Parotid gland and temporal region

• Parotid gland

  •Salivary gland –serous acini only

  •CT capsule and dense fibrous capsule that extends as stylomandibular ligament  (intervenes between parotid and submandibular salivary gland)

  •May be accessory tissue

  •Single duct 1 finger’s breadth below zygomatic arch

  The parotid gland sits on the lateral surface of the face (one each side) passing from near the external auditory meatus inferiorly towards the mandible. It varies in size and shape to a large degree between individuals.

  
• Parotid duct

  Sharp, medial turn to pierce buccal fat pad and buccinator to enter oral cavity at upper second molar

  Duct palpable if tense masseter muscle

  The duct turns to pierce buccinator (a muscle of fascial expression that forms the lateral walls of the oral cavity) and enter the mouth  and release saliva near the upper second molar. The parotid gland is supplied with parasympathetic secretomotor innervation by the glossopharyngeal nerve (CN IX).

  
• Facial nerve (CN VII)

  The facial nerve exits the skull via the stylomastoid and passes into the gland. It divides the gland into a superficial and deep part before dividing into branches that leave the gland and pass across the face to supply the muscles of facial expression.

  
• Facial nerve

  The temporal, zygomatic, buccal, marginal mandibular and cervical branches are said to spread across the face. The posterior auricular branch passes posterior to the auricle (external ear or pinna) to supply the posterior belly of occipitofrontalis a muscle of the scalp that is also classed as a muscle of facial expression.

  
• Other structures

  Deep to the facial nerve, lie two blood vessels. The superficial temporal vein drains the scalp and joins with the maxillary vein to form the retromandibular vein within the parotid gland. The external carotid artery enters the gland and divides to form its terminal branches – the superficial temporal artery that supplies the scalp and the maxillary artery that passes into the infratemporal fossa. The deepest structure in the gland is the auriculotemporal nerve, a branch of the trigeminal nerve that runs with the superficial temporal vessels.

  
• structures related to the parotid gland.

  ECA – forms superficial temporal and maxillary arteries

  Retromandibular vein = union of superficial temporal and maxillary veins

  
• Nerve supply to the parotid gland

  -Parasympathetic secretomotor supply from glossopharyngeal nerve (CN IX)

  -Postganglionic sympathetic fibres from plexus around ECA

  The secretomotor parasympathetic nerves that supply the parotid gland are from the glossopharyngeal nerve (CN IX).

  The trigeminal nerve (CN V) supplies sensory innervation to the face so does have branches that pass onto the face.

  
• Nerve supply to the parotid gland

  The glossopharyngeal nerve exits the skull via the jugular foramen, as it does this, some preganglionic parasympathetic nerve fibres leave the main part of the nerve to form a tympanic part that passes into a plexus in the middle ear. From this plexus, a nerve called the lesser petrosal nerve is formed that joins a structure called the otic ganglion that lies at the opening of the foramen ovale.

  
• Nerve supply to the parotid gland

  In this ganglion the pre-ganglionic nerves from the glossopharyngeal nerve synapse with postganglionic parasympathetic nerves which are then carried by the auriculotemporal nerve (a branch of the trigeminal nerve). This carries the parasympathetic innervation into the deep part of the parotid gland

  
• Lymphatics

  The parotid gland has lymph nodes that drain the gland and also part of the forehead and orbital region.

  
• Muscles of mastication

  •Four – temporalis, masseter, medial pterygoid and lateral pterygoid

  •All innervated by the mandibular division of trigeminal (CN V3)

  •Movements of the mandible – elevation, depression, protrusion, retrusion and lateral sliding

  •Depression may be by gravity or against force using supra-hyoid muscles
• Temporalis

  •Covered by temporal fascia

  •Temporal fossa and fascia to coronoid process and anterior border of the ramus of the mandible

  •Anterior and superior fibres elevate mandible

  •Posterior fibres retract mandible

  •Deep temporal nerves (x2) from anterior division of mandibular division of trigeminal nerve (CN V3)

