Spinal nerve C8
Nervus spinalis C8
- Related terms: Eighth cervical nerve; C8
Definition
The eighth cervical spinal nerve C8 is a mixed nerve, carrying both somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the spinal cord at the C8 spinal segment.
a) Roots
The spinal nerve C8 is formed by the union of two roots:
1. Posterior (dorsal) root:
Contains sensory fibers that transmit signals from peripheral structures (innervated by the anterior and posterior rami) to the spinal cord. These fibers enter the dorsal gray horn of the spinal cord.
2. Anterior (ventral) root:
Composed of motor fibers originating from the anterior gray horn of the spinal cord. These fibers send motor commands to peripheral muscles via the spinal nerve and its branches.
b) Mixed spinal nerve and rami
At the intervertebral foramen, the anterior and posterior roots join to form the mixed spinal nerve C8, which contains both sensory and motor fibers. This nerve exits the intervertebral foramen between the C7 and T1 vertebrae and quickly divides into two rami:
1. Anterior (ventral) ramus:
Provides motor and sensory innervation to the upper limb. It connects with the sympathetic trunk via the gray ramus communicans, which carries the postganglionic sympathetic fibers.
2. Posterior (dorsal) ramus:
Provides motor innervation to the deep intrinsic muscles of the upper back.
Supplies sensory innervation to the overlying skin of the upper back.
A. ANTERIOR RAMUS OF SPINAL NERVE C8:
The anterior ramus of the spinal nerve C8 exits the vertebral canal through the intervertebral foramen situated between the C8 and T1 vertebrae. As a mixed nerve, it contains motor (somatic efferent) and sensory (somatic afferent) fibers. Upon exiting, it joins the anterior ramus of the T1 spinal nerve to form the inferior trunk of the brachial plexus.
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
The anterior ramus of spinal nerve C8, a critical contributor to the inferior trunk of the brachial plexus, provides motor innervation to several upper limb muscles, including: 1. Muscles of the posterior wall of the axilla: Latissimus dorsi (C6-C8), via the thoracodorsal nerve. 2. Muscles of the anterior wall of the axilla: Pectoralis minor muscle (C8, T1) and the sternocostal head of the pectoralis major muscle (C6-T1), innervated via the medial pectoral branch of the ulnar nerve. 3. Muscles of the posterior arm: Long, medial, and lateral heads of the triceps brachii (C6-C8), supplied by the radial nerve. 4. Forearm muscles (flexor side): Flexor carpi ulnaris (C7, C8, T1), via the ulnar nerve, Palmaris longus (C7, C8), and flexor digitorum superficialis (C8, T1), both supplied by the median nerve, Flexor digitorum profundus (C8, T1); medial half innervated by the ulnar nerve, lateral half by the median (anterior interosseus) nerve. Flexor pollicis longus (C7, C8) and pronator quadratus (C7, C8), via the median (anterior interosseus) nerve. 5. Forearm muscles (extensor side): Anconeus (C6, C7, C8), via the radial nerve, Extensor carpi radialis brevis (C7, C8), innervated by the 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); via the posterior interosseus (deep) branch of radial nerve 6. Hand muscles: C8 contributes to the innervation of intrinsic hand muscles, supplied via: a)- Palmaris brevis, via the superficial branch of the ulnar nerve (C8, T1). b)- Hypothenar muscles (abductor, opponents, flexor digiti minimi), adductor pollicis, 3rd & 4th lumbricals, palmar interossei, dorsal interossei, via the deep branch of the ulnar nerve (C8, T1). c)- Thenar muscles (abductor, opponens, & flexor pollicis brevis), via the ecurrent branch of the median nerve (C8, T1). d)- 1st & 2nd lumbricals, innervated by the digital branches of median nerve (C8, T1). | The sensory fibers of the anterior ramus of spinal nerve C8 innervate the skin corresponding to the C8 dermatome. This dermatome includes the little finger, as well as the medial side of the palm. | ||
B. POSTERIOR RAMUS OF SPINAL NERVE C8:
The posterior ramus of the C8 is the posterior branch of the spinal nerve C8, 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 C8 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 C8:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the C8 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:
Through the gray rami communicantes, the spinal nerve C8 connects to the sympathetic trunk. The gray rami communicantes enable 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 C8 | |||
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). Latissimus dorsi (C6-C8), Pectoralis minor muscle (C8, T1) and the sternocostal head of the pectoralis major muscle (C6-T1), Long, medial, and lateral heads of the triceps brachii (C6-C8), Flexor carpi ulnaris (C7, C8, T1), Palmaris longus (C7, C8), and flexor digitorum superficialis (C8, T1), Flexor digitorum profundus (C8, T1), Flexor pollicis longus (C7, C8) and pronator quadratus (C7, C8), Anconeus (C6, C7, C8), 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), Palmaris brevis, hypothenar (abductor, opponens & flexor digiti minimi) muscles, thenar (abductor, opponens, & flexor pollicis brevis) muscles, adductor pollicis, lumbricals, palmar interossei, dorsal interossei. | C8 dermatome of skin encompassing the little finger of the hand, and the medial side of the palm. | Skin over the posterior cervical region. | |
References
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