Spinal nerve C6
Nervus spinalis C6
- Related terms: Sixth cervical nerve; C6
Definition
The sixth cervical spinal nerve C6 is a mixed nerve, containing both somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the C6 spinal cord segment.
a) Roots
Spinal nerve C6 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 of 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 C5 and C6 vertebrae, the anterior and posterior roots merge to form the mixed C6 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 C6:
The anterior ramus of the spinal nerve C6 exits the vertebral canal through the intervertebral foramen between the C5 and C6 vertebrae. This mixed nerve contains both motor and sensory fibers. In the neck, it joins the anterior ramus of spinal nerve C5 to form the superior trunk of the brachial plexus.
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
The C6 anterior ramus, which continues as the superior trunk of the brachial plexus, innervates various upper limb muscles: 1. Shoulder: Deltoid (C5, C6), via the axillary nerve. 2. Posterior scapular region: Supraspinatus (C5, C6) and Infraspinatus (C5, C6) via the suprascapular nerve. Teres minor (C5, C6) via the axillary nerve. 3. Posterior axilla: Subscapularis (C5-C7) via the upper and lower subscapular nerves. Teres major (C5-C7) via the lower subscapular nerve. Latissimus dorsi (C6-C8) via the thoracodorsal nerve. 4. Medial axilla: Serratus anterior (C5-C7) via the long thoracic nerve. 5. Anterior axilla: Clavicular (C5, C6) and sternocostal heads of the pectoralis major muscle (C6-T1) via the medial and lateral pectoral nerves. Subclavius (C5, C6) via the nerve to subclavius. 5. Anterior arm: Coracobrachialis muscle (C5-C7), biceps brachii (C5, C6), and brachialis (C5, C6) 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, 8. Forearm (extensor side): Anconeus (C6, C7, C8), brachioradialis (C5, C6), and extensor carpi radialis longus (C6, C7) via the radial nerve. Supinator muscle (C6, C7) via the posterior interosseus (deep) branch of radial nerve. Additional structures innervated by the spinal nerve C6 include the: Neck: anterior scalene (C4-C7), middle scalene (C3-C7), and posterior scalene muscles (C5-C7). Pre-vertebral muscles: longus colii (the inferior part). | The sensory fibers of the C6 anterior ramus innervate the skin of the C6 dermatome, which includes the thumb region. | ||
B. POSTERIOR RAMUS OF SPINAL NERVE C6:
The posterior ramus of the C6 gives off medial and lateral branches, each with distinct innervation pattern:
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 C6 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. However, it does not provide any cutaneous sensory innervation to the skin. |
C. ADDITIONAL STRUCTURES ASSOCIATED WITH SPINAL NERVE C6:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the C6 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 C6 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 C6 | |||
ANTERIOR RAMUS | POSTERIOR RAMUS | ||
MOTOR STRUCTURES | SENSORY STRUCTURES | MOTOR STRUCTURES | SENSORY STRUCTURES |
Deltoid (C5, C6), Supraspinatus (C5, C6), Infraspinatus (C5, C6), Teres minor (C5, C6), Teres major (C5, C6, C7), Subscapularis (C5-C7), Latissimus dorsi (C6-C8), Serratus anterior (C5-C7), Clavicular (C5, C6) and sternocostal heads of the pectoralis major muscle (C6-T1), Subclavius (C5, C6), Coracobrachialis muscle (C5-C7), biceps brachii (C5, C6), and brachialis (C5, C6), 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), Anconeus (C6, C7, C8), brachioradialis (C5, C6), and extensor carpi radialis longus (C6, C7), Supinator muscle (C6, C7). | C6 dermatome of skin encompassing the thumb region. | Skin over the posterior cervical region; lower neck. | |
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
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.970, 974.
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.
