Muscles of Mastication

Muscles of mastication: The muscles of mastication moves the mandible during mastication and speech. They are: 1) Masseter 2) Temporalis 3) Lateral pterygoid 4) Medial pterygoid Lateral pterygoid Temporalis Masseter Medial pterygoid

Masseter: It is a quadrilateral muscle which covers lateral surface of the Ramus of the mandible. Origin: It arises from lower border of Zygomatic arch and from Zygomatic process of maxilla. Insertion: The fibres are inserted into coronoid process and lateral surface of Ramus of mandible Zygomatic arch Masseter

Nerve supply: Masseteric nerve, a branch of the anterior division of the Mandibular nerve

Action: It elevates the mandible to close the mouth and clenches the teeth Clenching of the teeth Elevation

Temporalis: The muscle fills the temporal fossa Origin: Arises from temporal fossa, excluding zygomatic bone and from temporal fascia. Insertion: The margins and deep surface of the coronoid process and anterior border of the ramus of the mandible Temporal fascia Temporalis Coronoid process

Nerve supply: Deep temporal branches from anterior division of the Mandibular nerve Temporalis muscle Deep temporal nerve Mandibular nerve

Action: Retraction Elevation 1) It elevates the mandible 2) Posterior fibres retract the potruded mandible: Retraction Elevation

Lateral pterygoid: The muscle has upper head and lower head. Origin: It arises from the infratemporal surface and crest of the greater wing of sphenoid bone Lower head: It arises from the lateral pterygoid plate. Upper head Lower head

Capsule of Temporomandibular joint Insertion: The fibres get inserted into: a) Pterygoid fovea on the anterior surface of the neck of the mandible and to b) The anterior margin of the articular disc and capsule of the temporomandibular joint Articular disc Capsule of Temporomandibular joint

Nerve to lateral pterygoid Nerve supply: A branch from anterior division of Mandibular nerve. Nerve to lateral pterygoid

Depression Action: 1) Depresses the mandible to open the mouth. 2) The lateral and medial pterygoid acting together protrude the mandible. 3) Alternate contraction of lateral and medial pterygoid produces side to side movements. Depression

Lateral pterygoid plate Medial pterygoid: This is a quadrilateral muscle having small superficial head and a large deep head. Origin: Superficial head: From tuberosity of maxilla and adjoining bone Deep head: From medial surface of lateral pterygoid plate and adjoining part of palatine bone. Lateral pterygoid plate Deep head Superficial head

Insertion: The fibres are inserted into the medial surface of the angle of the mandible and adjoining part of the ramus of the mandible. Medial pterygoid muscle

Nerve to Medial pterygoid Medial pterygoid muscle Nerve supply: Nerve to Medial pterygoid, which is a branch of the main trunk of the Mandibular nerve Nerve to Medial pterygoid Medial pterygoid muscle

Protrusion Elevation Action: 1) Elevates the mandible: 2) Helps in protrude the mandible 3) Alternate contraction of Medial and Lateral pterygoid muscles produce side to side movements Protrusion Elevation

TEMPOROMANDIBULAR JOINT

Variety: It is a synovial joint of the condylar variety. Bones forming the joint: Above: Articular tubercle and anterior articular part of the mandibular fossa of the temporal bone. Below: Head (or) Condyle of the mandible. Mandibular fossa Head of mandible Articular tubercle

Menisco-mandibular compartment Menisco-temporal compartment Articular surfaces of both bones are covered with fibro-cartilage. The joint is completely divided by an articular disc into upper menisco-temporal compartment and a lower menisco-mandibular compartment. Articular disc Menisco-mandibular compartment Menisco-temporal compartment Fibro-cartilage

Ligaments: Capsular ligament with synovial membrane Articular disc The joint presents the following ligaments: Capsular ligament with synovial membrane Articular disc Lateral (or) Temporomandibular ligament Accessory ligaments: a) Sphenomandibular and b) Stylomandibular ligaments

Squamo-tympanic fissure 1) Capsular ligament: It envelops the joint and presents the following attachments: Above: Infront: To the articular tubercle Behind: To the Squamo-tympanic fissure And periphery of articular fossa between them Below: Attached around the neck of the mandible Above the disc the capsule is loose and below the disc it is tight Squamo-tympanic fissure Neck of the mandible Articular tubercle

Synovial membrane: It lines the inner aspect of the capsule of each compartment of the joint, but fails to cover the articular cartilages and articular disc. Synovial membrane

2) Articular disc: It is an oval plate of fibro-cartilage which caps the head of mandible and divides the joint cavity into two compartments.

