1. The Musculature RDN 803 Principles of Occlusion
02/10/04
The Musculature
RDN 803 Principles of Occlusion
Reading: Mohl, et al., Chapter 7
W.D. McCall, Jr., Ph.D.
These slides are available at:
Style
Will mix topics from Chapters 7 and 8.
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W.D. McCall, Jr., Ph.D.

2. Topics to be Covered I. Properties of muscle
II. Muscles of mandibular function
III. Electromyography
IV. Some trigeminal reflexes
V. Selected dental controversies
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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
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4. The Length-Tension Experiment
Set muscle length
2. Stimulate nerve to muscle
3. Record force
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5. Tetanic force > twitch force Fast & slow fibers differ
Features:
Tetanic force > twitch force
Fast & slow fibers differ
Part of force is passive
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6. The Force-Velocity Experiment
1. Set weight to lift
2. Stimulate muscle
3. Measure velocity
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7. Feature:
Faster is weaker
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8. Delay from action potential to twitch
Features:
Delay from action potential to twitch
More force from a shower of action potentials
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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
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10. II. Muscles of mandibular function
Jaw closing muscles
Masseter
Temporalis
Medial pterygoid
Jaw opening muscles
Anterior digastric
Lateral pterygoid
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11. Origin:
zygomatic process of the maxilla and inferior border of zygomatic arch
Insertion:
angle of the mandible inferior, lateral side of ramus
Innervation:
masseteric nerve
Function:
elevate mandible
Masseter
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14. Temporalis Origin: temporal fossa and temporal fascia Insertion:
coronoid process of the mandible
Innervation:
temporal nerve
Function:
elevate mandible
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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
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20. Sphenoid
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22. Origin of
Medial
Pterygoid
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23. Lateral Pterygoid -- Inferior Head
Origin:
lateral surface of lateral pterygoid plate
Insertion:
anterior neck of the mandible
Innervation:
branch of masseteric or buccal nerve
Function:
pull condyle and disk
along the eminence
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25. Origin of
Lateral
Pterygoid,
Inferior
head
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26. Lateral Pterygoid -- Superior Head
Origin:
infratemporal fossa of greater sphenoid wing
Insertion:
anterior neck of the mandible
Innervation:
branch of masseteric
or buccal nerve
Function:
pull condyle and disk
along the eminence
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27. Superior
Head of
Lateral
Pterygoid
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28. Digastric Origin: posterior digastric mastoid notch of temporal bone
Insertion:
anterior digastric lingual, inferior border of the mandible
Innervation:
Posterior digastric--facial nerve
Anterior digastric--mylohyoid, mandibular nerve
Function:
Lower mandible, raise hyoid
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30. ANTERIOR DIGASTRIC
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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
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33. III. Electromyography Mechanism Electrodes Electronics Caveats
Strengths
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34. A. MECHANISM: Muscle Action Potentials
Across membrane: 90 mV
Extracellular: about 90 V
EMG signal is attenuated at the skin by about 1000
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35. B. ELECTRODES
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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.)
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37. Determinants of Muscle Force Item Seen in EMG?
A. Recruitment Yes
B. Frequency Yes
C. Length No
D. Velocity No
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38. Strengths of Electromyography
RDN 803
02/10/04
Strengths of Electromyography
Know precisely when muscle is active.
Know roughly how active.
Insight into activity of motor neuron.
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W.D. McCall, Jr., Ph.D.

39. IV. Some trigeminal reflexes
Jaw closing reflex
Jaw opening reflex
Blink reflex
Tongue reflex
Gagging
Modulating influences
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40. Postural Protective Cardiovascular Respiratory Digestive Humoral
Types of Reflexes
Postural
Protective
Cardiovascular
Respiratory
Digestive
Humoral
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41. The Jaw Jerk Reflex (Postural)
R.M. Bradley, Figure 10-12
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42. The Jaw Opening Reflex (Protective)
R.M. Bradley, Figure 10-13
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43. V. Selected Controversies
Rest position: passive elasticity vs. active contraction
Mastication: alternating reflexes vs. central pattern generator
Electronic devices for TMD diagnosis
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44. A. Rest position hypotheses
1. Passive elasticity
2. Active contraction
a. Stretch reflex
b. TMJ receptors
c. Airway patency
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45. Rest Position: Evidence
Passive Elasticity
Length-tension curve
Negative EMG search
Stretch reflex
Sleep in chair
MN inhibition in sleep
Positive needle EMG
Positive surface EMG
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46. Surface EMG,mV
Vertical Jaw Opening, mm
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47. B. Mastication hypotheses
Alternating reflexes (Sherrington, 1917)
Central pattern generator (Lund, 1971)
Significance: part of the theme “Be skeptical and be critical”
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48. C. Electronic devices for TMD diagnosis
Hypotheses:
Resting EMG greater in TMD patients
(No convincing evidence)
2. Jaw position differs in TMD patients
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49. These slides are available at: http://www.acsu.buffalo.edu/~wdmccall/
Summary
Properties of muscle
II. Muscles of mandibular function
III. Electromyography
IV. Two trigeminal reflexes
V. Selected dental controversies
These slides are available at:
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