Rules and exceptions

Rules
- Supplies all Strap muscles
- Supples none of the suprahyoid muscles apart from Geniohyoid
- Provides sensory innervation to the anterior and lateral neck
Additional innervation includes
- Accessory nerve (CN XI)
  - Innervating the SCM and trapezius muscles
- Mylohyoid nerve (a branch of CN V 3 )
  - Innervates the mylohyoid muscle and anterior belly of the digastric muscle beneath the chin.
- Facial nerve (CN VII)
  - Innervates the platysma muscle through its cervical branch
  - Posterior belly of digastric
  - Stylohyoid
- Glossopharyngeal nerve (CN IX)
  - Supplies the carotid body and sinus (visceral sensory)
- The vagus nerve (CN X)
  - Supplies the larynx through its superior and recurrent (inferior) laryngeal nerves
- Hypoglossal nerve (CN XII)
  - Loops through the neck around the external carotid artery to innervate the tongue

Overview

Formed by loops between the Anterior Rami of C1-C4
- After each has received a grey ramus communicans from the Superior Cervical Ganglion
Relationships
- Lies in series with Brachial Plexus on Scalenus Medius
- Behind the Prevertebral Fascia
- Covered by the upper part of Sternocleidomastoid
- Does not lie in the Posterior Triangle
Branches
- Divided into cutaneous and muscular
  - Cutaneous head posterior-lateral
  - Muscle tend to head anterior-medial
Upper 3 nerves have meningeal branches for the Posterior Cranial Fossa
C1 fibres ascend with the Hypoglossal Nerve
C1 and C2 fibres ascend with the Vagus Nerve
C2 and C3 fibres ascend through the Foramen Magnum

Muscular Branches

Given off segmentally to prevertebral muscles (Longus Capitis, Longus Colli and Scalenes)
C1
- Branch from C1 joins Hypoglossal Nerve
- Splits off and gives three branches
  - Superior Root of Ansa Cervicalis
  - Nerves to Thyrohyoid
  - Nerves to Geniohyoid
C1-C2: Rectus capitis anterior and lateralis
C1-C3: Longus capitis
C2-C3: Contributions to the prevertebral muscles and sternocleidomastoid
C3-C4: Contributions to the levator scapulae, trapezius and scalenus medius

Phrenic Nerve

Formed from C3-C5
Runs down vertically over Anterior Scalene
Passes from lateral to medial borders
Beneath Prevertebral Fascia
Lateral to Ascending Cervical Branch of Inferior Thyroid Artery
Passes behind Subclavian Vein into mediastinum (anterior to the Subclavian Artery)

Ansa Cervicalis

Overview
- Nerves C1 to C3
- All strap muscles are supplied by Ansa Cervicalis apart from Thyrohyoid
Innervates four muscles
- Superior belly of the omohyoid muscle
- Inferior belly of omohyoid muscle
- Sternohyoid
- Sternothyroid
Two roots
- Superior root (C1)
  - Passes in fibers of the Hypoglossal Nerve
    - Leaves it in the carotid triangle
  - Passes around the occipital artery
  - Innervates
    - Superior belly of the omohyoid muscle
    - Superior portion of the sternothyroid and the sternohyoid muscles
  - Then unites with the inferior root of the ansa cervicalis.
- Inferior root (C2 and C3)
  - Courses inferiorly on the outer aspect of the Internal jugular vein
  - Then crosses roughly midway down this vessel to pass anterior to this vein.
  - Then passes in an anterior direction to unite with the superior root of the ansa cervicalis anterior to the common carotid artery.
  - Innervates
    - All the infrahyoid (“strap”) muscles
    - Except the thyrohyoid which is innervated by the first cervical nerve which accompanies the hypoglossal nerve for a short distance

Cutaneous Branches

Supply the front and sides of the neck
Contributes to supply of the scalp, face and chest
Branches:

Lesser Occipital Nerve (C2)

Hooks around Accessory Nerve
Runs up along posterior border of SCM
Supplies posterior upper neck and adjacent scalp behind auricle

Greater Auricular Nerve (C2, C3 – mostly C2)

Passes vertically upwards over SCM
Supplies skin over angle of Mandible, Parotid Gland, Parotid Fascia, Skin of Auricle over whole of its cranial surface, lower part of lateral surface below External Acoustic Meatus, skin over Mastoid region

Transverse Cervical Nerve (C2, C3)

Curves around posterior border of SCM
Perforates investing fascia
Divides into ascending and descending branches
Innervates skin on front of neck from chin to sternum
Ascending branch communicates with cervical branch of Facial Nerve

Supraclavicular Nerve (C3, C4 – mostly C4)

Emerges with other 3 nerves at posterior border of SCM
Sensation for supraclavicular fossa and upper thoracic region and sternoclavicular joint.

Posterior Rami

C1
- Suboccipital nerve
- Emerges above the posterior arch of the atlas and enters the suboccipital triangle
- Motor innervation to muscles around the suboccipital triangle and sensory innervation from the meninges and atlantooccipital joint
C2
- Divides
  - Medial (greater occipital nerve)
    - Motor innervation to obliquus capitis inferior and semispinalis capitis muscle and sensory innervation to scalp and dura mater in the posterior cranial fossa.
  - Lateral terminal branches
    - Motor innervation to longissimus capitis, semispinalis capitis, and splenius capitis.
- Largest
- Emerges between the posterior arch of atlas and the lamina of the axis and winds underneath the obliquus capitis inferior muscle before dividing into medial and lateral
C3-C8
- Run posteriorly around their respective articular pillars and provide motor innervation to various muscles including semispinalis capitis, multifidus, interspinalis, longissimus colli, splenius colli and iliocostalis colli muscles.
- In addition, sensory innervation is provided to the facet joints above and below the nerve and the skin around the medial back region.

1: Sternocleidomastoid muscle. 2: Mastoid process. 3: Clavicle. 4: External jugular vein. 5: Greater auricular nerve. Supraclavicular nerves are seen crossing the clavicle.