Anterior Triangle.txt

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emm64
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Anterior Triangle.txt
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2011-11-09 18:37:07
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Anterior Traingle Anatomy HN
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Anterior Triangle HN
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  1. Anterior Triangle Boundaries
    • midline
    • anterior margin of sternocleidomastoid
    • inferior margin of the mandible (superiorly).
  2. Hyoid bone
    • superior to the larnyx
    • attached to other structures by muscles and membranes
    • corresponds to vertebral levels C3-4.
  3. Thyroid cartilage
    • lies inferior to the hyoid bone and superior to the cricoid cartilage
    • protects laryngeal structures and forms the laryngeal prominence (or “Adam’s Apple)
    • thryohyoid membrane attaches from the thyroid cartilage to the hyoid bone
    • corresponds to vertebral levels C4-5 and is also at the level of the bifurcation of the common carotid artery
  4. Cricoid cartilage
    • inferior to the thyroid cartilage
    • cricothryoid membrane attaches from the cricoid cartilage to the thryoid cartilage
    • corresponds to vertebral level C6
    • At this level, the pharynx becomes the esophagus and the larynx becomes the trachea.
  5. Trachea
    • lies inferior to the cricoid cartilage
    • portion of the trachea superior to the thoracic inlet corresponds to vertebral levels C7-T1.
  6. Muscular Triangle Boundaries
    • midline
    • superior belly of the omohyoid
    • anterior margin of the sternocleidomastoid
  7. Muscular Triangle Contents
    • 4 infrahyoid or strap muscles (omohyoid, sternohyoid, sternothyroid, and thryohyoid)
    • anterior jugular vein
    • thyroid gland
    • larynx
    • trachea
  8. Infrahyoid muscles
    • attach to the hyoid bone inferiorly and are arranged into superficial and deep layers.
    • The superficial layer contains the omohyoid (laterally) and sternohyoid (medially).
    • The deep layer contains the sternothyroid (inferiorly) and thyrohyoid (superiorly).
    • These muscles, in general, act to depress the hyoid bone during swallowing and speaking.
    • They are all innervated by the ansa cervicalis except for the thryohyoid which is innervated by C1 via the hypoglossal nerve.
  9. Thyroid gland
    • highly vascular endocrine organ
    • secretes hormones which are needed for proper growth and development and which are primarily responsible for determining the basal metabolic rate (BMR).
    • right and left lobe connected by an isthmus
    • isthmus is anterior to the 2nd and 3rd tracheal rings
    • pyramidal lobe may sometimes be present extending from the isthmus region superiorly along the midline
    • supplied by the superior thyroid artery (a branch of the external carotid artery) and the inferior thyroid artery (a branch of the thyrocervical trunk of the subclavian artery).
    • drained by the superior thyroid and middle thyroid veins (tributaries of the internal jugular vein) and the inferior thyroid vein (a tributary of the brachiocephalic vein).
  10. Parathyroid glands
    • usually four parathyroid glands on the posterior surface of the thyroid gland lobes
    • secrete parathormone which is concerned with the metabolism of calcium and phosphorus
    • supplied by the inferior thyroid arteries.
    • Loss of the parathyroid glands results in hypocalcemia which can lead to tetany (muscle spasms).
  11. hypocalcemia
    Loss of the parathyroid glands results in hypocalcemia which can lead to tetany (muscle spasms)
  12. Recurrent laryngeal nerve
    ascends in a groove formed between the trachea and esophagus on its way toward the larynx where it will innervate most of the laryngeal muscles
  13. Carotid Triangle Boundaries
    • superior belly of the omohyoid
    • sternocleidomastoid
    • posterior belly of the digastric
  14. Carotid Triangle Contents
    • carotid sheath structures (common carotid artery, internal jugular vein, and the vagus nerve)
    • hypoglossal nerve
    • accessory nerve
    • ansa cervicalis
    • external carotid artery branches
    • superior laryngeal nerve and its branches
  15. Carotid sheath
    • fascial sheath that surrounds
    • common carotid artery (medially)
    • internal jugular vein (laterally)
    • vagus nerve (CN X) (posteriorly)
    • Embedded within the carotid sheath is the ansa cervicalis.
    • The carotid sheath is formed from a combination of investing fascia, pretracheal fascia, and prevertebral fascia.
