Muscles of mastication

MUSCLE OF MASTICATION, ANATOMICAL ASPECT

1. Muscles of mastication Dr. Mohammad Amaan D ept. of anatomy JLN medical college, Ajmer

2. Embryologic aspect Pharyngeal arches are rod like thickenings of the mesoderm present in the wall of foregut At first there are six arches. L ater, the 5 th arch disappear and only 5 remains Muscles of mastication develop from the 1 st branchial arch and are supplied by the mandibular nerve All the muscles derived from a pharyngeal arch are supplied by the nerve of the arch

3. Pharyngeal arches (rod like thickenings of the mesoderm)

4. Nerve and the muscle of pharyngeal arch Arch Nerve of the arch Muscles of the arch 1 st arch Mandibular nerve 4 muscles of mastication 4 other muscles 1. Lateral Pterygoid Mylohyoid 2. Medial Pterygoid 2. Anterior belly of digastric 3. Masseter 3. Tensor tympani 4. Temporalis 4. Tensor veli palatini

5. M uscles of mastication Main 1 . Lateral Pterygoid 2. Medial Pterygoid 3. Masseter 4. Temporalis Accessory 1. Digastric 2. Geniohyoid 3. M ylohyoid

6. 1. La teral Pterygoid Short, thick, conical muscle consisting of 2 heads It is the only DEPRESSOR of the mandible Most commonly affected in MPDS (caused by tension, fatigue or spasm in the masticatory muscles) Location – infratemporal fossa

7. Origin – 2 heads 1. Superior / upper head 2. Inferior / lower head Infratemporal crest and infratemporal surface of greater wing of sphenoid Lateral surface of lateral Pterygoid plate Insertion From the 2 origins – the fibres converge and pass backwards and laterally , to get inserted over – Pterygoid fovea Anterior part of capsule of TMJ Anterior margin of articular disc

8. Pterygoid fovea

9. 1. Superior head ORIGIN- It arises from the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone INSERTION- 1. most of the part gets inserted over the Pterygoid fovea 2. part of it gets inserted anteriorly into disc and capsule

10. Superior head features - Not active during opening of mandible It stabilizes the relationship of the disc to the eminence during mandibular closing Active during various jaw closing movements as – chewing, - clenching of the teeth and - during swallowing

11. 2. Inferior head ORIGIN- from the lateral surface of the lateral Pterygoid plate Insertion – over the Pterygoid fovea Active during- Jaw opening/ depression of the mandible Protrusion (forward movement) Contra lateral abduction (side to side movement), right lateral Pterygoid turns the chin to the left side

12. . Action Depression / opening of the mandible Protrusion of the mandible Contralateral abduction (side to side movements) along with medial Pterygoid Depressors- Lateral Pterygoid Digastric Geniohyoid mylohyoid

13. Lateral Pterygoid cont.. Nerve supply – nerve to lateral Pterygoid (a branch of anterior division of mandibular nerve) Applied – Paralysis of the muscle leads to difficulty in opening of the mouth Wide opening of mouth leads to lockjaw Muscle most commonly affected in MPDS (caused by tension, fatigue or spasm in the masticatory muscles)

14. 2 . Medial Pterygoid Thick, quadrilateral muscle consisting of 2 heads of origin 2 heads – small superficial and large deep head It is one of the ANTI GRAVITY muscle of the mastication Location – infratemporal fossa

15. Origin – 2 heads 1. Superior head 2. Deep head maxillary tuberosity pyramidal process of palatine bone Medial surface of lateral Pterygoid plate of sphenoid bone Insertion Both the head unite and get inserted over the- medial surface of angle and adjoining ramus below and behind the mandibular foramen and mylohyoid groove

16. -medial surface of angle and adjoining ramus -below and behind the mandibular foramen and mylohyoid groove

17. Medial Pterygoid cont.. Action Elevation / closing of the mandible Protrusion ( → )of the mandible Contralateral abduction (side to side movements) along with lateral Pterygoid Elevators / closing of the mandible Medial Pterygoid Masseter Temporalis (Anterior and middle fibres)

18. Medial Pterygoid cont.. Nerve supply – nerve to medial Pterygoid (a branch of main trunk of mandibular nerve) Applied – Paralysis of the muscle leads to difficulty in movements of the mandible IANB injection can occasionally cause hemorrhage into the muscle, which may give rise to painful trismus.

19. 3. Masseter Q uadrilateral muscle, consists of 3 layers Covers lateral surface of ramus of the mandible Most commonly affected in TETANUS It is one of the ANTI GRAVITY muscle of the mastication Location – it is the only muscle of mastication present outside the infratemporal fossa

20. masseter muscle cont.. SUPERFICIAL LAYER (largest) MIDDLE LAYER DEEP LAYER ORIGIN From anterior 2/3 rd of lower border of zygomatic arch From posterior 1/3 rd of lower border of zygomatic arch From deep surface of zygomatic arch INSERTION Lower part of the lateral surface of ramus of mandible Middle part of the lateral surface of ramus of mandible Upper part of the lateral surface of ramus of mandible

21. masseter muscle:- superficial, middle and deep layer

22. masseter muscle cont.. Action Elevate / close the mandible to occlude the teeth in mastication Small effect in - - Protrusion and - Contralateral abduction (side to side movements) Elevators / closing of the mandible Medial Pterygoid Masseter Temporalis (Anterior and middle fibres)

23. masseter muscle cont.. Nerve supply – masseteric nerve (a branch of anterior division of mandibular nerve) Applied – Wide opening of mouth leads to spasm of masseter. Most commonly affected in TETANUS

24. 4. Temporalis Fan shaped muscle, fills the temporal fossa It is one of the ANTI GRAVITY muscle of the mastication Location – temporal fossa for origin and infratemporal fossa for insertion

25. Temporalis cont.. ORIGIN – Inferior temporal line Temporal fossa and temporal fascia INSERTION – Coronoid process FIBRES Orientation - Anterior fibres – vertically Posterior fibres – horizontally Intermediate fibres - obliquely ( in the manner of a fan)

26. Anterior fibres – vertically Posterior fibres – horizontally Intermediate fibres - obliquely ( in the manner of a fan)

27. Temporalis cont.. Action Elevation / closing of the mandible Posterior fibres – retraction of the mandible Elevators / closing of the mandible Medial Pterygoid Masseter Temporalis (Anterior and middle fibres)

28. Temporalis cont.. Nerve supply – anterior and posterior deep temporal nerves (a branch of anterior division of mandibular nerve) Applied – Temporalis muscle and fascia can be used for reconstructive surgery for ankylosis of TMJ as well as any kind of craniofacial reconstructive surgeries

29. Thank you..