Spinal nerve C7
Nervus spinalis C7
- Related terms: Seventh cervical nerve; C7
Definition
The seventh cervical spinal nerve C7 is a mixed nerve, containing both somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the C7 spinal cord segment.
a) Roots
Spinal nerve C7 is formed by the union of two roots:
1. Posterior (dorsal) root:
Carries sensory information from peripheral structures (via the anterior and posterior rami) to the dorsal gray horn of the spinal cord.
2. Anterior (ventral) root:
Contains motor fibers originating from the anterior gray horn within the spinal cord, transmitting motor commands to peripheral muscles through the spinal nerve and its branches.
b) Mixed spinal nerve and rami
At the intervertebral foramen between the C6 and C7 vertebrae, the anterior and posterior roots merge to form the mixed C7 spinal nerve. This nerve divides into two rami:
1. Anterior (ventral) ramus:
Provides motor and sensory innervation to the upper limb. It connects to the sympathetic trunk via the gray ramus communicans, carrying postganglionic sympathetic fibers.
2. Posterior (dorsal) ramus:
Provides motor innervation to the deep muscles of the upper back and sensory innervation to the overlying skin.
A. ANTERIOR RAMUS OF SPINAL NERVE C7:
The anterior ramus of the spinal nerve C7 exits the vertebral canal through the intervertebral foramen between the C6 and C7 vertebrae. This mixed nerve contains both motor and sensory fibers. In the neck, it continues as the middle trunk of the brachial plexus.
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
The C7 anterior ramus, which continues as the middle trunk of the brachial plexus, innervates various upper limb muscles: 1. Posterior scapular region: Teres major (C5, C6, C7) via the inferior subscapular nerve. 2. Posterior axilla: Latissimus dorsi (C6-C8) via the thoracodorsal nerve. 3. Medial axilla: Serratus anterior (C5-C7) via the long thoracic nerve. 4. Anterior axilla: Sternocostal head of the pectoralis major muscle (C6-T1) via the medial pectoral nerve. 5. Anterior arm: Coracobrachialis (C5-C7) via the musculocutaneous nerve. 6. Posterior arm: Long, medial, and lateral heads of the triceps brachii (C6-C8) via the radial nerve. 7. Forearm (flexor side): Flexor carpi ulnaris (C7, C8, T1) via the ulnar nerve, Pronator teres (C6, C7), flexor carpi radialis (C6, C7), palmaris longus (C7, C8) via the median nerve, Flexor pollicis longus (C7, C8), and pronator quadratus (C7, C8) via the anterior interosseus branch of the median nerve. 8. Forearm (extensor side): Anconeus (C6, C7, C8), extensor carpi radialis longus (C6, C7) via the radial nerve, Extensor carpi radialis brevis (C7, C8) via deep branch of radial nerve, Extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis muscles (all C7, C8) and supinator muscle (C6, C7); all via the posterior interosseus (deep) branch of radial nerve. Additional structures innervated by the spinal nerve C7 include the scalene muscles of the neck, i.e. anterior scalene (C4-C7), middle scalene (C3-C7), and posterior scalene muscles (C5-C7). | The C7 anterior ramus innervates the skin of the C7 dermatome, which includes the index, middle, and ring fingers of the hand. | ||
B. POSTERIOR RAMUS OF SPINAL NERVE C7:
The posterior ramus of the C7 is the posterior branch of the spinal nerve C7, which divides into medial and lateral branches:
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. Cutaneous innervation: Toward its termination, this branch transitions to cutaneous innervation, supplying sensory fibers to the skin over the posterior cervical region. | The medial branch of the posterior ramus of the C7 nerve primarily innervates: Deep paraspinal muscles, including the multifidus, semispinalis cervicis and interspinales muscles. Facet joints: Supplies sensory fibers to the facet joints of the cervical spine. |
C. ADDITIONAL STRUCTURES ASSOCIATED WITH SPINAL NERVE C7:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the C7 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 C7 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 C7 | |||
ANTERIOR RAMUS | POSTERIOR RAMUS | ||
MOTOR STRUCTURES | SENSORY STRUCTURES | MOTOR STRUCTURES | SENSORY STRUCTURES |
Pectoralis minor muscle (C8, T1) and the sternocostal head of the pectoralis major muscle (C6-T1). Teres major (C5, C6, C7), Serratus anterior muscle (C5-C7). Latissimus dorsi (C6-C8), Pectoralis minor muscle (C8, T1) and the sternocostal head of the pectoralis major muscle (C6-T1), Coracobrachialis muscle (C5-C7), Long, medial, and lateral heads of the triceps brachii (C6-C8), Flexor carpi ulnaris (C7, C8, T1), Pronator teres (C6, C7), flexor carpi radialis (C6, C7), palmaris longus (C7, C8), Flexor pollicis longus (C7, C8) and pronator quadratus (C7, C8), Anconeus (C6, C7, C8), extensor carpi radialis longus (C6, C7), Extensor carpi radialis brevis (C7, C8), Extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis muscles (all C7, C8), and supinator muscle (C6, C7). | C7 dermatome of skin encompassing the index, middle, and ring fingers of the hand. | Skin over the posterior cervical region. | |
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.
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
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 7: Upper Limb’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.678, 680, 686, 688, 690 & 693.
