muscles of mastication, applied anatomy,functions

Muscles of mastication

1. MUSCLES OF MASTICATION

2. CONTENTS Introduction Development of muscles Classification Properties Muscles of mastication Primary muscle of mastication Palpation Accessory muscles of mastication Clinical considerations Previous years questions Conclusion References

3. DEFINITIONS Muscle:- an organ that by contraction produces movements of an animal; a tissue composed of contractile cells or fibres that effect movement of an organ or part of the body. Mastication :- is the mechanical process which breaks up larger food particles into smaller pieces which -make it easier for the food to be swallowed -mixes the food with the secretions of salivary glands to soften it. -increases the surface area of food particles thus helping in subsequent digestion of food.

4. Mastication is a sensory motor activity aimed at the preparation of food for swallowing. It is complex process involving activities of facial elevator and suprahyoid muscles and tongue. Rhythmic mandible movements , food manipulation and crushing of food between the Teeth. Saliva facilitates mastication, moistens the food particles, makes a bolus and assists swallowing. A. Van der Bilt et al/physiology and behavior 89(2006) 22-27

5. INTRODUCTION Muscle refers to a group of muscle fibres bound together by connective tissue. Muscle generates force and movements used in the regulation of the internal environment. By controlling the activity of these muscles the human mind ultimately expresses itself.

6. DEVELOPMENT OF MUSCLES The muscular system develops from mesoderm of first brachial arch But the posterior belly of digastric muscle develops from 2 nd brachial arch and supplied by facial nerve

7. CLASSIFICATION OF MUSCLES Depending upon striations 1) Striated muscles 2) Non- Striated muscles Depending upon control 1) Voluntary muscles 2) Involuntary muscles Depending upon functions 1) Skeletal muscles 2) Cardiac muscles 3) Smooth muscles

8. Skeletal – most are attached to the skeleton and form ‘somatic musculature’ Shows well developed cross striations thus called striated muscles. In general under voluntary control. Help to maintain body posture and position. Cardiac -present in heart Well developed cross striations Involuntary control Maintain arterial B.P. Smooth -mostly in hollow viscera Lack cross striations also called plain muscle . Involuntary responsible for maintaining vegetative function of day to day living i.e. its action favors digestion, respiration, excretion and reproduction.

9. MUSCLES OF MASTICATION Muscles of mastication- originate skull and insert mandible, only mandible moves during mastication and other activities. Four muscles are the primary participants in mastication, other accessory muscles. Each of these primary muscles of mastication is paired .

10. PRIMARY MUSCLES OF MASTICATION Temporalis Masseter Lateral pterygoid Medial pterygoid

11. ACCESSORY MUSCLES OF MASTICATION SUPRAHYOID INFRAHYOID Digastric Sternohyoid Stylohyoid Thyrohyoid Mylohyoid Omohyoid Geniohyoid

12. Functionally the muscle of mastication are classified as Jaw elevators- Masseter Temporalis Medial Pterygoid Jaw depressors- Lateral Pterygoid Anterior digastric Geniohyoid Mylohyoid

13. Temporalis Muscle It is a powerful fan shaped chewing muscle which feels temporal fossa. Origin Temporal fossa from infratemporal lines excluding -Zygomatic bone -Temporal fascia Insertion -Margins and deep surface of coronoid process of mandible -Anterior border of ramus of mandible Blood supply- Superficial temporal artery branch of Maxillary artery - Superficial temporal vein and middle temporal vein Nerve supply- Deep Temporal branches from anterior division of mandibular nerve

14. TEMPORALIS MUSCLE

15. FUNCTIONS:- Elevation of mandible Retraction of mandible Crushing of food between the molars Posterior fibres draw the mandible backwards after it has been protruded It is also a contribute side to side grinding movement. PALPATION:- - To locate the muscle, have the patient clench. - Apply two pounds of pressure. - The anterior region is palpated above the zygomatic arch and anterior to the TMJ. - The middle region palpated directly above the TMJ and superior to the zygomatic arch. - The posterior region is palpated above and behind the ear. APPLIED ANATOMY: Sudden reflex contraction of temporalis in times of trauma can cause the fracture of coronoid process

16. MASSETER MUSCLE The second most efficient masticatory muscle. ARRANGEMENT OF FIBRES: Superficial : Origin : thick aponeurosis. From zygomatic process of maxilla and anterior 2/3 of lower border of zygomatic arch, pass downward and backwards at an angle of 45 degree. Insertion: into lower part of lateral surface of ramus of mandible. Middle Layer : origin: anterior 2/3 of the deep surface and posterior 1/3 lower border of the zygomatic arch. Insertion: Middle part of ramus. Deep Layer : origin: deep surface of zygomatic arch. Insertion: upper part of the ramus and into the coronoid process.

