MUSCLES OF MASTICATION

CONTENTS Introduction Embryological development Masticator space Origin, Course, Insertion, Relation – Muscles

of Mastication Fascia- Masseteric, Temporalis, Pterygoid Mandibular sling Buccinator Muscle Nerve supply Blood supply Actions & Group actions Applied Anatomy Conclusion References

EMBRYOLOGICAL DEVELOPEMENT

• Mesoderm of the 1st Branchial Arch

MASTICATOR SPACE(PARVIZ)

CONTENTS4 Muscles of MasticationRamus & Posterior portion of body of

MandibleFascia – Masseteric , Pterygoid, Temporalis

MASSETER

Quadrilateral / Rectangular

Covers lateral surface of Ramus of mandible

3 superimposed layers, that blend anteriorly. (PARVIZ JANFAZA)

ORIGIN,

• MOST ANTERIOR FIBRES arises as a thick aponeurosis = Maxillary pocess of zygomatic

bone(GRAYS) • SUPERFICIAL (largest) = anterior 2/3 lower border, Zygomatic Arch

ORIGIN,

• MIDDLE

= anterior 2/3 posterior 1/3 deep surface & lower border zygomatic arch

• DEEP = posterior 1/3 deep surface zygomatic arch

Course of masseter

• Superficial layer – passes downwards& backwards at an angle of 45 degree

• Middle & Deep Layer – pass vertically downwards

INSERTION,

• SUPERFICIAL, = posterior lower ½, lateral surface, Ramus & angle of mandible• MIDDLE = central part, lateral, Ramus

• DEEP = upper ½ , lateral, Ramus & lateral surface,Coronoid Process

• Middle & Deep layers together constitute the deep part of the masseter,

refd to in the NOMINA ANATOMICA ( MacDougall ,1955 ); they form a cruciate muscle (GRAYS)

RELATIONS,

• SUPERFICIAL - Skin - Platysma - Risorius - Zygomatic Major - Antr part,Parotid Gland - Parotid duct - Facial n, terminal brs - Transverse Facial vessels

• DEEP - Ramus - Lower part of Temporalis - Massetric n & a , reach the deep surface of m. by

passing through the Dorsal part of Mandibular Incisure

• ANTERIORLY - Buccinator - Buccal n• POSTERIORLY – Parotid gland

PAROTID MASSETERIC FASCIA

• Covers Masseter (except,as its deep upper portion. Here there is a communication with fascial planes associated with the insertion of temporalis m.) &splits to invest ParotidGland

• Attaches, Zygomatic arch

Lower border of Mandible

Continues, Investing Cervical Fascia over Sternocleidomastoid m,

Extends deep & fuses with, Fascia Extends deep & fuses with, Fascia of Posterior Belly of Digastric m. of Posterior Belly of Digastric m. as Stylomandibular ligament.as Stylomandibular ligament.

Encircles, anteriorly- Ramus Encircles, anteriorly- Ramus deep- Medial Pterygoid deep- Medial Pterygoid m.m.

Fuses with, dense&tough Fuses with, dense&tough superficial fascia covering parotid superficial fascia covering parotid gland. Irregular septa into the gland. Irregular septa into the gland.gland.

TEMPORALIS

• Fan shaped

• Fills Temporal Fossa

ORIGIN, Bones forming Temporal fossa (excluding

zygomatic bone) Temporal Fascia (deep surface)

Course,

• Antr fibres- vertically downwards • Postr fibres – horizontally forwards• Intermediate – obliquely

-------- converge to form a tendon (TEMPORALIS TENDON) &

pass thr gap b/w Zygomatic arch and side of the skull

INSERTION,

Coronoid Process, = deep (medial) surface + = margins (apex, anterior & posterior

border)

Ramus, anteromedial aspect, nearly to the

last molar tooth

(GOSLING)

RELATIONS,

• SUPERFICIAL -Skin -Auricularis anterior -Auricularis superior -Temporal branch-Facial n -Zygomatico temporal nerve -Superficial temporal a & v -Galea aponeurotica -Zygomatic arch -Masseter m

• DEEP,

-Temporalis fossa

-Lateral pterygoid m

-Superficial head, medial pterygoid m

-Buccinator m

-Maxillary artery

-Deep temporalis n

-Buccal vessels & n

TEMPORAL FASCIA The most cranial extension of the Deep Cervical

Fascia Thick Fibrous Aponeurotic sheets, covers

Temporalis

Supr, single layered

Superior Temporal Line Infr, splits into 2 layers

inner&upper lips, upper bor, Zygo arch. Gap b/w 2, - Zygomatic br.of Superficial Temporal a.

