Spinal nerve C2
Nervus spinalis C2
- Related terms: Second cervical nerve; C2
Definition
The second cervical spinal nerve C2 is a mixed nerve containing somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the C2 spinal cord segment.
a) Roots
The spinal nerve C2 is formed by the union of two roots:
1. Posterior (dorsal) root:
This root carries sensory information from the periphery (via the anterior and posterior rami) to the dorsal gray horn of the spinal cord.
2. Anterior (ventral) root:
This root contains motor fibers originating in the anterior gray horn of the spinal cord. These fibers transmit motor commands to peripheral muscles via the spinal nerve and its branches.
b) Mixed spinal nerve and rami
The anterior and posterior roots merge at the intervertebral foramen between the C1 and C2 vertebrae, forming the mixed C2 spinal nerve. This nerve then divides into two primary rami:
1. Anterior (ventral) ramus:
This ramus provides motor and sensory innervation to the neck. It connects to the sympathetic trunk via the gray ramus communicans, which carries postganglionic sympathetic fibers.
2. Posterior (dorsal) ramus:
This ramus innervates the deep muscles of the posterior neck (motor) and provides sensory innervation to the skin of the posterior neck and scalp.
A. ANTERIOR RAMUS OF SPINAL NERVE C2:
The anterior ramus of the spinal nerve C2 exits the vertebral canal via the intervertebral foramen between the C1 and C2 vertebrae. It joins with the anterior rami of C1, C3, and C4 spinal nerves to form the cervical plexus.
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
The C2 anterior ramus, through its contribution to the cervical plexus, innervates the following muscles: 1. Sternocleidomastoid: primarily CN XI, with C2 and C3 anterior rami contributions. 2. Prevertebral muscles: Upper portion of longus colii, longus capitis (C1-C3). 3. Lateral muscles: Rectus capitis anterior (C1, 2), rectus capitis lateralis (C1, C2). 3. Anterior neck muscles: Infrahyoid group, which includes the sternohyoid (C1-C3), sternothyroid (C1-C3), and omohyoid muscles (C1-C3). | The sensory fibers of the C2 anterior ramus contribute to the C2 dermatome, which covers the anterior and lateral upper neck, potentially extending posteriorly to the mastoid process and behind the ear. This sensory innervation is distributed via cutaneous branches of cervical plexus nerves, including the great auricular nerve (C2, C3), the transverse cervical nerve (C2, C3), and the lesser occipital nerve (C2). | ||
B. POSTERIOR RAMUS OF SPINAL NERVE C2:
The posterior ramus of the spinal nerve C2, the largest of all cervical posterior rami, emerges between the posterior arch of the atlas and the lamina of the axis, inferior to the obliquus inferior muscle. It supplies a branch to this muscle, receives a communicating filament from the C1 posterior ramus, and then divides into larger medial and smaller lateral branches.
Lateral branch: | Medial branch (greater occipital nerve): | ||
The lateral (external) branch supplies filaments to the splenius capitis and is often joined by the corresponding branch of C3 posterior ramus. | The larger medial (internal) branch, known as the greater occipital nerve, ascends obliquely between the obliquus inferior and semispinalis capitis muscles. It pierces the semispinalis capitis and trapezius muscles, continuing superiorly as the greater occipital nerve to innervate the scalp as far anteriorly as the vertex. Muscular branch: primarily given off to the semispinalis capitis muscle. |
C. ADDITIONAL STRUCTURES ASSOCIATED WITH SPINAL NERVE C2:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the C2 spinal nerve 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:
The spinal nerve C2 connects to the sympathetic trunk via the gray ramus communicans, allowing postganglionic sympathetic fibers to innervate structures like sweat glands and blood vessels, thus regulating their autonomic functions.
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SUMMARY TABLE
STRUCTURES INNERVATED BY THE SPINAL NERVE C2 | |||
ANTERIOR RAMUS | POSTERIOR RAMUS | ||
MOTOR STRUCTURES | SENSORY STRUCTURES | MOTOR STRUCTURES | SENSORY STRUCTURES |
Sternocleidomastoid (accessory nerve, C2, C3), longus colii (superior part). longus capitis (C1-C3), rectus capitis anterior (C1, 2), rectus capitis lateralis (C1, C2). Sternohyoid (C1-C3), sternothyroid (C1-C3), and omohyoid muscles (C1-C3). | C2 dermatome of skin encompassing the anterior and lateral aspects of the upper neck, and the posterior auricular region. | Semispinalis capitis, splenius capitis. Sometimes obliquus inferior muscle. | Posterior scalp to the vertex. |
References
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 8: Head and Neck’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.875.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 2: Back’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.95-100.
Seichi A, Kimura A, Higashi T, Endo T, Kojima M, Inoue H, Hoshino Y. Localization of the medial branches of the cervical dorsal rami during cervical laminoplasty. Spine (Phila Pa 1976). 2012 Dec 15;37(26):E1603-6.
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.
