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Trunk and Neck Nerves
The peripheral nerves of the trunk and neck arise from cervical and thoracic spinal nerves and several cranial nerves. They provide motor, sensory, and proprioceptive innervation to the muscles, skin, joints, and other structures of the neck, thoracic wall, abdominal wall, and back.
Region-
SystemMusculoskeletal System
The peripheral nerves of the trunk and neck form an extensive network that provides motor, sensory, and proprioceptive innervation to the muscles, skin, joints, and related structures of the cervical region, back, thoracic wall, and abdominal wall. Most arise from the anterior or posterior rami of cervical and thoracic spinal nerves, while several important muscles also receive motor innervation from cranial nerves.
Unlike the upper and lower limbs, where large plexuses redistribute spinal nerve fibers into major named peripheral nerves, much of the thoracic wall retains a relatively segmental pattern of innervation. The anterior rami of thoracic spinal nerves continue primarily as intercostal nerves, while posterior rami supply the intrinsic muscles and skin of the back.
The neck has a more complex arrangement. The cervical plexus supplies numerous cutaneous and muscular structures, the phrenic nerve provides the principal motor supply to the diaphragm, and cranial nerves such as the accessory nerve contribute to important movements of the head, neck, and shoulder girdle.
Organization of Trunk and Neck Innervation
| Nerve or Group | Origin | Principal Distribution |
|---|---|---|
| Posterior rami | Spinal nerves | Intrinsic back muscles, vertebral joints, skin of back |
| Cervical plexus | C1-C4 anterior rami | Neck muscles and skin |
| Phrenic nerve | C3-C5 | Diaphragm and sensory structures |
| Accessory nerve | Cranial nerve XI | Sternocleidomastoid and trapezius |
| Intercostal nerves | T1-T11 anterior rami | Thoracic and abdominal walls |
| Subcostal nerve | T12 anterior ramus | Abdominal wall |
Spinal Nerves of the Trunk and Neck
A typical spinal nerve is formed by the union of a posterior sensory root and an anterior motor root. After emerging through an intervertebral foramen, the mixed spinal nerve divides into anterior and posterior rami.
Both rami are mixed nerves containing sensory and motor fibers. Their anatomical distributions differ considerably.
Posterior Rami
The posterior rami of spinal nerves pass posteriorly and provide segmental innervation to the intrinsic muscles of the back, vertebral joints, and overlying skin.
They remain relatively small compared with anterior rami and generally do not form the large limb plexuses characteristic of anterior rami.
Motor Supply of Posterior Rami
Posterior rami provide motor innervation to the intrinsic, or true, muscles of the back. These include muscles primarily responsible for maintaining posture and controlling movements of the vertebral column and head.
- Splenius muscles
- Erector spinae
- Transversospinalis muscles
- Segmental deep back muscles
- Suboccipital muscles
Sensory Supply of Posterior Rami
Cutaneous branches of posterior rami supply longitudinal regions of skin over the posterior head, neck, and trunk. Their territories maintain a broadly segmental organization.
Anterior Rami
The anterior rami of spinal nerves supply the anterolateral trunk and the limbs. In the cervical region, anterior rami participate in formation of the cervical and brachial plexuses.
In much of the thoracic region, anterior rami retain their segmental organization as intercostal nerves rather than forming a plexus.
Cervical Plexus
The cervical plexus is formed by the anterior rami of C1-C4. It lies deep to sternocleidomastoid and provides both superficial sensory branches and deeper motor branches.
Its branches innervate skin of the neck and neighboring regions, several infrahyoid and prevertebral muscles, and contribute to the phrenic nerve.
Cutaneous Branches of the Cervical Plexus
The major cutaneous branches emerge near the posterior border of sternocleidomastoid and spread across the superficial neck.
| Nerve | Roots | General Distribution |
|---|---|---|
| Lesser occipital nerve | C2 | Skin posterior and superior to auricle |
| Great auricular nerve | C2-C3 | Skin over parotid region, auricle, and angle of mandible |
| Transverse cervical nerve | C2-C3 | Skin of anterior and lateral neck |
| Supraclavicular nerves | C3-C4 | Skin over clavicle, shoulder, and upper thoracic region |
Lesser Occipital Nerve
The lesser occipital nerve commonly arises from C2. It ascends along the posterior border of sternocleidomastoid and supplies skin of the lateral occipital region and the area posterior to the auricle.
