The cervical plexus is a network of nerves formed by the upper four cervical spinal nerves (C1 through C4), situated deep in the neck alongside the upper vertebral column. It supplies sensation to much of the neck, the lower jaw area, the ear, and the back of the head, while also sending motor commands to several neck muscles and, critically, to the diaphragm. Although it gets far less attention than the brachial plexus of the arm or the lumbar plexus of the lower back, the cervical plexus is involved in everything from breathing to regional anesthesia for neck surgery, and its anatomy is more variable from person to person than most people realize.
Where It Sits and How It Forms
The cervical plexus lies deep in the neck, roughly behind the sternocleidomastoid muscle (the thick strap of muscle you can feel running from behind your ear down to your collarbone). The ventral rami, the forward-facing branches of spinal nerves C1 through C4, weave together to form the plexus. These rami link up in a series of loops, and from those loops emerge two broad categories of branches: sensory branches that carry touch, pain, and temperature information from the skin, and motor branches that control muscles.
The plexus sits within what anatomists call the posterior triangle of the neck, a region bounded by the sternocleidomastoid in front, the trapezius behind, and the collarbone below. Most of the sensory branches emerge from roughly the midpoint of the sternocleidomastoid’s rear edge, a landmark sometimes called Erb’s point or the nerve point of the neck. From there, the branches fan out in different directions to cover distinct territories of skin.
The Sensory Branches
Four named cutaneous nerves arise from the cervical plexus, each covering its own patch of skin. Understanding them matters clinically because they are the targets of nerve blocks used in surgery, and they can be sources of chronic pain when injured or compressed.
- Lesser occipital nerve: Arises mainly from C2 and curves upward behind the ear to supply the skin of the scalp behind and above the ear. It is sometimes implicated in cervicogenic headaches and occipital neuralgia.1PubMed Central. Nervous Interconnection Between the Lesser Occipital and Auriculotemporal Nerves A cadaver study found the nerve emerges from behind the sternocleidomastoid about 8 cm below the external occipital protuberance (the bony bump at the back of the skull) and typically branches before it reaches the hairline.2PubMed Central. Anatomic and Compression Topography of the Lesser Occipital Nerve
- Great auricular nerve: Formed by fibers from C2 and C3, this nerve ascends across the sternocleidomastoid toward the ear and jaw. It supplies sensation to the earlobe, the angle of the jaw, and skin over the parotid gland. Surgeons operating in this area can usually locate it roughly halfway between the angle of the mandible and the tip of the mastoid process.3PubMed Central. Identifying Great Auricular Nerve via Bony Landmarks: A Cadaver Study
- Transverse cervical nerve: Also called the transverse cutaneous nerve of the neck, it crosses the sternocleidomastoid horizontally to supply the front and side of the neck. In a cadaver study of 250 heads, it reached the mandibular area in about 97% of cases, sometimes providing accessory sensation to the lower jaw region that overlaps with the great auricular nerve’s territory.4PubMed. Transverse cervical and great auricular nerve distribution in the mandibular area: a study in human cadavers An anatomical mapping study found the transverse cervical nerve emerges at roughly the midpoint (about 53%) along the posterior border of the sternocleidomastoid, measured from the earlobe to the muscle’s lower attachment on the clavicle.5PubMed. Transverse Cervical Nerve for Landmark-Guided Cervical Cutaneous Analgesia
- Supraclavicular nerves: Arising from C3 and C4, these descend toward the collarbone and fan out to supply the skin of the lower neck, the shoulder, and the upper chest. They are the lowest of the cervical plexus’s sensory branches.
The overlap between these nerves’ territories is worth knowing about. Because the transverse cervical nerve and great auricular nerve both send branches toward the jaw, blocking or cutting one does not always produce complete numbness in that area. The body has a degree of built-in redundancy in its sensory wiring.
Motor Branches and the Ansa Cervicalis
The cervical plexus does more than sense. Its motor branches control muscles that move the neck and stabilize structures during swallowing and speech. The most distinctive motor structure in the plexus is the ansa cervicalis, a loop of nerve fibers formed by connections from C1, C2, and C3. It sits in the carotid triangle of the neck, lying over the carotid sheath.6PubMed Central. Unilateral anatomical variation of the ansa cervicalis The ansa cervicalis has two roots: a superior root carrying fibers from C1 and C2 that travel briefly with the hypoglossal nerve before branching off, and an inferior root descending from C2 and C3.7PubMed Central. Ansa cervicalis: a comprehensive review of its anatomy, variations, pathology, and surgical applications Together, these roots innervate the infrahyoid (“strap”) muscles of the neck, the group of muscles below the hyoid bone that pull the larynx downward during swallowing and help stabilize it during speech.
The ansa cervicalis has a practical surgical application beyond its day job. Because it controls expendable muscles, surgeons sometimes harvest a segment of the ansa to use as a nerve graft when repairing more important damaged nerves elsewhere, such as the recurrent laryngeal nerve that controls the vocal cords.
