Spinal nerve L2
Nervus spinalis L2
- Related terms: Second lumbar nerve; L2
Definition
The second lumbar spinal nerve L2 is a mixed nerve, containing both somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the spinal cord at the L2 spinal segment.
a) Roots
Like other nerves, the spinal nerve L2 is formed by the union of two roots:
1. Posterior (dorsal) root:
This root contains sensory fibers that carry signals from peripheral structures (innervated by the anterior and posterior rami) to the spinal cord.
These fibers enter the dorsal gray horn within the spinal cord.
2. Anterior (ventral) root:
This root consists of motor fibers originating from the anterior gray horn within the spinal cord.
These fibers transmit motor commands to peripheral muscles via the spinal nerve and its branches.
b) Mixed spinal nerve and rami
At the level of the intervertebral foramen, the anterior and posterior roots merge to form the spinal nerve L2. This mixed nerve, containing both sensory and motor fibers, exits the intervertebral foramen between the L2 and L3 vertebrae. Shortly after its emergence, the nerve divides into two primary rami:
1. Anterior (ventral) ramus:
This ramus further subdivides into ventral and dorsal divisions that contribute to the lumbar plexus, providing motor and sensory innervation to structures, primarily the lower limbs.
It also forms connections with the sympathetic trunk via the white and gray rami communicantes, which carry preganglionic and postganglionic sympathetic fibers.
2. Posterior (dorsal) ramus:
This ramus provides motor innervation to the deep muscles of the back.
It also provides sensory innervation to the skin overlying the back.
A. ANTERIOR RAMUS OF SPINAL NERVE L2:
The anterior ramus is the larger division of spinal nerve L2. As a mixed nerve, it carries both somatic efferent (motor) and somatic afferent (sensory) fibers. After leaving the vertebral column, it contributes significantly to the lumbar plexus, a network of nerves located within the psoas major muscle. The anterior ramus of L2 collaborates with the anterior rami of L1, L3, L4, and occasionally T12 to form this plexus.
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
The anterior ramus of L2 contains motor (somatic efferent) fibers that travel through branches of the lumbar plexus to innervate numerous muscles: 1- Direct branches: Psoas major (L1-L3) and quadratus lumborum (T12-L4). 2- Genital branch of the genitofemoral nerve (L1, L2): Cremaster muscle (facilitating cremasteric reflex in males). 3- Femoral nerve (L2, L3, L4) – muscular branches: a) Iliacus (L2, L3) b) Anterior thigh muscles, including, pectineus (L2, L3–dual innervation via the femoral and obturator nerves), sartorius (L2, L3), and the quadriceps femoris group (minor contribution from L2; main innervation is from L3, L4). 4- Obturator nerve (L2, L3, L4) – anterior and posterior muscular branches: Adductors of thigh such as adductor brevis (L2, L3), adductor longus (L2-L4), adductor magnus (L2-L4; dual innervation with the tibial nerve), gracilis (L2, L3), and pectineus (L2, L3; dual innervation with femoral nerve). | The somatic sensory fibers from spinal nerve L2 provide sensory innervation through the following nerves: 1- Femoral branch of genitofemoral nerve (L1, L2): Sensory input from the anterior central upper thigh. 2- Genital branch of genitofemoral nerve (L1, L2): Sensory input from the skin in the anterior part of the external genitalia in the perineum, including anterior scrotum in males, anterior mons pubis and anterior labium majus in females.. 3- Lateral femoral cutaneous nerve (L2, L3): Sensory input from the skin of the anterolateral thigh. 4- Femoral nerve (L2, L3, L4): Sensory input from the anterior thigh, anteromedial knee, medial leg, and medial foot. 5- Obturator nerve (L2, L3, L4): Sensory input from the skin on the upper medial thigh. 6- Sensory contributions to the hip joint via the obturator and femoral nerves. | ||
B. POSTERIOR RAMUS OF SPINAL NERVE L2:
The posterior ramus of the spinal nerve L2–similar to posterior rami of other lumbar spinal nerves–primarily innervates the deep intrinsic muscles of the back and the overlying skin, and thus plays a critical role in the stabilization and movement of the spine. After L2 spinal nerve exits the intervertebral foramen (between L2 and L3 vertebrae), its posterior ramus traverses the intertransverse ligament and the overlying intertransverse muscle, and ends up branching into lateral and medial branches:
Lateral branch: | Medial branch: | ||
Muscular branches: The lateral branch provides motor innervation to the longissimus and iliocostalis components of the erector spine muscles. Cutaneous branches: The lateral branch becomes cutaneous after piercing the lateral border of the iliocostalis lumborum and the aponeurosis of the latissimus dorsi. It then provides sensory innervation to the gluteal skin above the iliac crest. The terminal cutaneous branches of the lateral branches of the posterior rami of L1, L2, and L3 nerves are also known as the cluenal nerves. | The medial branch crosses the junction of the superior articular process and transverse process of the L3 vertebra, curving medially to provide: Articular branches Supply the intervertebral facet (zygoapophyseal) joints. Muscular branches: The medial branch descends along the lamina, deep to the multifidus muscle, innervating it from its deeper aspect. Interspinoius branch: Arises from the medial branch on the lamina, weaving medially between multifidus fascicles to innervate the interspinous muscles and ligament. |
C. ADDITIONAL STRUCTURES ASSOCIATED WITH SPINAL NERVE l2:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the spinal nerve L2 or one of its rami. This small nerve re-enters the vertebral canal through the intervertebral foramen and provides sensory innervation to::
The meninges (protective coverings of the spinal cord),
The annulus fibrosus of the intervertebral discs,
The vertebral bodies and periosteum,
Adjacent blood vessels.
b) Sympathetic connections:
Through the white and gray rami communicantes, the spinal nerve L2 connects to the sympathetic trunk. The white rami communicantes enable preganglionic sympathetic fibers to reach the sympathetic trunk, while the gray rami communicantes enable the postganglionic sympathetic fibers to reach peripheral targets such as sweat glands and blood vessels.
References
Snell, R.S. (2010). ‘Chapter 14: The spinal cord and the ascending and descending tracts’, in Clinical Neuroanatomy. (7th ed.) Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, pp. 137.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 4: Abdomen’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.276 & pp. 350.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 1: The Body’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.41-52.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 2: The Back’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.96 & Fig. 2.44.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 6: Lower limb’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.537-540.
Bogduk, N., Wilson, A. & Tynan, W. (1982) 'The human lumbar dorsal rami', Journal of Anatomy, 134, p. 383.
Boelderl, A., Daniaux, H., Kathrein, A. & Maurer, H. (2002) 'Danger of damaging the medial branches of the posterior rami of spinal nerves during a dorsomedian approach to the spine', Clinical Anatomy, 15, pp. 77–81.
