings, and free nerve endings. Ruffini endings, which function as mechanoreceptors, are more numerous on the lateral surfaces of these ligaments. Pacini-form endings are associated with blood vessels and are uniformly distributed, though their function remains unclear. Free nerve endings are typically found near the attachment points of the ligament to the spinous processes. Similarly, the supraspinous ligaments and thoraco-lumbar fascia are well innervated, containing nerve fibres, Ruffini endings, and pacini-form endings. In contrast, the ligamentum flavum is only sparsely innervated.

Variations

Variations in the innervation pattern of the dorsal rami include instances where an articular branch occasionally arises directly from the dorsal ramus proper, proceeding to innervate the ventral aspect of the adjacent facet joint. One author reported observing multiple articular branches originating from the spinal nerve itself, the lateral branch of the dorsal ramus, and along the entire length of the medial branch. However, these findings have not been replicated in other studies, leading Bogduk to suspect that collagen fibres may have been misidentified as nerves, particularly as the observations were not confirmed histologically.

Ventral Rami

The ventral rami of the lumbar spinal nerves pierce the ventral leaf of the intertransverse ligament as they pass through the intervertebral foramen. Once through, they come to lie within the substance of the psoas major muscle, anterior to the ligaments. Within this muscle, they form plexuses. Specifically, the ventral rami of L1-L4 unite to form the lumbar plexus, while the L4 and L5 ventral rami join to create the lumbosacral trunk. The L5 ventral ramus has a distinct course, crossing the ala of the sacrum, inferior to the L5 transverse process. In this location, it is susceptible to entrapment between these two bony structures, a condition sometimes referred to as "far out syndrome."

Dermatomes

Main article: Dermatomes

The use of fluoroscopically guided local anaesthetic blocks has facilitated a re-appraisal of classical data regarding the cutaneous distribution of the lumbar spinal nerves. While the total extent of the L4, L5, and S1 dermatomes can vary between individuals, they generally exhibit a consistent concentric pattern. Each of these dermatomes has the potential to extend from the posterior midline of the back, across the buttock, and down into the lower limb. However, only a minority of individuals demonstrates such an extensive distribution for the L4 and L5 dermatomes.

Typical areas of sensory deficit associated with these nerves are as follows: for L4, most people experience a deficit centered on the medial aspect of the lower leg; for L5, the deficit commonly involves the medial aspect of the foot, extending across the dorsum of the foot, and includes the lateral aspect of the lower leg; and for S1, the distribution is often more extensive, forming a band from the posterior sacrum, along the entire posterior length of the lower limb, to the lateral aspect of the foot. The distal nature of each of these distributions generally indicates the area of skin supplied by branches of the ventral ramus of the particular spinal nerve.

Distribution of sensory changes in the buttock, however, typically indicates supply from the dorsal ramus. Data from nerve blocks suggest that the L4 dorsal ramus provides a cutaneous distribution in 42% of individuals, the L5 dorsal ramus in 44%, and the S1 dorsal ramus in 92%. This nerve block data is somewhat inconsistent with classical anatomical data, which generally acknowledges a cutaneous distribution for S1 but not typically for L4 or L5. The L5 contribution might be explained by communication with the dorsal sacral plexus, but the pathway by which the L4 dorsal ramus reaches the skin remains a mystery.

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  L4 block pattern: Extending from the midline of the trunk posteriorly, across the buttock, through the lateral and anterior side of the thigh and the medial side of the leg to the first digit of the foot.
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  L5 block pattern: Extending from the midline of the trunk posteriorly, across the buttock, through the posterior, lateral aspect of the thigh and leg, to the 5th digit of the foot.
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  S1 block pattern: Extending from the midline of the trunk posteriorly, across the buttock, through the lateral side of the thigh, the lateral side of the leg, and the medial side of the dorsum of the foot to the first digit.
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  Distinctive regions. L4 is medial side of the lower leg in 88%. L5 is first dorsal digit in 82%. S1 is lateral side of 5th digit in 83%.
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  Proportion having band like deficits. L4 dorsal ramus: 42% have a cutaneous distribution, L5 dorsal ramus: 44%, and S1 dorsal ramus: 92%.