The Phrenic Nerve and Breathing
The most consequential motor branch associated with the cervical plexus is the phrenic nerve, which is the sole motor nerve to the diaphragm and therefore essential for breathing. Classically, the phrenic nerve originates from C3, C4, and C5 (the medical-school mnemonic “C3, 4, 5 keeps the diaphragm alive” captures this).8PubMed. Rare case of divided phrenic nerve variation: a cadaveric case report In reality, its root composition varies substantially. A cadaveric study found that only about 20% of cases showed the classic triple-root pattern from C3, C4, and C5. In 55% of cases, the phrenic nerve was formed by just C4 and C5, and in 10% it arose from C4 alone. The C4 root consistently made the largest contribution regardless of the pattern.9Translational Research in Anatomy. A study on the variants of phrenic nerve roots with histological correlation
A separate cadaveric study confirmed that the classic triple-root formation was present in about 58% of specimens, with a double-root C4-C5 pattern being the second most common at roughly 31%.10PubMed Central. Variational anatomy of cervical part of phrenic nerve: An observational human cadaveric study The discrepancy between these two studies is not alarming; the exact proportions shift depending on the population studied and how researchers define the contributions of each root. The consistent finding across both is that C4 is the dominant contributor and that “C3-4-5” is an oversimplification.
This matters in clinical practice because any procedure that accidentally damages the phrenic nerve, or any nerve block that inadvertently numbs it, can paralyze one side of the diaphragm. A person with healthy lungs can usually compensate for losing one side, but for someone with pre-existing respiratory disease, it can cause serious breathing difficulty.
The Accessory Phrenic Nerve
Adding to the anatomical unpredictability, more than a third of people have an accessory phrenic nerve, an extra nerve that also contributes motor fibers to the diaphragm. A meta-analysis pooling data from about 1,940 cadaveric half-necks estimated its prevalence at roughly 37%. The accessory phrenic nerve most commonly originates from the ansa cervicalis (about 17% of cases) or from the nerve to the subclavius muscle (about 16%).11PubMed. Origin and prevalence of the accessory phrenic nerve: A meta-analysis and clinical appraisal
Surgeons need to be aware of the accessory phrenic nerve during procedures in the lower neck and upper chest. If the main phrenic nerve is identified and carefully preserved but an unrecognized accessory phrenic nerve is severed, diaphragm function can still be compromised. Conversely, the presence of an accessory phrenic nerve can serve as a safety net: if the main trunk is damaged, the accessory branch may partially preserve diaphragmatic movement.
Connections to Cranial Nerves
The cervical plexus does not operate in isolation. Extensive and variable connections exist between the upper cervical nerves (C1 through C4) and the lower cranial nerves, specifically the glossopharyngeal, vagus, accessory, and hypoglossal nerves. These connections are so elaborate that some anatomists argue the lower cranial nerves and upper cervical nerves should be thought of collectively as a single interconnected plexus.12PubMed. A comprehensive review with potential significance during skull base and neck operations, Part II: glossopharyngeal, vagus, accessory, and hypoglossal nerves and cervical spinal nerves 1-4
The most clinically familiar of these connections is the one between C1 fibers and the hypoglossal nerve. Fibers from C1 hitchhike along the hypoglossal nerve for a short distance before splitting off as the superior root of the ansa cervicalis. This is why damage to the hypoglossal nerve near the skull base can sometimes affect ansa cervicalis function and vice versa. Connections to the vagus nerve also explain why cervical plexus blocks occasionally produce unexpected effects like a hoarse voice (from vagus involvement) or a sense of swallowing difficulty.
Nerve Blocks for Surgery
Regional anesthesia targeting the cervical plexus is widely used during operations on the neck, particularly carotid endarterectomy (surgery to clear a blocked carotid artery). There are two approaches: a superficial block, where anesthetic is injected into the tissue just behind the sternocleidomastoid to bathe the sensory branches as they emerge, and a deep block, where the needle is advanced closer to the vertebral column to reach the nerve roots themselves.
A systematic review covering over 10,000 blocks found that the superficial or intermediate approach is safer. Deep blocks, whether used alone or combined with a superficial injection, carried a higher rate of serious needle-related complications (with odds roughly twice as high compared to superficial blocks) and were associated with over five times the odds of needing conversion to general anesthesia.13PubMed. Superficial or deep cervical plexus block for carotid endarterectomy: a systematic review of complications The deeper the needle goes, the closer it gets to structures like the phrenic nerve root, the vertebral artery, and the spinal cord, which explains the higher complication rate.
A recent clinical study explored targeting the transverse cervical nerve specifically for cosmetic neck procedures. All nine participants achieved complete skin numbness on the blocked side, and every participant reported less pain on the blocked side compared to the opposite side. The injection point was guided by the anatomical finding that the transverse cervical nerve emerges at about the midpoint along the sternocleidomastoid’s back edge.14PubMed. Transverse Cervical Nerve for Landmark-Guided Cervical Cutaneous Analgesia This kind of targeted, single-nerve block could reduce the need for broader cervical plexus blocks in procedures where only the front-of-neck skin needs to be numbed.
