Anatomy of the Head & Neck - Mastication, TMJ, and Swallowing PDF

title Anatomy of the head and neck – Mastication, TMJ and swallowing Anatomy of the Head & Neck Mastication, TMJ and swallowing [email protected] ANATOMY 0 Lecture outcomes Ø Describe the functional anatomy of the TMJ in terms of its bony articular surfaces and articular disc Ø List the musc...

title Anatomy of the head and neck – Mastication, TMJ and swallowing Anatomy of the Head & Neck Mastication, TMJ and swallowing [email protected] ANATOMY 0 Lecture outcomes Ø Describe the functional anatomy of the TMJ in terms of its bony articular surfaces and articular disc Ø List the muscles of mastication, describe their attachments, actions, blood and innervation Ø Describe the infratemporal fossa with the view of understanding its main contents ANATOMY 1 Mastication Ø The process of mastication is possible through movement of the lower jaw Ø This particular movement is possible due to the synovial joint between the mandible and the temporal bone Ø Movement at this joint allows the incisors to function in biting, or the molars to grind the ingested food Ø The muscles of the tongue act to place or keep the food between the molars ANATOMY 2 The temporomandibular joint (TMJ) ANATOMY 3 Mandibular movement Ø The presence of the articular disc divides the joint cavity into two and allows for six types of movement, namely lateral deviation, protrusion, retrusion, elevation and depression Gliding (deviation) Ø This takes place in the upper compartment between the moving disc and the stationary fossa Hinge (rotation) ANATOMY Ø This takes place in the lower compartment between the stationary disc and the moving condyle 4 Movements of the TMJ Lateral Excursions When these gliding and hinge movements are combined the mandible is capable of six basic movements ANATOMY 5 The infratemporal fossa Ø The infratemporal fossa is the space found posterior (behind) the maxilla and deep to both the zygomatic arch and ramus of the mandible Ø This fossa is of relevance to the muscles of mastication as it allows the passage of the temporalis and pterygoid muscles Ø It also allows the passage of the maxillary artery and pterygoid venous plexus ANATOMY 6 Neurovasculature of the muscles of mastication Ø The muscles of mastication receive blood supply from the maxillary artery, the larger of the two terminal branches from the external carotid Ø The length of this artery is subdivided* into mandibular, pterygoid and pterygopalatine (*not branched) Ø The equivalent drainage is called the pterygoid venous plexus Ø Innervation is via the anterior trunk of the mandibular nerve – the same nerve responsible for innervation of both the musculature and mucosa of the oral cavity or cheeks ANATOMY 7 Maxillary artery Temporal artery Maxillary artery External carotid ANATOMY © Visible Body Facial artery 8 Neurovasculature of the muscles of mastication (cont.) Ø The pterygoid plexus of veins is the equivalent to the maxillary artery Ø This plexus lies between the temporalis and pterygoid muscles (described later) and anastomoses with the facial vein plus the cavernous sinus Ø The facial vein then drains into the internal jugular ANATOMY 9 Muscles of mastication Ø There are 4 major masticatory muscles to learn: - Masseter - Temporalis - Medial Pterygoid - Lateral Pterygoid Ø The main goal is to understand the action of each, which may appear complicated but is very repetitive and intuitive Ø There are also a number of minor masticatory muscles e.g. the superior and inferior hyoid muscles. ANATOMY 10 Masseter muscle Ø The masseter muscles is quadrilateral in shape Ø Originates from the zygomatic bone/arch and inserts on anterior border and angle of ramus of mandible Ø Its superficial fibres run obliquely, in contrast to the deep fibres that are almost vertical in orientation Superficial fibres ANATOMY © Visible Body Deep fibres 11 Masseter muscle actions Elevation – uses both masseter muscles, enabling the teeth to be clenched Retrusion – uses the superficial fibres of both masseter muscles, retruding a protruded mandible Ipsilateral excursion – a single masseter can move the mandible to the same side ANATOMY 12 Temporalis muscle Ø Temporalis is a fan shaped muscle Ø Originates from the side of the skull (next slide) and inserts at the coronoid process of the mandible Ø The muscle arises from two heads: - the temporal bone - the temporal fascia. © Visible Body ANATOMY 13 Temporalis muscle (cont.) Ø The origin of the temporalis muscle is a complex one: 1. 2. 3. 4. 5. 