  16. Hypoglossal nerve (CN XII) relations
    • Carotid Triangle
    • lies lateral to the carotid sheath and is related to the inferior margin of the posterior belly of the digastric
    • hooks around the occipital branch of the external carotid artery and then travels anteriorly into the submandibular triangle and lies between the hyoglossus and mylohyoid muscles
    • innervates most all of the tongue muscles.
    • Hitchhiking along the hypoglossal are motor fibers from C1 which leave the hypoglossal nerve to innervate the thyrohoid muscle.
  17. Accessory nerve (CN XI) relations
    • Carotid Triangle
    • spinal portion of the accessory nerve passes inferiorly between the posterior belly of the digastric and the internal jugular vein.
    • sends a branch to innervate the sternocleidomastoid before continuing across the posterior triangle towards the trapezius.
  18. Ansa cervicalis
    • Carotid Triangle
    • loop-like nerve structure formed by ventral rami fibers from C1-C3
    • has an inferior and superior root
    • upplies all the strap muscles (omohyoid, sternohyoid, and sternothyroid) except one – the thyrohyoid (innervated by C1 via hypoglossal).
    • part of the cervical nerve plexus.
  19. Cervical Plexus
    • comprised of ventral rami nerves of C1-C4.
    • comprised of cutaneous branches (transverse cervical, great auricular, lesser occipital, and supraclavicular nerves), the ansa cervicalis, the phrenic nerve (C3,4,5), and branches to prevertebral muscles.
    • You only see part of this plexus in your dissections.
  20. Common carotid artery (Carotid Triangle)
    • bifurcates into the internal and external carotid arteries.
    • internal carotid artery has no branches in the neck. It enters the cranium through the carotid canal, gives off the opthalmic artery (which accompanies the optic nerve through the optic canal into the orbit), and helps to form the Circle of Willis to supply the brain.
  21. carotid sinus
    • expansion of the internal carotid artery near its origin is called “the carotid sinus”
    • baroreceptor which responds to changes in blood pressure.
    • carotid sinus is mainly innervated by VA fibers of CN IX
  22. carotid body
    • A small mass of tissue near the bifurcation of the common carotid artery
    • chemoreceptor which responds to changes in the chemical composition of blood
    • mainly innervated by VA fibers of CN X.
  23. External carotid artery
    • 6 branches in the neck and 2 terminal branches to the head
    • from inferior to superior, these branches are:
    • a. superior thyroid artery – 1st branch; goes to the superior aspect of the thyroid gland.
    • b. ascending pharyngeal – 2nd branch; originates off the external carotid artery near the bifurcation of the common carotid; ascends medially toward the lateral aspect of the pharynx to the base of the skull.
    • c. lingual artery – 3rd branch; is usually crossed superficially by the hypoglossal nerve; travels deep to the hyoglossus muscle to enter the oral cavity; may come off a common trunk with the facial artery.
    • d. facial artery – 4th branch; lies deep to the submandibular gland as it crosses the body of the mandible and then heads toward the angle of the eye and nose.
    • e. occipital artery – 5th branch; is crossed by the hypoglossal nerve and is related to the inferior margin of the posterior belly of the digastric. It ascends to the occipital region.
    • f. posterior auricular artery – 6th branch; is related to the superior margin of the posterior belly of the digastric. It ascends to the region posterior to the external acoustic meatus.
    • g. maxillary artery – is one of the two terminal branches; it is related to the neck of the mandible where it travels deeply into the infratemporal fossa area.
    • h. superficial temporal artery – is one of the two terminal branches; it passes through the parotid gland superiorly, anterior to the ear to the lateral temporal region. The transverse facial artery is one of its branches.
  24. Superior laryngeal nerve
    • branch of the vagus which originates off the inferior vagal ganglion located at the superior end of the carotid triangle deep to the internal carotid artery.
    • not usually seen in dissection
    • gives rise to two branches: the external laryngeal nerve which innervates the cricothyroid muscle and the internal laryngeal nerve which pierces the thyrohyoid membrane to innervate the internal aspect of the laryngeal mucosa. These branches may be seen in dissection.
  25. Submandibular (Digastric) Triangle (paired) Boundaries
    • inferior margin of the mandible
    • posterior & anterior bellies of the digastric
    • floor of the submandibular triangle is formed by the hyoglossus and mylohyoid muscles
    • Note: The stylohyoid muscle belly lies immediately superior to the posterior belly of the digastric and its tendon splits as it attaches to the hyoid bone to allow the tendon of the posterior belly of the digastric to pass through. Both the posterior belly of the digastric and the stylohyoid muscles are innervated by the facial nerve.