Sympathetic Nerves

The rami communicantes is seen connecting from the sympathetic trunk to the ventral ramus

The lumbar sympathetic trunks travel inferiorly along the anterolateral borders of the lumbar spine. Each trunk is typically situated at the medial edge of the attachment of the psoas muscle. The number of ganglia associated with these trunks can vary from one to six, though four is the most common count.

Branches from the lumbar sympathetic trunks are distributed to the abdominal and pelvic blood vessels and viscera, with some direct branches also innervating the psoas muscle. The principal branches are the rami communicantes, which connect to the lumbar ventral rami. These include white rami communicantes, distributed to the L1 and L2 ventral rami, and grey rami communicantes, which are distributed to every lumbar ventral ramus.

The number of rami communicantes connecting to each lumbar nerve varies, typically from one to three, and rarely as many as five. These rami communicantes course through tunnels deep to the psoas muscle, run along the concave lateral aspects of the lumbar vertebral bodies, descend to the lower borders of the transverse processes, and ultimately join the ventral rami just outside the intervertebral foramina. Alternatively, they may reach the ventral rami by passing directly through the substance of the psoas muscle. Efferent fibres conveyed by these rami travel to the blood vessels and skin within the territories supplied by the lumbar spinal nerves. Furthermore, these sympathetic contributions are involved in the formation of the lumbar sinuvertebral nerves and play a role in the innervation of the lumbar intervertebral discs.

Sinuvertebral Nerves

Sinuvertebral nerves are formed from two roots: the ventral ramus and the gray ramus communicans. They provide the afferent pathways in lumbar discogenic pain. Sinuvertebral nerves are recurrent branches originating from the ventral rami, which re-enter the intervertebral foramina to be distributed within the vertebral canal. Each sinuvertebral nerve typically supplies the intervertebral disc at its level of entry into the vertebral canal, the disc immediately above, and the intervening segment of the posterior longitudinal ligament. These are mixed nerves, possessing both a somatic root derived from a ventral ramus and an autonomic root from a grey ramus communicans. Morphologically, they may present as a series of filaments or as a single trunk accompanied by additional fine filaments.

The sinuvertebral nerves run along the posterior surface of the vertebral body, just inferior to the upper pedicle. Within the vertebral canal, an ascending branch forms, passing rostrally parallel to the posterior longitudinal ligament (to which it sends branches), and ultimately terminating in and supplying the superjacent intervertebral disc. A shorter descending branch ramifies in the disc and ligament at the level of entry of the parent nerve. Each sinuvertebral nerve is also distributed to the blood vessels of the vertebral canal and to the ventral aspect of the dura mater. Within the dura mater, each nerve forms ascending and descending meningeal branches. The descending branches are generally longer, extending up to two segments caudally, while the ascending branch courses superiorly for up to one segment. The ventral surface of the dura mater is covered with a dense plexus of these nerves, which extends laterally but attenuates dorsally; the paramedian portion of the dura typically has no nerve fibres.

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  The sinuvertebral nerves
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  Lumbar disc innervation. ©2014 Chirogeek

Innervation of the Lumbar Intervertebral Discs

The innervation of lumbar intervertebral discs has historically been a controversial issue. Early studies often failed to demonstrate nerve fibres or nerve endings within the discs. However, subsequent research identified nerve fibres in the superficial layers of the anulus fibrosus (AF), as well as a variety of free and complex nerve endings, particularly in the outer third of the AF. The distribution of these receptors within the disc is not uniform; they are most abundant laterally, where nearly all encapsulated receptors are found. A smaller number of receptors are located posteriorly, and the least number are found anteriorly.

Histology

Developmentally, nerves are abundant in the fetal AF. Postnatally, unencapsulated receptors begin to arise, and by adulthood, five distinct types of nerve endings can be identified. There is also a relative decrease in the number of receptors located in the anterior region of the disc with maturation. The nerve endings found in the outer lamellae of the AF resemble Golgi tendon organs, Ruffini endings, and paciniform endings. These endings contain neuropeptides such as calcitonin gene-related peptide (CGRP), substance P, and vasoactive intestinal polypeptide (VIP); substance P, in this context, may also have a vasoactive role. Furthermore, the anterior and posterior longitudinal ligaments are also known to contain frequent nerve endings.