17. FUNCTIONS The main function of masseter muscle is Elevation of mandible Lateral movements of the mandible for efficient chewing and grinding of the food. Unilateral chewing Retraction of mandible BLOOD SUPPLY:- supplied by massetric artery branch of maxillary artery - Venous drainage through masseteric vein NERVE SUPPLY :- Massetric nerve branch of anterior division of mandibular nerve

18. Palpation The patient is asked to clench their teeth and using both hands, the practitioner palpates the masseter muscles on both sides extraorally, making sure that the patient continues to clench during the procedure. Palpate the origin of the masseter bilaterally along the zygomatic arch and continue to palpate down the body of the mandible where the masseter is attached. Palpate multiple areas of masseter muscle.

19. RELATIONS SUPERFICIAL- Skin Platysma Risorius Zygomaticus major parotid gland and duct Temporal branch of the facial nerve DEEP- Temporalis Ramus of mandible

20. LATERAL PTERYGOID MUSCLE It is short thick conical muscle with definite upper and lower heads. ORIGIN: Upper head- infratemporal surface and crest of greater wing of sphenoid bone Lower head- lateral pterygoid plate INSERTION : Fibres run backwards and laterally and converge into the Pterygoid fovea on the anterior surface of neck of mandible. Anterior margin of articular disc and capsule of TMJ NERVE SUPPLY : Pterygoid branch of Trigeminal nerve. BLOOD SUPPLY:- Pterygoid branch of maxillary artery - Ascending palatine artery.

21. FUNCTIONS Depress the mandible to open mouth Lateral and medial pterygoid of both sides contract to protrude the mandible. When contract alternatively producing chewing movements PALPATION Placing the forefinger, or the little finger, over the buccal area of the maxillary third molar region and exerting pressure in a posterior, superior, and medial direction behind the maxillary tuberosity

22. RELATIONS SUPERFICIAL Masseter Ramus of mandible Tendon of temporalis Maxillary artery DEEP Mandibular nerve Deep head of medial pterygoid Middle meningeal artery Sphenomandibular ligament

23. MEDIAL PTERYGOID MUSCLE This is quadrilateral muscle having a small superficial head and a large deep head which forms the major part of muscle. ORIGIN and INSERTION: superficial head from the maxillary tuberosity., deep head from medial surface of lateral pterygoid plate and part of palatine bone. Insertion is seen on the medial angle of the mandible. BLOOD SUPPLY : By facial artery by lingual vein NERVE SUPPLY :branch of main trunk of mandibular nerve

24. FUNCTIONS Elevates the mandible Closes the jaw Helps in side to side movement PALPATION -Gently palpate them on the medial aspect of the jaw. -simultaneously from both inside and outside the mouth. APPLIED ANATOMY - During improper inferior alveolar nerve block, the needle may prick and irritate the muscle causing spasm and consequently Trismus.

25. RELATIONS SUPERFICIAL- Upper part of muscle is separated from the lateral pterygoid muscles by; LATERAL PTERYGOID PLATE LINGUAL NERVE INFERIOR ALVEOLAR NERVE Lower part of muscle is separated from the RAMUS OF MANDIBLE MAXILLARY ARTERY SPHENOMANDIBULAR LIGAMENT

26. DEEP Superior constrictor of pharynx Styloglossus Stylopharyngeous

27. ACCESSORY MUSCLES OF MASTICATION SUPRAHYOID INFRAHYOID Digastric Sternohyoid Stylohyoid Thyrohyoid Mylohyoid Omohyoid Geniohyoid