6. ANATOMY Superior temporal line Inferior temporal line Temporalis fascia Zygomatic arch Frontal process of zygoma Frontal bone 14 Temporalis muscle action (on the mandible) ANATOMY Resting tonus – this muscle maintains a normal mandibular rest position when the subject is in the upright position Elevation – e.g. biting uses the fibres of both sides Retrusion – this involves the posterior horizontal fibres of both sides retruding a protruded mandible Ipsilateral excursion – using only one side the temporalis is capable of pulling the mandible to the same side. 15 Medial and lateral pterygoid muscles Ø The medial and lateral pterygoid muscles occupy the infratemporal fossa Ø To be seen a portion of the mandible has to be removed Ø The medial pterygoid is a mirror of the masseter muscle on the inner surface of the mandible ANATOMY 16 Medial and lateral pterygoid muscles (cont.) Medial pterygoid muscle ANATOMY 17 Medial pterygoid muscle actions (on mandible) Elevation – acting together, the medial pterygoid plus masseter are powerful elevators ANATOMY Protrusion – together the right and left muscles aid in protruding the jaw Contralateral excursion – the medial pterygoid from one side moves the jaw to the opposite side 18 Lateral pterygoid muscle Ø The lateral pterygoid is almost triangular in shape and is the only muscle of mastication to lie horizontally © Visible Body Superior head ANATOMY Inferior head 19 Lateral pterygoid muscle actions (on mandible) Protrusion – both sides together are prime protractors. Also the horizontal fibres pull the mandible forwards onto the articular disc. Depression – both sides together not only pull the mandible forwards but depress when combined with the hyoid muscles Contralateral excursion – one side moves the mandible in the opposite direction ANATOMY 20 Hyoid muscles Ø The supra- and infrahyoid muscles are primarily involved in swallowing and always contract bilaterally Ø The infrahyoid muscles act to depress the hyoid bone and larynx during swallowing Ø The suprahyoid muscles (form the floor of the mouth) generally act to raise the hyoid bone and the larynx when the mandible is stabilised. But can also depress the mandible when acting in conjunction with infrahyoid and lateral pterygoid muscles 1. Geniohyoid ANATOMY 2. Stylohyoid 3. Thyrohyoid 4. Sternothyroid 5. Sternocleidomastoid 6. Sternohyoid 7. Omohyoid 8. Digastric 9. Mylohyoid 21 ‘A tough act to swallow…’ Ø The incisors and canines take on small portions of solid foods into the oral cavity Ø This food is drenched with saliva from the glands that not only moistens but also contains ptyalin that breaks down the carbohydrates Ø At the same time food is broken down by mechanical action by the molars and premolars, as the mandible is opened and closed through muscle action, e.g. buccinators Ø This is assisted by the tongue that moves food towards the molars, while the cheeks stop it being forced into the vestibule Ø Lips, in turn, reduce the likelihood of the food falling out of the mouth. This is achieved by contracting the orbicularis oris muscle Ø Finally, bilateral contraction of the palatoglossus muscles narrows the oropharyngeal isthmus with the posterior part of the tongue filling the remainder of the gap. This allows breaking to continue while chewing with the mouth closed and prevent food entering the airway ANATOMY 22 Bolus formation and swallowing Bolus Formation: Ø Once sufficiently broken up the tongue gathers the food into a bolus and pushes it towards the oral pharynx by raising against the hard palate. Ø At the same time the palatoglossus muscles relax to open the oropharyngeal isthmus. Swallowing: (the following takes about 2 seconds, from the oropharynx to the stomach) Ø As the bolus reaches the oropharynx the soft palate is tensed and raised by the levator muscles Ø At the same time the superior constrictor contracts to close the nasopharynx from the oropharynx and the suprahyoid muscles contract to raise and bring the larynx forward, particularly geniohyoid and the anterior belly of digastric that sit under the tongue, forcing the epiglottis over the laryngeal opening Ø The epiglottis acts to deflect any food and drink into the piriform fossa Ø The middle and inferior constrictors then contract to push the bolus towards the oesophagus whereby, through peristalsis, the bolus is pushed towards the stomach Ø The aryepiglottic and transverse arytenoid muscles contract reducing the size of the laryngeal inlet. The vocal and vestibular folds also close. Ø Finally, once the bolus is through the muscles relax, the hyoid bone and larynx return to ANATOMY 23 their usual position and breathing can resume Swallowing Ø Swallowing starts as a voluntary movement but is mostly an involuntarily act 1. Buccal phase Compression of the bolus against the hard palate by the tongue starts the cascade of actions which are involuntary beginning with the raising of the soft palate. ANATOMY 2. Pharyngeal phase The bolus comes into contact with the pharyngeal wall. The larynx is elevated and the muscles propel the bolus towards the oesophagus. During swallowing both the intrinsic and extrinsic muscle 24 of the larynx prevent food or drink entering the glottis. Swallowing (cont.) 3. Oesophageal phase 3.1 The upper oesophageal phase Sphincter constricts and the bolus passes downwards. 3.2 The lower oesophageal phase The Sphincter relaxes to allow the bolus to enter the stomach Peristalsis drives the bolus down the oesophagus ANATOMY Constriction 25 Questions? Email: [email protected] ANATOMY 26