Spinal nerve T3
Nervus spinalis T3
- Related terms: Third thoracic nerve; T3
Definition
The third thoracic spinal nerve T3 is a mixed nerve, containing both somatic efferent (motor) and somatic afferent (sensory) fibers. It originates from the spinal cord at the T3 spinal segment.
a) Roots
Like other nerves, the spinal nerve T3 is formed by the union of two roots:
1. Posterior (dorsal) root:
This root contains sensory fibers that carry signals from peripheral structures (innervated by the anterior and posterior rami) to the spinal cord.
These fibers enter the dorsal gray horn within the spinal cord.
2. Anterior (ventral) root:
This root consists of motor fibers originating from the anterior gray horn within the spinal cord.
These fibers transmit motor commands to peripheral muscles via the spinal nerve and its branches.
b) Mixed spinal nerve and rami
At the level of the intervertebral foramen, the anterior and posterior roots merge to form the spinal nerve T3. This mixed nerve, containing both sensory and motor fibers, exits the intervertebral foramen between the T3 and T4 vertebrae. Shortly after its emergence, the nerve divides into two primary rami:
1. Anterior (ventral) ramus:
This ramus continues anteriorly along the chest wall as the third intercostal nerve, within the intercostal space, providing motor and sensory innervation to the chest wall.
It also forms connections with the sympathetic trunk via the white and gray rami communicantes, which carry preganglionic and postganglionic sympathetic fibers.
2. Posterior (dorsal) ramus:
This ramus provides motor innervation to the deep muscles of the back.
It also provides sensory innervation to the skin overlying the upper back.
A. ANTERIOR RAMUS OF SPINAL NERVE T3 (the third intercostal nerve):
The anterior ramus of the spinal nerve T3, commonly known as the third intercostal nerve, constitutes the larger branch of the T3 spinal nerve. As a mixed nerve, it carries both motor (somatic efferent) and sensory (somatic afferent) fibers. Emerging from the intervertebral foramen, it travels anteriorly through the chest wall within the third intercostal space. Here, it lies in the costal groove of the third rib, accompanied by the intercostal arteries and veins to form a neurovascular bundle. This bundle is positioned between the internal intercostal muscle on its superficial side and the innermost intercostal muscle on its deep side as it courses along the chest wall.
Key functions and innervations
Motor Innervation (Somatic Efferent Fibers): | Sensory Innervation (Somatic Afferent Fibers): | ||
As the anterior ramus of T3 passes beneath the third rib—and continues as the third intercostal nerve—it provides motor innervation to several thoracic wall muscles, including: External, internal, and innermost intercostal muscles (T1-T11) Subcostal, and transversus thoracis muscles | The sensory fibers of the third intercostal nerve innervate the skin through two primary cutaneous branches: 1- Lateral cutaneous branch: This branch arises from the third intercostal nerve as it courses anteriorly along the chest wall within the costal groove of the third rib. Within the intercostal space, the lateral branch bifurcates into anterior and posterior branches. 2- Anterior cutaneous branch: The anterior branch continues medially, emerging near the sternum between adjacent costal cartilages as the terminal anterior cutaneous nerve. It subsequently divides into medial and lateral branches. The lateral and anterior cutaneous branches of the third intercostal nerve collaborate to provide sensory innervation to the T3 dermatome. This dermatome includes the upper portion of the anterior chest wall, encompassing the upper breast tissue, Beyond its cutaneous distribution, the third intercostal nerve also supplies sensory innervation to deeper structures, including the parietal pleura, located beneath the chest wall muscles. | ||
B. POSTERIOR RAMUS OF SPINAL NERVE T3:
The posterior ramus of the T3 spinal nerve is the smaller, posterior branch of the spinal nerve T3. As with other posterior rami of thoracic spinal nerves, it innervates the deep intrinsic muscles of the back and the overlying skin, playing a vital role in spine stabilization and movement. Once the T3 spinal nerve exits the intervertebral foramen (between the T3 and T4 vertebrae), its posterior ramus passes through the intertransverse ligament and the overlying intertransverse (intertransversarii) muscle. It divides into lateral and medial branches:
Lateral branch: | Medial branch: | ||
Muscular branches: These innervate: - The erector spinae muscles, specifically the iliocostalis and longissimus portions. - Segmental muscles: These include the levtores costarum muscles. Cutaneous branch: After piercing the iliocostalis muscle, the lateral branch extends to supply the skin of the back. | The medial branch travels posterolaterally before curving medially along the edge of the multifidus muscle. Along its course it gives rise to following branches: Articular branches: These branches innervate the zygapophyseal joints. Muscular branches: These branches supply the intrinsic muscles of the back, including: - Erector spinae: primarily the spinalis potion, with a minor contribution to the longissimus. - Transversospinalis group: This includes the multifidus, semispinalis (specifically the semispinalis thoracis and cervicis), and the rotatores (rotatores thoracics and cervicis). - Segmental muscles: These include the interspinales and medial slips of the intertransversarii muscles. Cutaneous branch: After innervating the multifidus muscle, the medial branch pierces the thoracolumbar fascia and the extrinsic back muscles, to become a cutaneous branch. |
C. ADDITIONAL STRUCTURES ASSOCIATED WITH SPINAL NERVE T3:
a) Recurrent Meningeal Nerve (Meningeal branch):
The recurrent meningeal nerve (or meningeal branch) originates from either the T3 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 white and gray rami communicantes, the spinal nerve T3 connects to the sympathetic trunk. The white rami communicantes enable preganglionic sympathetic fibers to reach the sympathetic trunk, while the gray rami communicantes enable the postganglionic sympathetic fibers to reach peripheral targets such as sweat glands and blood vessels.
_________________________
SUMMARY TABLE
STRUCTURES INNERVATED BY THE SPINAL NERVE T3 | |||
ANTERIOR RAMUS | POSTERIOR RAMUS | ||
MOTOR STRUCTURES | SENSORY STRUCTURES | MOTOR STRUCTURES | SENSORY STRUCTURES |
External, internal, and innermost intercostal muscles, subcostal, and transversus thoracis muscles | T3 dermatome skin (upper portion of the anterior chest wall, encompassing the upper breast tissue). | Erector spinae muscles (iliocostalis, longissimus, spinalis), transversospinales muscles (multifidus, semispinalis, rotatores), segmental muscles (interspinales, intertransversarii, levtores costarum). | Zygapophyseal joints between T3 & T4 vertebrae, skin of the upper back corresponding to the T3 dermatome level. |
References
Ishizuka K, Sakai H, Tsuzuki N, Nagashima M. Topographic anatomy of the posterior ramus of thoracic spinal nerve and surrounding structures. Spine (Phila Pa 1976). 2012 Jun 15;37(14):E817-22.
Koutp A, Petritsch J, Skias C, Grechenig P, Andrianakis A, Kieser DC, Feigl GC. Anatomical Topographical Investigation of the Medial Branch of the Dorsal Thoracic Branch of the Spinal Nerve in the Segments T10-T12. Pain Med. 2022 Oct 29;23(11):1863-1868.
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.
Kottlors M, Glocker FX. Polysegmental innervation of the medial paraspinal lumbar muscles. Eur Spine J. 2008 Feb;17(2):300-6.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 2: The Back’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.95-99 & Fig. 2.44 & 2.45.
Drake, R.L., Vogl, A.W., and Mitchell, A.W.M. (2010). ‘Chapter 3: Thorax’, in Gray’s anatomy for students. (2nd ed.) Churchill Livingstone Elsevier, Philadelphia PA 19103, pp.149-155.
Tran J, Peng P, Loh E. Anatomical study of the medial branches of the lumbar dorsal rami: implications for image-guided intervention. Reg Anesth Pain Med. 2022 May 19:rapm-2022-103653.
Ishizuka K, Sakai H, Tsuzuki N, Nagashima M. Topographic anatomy of the posterior ramus of thoracic spinal nerve and surrounding structures. Spine (Phila Pa 1976). 2012 Jun 15;37(14):E817-22.