It should be distinguished from the greater occipital nerve, which arises from the posterior ramus of C2.
Great Auricular Nerve
The great auricular nerve arises from C2-C3 and ascends superficially across sternocleidomastoid toward the parotid and auricular regions.
It supplies skin over parts of the external ear, parotid region, mastoid region, and angle of the mandible.
Transverse Cervical Nerve
The transverse cervical nerve arises from C2-C3 and travels horizontally across sternocleidomastoid. Its branches provide cutaneous innervation to the anterior and lateral regions of the neck.
Supraclavicular Nerves
The supraclavicular nerves arise from C3-C4 and descend toward the clavicle. They divide into medial, intermediate, and lateral branches.
They supply skin over the clavicle, upper anterior chest, and superior shoulder region.
Motor Branches of the Cervical Plexus
Deep branches of the cervical plexus contribute motor fibers to several muscles of the neck. Important pathways include the ansa cervicalis, direct fibers from C1 traveling with the hypoglossal nerve, and contributions to the phrenic nerve.
Ansa Cervicalis
The ansa cervicalis is a nerve loop embedded in or closely related to the carotid sheath. It is formed by cervical spinal nerve fibers and supplies most of the infrahyoid muscles.
Its superior root contains fibers from C1 that initially travel with the hypoglossal nerve. Its inferior root is formed mainly by fibers from C2-C3.
Muscles Supplied by Ansa Cervicalis
- Sternohyoid
- Sternothyroid
- Omohyoid
Thyrohyoid and geniohyoid receive C1 fibers traveling with the hypoglossal nerve rather than motor fibers passing through the complete ansa cervicalis loop.
C1 Fibers Traveling with the Hypoglossal Nerve
Some fibers originating from the anterior ramus of C1 temporarily travel with the hypoglossal nerve. These cervical spinal fibers eventually leave it to supply structures including geniohyoid and thyrohyoid and to contribute to the superior root of the ansa cervicalis.
The motor fibers supplying these muscles are therefore spinal fibers rather than motor fibers originating from the hypoglossal nucleus.
Phrenic Nerve
The phrenic nerve arises primarily from the anterior rami of C3-C5, with C4 typically providing the largest contribution. It is the principal motor nerve of the diaphragm.
Within the neck, the phrenic nerve descends on the anterior surface of the anterior scalene muscle, deep to the prevertebral fascia, before entering the thorax.
Motor Function of the Phrenic Nerve
The phrenic nerve provides the motor innervation of the diaphragm. Contraction of the diaphragm increases the vertical dimension of the thoracic cavity and is fundamental to normal inspiration.
Sensory Function of the Phrenic Nerve
The phrenic nerve also carries sensory fibers from structures including the fibrous pericardium, parietal layer of serous pericardium, mediastinal pleura, and central portions of the diaphragmatic pleura and peritoneum.
Phrenic Nerve and Referred Pain
Sensory fibers from the central diaphragm enter spinal cord segments associated principally with C3-C5. Irritation of these structures can therefore produce referred pain to the shoulder region, whose cutaneous innervation includes cervical spinal levels through the supraclavicular nerves.
Phrenic Nerve Injury
Damage to a phrenic nerve can weaken or paralyze the corresponding half of the diaphragm. The functional consequences depend on whether injury is unilateral or bilateral and on the patient's underlying respiratory function.
Diaphragmatic movement can be assessed clinically using imaging techniques when phrenic nerve dysfunction is suspected.
Accessory Nerve
The accessory nerve, or cranial nerve XI, provides motor innervation to sternocleidomastoid and trapezius. Its spinal root arises from motor neurons in the upper cervical spinal cord and ascends into the cranial cavity through the foramen magnum before exiting through the jugular foramen.
After leaving the skull, the nerve supplies sternocleidomastoid and crosses the lateral cervical region toward trapezius.
Sternocleidomastoid Innervation
The sternocleidomastoid receives motor innervation from the accessory nerve. Cervical spinal nerves provide proprioceptive contributions.
