A nerve plexus is a network in which anterior rami of spinal nerves mix and redistribute fibres into peripheral nerves. Plexuses allow one peripheral nerve to contain fibres from several spinal levels, so a single root lesion and a single peripheral-nerve lesion produce different patterns. The cervical plexus serves the neck and diaphragm; the brachial plexus supplies almost the entire upper limb.
Add your labelled plexus diagram here.
Why plexus anatomy matters in physiotherapy
Weakness, numbness, pain and loss of function may arise from the spinal root, plexus, peripheral nerve, muscle, tendon or joint. Understanding the sequence roots → trunks → divisions → cords → terminal nerves helps localise a lesion, select a safe examination and communicate findings accurately.
Learning outcomes
- Define a nerve plexus and distinguish a root, trunk, division, cord and terminal nerve.
- Describe the formation, branches and distribution of the cervical plexus.
- Trace the brachial plexus from C5–T1 roots to terminal nerves.
- Relate plexus anatomy to motor, sensory and respiratory functions.
- Recognise common plexus injuries and plan a safe physiotherapy examination/referral.
1. General organisation of a spinal nerve
Each spinal nerve is formed by a posterior (dorsal) sensory root and anterior (ventral) motor root. After leaving the intervertebral foramen, it divides into posterior and anterior rami. The anterior rami form plexuses in the cervical, brachial, lumbar and sacral regions, except in the thoracic region where they mainly remain segmental intercostal nerves.
| Term | Meaning | Clinical use |
|---|---|---|
| Root | Spinal nerve level before the plexus; e.g., C6. | Root lesions follow myotome/dermatome patterns and may alter reflexes. |
| Trunk | Early merger in a plexus; superior, middle or inferior in the brachial plexus. | Upper/middle/lower trunk injury creates characteristic combined deficits. |
| Division | Anterior or posterior pathway from each trunk. | Separates fibres destined for flexor/anterior or extensor/posterior regions. |
| Cord | Lateral, posterior or medial cord named around the axillary artery. | Gives rise to major terminal nerves. |
| Peripheral nerve | Named mixed nerve carrying motor, sensory and autonomic fibres. | Mononeuropathy produces a nerve-specific pattern. |
2. Cervical plexus
The cervical plexus is formed by anterior rami of C1–C4, lying deep to sternocleidomastoid and on the prevertebral muscles. It supplies skin and muscles of the head/neck and contributes the phrenic nerve to the diaphragm. C5 contributes to the phrenic nerve but belongs to the brachial region.
2.1 Cutaneous branches
| Nerve | Roots | Area supplied | Clinical relevance |
|---|---|---|---|
| Lesser occipital | C2 | Posterolateral scalp behind the ear. | Sensory change in upper neck/occipital region. |
| Great auricular | C2–3 | Skin over parotid, mastoid and lower auricle. | Protect in neck surgery and palpation. |
| Transverse cervical | C2–3 | Anterior neck skin. | Useful reference for cervical sensory testing. |
| Supraclavicular nerves | C3–4 | Skin over clavicle, shoulder and upper chest. | Shoulder-tip sensation is not purely C5; include C3–4. |
2.2 Motor branches
- Ansa cervicalis (C1–3): supplies most infrahyoid muscles, which stabilise the hyoid and assist swallowing.
- C1 fibres travelling with hypoglossal nerve: supply geniohyoid and thyrohyoid.
- Branches to prevertebral muscles and scalenes: contribute to neck posture and breathing assistance.
- Phrenic nerve (C3–5, mainly C4): motor supply to the diaphragm and sensory supply to central diaphragmatic pleura, pericardium and parts of the peritoneum.
Phrenic memory aid
“C3, 4, 5 keep the diaphragm alive.” A high cervical lesion or phrenic impairment can compromise ventilation; respiratory assessment and urgent escalation are essential.
3. Brachial plexus overview
The brachial plexus is formed by anterior rami of C5, C6, C7, C8 and T1. It begins between anterior and middle scalene muscles, passes behind the clavicle and enters the axilla. It supplies motor and sensory innervation to the pectoral girdle and upper limb, except for trapezius (spinal accessory nerve) and a small area of skin supplied by cervical nerves/intercostobrachial nerve.
3.1 Roots (C5–T1)
Roots are proximal to the trunks and lie in the neck. Important branches include:
- Dorsal scapular nerve (C5): rhomboids and levator scapulae.
- Long thoracic nerve (C5–7): serratus anterior; injury produces medial scapular winging.
- Nerve to subclavius (C5–6): subclavius.
3.2 Trunks
| Trunk | Roots | Important branches/clinical pattern |
|---|---|---|
| Superior (upper) | C5–6 | Suprascapular nerve; nerve to subclavius. Upper-trunk injury affects shoulder abduction/external rotation and elbow flexion. |
| Middle | C7 | Contributes to posterior and anterior divisions; isolated injury is uncommon. |
| Inferior (lower) | C8–T1 | Lower-trunk injury affects intrinsic hand function and medial forearm/hand sensation. |
3.3 Divisions
Each trunk divides into an anterior and posterior division behind the clavicle. Anterior divisions generally supply flexor/anterior compartments; posterior divisions generally supply extensor/posterior compartments. The divisions reorganise into three cords around the second part of the axillary artery.
