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TSM33: NECK AND PHARYNX 16/10/08 LEARNING OUTCOMES Describe the basic anatomy of the neck and pharynx The anterior neck can be divided into two regions: o Anterior triangle – between the two sternocleidomastoid muscles down to the sternum o Posterior triangle – between sternocleidomastoid and trapezius (little clinical significance) The pharynx can be divided into three regions: o Nasopharynx – from the posterior nares to the soft palate o Oropharynx – from the soft palate to the superior margin of the epiglottis o Laryngopharynx – from the superior margin of the epiglottis to the oesophagus Describe the clinical anatomy of the neck CERVICAL FASCIA AND COMPARTMENTS The neck contains unique sheets of cervical fascia arranged in various fascial layers: o Superficial fascia – surrounds anterior neck; innervated by facial nerve (CNVII) o Deep fascia – surrounds rest of the neck; several different layers: Investing layer – surrounds all structures within the neck Carotid sheaths – laterally; surround the neurovascular components Pre-tracheal layer – ventrally; surrounds the viscera Pre-vertebral layer – dorsally; surrounds the vertebrae and associated muscles These fascia enclose four distinct longitudinal compartments within the neck: o Vascular – two bilaterally; covered by carotid sheath Contain the internal jugular vein, common carotid artery and vagus nerve o Visceral – ventrally; covered by pre-tracheal fascia Contains the pharynx, larynx, trachea, oesophagus and thyroid gland o Vertebral – dorsally; covered by pre-vertebral fascia Contains the vertebral column and associated deep muscles MUSCLES There are two important sets of muscles in the neck – the suprahyoid and infrahyoid (strap) Supra-hyoid – includes mylo- and geniohyoid (see TSM31 - Mouth and Tongue) o Digastric – two ‘bellies’; both insert around a looped tendon on the medial hyoid Anterior belly arises from the mandible; innervated by nerve to mylohyoid (of V3) Posterior belly arises from the mastoid process; innervated by facial nerve (CNVII) o Stylohyoid – arises from the base of the styloid process and inserts onto the lateral hyoid Innervated by the facial nerve (CNVII) o Generally these muscles depress the mandible or raise the hyoid depending which is fixed Infra-hyoid – strap muscles; all innervated by C1-C3 via ansa cervicalis o Omohyoid – most superficial, from the scapula to the lateral hyoid; crosses the carotid sheath o o o o Sternohyoid – long thin muscle, from the sternum to the hyoid Thyrohyoid – deeper muscle, from the inferior margin of the thyroid cartilage to the hyoid Sternothyroid – deepest, from the medial sternum to the inferior thyroid cartilage These muscles either depress the hyoid or fix the hyoid so that the supra-hyoids can act BRANCHES OF THE EXTERNAL CAROTID ARTERY The common carotid artery ascends the neck bifurcating at the superior margin of thyroid cartilage o The internal carotid artery gives off no branches in the neck and ascends to the skull The external carotid artery gives off numerous branches as it ascends the neck: o Superior thyroid – descends from the bifurcation to supply the superior thyroid o Ascending pharyngeal – small posterior branch supplying (around) the pharynx o Lingual – anterior branch to the tongue with the lingual nerve and submandibular duct o Facial – supplies the front of the face, soft palate, submandibular glands o Occipital – posterior branch, ascends to supply the posterior scalp o Posterior auricular – small branch supplying (around) the ear and parotid glands The external carotid artery terminates in the parotid gland bifurcating into two terminal branches: o Superficial temporal – supplies the parotid gland, lateral face and temple region o Maxillary – larger branch, supplies numerous structures around the maxilla and mandible Describe the clinical anatomy of the pharynx CONSTRICTOR MUSCLES The pharynx is a muscular semicircular tube that extends from the base of the skull to the oesophagus Three overlapping constrictor muscles with internal mucous linings make up the pharyngeal walls: o Superior constrictor – from the pterygomandibular raphe to the pharyngeal tubercle o Middle constrictor – from the hyoid bone o Inferior constrictor – from the thyroid cartilage These muscles are effectively suspended from the base of the skull at the pharyngeal tubercle o They are all continuous posteriorly and meet along the pharyngeal raphe o They are all innervated by branches of the vagus nerve (CNX) o Anteriorly they are paired with lateral openings between them o In swallowing they contract in a supero-inferior sequence to propel food to the oesophagus LONGITUDINAL MUSCLES Along with the constrictors there are three longitudinal muscles that contribute to the laryngeal wall: o Stylopharyngeus – from the styloid process; innervated by the glossopharyngeal nerve (CNIX) o Salpingopharyngeus – from the auditory tube; innervated by the vagus nerve (CNX) o Palatopharyngeus – from the palatine aponeurosis; innervated by the vagus nerve (CNX) These muscles all act to elevate the pharynx - salpingopharyngeus also facilitates pressure equalisation between the oropharynx and middle ear