Unilateral contraction of sternocleidomastoid produces ipsilateral lateral flexion and rotation of the face toward the opposite side. Bilateral contraction contributes to flexion and other movements of the cervical region depending on fixation and position.
Trapezius Innervation
Trapezius receives its principal motor supply from the accessory nerve, with cervical spinal nerves contributing proprioceptive fibers.
The different portions of trapezius participate in elevation, retraction, depression, and upward rotation of the scapula.
Accessory Nerve Injury
The accessory nerve is relatively superficial in the lateral cervical region and can be vulnerable during trauma or surgical procedures.
Injury may cause weakness of trapezius, resulting in shoulder droop and impaired ability to elevate and upwardly rotate the scapula. Sternocleidomastoid weakness may also occur depending on the location of the lesion.
Suboccipital Nerve
The suboccipital nerve is the posterior ramus of C1. It is predominantly motor and supplies the muscles of the suboccipital region.
It emerges between the occipital bone and posterior arch of the atlas and travels within the suboccipital region.
Muscles Supplied by the Suboccipital Nerve
- Rectus capitis posterior major
- Rectus capitis posterior minor
- Obliquus capitis superior
- Obliquus capitis inferior
These muscles participate in fine movements and stabilization of the head and upper cervical vertebral column.
Greater Occipital Nerve
The greater occipital nerve is the medial branch of the posterior ramus of C2. It emerges through the deep muscles of the posterior neck and ascends into the scalp.
It provides sensory innervation to a large portion of the posterior scalp extending toward the vertex.
Third Occipital Nerve
The third occipital nerve arises from the medial branch of the posterior ramus of C3. It supplies skin over the lower occipital and upper posterior cervical region and also has relationships with the upper cervical facet joints.
Occipital Neuralgia
Irritation of occipital nerves can produce pain involving the posterior scalp. Occipital neuralgia is associated particularly with the greater, lesser, or third occipital nerves and may produce paroxysmal pain or tenderness within their sensory territories.
Thoracic Spinal Nerves
The anterior rami of thoracic spinal nerves largely preserve a segmental pattern. The anterior rami of T1-T11 are associated with intercostal spaces and are termed intercostal nerves, while the anterior ramus of T12 is the subcostal nerve.
Intercostal Nerves
The intercostal nerves are the anterior rami of T1-T11. They travel within intercostal spaces and provide motor and sensory innervation to the thoracic wall.
The lower intercostal nerves continue beyond the costal margin to contribute to innervation of the abdominal wall.
Typical Intercostal Nerves
Intercostal nerves T3-T6 are often considered typical because they remain primarily within their corresponding intercostal spaces. They travel in the neurovascular plane between the internal and innermost intercostal muscle layers.
Within much of the intercostal space, the principal neurovascular bundle lies near the inferior border of the rib above.
Intercostal Neurovascular Bundle
The main intercostal vein, artery, and nerve run together within the costal groove. Their typical superior-to-inferior arrangement is:
- Vein
- Artery
- Nerve
This arrangement is commonly remembered as VAN.
Motor Supply of Intercostal Nerves
Intercostal nerves provide segmental motor innervation to muscles of the thoracic wall, including the intercostal muscle layers. Lower thoracic nerves also supply muscles of the anterior and lateral abdominal wall.
Sensory Supply of Intercostal Nerves
Intercostal nerves carry sensory fibers from the skin and deeper structures of the thoracic and abdominal walls. Their cutaneous branches include lateral cutaneous and anterior cutaneous branches.
Lateral Cutaneous Branches
The lateral cutaneous branches generally emerge near the lateral thoracic wall and divide into anterior and posterior branches. They supply skin over the lateral trunk.
Anterior Cutaneous Branches
The anterior cutaneous branches emerge near the parasternal region in the thorax and near the anterior midline in the abdominal wall. They supply skin of the anterior trunk.
Atypical Intercostal Nerves
Several thoracic anterior rami differ from the typical pattern. T1 contributes substantially to the brachial plexus, T2 gives rise to the intercostobrachial nerve, and T7-T11 continue into the abdominal wall as thoracoabdominal nerves.
