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ANTERIOR TRIANGLES OF THE NECK - FILL_IN_THE_BLANK FLASHCARDS

ANTERIOR TRIANGLE

  • The neck is divided into anterior and posterior triangles by the sternocleidomastoid muscle; the anterior triangle lies in front of the muscle, the posterior triangle behind it.
  • Boundaries of the anterior triangle:
    • Anterior: Median plane
    • Posterior: Anterior border of sternocleidomastoid
    • Superior: Base of mandible
    • Apex: Sternum
  • The sternocleidomastoid muscle divides the neck into two triangles; each triangle is subdivided into smaller triangles.
  • Under the fascia, two longitudinal strap muscle groups extend from the inferior border of the mandible to the sternum; hyoid bone lies at the level of C_3 vertebra and provides attachment.
  • The anterior triangle is subdivided by the anterior and posterior digastric muscles and the superior belly of the omohyoid into 4 smaller triangles: Digastric, Submental, Carotid, and Muscular. The digastric, carotid, and muscular triangles are paired; the submental triangle is unpaired.

DIGASTRIC OR SUBMANDIBULAR TRIANGLE

  • Boundaries:
    • Superior base: lower border of the mandible and a line from the angle of the mandible to the mastoid process
    • Anterior: anterior belly of the digastric
    • Posterior: posterior belly of the digastric and stylohyoid
  • Floor: mylohyoid (anterior) and hyoglossus (posterior)
  • Roof: skin, superficial fascia with platysma, cervical branch of the facial nerve, transverse cutaneous nerve; investing layer of deep cervical fascia
  • Contents (essential):
    • Submandibular gland and submandibular lymph nodes
    • Vessels: facial artery and facial vein (artery deep to gland; vein superficial to gland)
    • Other vessels: submental and lingual arteries; corresponding veins
    • Nerves: hypoglossal nerve, nerve to mylohyoid, marginal mandibular branch of facial nerve, lingual nerve
    • Part of Parotid gland; part of external carotid artery; part of carotid sheath and its contents

SUBMENTAL TRIANGLE

  • Boundaries:
    • Apex: Symphysis menti
    • Base (inferior): Hyoid bone
    • Laterally: anterior belly of each digastric
  • Roof: skin, superficial fascia with platysma; investing layer of deep cervical fascia
  • Floor: left and right mylohyoid muscles; they meet in the midline as the median raphe (diaphragm oris)
  • Contents:
    • Submental lymph nodes
    • Submental artery (from facial artery)
    • Submental veins forming the anterior jugular vein
    • Nerve to mylohyoid

CAROTID TRIANGLE

  • Called the carotid triangle because it contains the common carotid artery and its bifurcation into internal and external carotid arteries
  • Boundaries:
    • Anterosuperiorly: posterior belly of digastric and stylohyoid
    • Anteroinferiorly: superior belly of omohyoid
    • Posteriorly: upper half of the anterior border of sternocleidomastoid
  • Roof: skin, superficial fascia with platysma, cervical branch of facial nerve, cutaneous nerve of the neck; investing layer of deep cervical fascia
  • Floor: anteriorly by thyrohyoid and hyoglossus; posteriorly by middle and inferior pharyngeal constrictors
  • Contents:
    • Vessels: upper part of the common carotid and bifurcation into external and internal carotid; internal carotid; external carotid and its branches (superior thyroid, lingual, facial, ascending pharyngeal, occipital); internal jugular vein
    • Nerves: vagus and its superior laryngeal branch; spinal accessory nerve; hypoglossal nerve; sympathetic trunk
    • Lymph nodes: deep cervical along the internal jugular vein; jugulodigastric and jugulo-omohyoid nodes
    • Carotid sinus (dilatation at bifurcation) and carotid body (posterior to bifurcation, chemoreceptor)