  Temporalis is the largest muscle of mastication

  
• Masseter

  •Zygomatic arch to the lateral aspect of the ramus of the mandible

  •Elevate mandible

  •Masseteric nerve from anterior division of CN V3

  
• Lateral pterygoid

  •Upper head from infratemporal surface of greater wing of sphenoid

  •Lower head from lateral surface of the lateral pterygoid plate

  •Inserts into neck of mandible and articular disc

  •Pulls neck of mandible forwards with articular disc (protrusion = both)

  •Helps in lateral chewing movements with medial pterygoid (one side)

  •Nerve to lateral pterygoid – anterior division of CNV3

  
• Medial pterygoid

  •Superficial head from the tubercle of the maxilla

  •Deep head from the medial surface of the lateral pterygoid plate

  •Inserts into the medial surface of the angle of the mandible

  •Assists in elevation

  •Nerve to medial pterygoid from the main trunk of the mandibular division of the trigeminal nerve (CNV3)

  
• Movements of the mandible

  •Elevation  = head of mandible and disc move backward and head rotates on lower surface of disc – temporalis, masseter and medial pterygoid

  •Depression = head of mandible rotates on undersurface of articular disc and mandible is pulled forward - lateral pterygoid, digastric, geniohyoid, mylohyoid, gravity

  •Protrusion = articular disc and head of mandible move forward. Movement in upper part of cavity - lateral pterygoid (medial pterygoid assists)
• Movements of the mandible

  •Retrusion = articular disc and head of mandible pulled backward into mandibular fossa – posterior fibres of temporalis

  •Lateral chewing = protrusion and retrusion combined - pterygoids
• Mandibular division of trigeminal nerve (CNV3)

  The trigeminal nerve has three main divisions – ophthalmic, maxillary and mandibular. The ophthalmic and maxillary divisions are purely sensory and only the mandibular division caries both sensory and motor fibres. The mandibular division of the trigeminal nerve passes through the foramen ovale and divides into branches. The posterior division is usually larger than the anterior division.

  
• CN V3 carrier

  •Part of nerve to medial pterygoid passes through the otic ganglion. No synapse – pass to tensor veli palatini and tensor tympani

  •Auriculotemporal nerve carries postganglionic parasympathetic fibres from the otic ganglion to the parotid. Fibres originate in CN IX glossopharyngeal

  •Lingual nerve joined by the chorda tympani carrying parasympathetic fibres from the facial nerve to the submandibular (ganglion) and sublingual glands. Taste fibres from the anterior two thirds of the tongue
• External carotid artery (ECA)

  Most of the blood supply to the head and neck is from branches derived from the carotid arteries. Some vessels such as the vertebral arteries that supply the brain are branches of the subclavian artery instead. The common carotid artery divides to form the internal carotid and the external carotid arteries. The external carotid artery forms anterior, posterior, ‘deep’ and terminal branches.

  
• Posterior branches of ECA

  •Occipital – close to origin of facial artery, crossed by the hypoglossal nerve. Passes under the posterior belly of digastric to enter the posterior triangle. Back of scalp

  •Posterior auricular – level of upper border of belly of digastric. Scalp

  •From ‘deep surface’ of carotid = ascending pharyngeal. Ascends between internal carotid and pharynx. Branches to pharynx

  
• Anterior branches of ECA

  •Superior thyroid – near origin, runs with external laryngeal nerve. Branch to SCM and superior laryngeal artery

  •Lingual – opposite tip greater cornu of hyoid bone, passes deep to hyoglossus, crossed by the hypoglossal nerve. Oral cavity

  •Facial – above tip of greater cornu, passes deep to posterior belly of digastric. Superior and inferior labial branches and angular artery to face

  
• Terminal branches of ECA

  •Superficial temporal – smaller branch, ascends in front of the auricle, divides into anterior and posterior branches which supply the skin over the frontal and temporal regions

  •Maxillary – arises behind neck of mandible, branches to muscles of mastication, tympanic membrane, upper and lower teeth, palate, nasal cavity, nasopharynx and meninges

  The external carotid artery ends in the parotid gland as the superficial temporal artery and the maxillary artery. The superficial temporal artery supplies the lateral side of the face and the scalp.

  
• ECA