Intercostobrachial Nerve
The intercostobrachial nerve is usually the lateral cutaneous branch of the second intercostal nerve, T2. It crosses the axilla and supplies sensation to portions of the axillary region and upper medial arm.
Its anatomical course makes it clinically important during procedures involving the axilla.
Thoracoabdominal Nerves
The lower intercostal nerves, particularly T7-T11, continue beyond the costal margin into the abdominal wall and are commonly called thoracoabdominal nerves.
They travel within the neurovascular plane of the abdominal wall and supply abdominal muscles and overlying skin.
Subcostal Nerve
The subcostal nerve is the anterior ramus of T12. It travels inferior to the twelfth rib and continues into the abdominal wall.
It provides motor innervation to abdominal wall muscles and sensory innervation to skin of the lower anterolateral abdominal region.
Innervation of the Anterior Abdominal Wall
The muscles of the anterior and lateral abdominal wall receive segmental innervation primarily from the lower thoracic anterior rami and the first lumbar nerve.
| Muscle | Major Peripheral Supply |
|---|---|
| External oblique | Thoracoabdominal nerves and subcostal nerve |
| Internal oblique | Thoracoabdominal nerves, subcostal nerve, and L1 branches |
| Transversus abdominis | Thoracoabdominal nerves, subcostal nerve, and L1 branches |
| Rectus abdominis | Thoracoabdominal nerves |
Segmental Nature of Abdominal Innervation
The nerves supplying the abdominal wall enter muscles at multiple segmental levels. This distributed innervation helps preserve some muscular function when a single segmental nerve is injured.
Iliohypogastric and Ilioinguinal Nerves
The iliohypogastric and ilioinguinal nerves arise principally from L1 and contribute to the lower abdominal wall. They provide motor branches to portions of internal oblique and transversus abdominis and sensory branches to defined cutaneous territories.
Although these nerves arise from the lumbar plexus rather than thoracic spinal nerves, they complete the segmental innervation of the inferior abdominal wall.
Innervation of the Intrinsic Back Muscles
The intrinsic back muscles are supplied by posterior rami of spinal nerves. This distinguishes them from many superficial and intermediate back muscles, which are supplied by anterior rami or cranial nerves.
| Muscle Group | Innervation |
|---|---|
| Splenius | Posterior rami of cervical spinal nerves |
| Erector spinae | Posterior rami of spinal nerves |
| Transversospinalis | Posterior rami of spinal nerves |
| Interspinales | Posterior rami of spinal nerves |
| Multifidus | Posterior rami of spinal nerves |
Innervation of Superficial Back Muscles
Superficial extrinsic back muscles are associated functionally with movements of the upper limb and shoulder girdle. Their innervation differs from that of the intrinsic back muscles.
Trapezius receives motor supply from the accessory nerve, while latissimus dorsi, rhomboids, and levator scapulae receive branches associated with the brachial plexus or cervical spinal nerves.
Dorsal Scapular Nerve
The dorsal scapular nerve usually arises predominantly from C5 and supplies the rhomboid muscles and commonly levator scapulae.
It descends along the medial border of the scapula in association with the dorsal scapular vessels.
Long Thoracic Nerve
The long thoracic nerve arises from C5-C7 and supplies serratus anterior. Although associated with the brachial plexus, the nerve is important in the functional anatomy of the thoracic wall and scapula.
Serratus anterior protracts the scapula and holds its medial border against the thoracic wall. It also contributes to upward rotation of the scapula.
Long Thoracic Nerve Injury
Injury to the long thoracic nerve weakens serratus anterior and can produce scapular winging. The medial border of the scapula becomes abnormally prominent, particularly when the patient pushes against resistance.
Upward rotation of the scapula can also be impaired, affecting elevation of the upper limb above shoulder level.
Thoracodorsal Nerve
The thoracodorsal nerve arises from the posterior cord of the brachial plexus, principally carrying fibers from C6-C8, and supplies latissimus dorsi.
Latissimus dorsi extends, adducts, and medially rotates the humerus and can contribute to movements involving the trunk and upper limb when either attachment is fixed.
Intercostal Nerve Injury
Intercostal nerves can be affected by trauma, surgical incisions, rib fractures, compression, or inflammatory processes. Because these nerves contain both motor and sensory fibers, injury can affect thoracic wall muscle activity and cutaneous sensation.