3.4 Cords and branches
| Cord | Position | Major branches |
|---|---|---|
| Lateral cord | Lateral to axillary artery. | Lateral pectoral, musculocutaneous and lateral root of median nerve. |
| Medial cord | Medial to axillary artery. | Medial pectoral, medial cutaneous nerves of arm/forearm, ulnar and medial root of median nerve. |
| Posterior cord | Posterior to axillary artery. | Upper/lower subscapular, thoracodorsal, axillary and radial nerves. |
3.5 Terminal nerves
| Nerve | Roots/cord | Main motor distribution | Main sensory distribution |
|---|---|---|---|
| Musculocutaneous | C5–7; lateral cord | Anterior arm: coracobrachialis, biceps and brachialis. | Lateral cutaneous forearm. |
| Axillary | C5–6; posterior cord | Deltoid and teres minor. | Upper lateral arm/regimental-badge area. |
| Radial | C5–T1; posterior cord | Posterior arm/forearm extensors; supinator via deep branch. | Posterior arm/forearm and dorsolateral hand areas. |
| Median | C6–T1; lateral + medial roots | Most anterior forearm and thenar muscles. | Lateral palm and palmar thumb, index, middle and radial half ring finger. |
| Ulnar | C8–T1; medial cord | FCU, medial FDP and most intrinsic hand muscles. | Medial hand and little/radial half ring finger. |
4. Plexus relationships and injury mechanisms
| Region | Structures at risk | Common mechanism | Possible finding |
|---|---|---|---|
| Neck/interscalene | Roots and trunks between scalenes. | Traction, tumour, cervical rib or compression. | Neck/arm pain, weakness or sensory change in several nerve territories. |
| Costoclavicular space | Trunks/divisions, subclavian vessels. | Clavicle injury, posture or thoracic outlet compression. | Neurovascular symptoms varying with arm position. |
| Axilla | Cords around axillary artery. | Shoulder dislocation, traction or axillary surgery. | Combined motor and sensory loss involving multiple terminal nerves. |
| Birth traction | Upper or lower plexus. | Excessive neck/shoulder traction during delivery. | Erb-type or Klumpke-type posture and weakness; urgent paediatric assessment. |
5. Physiotherapy examination of a suspected plexus lesion
- Take a mechanism and time course: trauma, traction, surgery, birth injury, tumour, repetitive compression or gradual onset.
- Inspect posture, scapular position, muscle bulk, limb colour, swelling and protective positioning.
- Screen active movement by root and peripheral nerve, comparing sides.
- Map light touch/pinprick in dermatomes and named nerve territories where trained.
- Check reflexes, pain behaviour, autonomic/vascular signs and functional tasks.
- Protect insensate skin and weak joints; avoid aggressive stretching or loading.
- Refer urgently for rapidly progressive weakness, respiratory compromise, severe trauma, vascular change or suspected spinal cord involvement.
Clinical scenario: winged scapula after surgery
A patient reports difficulty raising the arm and the medial border of the scapula lifts away from the thorax during wall push-up. Consider long thoracic nerve/serratus anterior dysfunction, but also assess pain, rotator cuff, spinal accessory function and shoulder mechanics. Document the movement, fatigue, sensory findings and functional effect; refer for medical/neurophysiological evaluation rather than treating the winging as an isolated posture problem.
6. Examination points and revision questions
High-yield points
- The cervical plexus is C1–4; the phrenic nerve is mainly C4 with C3 and C5 contributions.
- The brachial plexus is C5–T1 and organised as roots, trunks, divisions, cords and branches.
- The lateral, medial and posterior cords are named in relation to the axillary artery.
- Long thoracic nerve injury weakens serratus anterior; spinal accessory injury affects trapezius; phrenic injury affects diaphragm.
- Root, plexus and peripheral nerve lesions produce different combinations of weakness and sensory loss.
- Describe the formation and branches of the cervical plexus.
- Trace C5–T1 through the roots, trunks, divisions and cords of the brachial plexus.
- List the terminal branches of each brachial cord.
- Compare an upper-trunk, lower-trunk and long-thoracic-nerve lesion.
- Explain why one peripheral nerve can contain fibres from multiple spinal roots.
- Design a safe motor and sensory screen for a suspected plexus injury.
References for further study
- NCBI Bookshelf: Brachial plexus
- NCBI Bookshelf: Brachial plexus anatomy
- TeachMeAnatomy: Brachial plexus
- Johns Hopkins: Brachial plexus injuries
- NCBI Bookshelf: Cutaneous innervation of the upper limb
Educational note: Neurological examination and nerve mobilisation require supervised instruction. Follow local referral and emergency procedures.