Lecture 25: Gross Anatomy - Neck Triangles PDF

Lecture 25: Gross Anatomy - Neck Triangles Neck: Superior border: inferior margin of mandible (anterior), base of skull (posterior) Inferior border: top of sternum → clavicle → adjacent acromion (anterior), approximate line from acromion to spinous process of CVII (posterior) Functions: position &...

Lecture 25: Gross Anatomy - Neck Triangles Neck: Superior border: inferior margin of mandible (anterior), base of skull (posterior) Inferior border: top of sternum → clavicle → adjacent acromion (anterior), approximate line from acromion to spinous process of CVII (posterior) Functions: position & support head, passage of major vessels & nerves, connect oral cavity to esophagus (pharynx), connect nasal cavity to trachea (larynx) Cervical vertebrae: atlas (C1), axis (C2), & others (C3-C7); features = small body (except C1), bifid spinous process (except C1); transverse process w/ foramen (for passage of vertebral aa. & vv.); unique articulation w/ C2 & occipital bone of skull (C1) Hyoid bone: interface b/w floor of oral cavity (sup.), larynx (inf.), pharynx (post.); serves as anchor Vertebral compartment: encloses C vertebrae, spinal cord, CN, & associated postural muscles Visceral compartment: wraps around glands (thyroid and parathyroid), & parts of the respiratory & digestive tracts that pass b/w the head & thorax (larynx & pharynx) Vascular compartments: one on each side; contain the major blood vessels & vagus nerve (CN X) Superficial fascia: LCT which contains a thin sheet of platysma m. Deep cervical fascia: wraps around to delineate compartments w/in neck Investing layer: surrounds all structures in the neck; splits to enclose SCM, trap, & infra/supra-hyoid mm. Prevertebral layer: surrounds vertebral column & the deep muscles of the back; splits b/w transverse processes → anterior part = alar fascia Pretracheal layer: encloses the viscera of the neck; buccopharyngeal fascia (post. part) encloses pharynx & esophagus Carotid sheaths: surround the major NVBs on either side of the neck; very thick Pretracheal space: b/w the investing & pretracheal layers of the deep cervical fascia; passes b/w neck & ant. part of sup. mediastinum Retropharyngeal space: b/w buccopharyngeal & prevertebral fascia; extends from base of skull to upper part of posterior mediastinum Prevertebral space: a longitudinal space filled w/ LCT b/w the 2 layers of prevertebral fascia; extends from the base of the skull through the posterior mediastinum to the diaphragm Fascial spaces (CC): provide a conduit for the spread of infections from neck to mediastinum Structures in superficial fascia: Platysma m.: large, thin sheet of muscle in superficial fascia of neck; superficial fascia of upper thorax → mandible & muscles around mouth; functions to tense skin of neck & pull lips down; innervated by CN VII External jugular v.: formed post. to angle of mandible by post. auricular v. & retromandibular v.; courses downward superficial to SCM; pierces investing layer to join subclavian v. at inf. aspect of SCM Anterior jugular v.: variable & inconsistent; begin as small veins which come together around hyoid bone & extend inferiorly, connecting at jugular venous arch; join subclavian v. directly or join ext. jugular v.  Posterior triangle: Boundaries: post. border of SCM (ant.), ant. border of trapezius (post.), middle ⅓ of clavicle (inf.), investing layer of deep cervical fascia (roof), muscles of neck in prevertebral fascia (floor) Muscle Origin Insertion Action Innervation Sternocleidomastoid Sternum and clavicle mastoid process and superior tilts and rotates the head, and CN XI with proprioception nuchal line of skull pulls it forward when both from ant. rami of C2-C3 contract Trapezius sup. nuchal line, ext. occipital lat. ½ of clavicle, acromion, & Rotates, elevates, retracts and CN XI w/ proprioception from protuberance, ligamentum nuchae, & spine of scapula depresses scapula ant. rami of C3-C4 spinous processes of C7-T12 Lesser occipital n. (C2): ascends along the posterior border of the SCM & distributes to the skin of the neck & scalp posterior to the ear Great auricular n. (C2 & C3): emerges from post. border of SCM & ascends