Spinal nerve C4
Nervus spinalis C4
- Related terms: Fourth cervical nerve; C4
Definition
The fourth cervical spinal nerve C4 is a mixed nerve, containing both somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the spinal cord at the C4 spinal segment.
a) Roots
Like all spinal nerves, the C4 is formed by the union of two roots:
1. Posterior (dorsal) root:
This root consists of sensory fibers that transmit signals from peripheral structures back to the spinal cord. Upon entering the spinal cord, these fibers synapse in the dorsal gray horn.
2. Anterior (ventral) root:
This root is composed of 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 unite at the level of the intervertebral foramen to form the mixed spinal nerve C4. This nerve, containing both sensory and motor components, exits the vertebral column between the C3 and C4 vertebrae. Immediately after its emergence, C4 divides into two primary rami, each serving distinct roles:
1. Anterior (ventral) ramus:
The anterior ramus of C4 supplies motor and sensory innervation to the neck and shoulder regions. It also communicates with the sympathetic trunk via the gray ramus communicans, which conveys postganglionic sympathetic fibers.
2. Posterior (dorsal) ramus:
The posterior ramus provides motor innervation to the deep muscles of the upper back and sensory innervation to the skin overlying the same region.
A. ANTERIOR RAMUS OF SPINAL NERVE C4:
The anterior ramus of the spinal nerve C4 emerges through the intervertebral foramen between the C3 and C4 vertebrae. It carries motor (somatic efferent) and sensory (somatic afferent) fibers as a mixed nerve. In the cervical region, it contributes to the cervical plexus by communicating with the anterior rami of spinal nerves C1, C2, and C3..
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
The anterior ramus of spinal nerve C4, which forms part of the cervical plexus, supplies motor innervation to the following muscles: Trapezius: Supplies proprioceptive fibers that work in conjunction with the accessory nerve (C3, C4). Rhomboid minor and major: (C4, C5), via the dorsal scapular nerve. Levator scapulae: Supported through direct branches of C3 and C4, as well as from the dorsal scapular nerve (C4, C5). Scalene muscles: Innervates portions of the anterior scalene (C4-C7) and middle scalene (C3-C7). Pre-vertebral muscles: Specifically, portions of the longus colii, particularly its vertical and/or inferior parts. Diaphragm: Crucially contributes motor fibers to the phrenic nerve (C3, C4, C5), instrumental in voluntary and reflexive respiratory control. | The sensory fibers of the anterior ramus of spinal nerve C4 travel via the supraclavicular nerves, to innervate the skin in the region of the C4 dermatome, including the shoulder region and the upper anterior chest wall area. | ||
B. POSTERIOR RAMUS OF SPINAL NERVE C4:
The posterior ramus of the spinal nerve C4 divides into medial and lateral branches, each with distinct patterns of innervation:
Lateral branch: | Medial branch: | ||
The lateral branch of the posterior ramus courses laterally to supply: Muscles of the erector spinae group: including the iliocostalis cervicis and longissimus cervicis. and also including longissimus capitis. Cutaneous innervation: Toward its termination, this branch transitions to cutaneous innervation, supplying sensory fibers to the skin over the posterior cervical region, including the lower neck and upper shoulder. | The medial branch of the posterior ramus of the C4 nerve primarily innervates: Deep paraspinal muscles, including the multifidus and semispinalis cervicis muscles, and may also contribute to the innervation of the semispinalis capitis. Facet joints: Supplies sensory fibers to the facet joints of the cervical spine. However, it does not provide any cutaneous sensory innervation to the skin. |
C. ADDITIONAL STRUCTURES ASSOCIATED WITH SPINAL NERVE C4:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the C4 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 C4 connects to the sympathetic trunk through the gray ramus communicant. The gray ramus communicant enables the postganglionic sympathetic fibers to reach peripheral targets such as sweat glands and blood vessels.
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SUMMARY TABLE
STRUCTURES INNERVATED BY THE SPINAL NERVE C4 | |||
ANTERIOR RAMUS | POSTERIOR RAMUS | ||
MOTOR STRUCTURES | SENSORY STRUCTURES | MOTOR STRUCTURES | SENSORY STRUCTURES |
Trapezius (proprioceptive fibers from C3, C4), Rhomboid minor and major (C4, C5), Levator scapulae (C3, C4 direct branches, and C4, C5 via the dorsal scapular nerve). Scalene muscles of the neck, i.e. anterior scalene (C4-C7), and middle scalene (C3-C7) muscles. Pre-vertebral muscles, such as the longus colii (its vertical and/or inferior parts). | C4 dermatome of skin encompassing the shoulder region and the upper anterior chest wall area. | iliocostalis cervicis and longissimus cervicis. longissimus capitis. | Skin over the posterior cervical region; lower neck and upper shoulder. |
References
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.
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.955, 970, 974.
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.
Zhang J, Tsuzuki N, Hirabayashi S, Saiki K, Fujita K. Surgical anatomy of the nerves and muscles in the posterior cervical spine: a guide for avoiding inadvertent nerve injuries during the posterior approach. Spine (Phila Pa 1976). 2003 Jul 1;28(13):1379-84
