The Musculature

1. The Musculature RDN 803 Principles of Occlusion Reading: Mohl, et al., Chapter 7 W.D. McCall, Jr., Ph.D. These slides are available at:http://www.acsu.buffalo.edu/~wdmccall/ RDN 803

2. Topics to be Covered I. Properties of muscle II. Muscles of mandibular function III. Electromyography IV. Some trigeminal reflexes V. Selected dental controversies RDN 803

3. I. Properties of Muscle • Common with limb muscle • Length-tension curve • Force-velocity curve • Determinants of muscle force • Peculiar to jaw muscles • Anatomy of origins and insertions • Location of some sensory cell bodies • Organization of some reflexes RDN 803

4. The Length-Tension Experiment 2. Stimulate nerve to muscle Set muscle length 3. Record force RDN 803

5. Features: Tetanic force > twitch force Fast & slow fibers differ Part of force is passive RDN 803

6. The Force-Velocity Experiment 1. Set weight to lift 2. Stimulate muscle 3. Measure velocity RDN 803

7. Feature: Faster is weaker RDN 803

8. Features: Delay from action potential to twitch More force from a shower of action potentials RDN 803

9. Determinants of Muscle Force • Length • Velocity • Delay from electrical to mechanical events • Number of motor units recruited • Frequency of stimulation • Anatomy of origin and insertion RDN 803

10. II. Muscles of mandibular function • Jaw closing muscles • Masseter • Temporalis • Medial pterygoid • Jaw opening muscles • Anterior digastric • Lateral pterygoid RDN 803

11. Origin: zygomatic process of the maxilla and inferiorborder of zygomatic arch Insertion: angle of the mandibleinferior, lateral side of ramus Innervation: masseteric nerve Function: elevate mandible Masseter RDN 803

12. RDN 803

13. RDN 803

14. Temporalis Origin: temporal fossa andtemporal fascia Insertion: coronoid process ofthe mandible Innervation: temporal nerve Function: elevate mandible RDN 803

15. RDN 803

16. RDN 803

17. Medial Pterygoid Origin: pterygoid fossa and medial surface of lateral pterygoid plate Insertion: ramus and angle of the mandible Innervation: medial pterygoid nerve Function: elevate mandible RDN 803

18. RDN 803

19. RDN 803

20. Sphenoid RDN 803

21. RDN 803

22. Origin of Medial Pterygoid RDN 803

23. Lateral Pterygoid -- Inferior Head Origin: lateral surface of lateral pterygoid plate Insertion: anterior neck of themandible Innervation: branch of masseteric or buccal nerve Function: pull condyle and disk along the eminence RDN 803

24. RDN 803

25. Origin of Lateral Pterygoid, Inferior head RDN 803

26. Lateral Pterygoid -- Superior Head Origin: infratemporal fossa of greater sphenoid wing Insertion: anterior neck of themandible Innervation: branch of masseteric or buccal nerve Function: pull condyle and disk along the eminence RDN 803

27. Superior Head of Lateral Pterygoid RDN 803

28. Origin: posterior digastricmastoid notch of temporalbone Insertion: anterior digastriclingual, inferior border ofthe mandible Innervation: Posterior digastric--facial nerve Anterior digastric--mylohyoid, mandibular nerve Function: Lower mandible, raise hyoid Digastric RDN 803

29. RDN 803

30. ANTERIOR DIGASTRIC RDN 803

31. RDN 803

32. THE BIG PICTURE FUNCTION EXAMPLE NEURAL CIRCUIT LOCATION Protection Jaw jerk, Reflex Brain stem Jaw opening, Gagging Rhythmic Chewing, Pattern generator Brain stem activity Breathing, Walking Complex Speech Cortex function RDN 803

33. III. Electromyography • Mechanism • Electrodes • Electronics • Caveats • Strengths RDN 803

34. A. MECHANISM: Muscle Action Potentials Extracellular: about 90 V Across membrane: 90 mV EMG signal is attenuated at the skin by about 1000 RDN 803

35. B. ELECTRODES RDN 803

36. Caveats • Electrical activity must be calibrated to be directly related to muscle force. • Jaw muscles are redundant: six jaw closers, and they all are active in closing. (You cannot control the muscles independently. The forces on the jaw must satisfy Newton’s equations.) RDN 803

37. Determinants of Muscle ForceItem Seen in EMG? A. Recruitment Yes B. Frequency Yes C. Length No D. Velocity No RDN 803

38. Strengths of Electromyography • Know precisely when muscle is active. • Know roughly how active. • Insight into activity of motor neuron. RDN 803

39. IV. Some trigeminal reflexes • Jaw closing reflex • Jaw opening reflex • Blink reflex • Tongue reflex • Gagging • Modulating influences RDN 803

40. Types of Reflexes Postural Protective Cardiovascular Respiratory Digestive Humoral RDN 803

41. The Jaw Jerk Reflex (Postural) R.M. Bradley, Figure 10-12 RDN 803

42. The Jaw Opening Reflex (Protective) R.M. Bradley, Figure 10-13 RDN 803

43. V. Selected Controversies • Rest position: passive elasticity vs. active contraction • Mastication: alternating reflexes vs. central pattern generator • Electronic devices for TMD diagnosis RDN 803

44. A. Rest position hypotheses 1. Passive elasticity 2. Active contraction a. Stretch reflex b. TMJ receptors c. Airway patency RDN 803

45. Passive Elasticity Length-tension curve Negative EMG search Stretch reflex Sleep in chair MN inhibition in sleep Positive needle EMG Positive surface EMG Rest Position: Evidence RDN 803

46. Surface EMG,mV Vertical Jaw Opening, mm RDN 803

47. B. Mastication hypotheses • Hypotheses • Alternating reflexes (Sherrington, 1917) • Central pattern generator (Lund, 1971) • Significance: part of the theme “Be skeptical and be critical” RDN 803

48. C. Electronic devices for TMD diagnosis Hypotheses: Resting EMG greater in TMD patients (No convincing evidence) 2. Jaw position differs in TMD patients (No convincing evidence) RDN 803

49. Summary • Properties of muscle II. Muscles of mandibular function III. Electromyography IV. Two trigeminal reflexes V. Selected dental controversies These slides are available at:http://www.acsu.buffalo.edu/~wdmccall/ RDN 803