Plexus Formation - Neck's Nerve Nexus
-
Definition: A nerve network in the neck providing cutaneous and motor innervation to structures in the neck and supero-thoracic region.
-
Vertebral Levels: Formed by the ventral rami of spinal nerves C1-C4.
- Often receives a contribution from C5 (especially for the phrenic nerve).
-
Location: Lies deep to the Sternocleidomastoid (SCM) muscle and prevertebral fascia, anterior to the Scalenus Medius and Levator Scapulae muscles.
-
Formation: Arises from a series of communicating loops (ansae) between the ventral rami of C1, C2, C3, and C4.
⭐ A key contribution to the phrenic nerve often comes from the C5 ventral ramus, joining the primary roots from C3 and C4. Remember: "C3, C4, C5 keeps the diaphragm alive."
Plexus Branches - Nerve Pathways Charted
The cervical plexus gives rise to superficial (sensory) and deep (motor) branches.
- Sensory branches emerge at Erb's point (posterior border of SCM). 📌 Mnemonic for sensory branches: L-G-T-S (Lesser occipital, Great auricular, Transverse cervical, Supraclavicular).
Branch Details:
| Nerve Name | Root Value(s) | Type | Innervation/Distribution |
|---|---|---|---|
| Superficial (Sensory) | |||
| Lesser Occipital | C2 | Sensory | Skin of scalp posterosuperior to auricle |
| Great Auricular | C2, C3 | Sensory | Skin over parotid, mastoid, auricle, angle of mandible |
| Transverse Cervical | C2, C3 | Sensory | Skin of anterior & lateral neck |
| Supraclavicular | C3, C4 | Sensory | Skin over shoulder, clavicle, upper pectoral region |
| Deep (Motor) | |||
| Ansa Cervicalis | C1, C2, C3 | Motor | Infrahyoid muscles (sternohyoid, sternothyroid, omohyoid) |
| - Superior Root | C1 | Motor | From C1 (travels with CN XII); to sup. belly omohyoid, upp. sternohyoid/thyroid |
| - Inferior Root | C2, C3 | Motor | From C2,C3; to inf. belly omohyoid, low. sternohyoid/thyroid |
| Phrenic Nerve | C3, C4, C5 | Motor & Sensory | Diaphragm (sole motor); sensory to diaphragm, pericardium, pleura |
| Segmental Branches | C1-C4 | Motor | Prevertebral muscles (longus colli/capitis), scalenes, levator scapulae & some strap muscles (e.g. thyrohyoid via C1) |
Clinical Significance - When Nerves Cry Out
- Cervical Plexus Block: Regional anesthesia for neck/shoulder procedures.
- Superficial Block:
- Sensory nerves; landmark: Erb's point (mid-posterior SCM border).
- Sensory nerves; landmark: Erb's point (mid-posterior SCM border).
- Deep Block:
- Nerve roots (motor/sensory); landmarks: Chassaignac's tubercle (C6), mastoid.
- ⚠️ Risks: Phrenic nerve block, vertebral artery/subarachnoid injection.
- Superficial Block:
- Phrenic Nerve Palsy (C3,C4,C5 keep diaphragm alive 📌):
- Causes: Trauma (surgical, iatrogenic e.g., interscalene block), tumor compression.
- Signs: Dyspnea (esp. supine/exertion), paradoxical abdominal movement (abdomen in on inspiration), unilateral elevated diaphragm (CXR).
- Referred Pain:
- Diaphragmatic irritation (e.g., peritonitis, cholecystitis) → shoulder tip pain.
- Mechanism: Shared C3-C5 segments for Phrenic n. (diaphragm) & Supraclavicular n. (shoulder).
⭐ Erb's point (punctum nervosum): Emergence of 4 superficial cervical plexus branches (Lesser occipital, Great auricular, Transverse cervical, Supraclavicular) at posterior SCM border.
High‑Yield Points - ⚡ Biggest Takeaways
- Formed by ventral rami of C1-C4 spinal nerves.
- Phrenic nerve (C3, C4, C5) is vital, innervating the diaphragm.
- Ansa cervicalis (C1-C3 loop) supplies most infrahyoid muscles.
- Four main cutaneous branches provide sensation to the neck, ear, and clavicular region.
- These sensory nerves emerge at Erb's point, a key landmark for cervical plexus block.
- Deep motor branches also supply prevertebral muscles, scalenes, and levator scapulae.
Unlock the full lesson and continue reading
Signup to continue reading this lesson and unlimited access questions, flashcards, AI notes, and more