across the muscle to the base of the ear, supplying the skin of the parotid region, ear, & mastoid area Transverse cervical n. (C2 & C3): passes around the midpart of the SCM & continues horizontally across the muscle to supply the lateral and anterior parts of the neck Supraclavicular nn. (C3 & C4): a group of cutaneous nerves; after emerging from beneath the posterior border of SCM, descend & supply the skin over the clavicle & shoulder as far inferiorly as rib II Accessory n. (CN XI): exits cranium through jugular foramen → passes deep to or through SCM, innervating it → extends obliquely downward w/in investing layer → reaches trapezius from deep surface ​ CC: superficial location as it crosses posterior triangle makes it susceptible to injury Anterior triangle: bounded by ant. edge of SCM (post.), inf. edge of mandible (sup.), neck midline (med.) Submandibular triangle: bounded by inf. border of mandible (sup.), digastric m. (ant./post.), investing layer of deep cervical fascia (roof), mylohyoid & hypoglossus mm. (floor) Submandibular gland: large salivary gland “hooked” around free post. margin of mylohyoid m. Facial a.: courses through or deep to submandibular gland & emerges anteriorly (v. posses superficial to submandibular gland & emerges more posteriorly) Submental triangle: bounded by hyoid bone (inf.), ant. belly of digastric m. (lat.), neck midline (med.) Muscular triangle: bounded by hyoid bone (sup.), sup. belly of omohyoid & ant. border of SCM (lat.) Muscle Origin Insertion Action Innervation Omohyoid: inf. belly passes Inferior belly: sup. border Inferior belly: depress hyoid bone ansa cervicalis (ant. rami through post. triangle; sup belly. of scapula intermediate tendon of C1-C3) divides musc. & vasc. triangles in Superior belly: Superior belly: inf. border ant. triangle intermediate tendon of hyoid, lat. to sternohyoid m. Sternohyoid post. part of body of hyoid, med. to depresses hyoid bone after ansa cervicalis sternoclavicular joint omohyoid swallowing Thyrohyoid: deep to sup. parts of oblique line of thyroid greater horn & adjacent fixed thyroid c. → depresses n. to thyrohyoid m. (ant. omohyoid & sternohyoid cartilage body of hyoid bone hyoid; fixed hyoid → raises ramus of C1 that travels larynx w/ hypoglossal n.) Sternothyroid: deep to sternohyoid post. surface of sternal oblique line of thyroid draws the larynx (thyroid ansa cervicalis m. manubrium cartilage cartilage) downward Suprahyoid muscles: Muscle Origin Insertion Action Innervation Stylohyoid Base of styloid process Lat. body of hyoid by Pulls hyoid posterosuperiorly Facial n. (CN VII) straddling int. tendon during swallowing (digastric) Digastric Posterior belly: mastoid Intermediate tendon, attached mandible fixed → raises Posterior belly: facial n. (CN notch to body of hyoid hyoid; hyoid fixed → opens VII) Anterior belly: digastric mouth by lowering mandible Anterior belly: V3 of CN V via fossa on inf. mandible inf. alveolar n. Mylohyoid Mylohyoid line on med. body Hyoid bone & muscle on Forms floor of mouth Inferior alveolar branch of V3 of mandible opposite side (supports & elevates) & elevates hyoid Geniohyoid: deep to Inf. mental spine on inner Ant. surface of body of hyoid mandible fixed → elevates Ant. ramus of C1 (travels w/ mylohyoid mandible hyoid; hyoid fixed → pulls CN XII) mandible down- & in- ward Mandible: be familiar w/ mylohyoid line, inf. mental spine (genial tubercles), & digastric fossa Thyroid cartilage: be familiar w/ R/L lamina (sides), sup. horns, inf. horns, oblique line Temporal bone: be familiar w/ mastoid process & styloid process Carotid triangle: Carotid sheath: thick fascia which encloses the vascular compartment of the neck Common carotid a.: bifurcates w/in the sheath to give rise to external & internal carotid a. (gives no branches in neck, runs posterior to ECA, enters cranial cavity through carotid canal in temporal bone) External carotid a.: supplies most tissues of the head/neck region, gives several branches… 1.​ Sup. thyroid a.: 1st branch, arises anteriorly & passes downward & forward to supply the thyroid gland, thyrohyoid m., internal structures of larynx, SCM, & cricothyroid mm. 2.