28. DIGASTRIC Two bellies united by Tendon Origin anterior belly- digastric fossa present lateral to the symphysis menti on lower border of mandible. Posterior belly- mastoid notch on temporal bone INSERTION: Intermediate tendon ( hyoid bone) ARTERY: Anterior belly- Sub mental branch of facial artery Posterior belly- occipital artery NERVE : anterior belly- mandible division of the trigeminal nerve via the mylohyoid nerve; Posterior belly - by facial nerve

29. STYLOHYOID Thin muscle sheet It accompanies the posterior belly of digastric ORIGIN : middle of the posterior surface of styloid process. INSERTION : junction of the body and greater cornua of hyoid bone anteriorly. ACTION : draws the hyoid bone upwards and backwards. NERVE SUPPLY : Facial nerve

30. GENIOHYOID MUSCLE Short and narrow muscle lies above mylohyoid ORIGIN: Inferior mental spine INSERTION: Anterior surface of body of hyoid bone ARTERY : Facial Artery NERVE : C1 via hypoglossal nerve ACTION : - Geniohyoid elevates the hyoid bone and draws it forward, thus acting as a partial antagonist to stylohyoid. -when the hyoid bone is fixed it depresses the mandible

31. MYLOHYOID MUSCLE Flat triangular muscle ORIGIN: Mylohyoid line of mandible INSERTION: Middle and anterior fibres into median raphae. Posterior fibres body of hyoid bone ARTERY : Mylohyoid branch of inferior alveolar artery NERVE ; Mylohyoid nerve, from inferior alveolar branch of mandibular nerve ACTIONS: the secondary role of this muscle is evident as a depressor seen in action when mouth is to be opened against resistance. It elevates the floor of mouth to help in deglutition.

32. STERNOHYOID MUSCLE ORIGIN : Posterior surface of manubrium deep to sternohyoid Adjoining part of medial end of 1st coastal cartilage INSERTION : Oblique line of thyroid cartilage below thyrohyoid ARTERIAL SUPPLY : Superior thyroid artery NERVE SUPPLY : Ansa cervicalis (C2, C3) ACTION : depression of larynx

33. THYROHYOID MUSCLE ORIGIN : Upper part of oblique line on thyroid cartilage INSERTION : Lower border of greater cornea of hyoid bone ARTERIAL SUPPLY : Superior thyroid artery NERVE SUPPLY : Fibres of c1 via hypoglossal nerve ACTION : Depression of hyoid bone

34. CLINICAL CONSIDERATIONS

35. BRUXISM BRUXISM: Jaw clenching with or without forcible extrusive movements, where the intensity of the clenching dictates severity (or lack of) grinding. CLENCHING: it can occur as a brief rhythmic strong contractions of the jaw muscles during eccentric lateral jaw movements, or in maximum inter- cuspation . CAUSES: 1- Associated with stressful events 2- Non stress related or hereditary Bruxism may lead to - tooth wear - fracture of the teeth or restoration - uncosmetic muscle hypertrophy TREATMENT: - cornoplasty - maxillary stabilization appliance

36. TETANUS Caused by exotoxins of gram positive bacillus Clostridium tetani Disease of the nervous system characterized by intense activity of motor neuron and resulting in severe muscle spasm. CLINICAL FEATURES: Pain and stiffness in the jaw and neck muscles, with muscle rigidity producing trismus and dysphagia . TREATMENT: All patients should receive antimicrobial drugs Active and passive immunization. Surgical wound care. Anticonvulsant if indicated

37. Stylomandibular Ligament Strain- This is usually felt as a sharp to aching pain in the region behind the jaw bone and below the ear. It can be result of bad bite or from a traumatic injury. Temporal strain Tendonitis- This can occur when there is chronic strain from the temporalis muscle pulling on the tendon that attaches to the mandible. This can cause sharp headaches in the temple, just to the sides of the eyes .

38. CONCLUSION The masticatory muscles include a vital part of the orofacial structure and are important both functionally and structurally. Precise movement of mandible by the musculature is required to move the teeth effectively across each other during function. The knowledge of the anatomy physiology and mechanisms of these muscles are basic to understand the movements.

39. Previous year questions Muscles of mastication (10 marks) Bruxism and it’s management (10 marks)

40. REFERENCES Mahindra Kumar Anand - Human Anatomy -3 rd edition Gray’s Anatomy-38 th edition BD Chaurasia’s Human Anatomy volume 3- 5 th edition