Intercostal Nerve Block
An intercostal nerve block involves delivery of local anesthetic near an intercostal nerve to reduce sensory transmission from its segmental territory.
Knowledge of the relationship between the nerve and the inferior border of the rib is important when performing procedures in the intercostal space.
Dermatomes of the Trunk
Thoracic dermatomes form approximately segmental bands around the trunk. Certain surface landmarks are commonly used during neurological examination, although exact boundaries vary between individuals.
| Spinal Level | Common Surface Landmark |
|---|---|
| T4 | Nipple region in the conventional male anatomical reference |
| T6 | Xiphoid region |
| T10 | Umbilical region |
| T12 | Suprapubic or lower anterior abdominal region |
Dermatomes represent spinal nerve root territories and should not be treated as identical to the distributions of individual peripheral nerve branches.
Cervical Dermatomes
Cervical spinal nerves contribute sensation to the posterior head, neck, shoulders, and upper limbs. In the neck, cutaneous branches from both anterior and posterior rami participate in the sensory pattern.
C2 is associated with portions of the posterior scalp, C3 with parts of the neck, and C4 with the shoulder and supraclavicular region.
Peripheral Nerve Territory Versus Dermatome
| Feature | Peripheral Nerve Territory | Dermatome |
|---|---|---|
| Represents | Distribution of a named peripheral nerve | Distribution associated with a spinal nerve root |
| Fiber origins | May contain several spinal levels | Predominantly one spinal level |
| Clinical use | Localizing peripheral nerve lesions | Localizing spinal root lesions |
Muscular Innervation of the Neck
The neck contains muscles with several different embryological and functional origins, and consequently its motor innervation is diverse. Cervical spinal nerves, the accessory nerve, branches of the brachial plexus, and other cranial nerves all participate.
| Muscle or Group | Principal Motor Supply |
|---|---|
| Sternocleidomastoid | Accessory nerve |
| Trapezius | Accessory nerve |
| Infrahyoid muscles | Ansa cervicalis, with exceptions |
| Geniohyoid | C1 fibers via hypoglossal nerve |
| Thyrohyoid | C1 fibers via hypoglossal nerve |
| Suboccipital muscles | Suboccipital nerve |
| Intrinsic back muscles | Posterior rami |
Scalene Muscle Innervation
The scalene muscles receive branches from anterior rami of cervical spinal nerves. They participate in movements of the cervical vertebral column and can elevate the upper ribs during respiratory effort.
Their close relationships with the brachial plexus, subclavian vessels, and phrenic nerve make the scalene region an important anatomical passage.
Prevertebral Muscle Innervation
Prevertebral muscles such as longus capitis and longus colli receive muscular branches from cervical spinal nerves. These muscles contribute to flexion and stabilization of the cervical vertebral column and head.
Segmental Innervation of the Back
Intrinsic back muscles receive repeated segmental branches from posterior rami rather than being supplied by a single large peripheral nerve. This pattern reflects their developmental relationship with the epaxial musculature.
The segmental arrangement allows localized control of vertebral movements and postural adjustments.
Epaxial and Hypaxial Innervation
The distinction between epaxial and hypaxial musculature provides an important developmental basis for understanding trunk innervation.
| Muscle Division | General Location | Innervation |
|---|---|---|
| Epaxial muscles | Intrinsic muscles of the back | Posterior rami of spinal nerves |
| Hypaxial muscles | Anterolateral body wall and limbs | Anterior rami of spinal nerves |
Autonomic Fibers in Spinal Nerves
Peripheral spinal nerves of the trunk and neck also carry postganglionic sympathetic fibers to structures such as blood vessels, sweat glands, and arrector pili muscles.
These autonomic fibers distribute through both anterior and posterior rami after joining spinal nerves through gray rami communicantes.
Sympathetic Trunk Connections
The sympathetic trunks lie alongside the vertebral column and communicate with spinal nerves through rami communicantes. White rami communicantes are present only at spinal levels associated with thoracolumbar sympathetic outflow, while gray rami occur at all spinal levels.
This arrangement allows sympathetic fibers to reach peripheral targets throughout the trunk, neck, and limbs.