What Happens When Cervical Plexus Branches Are Cut
The cervical plexus’s sensory branches are frequently at risk during neck dissections performed for cancer. Surgeons removing lymph nodes from the neck must decide whether to spare or sacrifice the cutaneous nerve branches running through the surgical field. The consequences of not preserving them are well documented.
A study comparing nerve-preserving and non-preserving neck dissections found that patients whose cervical root branches were not preserved were left with numbness throughout the same side of the neck, and this numbness was statistically more likely to persist than in the nerve-preserving group across nearly all neck regions tested.15JAMA Otolaryngology–Head & Neck Surgery. Sensory Changes Associated With Selective Neck Dissection A separate study confirmed that the nerve-preserved group had less neck and shoulder pain, while the nerve-removed group experienced more frequent numbness of the earlobe and lateral neck. The nerve-removed group also showed higher depression scores and lower quality-of-life scores, which correlated with pain intensity.16PubMed. Cervical sensory preservation during neck dissection
The great auricular nerve deserves special mention here. It is commonly sacrificed during parotid gland surgery and some neck dissections. Research notes that while losing it does cause numbness around the ear and jaw angle, the sensory loss does not appear to produce a major decrease in overall quality of life for most patients.17PubMed Central. Identifying Great Auricular Nerve via Bony Landmarks: A Cadaver Study The earlobe numbness can be disorienting at first, but many patients adapt to it.
Cervical Plexus Pain Syndromes
When cervical plexus branches become irritated, compressed, or damaged, the result can be chronic neuropathic pain in the neck, scalp, or ear. These pain syndromes can be frustratingly difficult to diagnose because the pain often mimics other conditions. A headache caused by the lesser occipital nerve being compressed behind the sternocleidomastoid might be mistaken for a tension headache or migraine. Pain from the great auricular nerve can mimic temporomandibular joint disorder.
One case report described a patient with postoperative cervical neuropathic pain who responded to a diagnostic superficial cervical plexus block under ultrasound guidance. After the block confirmed the plexus as the pain source, the patient underwent pulsed radiofrequency treatment. Pain scores dropped to zero at one month, though the benefit faded over the following months.18PubMed Central. Cervical plexus as anatomical target for the treatment of postoperative cervical neuropathic pain This pattern, where a diagnostic block both confirms the diagnosis and provides temporary relief, is a common approach for cervical plexus-related pain. The challenge is achieving long-lasting relief, and no single treatment has emerged as consistently effective for every patient.
Imaging the Cervical Plexus
Until recently, visualizing the cervical plexus and its branches in a living person was difficult. MRI can show the plexus, but fine-resolution detail of individual branches is often limited. High-frequency ultrasound has changed this. A study evaluating high-frequency ultrasonography for cervical plexus tumors found that ultrasound correctly identified about 91% of tumors, outperforming both MRI (about 73%) and CT (25%).19PubMed Central. Diagnosis of cervical plexus tumours by high-frequency ultrasonography
For individual branches, high-resolution ultrasound has been shown to reliably visualize even small nerves like the transverse cervical nerve in both cadavers and healthy volunteers, with dissection confirming the ultrasound findings in every specimen tested.20PubMed. High-Resolution Ultrasonography of the Transverse Cervical Nerve This is valuable not just for diagnosis but for guiding nerve blocks. When an anesthesiologist can see the nerve on the ultrasound screen, they can place the needle tip precisely where the anesthetic needs to go, reducing the volume of drug required and minimizing the risk of hitting the wrong structure.
The Phrenic Nerve Across Species
The phrenic nerve’s root contributions vary not just among individual humans but across mammalian species. In Akkaraman sheep, for instance, the phrenic nerve forms from C5, C6, and C7 in about 57% of specimens, and from C5 and C6 alone in the rest.21PubMed. Gross Anatomy and Cervical Ventral Branch Variations of the Phrenic Nerve in Akkaraman Sheep (Ovis aries) That is a completely different spinal level from the human C3-C5 pattern. Among carnivores, comparative work has found that the maned wolf’s phrenic nerve resembles that of the crab-eating fox but differs from the domestic dog, suggesting that even within closely related species, there is meaningful variability in how the phrenic nerve develops.22PubMed Central. Anatomical Behaviour of the Phrenic Nerve and Innervation of the Diaphragm in the Maned Wolf (Chrysocyon brachyurus)
These cross-species differences reflect the fact that the cervical plexus and its branches evolved in the context of each species’ neck length, posture, and respiratory mechanics. Animals with longer necks tend to have the phrenic nerve arising from lower cervical segments, because the diaphragm has effectively migrated farther from the brainstem during development. It is a reminder that the human arrangement, with C3-C5 controlling the diaphragm despite the diaphragm sitting far below the neck, is itself a quirk of embryological development: the diaphragm muscle originates from cervical tissue that migrates downward during fetal life, dragging its nerve supply behind it.