Sources

Extensive microscopic plexuses of nerves accompany the anterior and posterior longitudinal ligaments. These plexuses provide innervation around the entire circumference of the vertebral bodies and intervertebral discs. Specifically, the anterior and posterior plexuses supply the periosteum of the vertebral bodies via superficial branches, and the intervertebral disc and vertebral bodies themselves via long penetrating branches, which follow blood vessels as far as the centre of the vertebral body. Direct branches from the ventral rami enter the posterolateral corner of the discs, constituting one of several sources that contribute to the plexus overlying the discs and vertebral bodies. Other contributing sources include the grey rami communicantes, which send branches to the discs across their lateral surface and at their posterolateral corner. Somatic afferent fibres appear to utilize the course of the rami communicantes to return to the ventral rami, rather than returning via the sympathetic trunk.

Plexus	Formation	Relation
Anterior Plexus	Formed by branches from the sympathetic trunks and their ganglia	Lies anterior to the lumbar vertebral bodies and discs
Posterior Plexus	Formed by the sinuvertebral nerves and branches from the sympathetic trunks	Lies posterior to the lumbar vertebral bodies and discs, within the vertebral canal
Lateral plexus	Formed by direct branches from the ventral rami and grey rami communicantes	Located on the lateral aspects of the intervertebral discs

Additionally, there is nerve supply to the endplate, indicating that both the AF and the nucleus pulposus (NP) can be innervated, particularly at their junction with the vertebral body. These nerves typically accompany the basivertebral veins and arteries, branching through the spongiosa of the vertebral body to reach the endplate. Endplate innervation has been observed to be greater in discs that are identified as painful. The nerve endings in this region contain substance P and CGRP and are often not directly related to blood vessels, suggesting they are primarily sensory rather than vasomotor nerves.

The role of intervertebral disc innervation is thought to be primarily nociceptive, as there are few blood vessels within the disc itself, making a significant vasomotor role unlikely. While there is currently no direct evidence for a proprioceptive function, this possibility cannot be entirely excluded.

Nerve Ingrowth

Under normal conditions, nerve fibres are typically found only in the outer third of the AF. However, in discs that are a source of pain, nerve fibres have been observed to extend into the deeper layers of the AF, and in some cases, even into the nucleus pulposus (NP). This ingrowth of nerves in painful discs often accompanies blood vessels that proliferate along annular fissures.

Summary

• Posteriorly, branches of the lumbar dorsal rami supply the intrinsic back muscles and the facet joints.
• Anteriorly, the ventral rami innervate muscles such as the psoas major and quadratus lumborum, and also contribute to the lumbar plexus.
• The vertebral bodies and intervertebral discs are surrounded by extensive nerve plexuses that accompany the longitudinal ligaments; these plexuses are largely derived from the lumbar sympathetic trunks.
• Within the posterior plexus, larger nerve filaments constitute the sinuvertebral nerves, which re-enter the vertebral canal.
• From these plexuses, short branches innervate the vertebral periosteum, while long penetrating branches provide innervation deep into the vertebral body around its entire circumference.
• The outer third of the AF receives innervation circumferentially from these longitudinal plexuses.
• The posterior plexus also supplies the dura mater and the nerve root sleeves, particularly on their anterior and lateral aspects.

Resources

See [[1](https://tomjesson.substack.com/p/a-visual-tour-of-the-lumbar-nerve) this brilliant visual tour] of the lumbar nerve roots by a US physiotherapist.

Innervation of the Lumbar Spine - Bogduk 1983.pdf - 632 KB (f)

Lumbar dorsal Rami - Bogduk 1982.pdf - 1.78 MB (f)

References

These are study notes taken from Chapter 10 of:

• Bogduk, Nikolai. Clinical and radiological anatomy of the lumbar spine. Edinburgh: Elsevier/Churchill Livingstone, 2012.