Neck Anatomy: Triangles and Deep Structures

• The presentation is about the triangles and deep structure of the neck.
• The topics covered include the contents of the anterior and posterior triangles, major blood vessels of the head and neck, cranial nerves in the neck region, and the position/drainage areas of lymph nodes

Triangles of the Neck

• The neck region is situated between the lower border of the mandible and the suprasternal notch, extending up to the upper border of the clavicle.
• Neck divided into anterior and posterior triangles.

Posterior Triangle - Borders

• Anterior border is the posterior edge of the sternocleidomastoid muscle.
• Posterior border is the anterior edge of the trapezius muscle.
• Basal border is the middle one-third of the clavicle.
• Apical border is the occipital bone, posterior to the mastoid process.

Posterior Triangle – Muscular floor

• Muscular floor includes semispinalis capitis, splenius capitis, levator scapulae, scalenus medius, and scalenus anterior muscles.
• The muscular floor of the posterior triangle is covered by prevertebral fascia.
• Function of these muscles: head extension and rotation

Posterior Triangle – Division

• The inferior belly of the omohyoid muscle separates the posterior triangle into two parts:
  • The occipital triangle
  • The omoclavicular or subclavian triangle
• Omohyoid muscle receives nerve supply from ansa cervicalis (C1, 2, 3)
• Omohyoid muscle action: depresses the hyoid bone
• Inferior belly: Arises from the upper margin of scapula
• Narrow, flat muscle
• Passes upward & forward across the lower part of posterior triangle
• Superior belly: ascends vertically in the anterior triangle
• Is inserted into the lower border of the body of the hyoid bone

Posterior Triangle – Content (Arteries)

• Occipital artery:
  • Branch of the external carotid artery
  • Enters the triangle at the apex
  • Appears between the sternocleidomastoid and trapezius muscles
• Superficial cervical & suprascapular artery:
  • Branch of the thyrocervical trunk
  • Branch of the first part of the subclavian artery
  • Runs across the lowest part of the posterior angle
  • Disappears deep into the trapezius muscle
• Third part of subclavian artery

Posterior Triangle – Content (Veins)

• External jugular vein is the most superficial structure passing through the posterior triangle.
• Forms near the angle of the mandible
• Formed by the posterior branch of the retromandibular and posterior auricular veins.
• Termination of subclavian veins.
• Tributaries:
  • Transverse cervical
  • Suprascapular
  • Anterior jugular

Posterior Triangle – Content (Nerves)

• Branches of cervical plexus: muscular (deep) branches that include the phrenic nerve, and cutaneous (superficial) branches
• Spinal part of the accessory nerve:
  • Innervates the deep surface of the trapezius muscle.
  • Its superficial location makes it susceptible to injury
• Brachial plexus

Anterior Triangle

• Superior border: inferior border of the mandible
• Posterior border: anterior border of the sternocleidomastoid (SCM)
• Anterior border: median line of the neck
• Apex: suprasternal notch of the manubrium.
• Roof: subcutaneous tissue containing the platysma muscle.
• Floor: pharynx, larynx, and thyroid gland.

Anterior Triangle - Divisions

• The anterior triangle is divided by the digastric and omohyoid muscles into smaller triangles:
  • Submental triangle
  • Submandibular triangle
  • Carotid triangle
  • Muscular triangle

Anterior Triangle – (1. Submental triangle)

• Boundaries:
  • Hyoid bone
  • Anterior belly of the digastric muscle
• Floor: mylohyoid muscles
• Contents: submental lymph nodes, small (anterior jugular) veins

Anterior Triangle – (2. Submandibular triangle)

• Boundaries:
  • Inferior border of the mandible
  • Anterior and posterior bellies of the digastric muscle
• Floor: mylohyoid & hyoglossus muscles, middle pharyngeal constrictor
• Contents: submandibular gland & lymph nodes, facial artery & vein, mylohyoid nerve, hypoglossal nerve (provides motor function to the tongue muscles, except palatoglossus)
• Mylohyoid nerve arises from the inferior alveolar nerve (IAN) just before foramen entry

Anterior Triangle – (3. Carotid triangle)

• Boundaries: superior belly of omohyoid, posterior belly of digastric, and anterior border of SCM
• Floor: thyrohyoid, hyoglossus muscle, middle and inferior pharyngeal constrictors
• Contents: bifurcation of common carotid artery (CCA), branches of external carotid artery (ECA), internal jugular vein (IJV), deep cervical lymph nodes, glossopharyngeal CN IX, vagus CN X, spinal accessory CN XI, hypoglossal CN XII, and ansa cervicalis

Anterior Triangle – (3. Carotid triangle) cont...

• Ansa Cervicalis
  • Component of the cervical plexus, formed by nerve roots C1-C3.
  • Provides muscular branches to all infrahyoid muscles (superior belly of the omohyoid muscle, inferior belly of the omohyoid muscle, sternohyoid, sternothyroid), except thyrohyoid.

