Neck is one of the most vital regions of the Human Body which is divided into Triangles of Neck as it consists of multiple essential structures of the Human Body which are vital for survival. So the Neck has been divided into multiple triangles to help categorize and understand the contents of neck, by dividing them into triangles it becomes easy to communicate and also help plan for a Surgery. the triangles of nerve are very important as many Cranial Nerves pass through it. The Neck is divided mainly into two types – Anterior Triangle and Posterior Triangle which are further divided into Subdivisions.
It is divided into 4 Subdivisions – Submental triangle (unpaired), Submandibular triangle (paired), Carotid triangle (paired), Muscular triangle. Digastric Triangle.
It is divided into 2 Subdivisions – Occipital Triangle and Supraclavicular Triangle
Let us look at each triangle and their Subdivisions in detail –
Anterior Triangle of Neck:
Boundaries of Anterior Triangle of Neck –
- Anteriorly by the median line of the neck
- Posteriorly by the anterior margin of sterno-cleidomastoid
- Base is the inferior border of the mandible
- Apex is at the menubrium sterni
- Its projection into the mastoid process
It the portion of the neck which has median line of the neck anteriorly and anterior margin of sterno-cleidomastoid posteriorly. Its Apex is at the manubrium sterni and its projection to the mastoid process.
Digastric triangle: The borders of this triangle are
- Roof or Above: base of the mandible and its projection to the mastoid process
- Posteriorinferiorly – posterior belly of the digastric and by stylohyoid
- Posterior region of the triangle contains lower part of the parotid gland
- Anteriorinferiorly – Anterior belly of digastric
- Anteriorly: It contains the submandibular gland which has the facial being superficial to tit and the facial artery deeper to it
- Floor – Mylohyoid and hyoglossus
- It is covered by – Skin, Fascia, platysma and deep fascia, this fascia contains branches of facial and transverse cutaneous cervical nerves.
Submental Triangle: It is an undivided subdivision of the Anterior triangle of the neck, its boundaries are – Mandibular symphysis, anterior belly of digastric and body of hyoid bone. It contains lymph nodes and tributaries forming the anterior jugular vein. Apex – Chin, Base – body of hyoid bone, Floor – mylohyoid muscles. It contains lymph nodes, small veins which form the anterior jugular vein.
Submandibular Triangle: It is a paired subdivision of the Anterior triangle of the neck, its boundaries are Lower border of mandible, anterior belly of digastric muscle, posterior belly of digastric muscle. It contents are Submandibular glands, submandibular lymph nodes, hypoglossal nerve. mylohyoid nerve and facial artery and vein.
Carotid Triangle: It is a paired subdivision of the Anterior Triangle of neck, its boundaries are Posterior belly of Digastric muscle, superior belly of omohyoid muscle, anterior border of sternocleidomastoid muscle. Its Contents are – Tributaries to common facial vein, cervical branch of facial nerve, common carotid artery, external and internal carotid arteries, superior thyroid, ascending pharyngeal, lingual facial, and occipital arteries, internal jugular vein, vagus (X), Accessory (XI) and hypoglossal (XII) nerves, superior and inferior roots of ansacervicalis, transverse cervical nerve.
Muscular Triangle: It is a paired subdivision of Anterior triangle, its boundaries are Midline of neck, superior belly of omohyoid muscle, anterior border of sternocleidomastoid muscle. Its contents are Sternohyoid, omohyoid, sternohyoid and thyrohyoid muscles, thyroid and parathyroid glands, pharynx.
Muscles of Anterior Triangle of Neck:
Stylohyoid: Origin: Base of styloid process, Insertion: Lateral area of body of hyoid , Innervation: Facial Nerve (VII), Function: Pulls hyoid bone upwards in a posteriosuperior direction.
Digastric – Anterior belly: Origin: Digestric fossa on lower inside of mandible, Insertion: Attachment of tendon between two bellies to body of hyoid bone, Innervation: Mylohyoid nerve from inferior alveolar branch of mandibular nerve (V3), Function: Open mouth by lowering mandible and raises hyoid bone.
Digastric – Posterior belly: Origin: Mastoid notch on medial side of mastoid process of temporal bone, Insertion: —, Innervation: Facial nerve , Function: — .
Mylohyoid: Origin: Mylohyoid line on mandible, Insertion: Body of hyoid bone and fibers from muscles on opposite side, Innervation: Mylohyoid nerve from inferior alveolar branch of mandibular nerve (V3), Function: Support and elevation of floor of mouth and elevation of hyoid bone.
Genohyoid: Origin: Inferior mental spine on inner surface of mandible, Insertion: Anterior surface of body of hyoid bone, Innervation: Branch from anterior ramus of C1, Function: Fixed Mandible elevates and pulls hyoid bone forward, fixed hyoid bone pulls mandible downward and in-ward.