3) Lateral (or) Temporomandibular ligament: It reinforces and strengthens the lateral part of the capsular ligament and extends downwards and backwards from the articular tubercle to the posterolateral aspect of neck of mandible. Lateral ligament Articular tubercle

Sphenomandibular ligament Accessory ligaments: Sphenomandibular ligament: It is situated medial to the capsule and is attached superiorly to the spine of sphenoid and inferiorly to the lingula of the mandibular foramen. Lingula Spine of sphenoid Sphenomandibular ligament

Sylomandibular ligament 2) Stylomandibular ligament: It is formed by the thickening of deep cervical fascia and extends from the tip of styloid process of temporal bone to angle of mandible. Sylomandibular ligament

Arterial supply: Nerve supply: Branches from superficial temporal and maxillary arteries Nerve supply: By Auriculo temporal and Masseteric nerves

Movements: Movements permitted at the Temporamandibular joints are Protrusion Retraction Depression Elevation Side-side movements (chewing movements) Protrusion Retraction Elevation Depression

Muscles Producing Movement Muscles producing movements: Movement Muscles Producing Movement Protrusion Lateral pterygoid & Medial pterygoid muscle Retraction Posterior fibres of Temporalis, Masseter & Digastric Depression Lateral pterygoid muscle Wide opening Digastric, Geniohyoid, Mylohyoid Elevation Masseter, Temporalis, Medial pterygoid of both sides Side to Side Movements Medial & Lateral pterygoids of both sides acting alternately

Applied anatomy: Dislocation of Mandible: During excessive opening of the mouth, the head of mandible of one (or) both sides may slip anteriorly into the infratemporal fossa, as a result of which there is inability to close the mouth. Reduction is done by depressing the jaw with the thumbs placed on the last molar teeth and at the same time elevating the chin

SUBMANDIBULAR GLAND

Submandibular salivary gland: It is one of the three paired salivary glands Situation: It is situated in digastric triangle and lodges partly in submandibular fossa of the mandible upto Mylohyoid line opposite the molar and premolar teeth. Mylohyoid line Submandibular fossa

It weights about 10-20gms and appears like walnut Divisions of the gland: The gland consists of a large superficial part and a small deep part, both the parts are continuous with each other around posterior border of Mylohyoid muscle. Deep part Mylohyoid muscle Superficial part

Superficial part: It presents Two ends: 1) Anterior end 2) Posterior end Three surfaces: 1) Inferior 2) Lateral 3) Medial Lateral surface Anterior end Medial surface Posterior end

Anterior belly of digastric Parts: Anterior end: it extends upto anterior belly of digastric Posterior end: It extends upto Stylomandibular ligament and separates Sumbandibular from parotid gland. Anterior belly of digastric

f a b c e d Surfaces of superficial part: The surfaces are covered by investing layer of deep cervical fascia 1) Inferior surface: It presents the following relations: Skin, Platysma, Cervical branch of facial nerve, Deep cervical fascia Facial vein, Submandibular lymph node. f a b c e d

2) Lateral surface: It is related to Submandibular fossa on the mandible Insertion of Medial pterygoid muscle Facial artery Facial artery

c b a 3) Medial surface: It is related to a. Mylohyoid muscle, nerves and vessels b. Hyoglossus and Styloglossus c. Lingual and Hypoglossal d. Stylohyoid ligament, Glossopharyngeal Nerve(IX) e. Wall of the pharynx b c a

Anteriorly it extends upto the posterior end of sublingual gland Deep part : It is small in size and lies deep to Mylohyoid and superficial to Hyoglossus and styloglossus Anteriorly it extends upto the posterior end of sublingual gland Posteriorly it continuous with the superficial part around the posterior border of Mylohyoid. Styloglossus Hyoglossus Mylohyoid

Submandibulat Duct (or) Wharton’s duct: It is thin walled and is about 5 cm long and emerges at the anterior end of the deep part of the gland Submandibular duct Hypoglossal nerve Lingual nerve

Supplied by facial artery Arterial Supply Supplied by facial artery Venous Drainage Drains into common facial (or) lingual vein Lymphatic Drainage Submandibular lymph nodes

Nerve supply: The Secreto-motor supply of gland is supplied by both Parasympathetic and Sympathetic nerves.

Superior salivatory nucleus of Pons Submandibular Ganglion  Facial Nerve Chorda Tympani Lingual Nerve Submandibular Ganglion Submandibular Gland Parasympathetic Preganglionic Fibers Parasympathetic Postganglionic Fibers

Sympathetic fibres: Sympathetic fibers reach the gland around the facial artery and convey postganglionic fibers from the superior cervical ganglion of the sympathetic trunk

Nerve supply: Preganglionic parasympathetic fibres ------------------ Postganglionic parasympathetic fibres ------------------ Sympathetic fibres

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