Anterior Triangle – (4. Muscular triangle)

• Boundaries: superior belly of omohyoid, anterior border of the sternocleidomastoid muscle (SCM), and midline of the neck.
• Contents: infrahyoid muscles, thyroid and parathyroid glands, and parts of the larynx, trachea, pharynx, and esophagus.

Muscles of the neck

• Superficial muscles: platysma, sternocleidomastoid (SCM), and trapezius muscles.
• Deep muscles: scalene, suprahyoid, and infrahyoid muscles.

Deep Muscle – Scalene muscles

• Anterior scalene, middle scalene, and posterior scalene
• Anterior: C3-C6 (transverse processes, anterior tubercle)
  • Insertion: 1st rib (scalene tubercle)
  • Innervation: Direct branches the cervical and brachial plexus (C3-C6)
  • Action: with ribs mobile, it raises ribs for inspiration; with ribs fixed, bends cervical spine to same side (unilateral); flexes neck (bilateral)
• Middle: C2-C7(transverse processes, posterior tubercles)
  • Insertion: 1st rib (Superior border)
  • Innervation: Direct branches from brachial plexus (C3-C7)
  • Action: Elevates rib 2, lateral flexion of neck
• Posterior: C4-C6(transverse processes, posterior tubercles)
  • Insertion: 2nd rib (lateral surface)
  • Innervation: Direct branches from brachial plexus (C5-C7)
  • Action: Elevates rib 2, lateral flexion of neck

Deep Muscle – Suprahyoid muscles

• Stylohyoid: supplied by the muscular branch of CN7.
• Digastric:
  • Anterior belly: mylohyoid nerve (branch of V3)
  • Posterior belly: muscular branch of CN7.
• Mylohyoid: supplied by the mylohyoid nerve (branch of V3)
• Geniohyoid: supplied by C1 via CN12
• Action: i. Forms floor of the mouth; ii. Elevates hyoid bones and larynx

Deep Muscle – Infrahyoid muscles

• All innervated by Ansa cervicalis (C1-C3)
• Action: Depresses hyoid bone and larynx
• Omohyoid
• Sternohyoid
• Sternothyroid
• Thyrohyoid
• Action: C1 via CN12 (hypoglossal nerve)

Arterial supply of the neck

• Derives from the external carotid artery (ECA) and the thyrocervical trunk (branch of subclavian artery).

1. ECA

• A branch of the common carotid artery (CCA) that ends posterior to the neck of the mandible.
• Supplies the face and anterior neck region.
• Branches:
  • Superior thyroid artery (larynx, thyroid gland)
  • Lingual artery (oral floor, tongue)
  • Facial artery (superficial facial region)
  • Ascending pharyngeal artery (plexus to the skull base)
  • Maxillary artery (muscles of mastication, posteromedial part of facial skeleton, meninges)
  • Superficial temporal artery (temporal region, part of the ear)
  • Occipital artery (scalp, occipital region)
  • Posterior auricular artery (ear)

1. Subclavian artery

• Branches:
  • 1st part: vertebral, internal thoracic, thyrocervical trunk
  • 2nd part: costocervical trunk
  • 3rd part: no branches, continues as the axillary artery
• Supplies:
  • Thyroid gland via the inferior thyroid artery.
  • Trapezius and SCM via the transverse cervical artery.
  • Posterior shoulder area with the suprascapular artery.

Venous drainage of neck

• Enters Internal Jugular Vein (IJV)
• A continuation of the sigmoid sinus, exiting the skull through the jugular foramen.
• Joins with the subclavian vein in the neck, leading to the brachiocephalic vein.
• Tributaries: inferior petrosal sinus, pharyngeal veins, facial vein, lingual vein, and thyroid vein.

Innervation of neck

• Sensory nerve: cutaneous branches from C2-C5 that supply the skin of the neck area.
• Motor:
  • Mylohyoid nerve (branch of V3): anterior belly of digastric muscle, mylohyoid muscle.
  • Muscular branch of CN7: posterior belly of digastric, stylohyoid muscle.
  • Ansa cervicalis: provides innervation to all infrahyoid muscles, except the thyrohyoid.
  • C1 via CN12: geniohyoid and thyrohyoid muscle.
  • CN11 (spinal part): sternocleidomastoid (SCM) and trapezius muscles.

Lymphatic drainage of neck

• Divided into:
  • Regional lymph nodes that include:
    • Occipital
    • Mastoid
    • Parotid
    • Submandibular
    • Submental
    • Anterior cervical (along anterior jugular vein)
    • Superficial cervical (along external jugular vein)
    • Retropharyngeal, laryngeal, and paratracheal nodes.
  • Deep cervical nodes:
    • Located along the internal jugular vein (IJV)
    • Drain into the thoracic duct on the left and the right lymphatic duct on the right.

Exploration of the neck's triangles, including anterior and posterior divisions. Covers major blood vessels, cranial nerves, and lymph node locations. Focuses on the anatomical structures within the neck region.