​ Ascending pharyngeal a.: 2nd branch; arises posteriorly & supplies pharyngeal constrictors & stylopharyngeus m., palate, tonsil, pharyngotympanic tube, meninges in post. cranial fossa 3.​ Lingual a.: arises anteriorly, passes deep to CN XII & b/w middle constrictor & hyoglossus mm.; supplies tongue mm., palatine tonsil, soft palate, epiglottis, floor of mouth, sublingual gland 4.​ Facial a.: 3rd ant. branch, passes deep to stylohyoid & post. digastric mm → continues b/w submandibular gland & mandible → emerges over edge of mandible ant. to masseter m. to enter face; supplies face (b/w inf. mandible med. to masseter m. & medial corner of eye), soft palate, palatine tonsil, pharyngotympanic tube, & submandibular gland 5.​ Occipital a.: arises posteriorly → passes sup/post-eriorly deep to post. belly of digastric m → emerges on post. scalp; supplies SCM, meninges, mastoid cells, deep mm. of back, post. scalp 6.​ Post. auricular a.: small posterior branch which supplies parotid gland & nearby muscles, external ear & scalp post. to ear, middle & inner ear structures 7.​ Superficial temporal a.: posterior terminal branch (not seen in dissection of neck) 8.​ Maxillary a.: larger, anterior terminal branch (not seen in dissection of neck) Internal jugular v.: main drainage of head & neck region; sigmoid sinus → joins inf. petrosal sinus → exits skull via jugular foramen → travels interiorly in carotid sheath → joins subclavian v. 1.​ Major branches: facial, lingual, pharyngeal, occipital, sup. thyroid, & middle thyroid 2.​ Central venous access (CC): IJV often use to place large-bore catheters for dialysis, parenteral nutrition, & administration of drugs that have a tendency to induce phlebitis 3.​ Jugular venous pulse (CC): a clinical sign that reflects the function of the right side of the heart Hypoglossal n. (CN XII): appears in anterior triangle as it passes forward, hooking around the occipital, int. carotid, ext. carotid, & lingual aa. → passes deep to post. belly of digastric & stylohyoid mm. → passes over surface of hyoglossus m. & disappears deep to mylohyoid m. → supplies tongue Nerve to thyrohyoid m.: from spinal n. C1, travels w/ CN XII but is not a branch of CN XII Ansa cervicalis: loop of nerves that innervate omohyoid, sternohyoid, & sternothyroid mm. 1.​ Superior root: mainly fibers from C1, travels w/ CN XII for a short while, then runs downward on ant. side of carotid sheath b/w common/internal carotid a. & internal jugular v. 2.​ Inferior root: from anterior rami of C2 & C3, passes around lateral side of carotid sheath & joins superior root to form a loop Carotid sinus: sensor for blood pressure; located at beginning of int. carotid a., innervated by CN IX ​ Spontaneous syncope (CC): can be caused by a hypersensitive carotid sinus Carotid body: sensor for blood chemistry (O2); same location as sinus, innervated by CN IX & CN X Hyperplastic tumors (CBTs; CC): chronic hypoxic conditions can overburden carotid bodies –. hypertrophy, hyperplasia, & neoplasia of chief cells (seen in CBTs) Branches of vagus n. (CN X): sup. laryngeal n. divides into internal & external branches, travels medial to carotid sheath; internal passes through thyrohyoid membrane to innervate (sensory) mucosa of larynx above vocal cord; external innervates (motor) cricothyroid m. & part of inferior pharyngeal constrictor m. ​ Pharyngeal branch: motor branch to pharynx Facial n. (CN VII): innervates post. belly of digastric, stylohyoid, & part of platysma m. Glossopharyngeal n. (CN IX): innervates carotid body & sinus Transverse cervical n.: branch of cervical plexus from ant. rami of C2-C3, provides cutaneous innervation to this area Lymphatic drainage: Superficial nodes around the head: occipital, mastoid (retro-auricular & posterior auricular), preauricular, parotid, submandibular, & submental nodes Superficial cervical nodes: lie along the external jugular vein Deep cervical nodes: form a chain along the internal jugular v., include the jugulodigastric node & jugulo-omohyoid node Cervical lymphadenopathy (CC): enlargement of neck lymph nodes, often caused by a disease occurring in the head/neck; soft/tender suggests acute inflammatory process, firm/rubbery multinodular large nodes suggest lymphoma