Clinical Examination of Neck Nerves
Assessment of peripheral nerve function in the neck can include testing shoulder elevation, head rotation, diaphragmatic function, cutaneous sensation, and muscle strength.
Patterns of weakness or sensory change can help distinguish lesions of individual nerves from cervical spinal root or plexus disorders.
Testing the Accessory Nerve
Trapezius function can be assessed by asking the patient to elevate the shoulders against resistance. Sternocleidomastoid can be evaluated by testing head rotation against resistance.
Because each sternocleidomastoid rotates the face toward the opposite side, weakness must be interpreted in relation to the direction of attempted rotation.
Testing the Phrenic Nerve
Phrenic nerve function is closely related to diaphragmatic movement. Suspected dysfunction can be investigated by observing diaphragmatic position and motion using appropriate imaging or physiological techniques.
Radiculopathy and Peripheral Nerve Lesions
A cervical or thoracic radiculopathy affects a spinal nerve root and may produce sensory symptoms in an approximately dermatomal pattern together with weakness involving muscles sharing the affected root.
A peripheral nerve lesion instead follows the anatomical distribution of the affected named nerve or branch.
Herpes Zoster and Thoracic Nerves
Reactivation of varicella-zoster virus within a sensory ganglion can produce pain and a vesicular eruption in the territory of the affected sensory neurons. On the trunk, the resulting eruption frequently follows an approximately dermatomal band.
The segmental organization of thoracic nerves makes this distribution particularly recognizable.
Procedural Anatomy of Intercostal Nerves
Because the principal intercostal neurovascular bundle lies in the costal groove near the inferior border of a rib, procedures entering an intercostal space must account for its location.
Collateral branches and variations mean that knowledge of the main bundle does not eliminate the possibility of injury to smaller neurovascular structures.
Key Nerves of the Neck
| Nerve | Roots or Origin | Major Function |
|---|---|---|
| Accessory nerve | Cranial nerve XI | Motor to sternocleidomastoid and trapezius |
| Phrenic nerve | C3-C5 | Motor to diaphragm |
| Ansa cervicalis | C1-C3 | Motor to most infrahyoid muscles |
| Suboccipital nerve | Posterior ramus of C1 | Motor to suboccipital muscles |
| Greater occipital nerve | Posterior ramus of C2 | Sensation to posterior scalp |
| Cervical plexus cutaneous branches | C2-C4 | Sensation to neck, auricular, and shoulder regions |
Key Nerves of the Trunk
| Nerve Group | Origin | Major Function |
|---|---|---|
| Posterior rami | Spinal nerves | Intrinsic back muscles and posterior trunk sensation |
| Intercostal nerves | T1-T11 anterior rami | Thoracic wall motor and sensory supply |
| Thoracoabdominal nerves | Primarily T7-T11 | Abdominal wall motor and sensory supply |
| Subcostal nerve | T12 anterior ramus | Inferior abdominal wall |
| Iliohypogastric nerve | Primarily L1 | Inferior abdominal wall and cutaneous supply |
| Ilioinguinal nerve | Primarily L1 | Inferior abdominal wall and inguinal-region sensory supply |
Functional Importance
The nerves of the trunk and neck demonstrate the fundamental segmental organization of the peripheral nervous system. Posterior rami supply the intrinsic muscles and skin of the back, while anterior rami supply the anterolateral body wall and participate in cervical plexus formation.
The cervical region contains several particularly important neural pathways. The cervical plexus supplies skin and muscles of the neck, the phrenic nerve connects cervical spinal segments with the diaphragm, and the accessory nerve controls sternocleidomastoid and trapezius.
Within the thorax, intercostal nerves preserve a segmental arrangement and provide both motor and sensory innervation. Lower intercostal nerves continue into the abdominal wall, creating continuity between thoracic and abdominal segmental innervation.
Knowledge of these nerves is essential for understanding neck movement, posture, respiration, abdominal wall function, spinal movement, cutaneous sensation, dermatomes, referred pain, peripheral nerve injury, intercostal nerve blocks, cervical radiculopathy, and clinical neurological examination.
Published on October 16, 2026
Last updated on October 16, 2026
Last updated on October 16, 2026