  26. Submandibular (Digastric) Triangle Contents
    • submandibular gland
    • facial artery and facial vein
    • hypoglossal nerve (CN XII)
    • submandibular lymph nodes
  27. Submandibular gland
    • one of the three salivary glands (along with the parotid gland and sublingual gland).
    • innervated by secretomotor parasympathetic fibers from the submandibular ganglion.
    • has superficial and deep parts.
    • The superficial part occupies most of the submandibular triangle.
    • The deep part is deep (or superior) to the mylohyoid muscle in the oral cavity.
    • The deep part of the gland has a duct – the submandibular duct (Wharton’s Duct).
    • The blood supply to the gland is by the facial artery.
  28. Facial artery
    • branch of the external carotid artery
    • courses deep to the superficial part of the submandibular gland as it crosses the body of the mandible and crosses the face toward the angle of the eye and nose
    • facial artery will give off a superior labial artery to the upper lip and an inferior labial artery to the lower lip
  29. Facial vein
    • begins at the angle of the eye and nose and descends across the face crossing the body of the mandible and crossing the superficial part of the submandibular gland superficially
    • drains into the internal jugular vein.
  30. Hypoglossal nerve
    • enters the submandibular triangle deep to the posterior belly of the digastric and then courses anteriorly superficial to the hyoglossus and deep to the mylohyoid
    • innervates most of the muscles of the tongue
  31. Submandibular lymph nodes
    along with the submental lymph nodes are called “the dental nodes” because they drain lymph from the oral cavity. Infection of the oral cavity may cause them to become inflamed.
  32. Submental Triangle (unpaired) Boundaries
    • hyoid bone
    • two anterior bellies of the digastric muscles
    • floor is the mylohyoid muscle.
  33. Submental Triangle Contents
    • submental lymph nodes which, along with the submandibular lymph nodes, drain lymph from the oral cavity.
    • mylohyoid nerve, which innervates the anterior belly of the digastric and mylohyoid, may be found on the surface of the mylohyoid muscle.
  34. Digastric
    • Suprahyoid Muscles
    • Attach: posterior belly - from the mastoid process of the temporal bone
    • anterior belly - from the digastric fossa on the inner lower anterior mandibular margin
    • both bellies - attach via a tendon which perforates the stylohyoid muscle to the greater horn of the hyoid bone.
    • Nerve: anterior belly – mylohyoid nerve (branch of V3), posterior belly – facial nerve (CN VII)
    • Action: elevates the hyoid bone and opens the jaw.
  35. Sylohyoid
    • Suprahyoid Muscles
    • Attach: styloid process of temporal bone; body of hyoid bone
    • Nerve: facial nerve (CN VII)
    • Action: elevates the hyoid bone and draws it posteriorly
  36. Mylohyoid
    • Suprahyoid Muscles
    • Attach: mylohyoid line of mandible; body of hyoid bone and midline raphe
    • Nerve: mylohyoid nerve (branch of V3)
    • Action: elevates the hyoid bone (and tongue) during swallowing
  37. Geniohyoid
    • Suprahyoid Muscles
    • Attach: genial tubercles on inner anterior surface of mandible
    • Nerve: C1 via hypoglossal nerve (CN XII)
    • Action: assists the action of the mylohyoid muscle
  38. Omohyoid
    • Infrahyoid (Strap) Muscles
    • Attach: superior margin of scapula; body of hyoid bone
    • Nerve: ansa cervicalis
    • Action: depresses the hyoid bone during swallowing and speaking
  39. Sternohyoid
    • Infrahyoid (Strap) Muscles
    • Attach: manubrium of sternum; body of hyoid bone
    • Nerve: ansa cervicalis
    • Action: depresses the hyoid bone during swallowing and speaking
  40. Sternothyroid
    • Infrahyoid (Strap) Muscles
    • Attach: 1st costal cartilage & manubrium of sternum; thyroid cartilage
    • Nerve: ansa cervicalis
    • Action: depresses the thyoid cartilage & larynx during swallowing and speaking
  41. Thyrohyoid
    • Infrahyoid (Strap) Muscles
    • Attach: thyroid cartilage; greater horn of hyoid bone
    • Nerve: C1 via hypoglossal nerve (CN XII)
    • Action: depresses the hyoid bone during swallowing and speaking

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