Omohyoid: Origin: Superior border of scapula medial to suprascapular notch, Insertion: Lower border of body of hyoid bone just lateral to attachment of sternohyoid, Innervation: Anterior rami of C1 to C3 through the ansa cervicalis, Function: Depresses and fixes hyoid bone.
Thyrohyoid: Origin: Oblique line on lamina of thyroid cartilage, Insertion: Greater horn and adjacent aspect of body of hyoid bone, Innervation: Fibers from anterior ramus of C1 carried along Hypoglossal Nerve, Function: Depresses hyoid bone, but when hyoid bone is fixed raises larynx.
Sternohyoid: Origin: Posterior surface of manubrium of sternum, Insertion: Oblique line on lamina of thyroid cartilage, Innervation: Anterior rami of C1 to C3 through the ansa cervicalis, Function: Draws larynx (thyroid cartilage) downward.
Posterior Triangles of Neck:
The posterior triangle of neck has the Sternocleidomastoid muscle anteriorly and the Anterior edge of trapezius muscle posteriorly, while the middle third of the clavicle is present on the inferior border. The Apex of the Posterior Triangle is between the attachments of Sternocleidomastoid and trapezius to the occiput which is blunted and it is more like a quadrilateral than a triangle.
Roof of Posterior Triangle: Investing layer of the deep cervical fascia
Floor of Posterior Triangle: Prevertebral fascia overlying splenius capitis, levator scapule and the scalene muscles.
It is subdivided into Occipital and Supraclavicular triangles by the inferior belly of the omohyoid. These subdivisions consists of cervical and brachial plexus, the subclavian artery and spinal accessory nerve.
It constitutes the larger part of the Posterior triangle and in located on the upper portion. It extends inferiorly till the inferior belly of Omohyoid. Floor of Occipital triangle splenius capitis, levator scapulae, and scaleni medius and posterior and semispinalis capitis. It is covered by Skin – superficial and deep fasciae and platysma in the bottom.
It is the lower and makes up the smaller portion of the Posterior triangle, it shares the lower border with it but superiorly it is limited by omohyoid. The floor is made up of First Rib, scalenus medius and the first slip of serratus anterior. It is covered by skin, superficial and deep fasciae and platysma and crossed by the superclavicular nerves.
Muscles associated with Posterior Triangle of Neck:
Trapezius: Origin: Superior nuchal line, external occipital protruberancem, ligamentum nuchae, spinous processes of vertebrae CVII to TXII, Insertion: Lateral one-third of clavicle, acromion, spine of scapula, Innervation: Motor-accessory nerve XII, proprioception – C3 and C4, Function: Assists in rotating the scapula during abduction of humerus above horizontal upper fibers-elevate, middle fibers-adduct, lower fibers-depress ecapula.
Sternal head of Sternocleidomastoid: Origin: Upper part of anterior surface of manubrium of sternum, Insertion: Lateral one-half of superior nuchal line, Innervation: Accessory nerve (XI) and branches from anterior rami of C2 and C3, Function: Individually – will tilt head towards shoulder on same side rotating head to turn face to opposite side, acting together, draw head forwards..
Clavicular Head of Sternocleidomastoid: Origin: Superiro surface of medial one-third of clavicle, Insertion: Lateral surface of mastoid process, Innervation: –, Function: –.
Splenius capits: Origin: Lower half of ligamentum nuchae, spinous processes of vertebrae CVII to TVI, Insertion: Mastoid process, skull below lateral one-third of superior nuchal line, Innervation: Together, draw head backwards, individually, draw and rotate head to one side (turn face to same side).
Levator Scpulae: Origin: Transverse processes of C1 to C4, Insertion: Upper part of medial border of scapula, Innervation: C3, C4, and dorsal scapular nerve (C4 and C5), Function: Elevates Scapula.
Posterior Scalene: Origin: Posterior tubercles of transverse processes of vertebrae CIV to CVI, Insertion: Upper surface of Rib 2 , Innervation: Anterior Rami of C5 to C7, Function: Elevation of Rib 2.
Middle scalene: Origin: Transverse processes of vertebrae CII to CVII, Insertion: Upper surface of rib I between tubercle and groove for subclavian artery, Innervation: Anterior rami of C3 to C7, Function: Elevates Rib I.
Anterior Scalene: Origin: Anterior tubercles of the transverse processes of vertebrae CIII to CVI, Insertion: Scalene tubercle and upper surface of Rib I, Innervation: Anterior rami of C4 to C7, Function: Elevation of Rib I.
Omohyoid: Origin: Superior border of scapula medial to scapular notch, Insertion: Inferior border of body of hyoid bone, Innervation: Ansa cervicalis, anterior rami of C1 to C3, Function: Depress the hyoid bone.