جامعة تكريت كلية طب االسنان التشريح مادة املرحلة الثانية أ.م.د. بان امساعيل صديق 6102/6102
Parotid region The part of the face in front of the ear and below the zygomatic arch is the parotid region. The principal features are the parotid gland and the masseter muscle. Masseter This muscle of mastication arises from the lower border of the zygomatic arch and is inserted into almost the whole of the lateral surface of the mandibular ramus. Most of its fibers slope downwards and backwards at 45. On the lateral surface of the muscle, the parotid duct and the accessory parotid gland lie. The muscle receives blood supply from branches of the facial artery, maxillary artery and superficial temporal artery, particularly its transverse facial artery. These vessels form an anastomotic network on the surface of and within the muscle. Nerve supply. By the masseteric branch of the mandibular nerve, which passes through the mandibular notch. Action. Masseter elevates the mandible and close the mouth.
Parotid gland The parotid gland is the largest of the major salivary glands, It is a mainly serous gland, with only a few scattered mucous acini.عناقيد It is a large, irregular, lobulated gland which extends from the zygomatic arch to the upper part of the neck, where it overlaps the posterior belly of digastric and the anterior border of sternocleidomastoid. Anteriorly the gland overlaps masseter and a small, usually detached accessory parotid lies above the parotid duct on the masseter. Posteriorly the gland extends in front and below the external acoustic meatus and in front the mastoid process.
In transverse section the gland is wedge-shaped الشكل,وتدية occupying the gap between the ramus of the mandible and the mastoid and styloid processes of the temporal bone, and reaching close to the lateral wall of the oropharynx. The lateral (superficial) surface of the gland is covered by skin and superficial fascia. The investing layer المغلقة ofالطبقة deep cervical fascia splits to envelope the gland and the inner leaf صفحة passes up to the base of the skull. The outer leaf extends superiorly as the parotidomasseteric fascia and reaches up to the zygomatic arch. On the gland, the fascia tends to be termed the parotid capsule and, more anteriorly, the masseteric fascia. More medially, the styloid process and its attached muscles (stylohoid, stylopharyngeus and styloglossus) separate the gland from the carotid sheath and its contained internal jugular vein, vagus nerve and internal carotid artery. The external carotid artery enters the gland through the lower part of this surface. The facial nerve divides the gland into superficial and deep lobes. Within the gland the nerve branches communicate with each other, forming a plexiform arrangement that lies superficial to the retromandibular vein, which in turn is superficial to the external carotid artery. The retromandibular vein is formed within the parotid by the confluence of the superficial temporal and maxillary veins. The retromandibular vein emerges from the lower part (pole) of the gland and divides into an anterior branch which joins the facial vein and a posterior branch which joins the posterior auricular vein to form the external jugular vein; however, the division may occur within the gland and the two branches emerge from the lower pole. Lymph nodes of the preauricular (parotid) group lie on or deep to the fascial capsule of the parotid, as well as within the gland. The parotid duct (of Stensen), about 5 cm long, passes forwards across the masseter and turns around its anterior border to pass through the buccal fat pad and pierce the buccinator. The duct opens on the mucous membrane of the cheek
opposite the second upper molar tooth; it pierces the buccinator further back and runs forwards beneath the mucous membrane to its orifice. Blood supply Branches from the external carotid artery supply the gland. Venous return is to the retromandibular vein. Lymph drainage Lymph drains to the preauricular (parotid) nodes and then to the deep cervical nodes. Nerve supply 1/The preganglionic parasympathetic fibers travel by way of the glossopharyngeal nerve, its tympanic branch, the tympanic plexus and the lesser petrosal nerve to the otic ganglion. The postganglionic fibers arise from cell bodies in the otic ganglion and reach the gland along the auriculotemporal nerve. 2/Sympathetic (vasoconstrictor) fibers reach the gland from the superior cervical ganglion by way of the plexus on the external carotid and middle meningeal arteries.
3/Sensory innervation is supplied by the auriculotemporal nerve, a branch of the mandibular nerve. Facial Nerve: The facial nerve has a motor root and a sensory root (nervus intermedius). The nerve emerges from the brain between the pons and the medulla oblongata. The roots pass laterally in the posterior cranial fossa with the vestibulocochlear nerve and enter the internal acoustic meatus in the petrous part of the temporal bone. Near the middle ear the nerve makes a sharp posterior bend, which is enlarged by the cell bodies of the afferent (taste) fibers to form the geniculate ganglion. From here the nerve runs back in the facial canal in the medial wall of the middle ear.
It now curves downwards behind the middle ear, and passes vertically down in the facial canal. After shedding all the nervus intermedius fibers, the nerve emerges from the stylomastoid foramen as a motor nerve and passes through the parotid gland to its distribution. Important Branches of the Facial Nerve -Greater petrosal nerve arises from the nerve at the geniculate ganglion. It contains preganglionic parasympathetic fibers that synapse in the pterygopalatine ganglion. The postganglionic fibers are secretomotor to the lacrimal gland and the glands of the nose and the palate. The greater petrosal nerve, consisting of nervus intermedius fibres, leaves the ganglion and travels forwards and medially at a 45 slant through the petrous bone. It emerges from the anterosuperior surface of the petrous
bone and runs forwards. The nerve passes beneath the trigeminal ganglion and reaches the foramen lacerum, where it is joined by the deep petrosal nerve from the sympathetic plexus on the internal carotid artery. The two unite and pass forwards through the pterygoid canal. This nerve of the pterygoid canal [vidian nerve] emerges into the pterygopalatine fossa and enters the pterygopalatine ganglion. Here the parasympathetic fibers relay. Taste fibers from the soft palate and sympathetic fibers pass straight through the ganglion. Postganglionic secretomotor fibers are distributed with the branches of the ganglion to the nose, paranasal sinuses, hard and soft palates, and nasopharynx. Lacrimatory postganglionic fibers join the maxillary nerve and enter the orbit in its zygomatic branch.
Nerve to stapedius supplies the stapedius muscle in the middle ear. The nerve to stapedius is given off in the facial canal and reaches the muscle by a minute canaliculus. Chorda tympani arises from the facial nerve in the facial canal in the posterior wall of the middle ear. It runs forward over the medial surface of the upper part of the tympanic membrane and leaves the middle ear through the petrotympanic fissure, thus entering the infratemporal fossa and joining the lingual nerve. The chorda tympani contains preganglionic parasympathetic secretomotor fibers to the submandibular and the
sublingual salivary glands. It also contains taste fibers from the anterior two thirds of the tongue. By the lingual nerve its taste fibers are taken to the anterior part of the tongue. Its secretomotor fibers relay in the submandibular ganglion for the submandibular gland, sublingual gland. Posterior auricular, the posterior belly of the digastric, and the stylohyoid nerves are muscular branches given off by the facial nerve as it emerges from the stylomastoid foramen. Five terminal branches to the muscles of facial expression. These are the temporal, the zygomatic, the buccal, the marginal mandibular, and the cervical branches. The facial nerve thus controls facial expression, salivation, and lacrimation and is a pathway for taste sensation from the anterior part of the tongue.