- Zygomaticotemporal n. Continues, Masseteric Fascia

Relations, Temporal Fascia SUPERFICIAL- 1.Skin 2.Auricularis Anterior Auricularis Superior (gives origin to) 3.Superficial Temporal a & v 4.Auriculo-temporal N 5.Facial N – temporal br 6.Galea Aponeurotica (Epicranial Aponeurosis) DEEP – (gives origin to) superficial fibers of Temporalis

LATERAL PTERYGOID

• 2 heads – upper, small _ lower, large

ORIGIN UPPER HEAD. = Infratemporal surface = Infratemporal crest of Greater Wing of Sphenoid LOWER HEAD = Lateral surface of Lateral Pterygoid Plate

Course,

• Both heads converge &

run Backwards_laterally

INSERTION,

Pterygoid Fovea (a depression),

on Anterior surface, Neck of

mandible Anterior margin of,

Articular disc &

Capsule of TMJ

INSERTION,

Pterygoid Fovea (a depression),

on Anterior surface, Neck of

mandible Anterior margin of,

Articular disc &

Capsule of TMJ

Relations

key muscle of the region,because its relations provide a fair idea about the layout of structure in Infratemporal Fossa

SUPERFICIAL 1.Ramus 2.Maxillary a 3.Tendon of temporalis 4.Masseter

• 1.Deep head of Medial Pterygoid m.

• 2.Sphenomandibular Ligament

• 3.Middle Meningeal a

• 4.Mandibular n

DEEPDEEP

STRUCTURES EMERGING AT THE UPPER BORDER

1.Masseteric n

2.Deep Temporal n

STRUCTURES EMERGING AT THE LOWER BORDERSTRUCTURES EMERGING AT THE LOWER BORDER 1.Lingual n1.Lingual n 2.Infr.Alveolar n2.Infr.Alveolar n 3.Middle Meningeal a3.Middle Meningeal aSTRUCTURES PASSING THROUGH THE GAP STRUCTURES PASSING THROUGH THE GAP BETWEEN 2 HEADSBETWEEN 2 HEADS 1.Maxillary a 1.Maxillary a 2.Mandibular n, Buccal br 2.Mandibular n, Buccal br

Pterygoid Plexus Of Veins Surround The Lateral Pterygoid Plexus Of Veins Surround The Lateral PterygoidPterygoid

MEDIAL PTERYGOID

• Quadrilateral Muscle

• 2 heads – Superficial, small

Deep, large

ORIGIN

• Superficial

- Tuberosity of Maxilla

- Grooved surface (Lateral aspect)of Pyramidal process,Palatine bone

• Deep - Medial surface,Lateral Pterygoid Plate

- adjoining part of Pyramidal process,Palatine Bone

course

• Incline obliquely,

run Downwards_Backwards_Laterally

INSERTION

as a strong tendinous lamina,

Roughened area on the Medial surface of

Angle adjoining part of Ramus

below – Mandibular Foramen

behind – Mylohyoid Groove

RELATIONS

SUPERFICIAL (upper part)- seperates Lateral Pterygoid

Lateral Pterygoid Plate Lingual Nerve

Inf.Alveolar Nerve Superficial (lower part) –seperates Ramus Lingual Nerve Inf. Alveolar Nerve Maxillary Artery Sphenomandibular Ligament

DEEP Superior Constrictor- anteriorly,tendinous band i.e. Pterygomandibular Raphe

crossed by, Styloglossus m Stylopharyngeus m Stylohyoid ligament Glossopharyngeal n.Gap b/w upper border of superior constrictor & base of skull Tensor palati Levator palatiAnterior to Tensor palati, Medial Pterygoid plate (I. Singh)

PTERYGOID FASCIA

• Encases both Pterygoid muscles and attaches to the Stylomandibular Ligament

• Between the sphenoid spine and the lingula of the mandible facial condensation to form the sphenomandibular ligament

• The terminal part of this facia between the sphenoid spine and the posterior margin of the lateral pterygoid muscle is called the pterygospinous ligament

MANDIBULAR SLING

• Mac Conaill (1975) – the most superficial fibres of masseter are continuous at the lower border of the mandible with the attachment of the medial pterygoid m.

• The attachments of the medial pterygoid & the masseter muscle provide a muscular sling that suspends the angle of the of the jaw.

• They provide a functional articulation b/w the maxilla & mandible,with the TMJ acting as a guide

• When the jaw opens or closes, the mandible moves along a center of rotation created by the attachment of the sling & the sphenomandibular ligament

Buccinator muscle

• Which assists in chewing by helping ( to keep food b/w upper & lower teeth) & (away from the cheeks)

• Is not classified as Muscle of Mastication as it does not move the mand

(Mc Minns )

MOTOR NERVE INNERVATIONS,5TH Cranial Nerve, Mandibular br.

Masseter- -Masseteric NTemporalis- -Antr & Postr Deep

Temporal N

Lat.Pterygoid -N to Lat.PterygoidMed.Pterygoid- N to Med. pterygoid

Blood Supply

MAXILLARY ARTERY (second part)

ACTION, MASSETER

Elevation Protrusion / Protraction

( by, Anterior fibres )

ACTION, TEMPORALIS

Elevation

Retraction

( by, Posterior horizontal fibres )

ACTION, LATERAL PTERYGOID

• Depression

• Protrusion

• Side to Side Movement

ACTION, MEDIAL PTERYGOID

• Elevation

• Protrusion

• Side to Side Movement

ACCESSORY MUSCLES OF

MASTICATION Digastric

Geniohyoid

Mylohyoid

Biomechanics of the

MASTICATORY SYSTEM

( Hannam )

Applied Anatomy_ Surgical Implications