MUSCULAR TRIANGLE

  • Also called the infrahyoid or omotracheal triangle
  • Boundaries:
    • Anterior: anterior midline of the neck
    • Posterosuperior: superior belly of the omohyoid
    • Posteroinferior: lower part of the anterior border of the sternocleidomastoid
  • Floor: prevertebral fascia over splenius capitis, levator scapulae, scalenus posterior, scalenus medius (sometimes a part of semispinalis capitis at the apex)
  • Contents:
    • Infrahyoid (strap) muscles: sternohyoid, omohyoid, sternothyroid, thyrohyoid
    • Viscera: thyroid and parathyroid glands, larynx, trachea, esophagus
    • Vessels: superior and inferior thyroid arteries; anterior jugular veins
    • Nerves: spinal root of accessory nerve; branches of the cervical plexus (muscular and cutaneous)
    • Upper part of the brachial plexus
    • Lymph nodes along the posterior border of sternocleidomastoid, supraclavicular nodes, occipital nodes

SUPRAHYOID MUSCLES

  • Four muscles lie above the hyoid bone: digastric, stylohyoid, mylohyoid, geniohyoid
  • Digastric:
    • Digastric notch on the medial surface of the mastoid process and on the inner surface of the mandible; connects to an intermediate tendon to the lesser horn of the hyoid bone
    • Nerve supply: posterior belly – facial nerve; anterior belly – nerve to mylohyoid
    • Action: depress and retract the chin; assist mouth opening
  • Stylohyoid: nerve supply – facial nerve; action – retract and raise the hyoid during swallowing
  • Geniohyoid: from genial tubercle of mandible to upper border of hyoid; nerve supply – hypoglossal (C1 fibers); action – elevate the hyoid or fix mandible during swallowing
  • Mylohyoid: from the mylohyoid line to the body of the hyoid; nerve supply – nerve to mylohyoid; action – form a mobile but stable floor and elevate tongue/hyoid during swallowing

INFRAHYOID MUSCLES

  • Four muscles below the hyoid bone: sternohyoid, omohyoid, thyrohyoid, sternothyroid
  • Sternohyoid: from the lower border of the hyoid to the sternoclavicular joint and clavicle; nerve supply – ansa cervicalis
  • Omohyoid: two bellies joined by a tendon, passes beneath SCM over carotid sheath; nerve supply – ansa cervicalis
  • Thyrohyoid: from greater horn of the hyoid to the oblique line of the thyroid cartilage; nerve supply – hypoglossal (C1)
  • Sternothyroid: from oblique line of thyroid cartilage to manubrium and first costal cartilage; nerve supply – ansa cervicalis
  • Action: depress hyoid and larynx

THYROID GLAND

  • Structure: two symmetrical lobes connected by an isthmus; lies anterior to the 2^{nd} - 4^{th} tracheal rings; covered by pretracheal fascia
  • Shape: pear-shaped with a narrower upper pole and broader lower pole; surfaces as lateral, medial, and posterior
  • Development: endodermal outgrowth from the pharynx; thyroglossal duct; foramen cecum at the junction of the posterior third with anterior two-thirds of the tongue
  • Clinical anatomy:
    • Lingual thyroid can remain at the tongue base
    • Thyroglossal cysts occur above or below the hyoid; mobile with swallowing
    • Goitre can compress trachea and recurrent laryngeal nerve
  • Blood supply and drainage: thyroid arteries (superior and inferior); veins draining into the thyroidal venous system; paracrine and parathyroid relations not shown here

PARATHYROID GLANDS

  • Four yellowish-brown ovoid glands located within the thyroid fascia in the posterior aspect of the thyroid

COMMON CAROTID ARTERY

  • Origin:
    • Right common carotid from the brachiocephalic trunk
    • Left common carotid from the arch of the aorta
  • Bifurcation: into external and internal carotid arteries at the upper border of the thyroid cartilage
  • Carotid sinus: a dilatation at bifurcation; contains baroreceptors; glossopharyngeal nerve supplies its afferents
  • Carotid body: small reddish chemoreceptor body posterior to the bifurcation
  • Notes:
    • Carotid sheath and its contents lie in the vicinity of these structures