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/
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Topics to be Covered
I.
II.
III.
IV.
V.
Properties of muscle
Muscles of mandibular function
Electromyography
Some trigeminal reflexes
Selected dental controversies
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I. Properties of Muscle
A.
Common with limb muscle
1.
2.
3.
B.
Length-tension curve
Force-velocity curve
Determinants of muscle force
Peculiar to jaw muscles
1.
2.
3.
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Anatomy of origins and insertions
Location of some sensory cell bodies
Organization of some reflexes
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The Length-Tension Experiment
1. Set muscle length
2. Stimulate nerve to muscle
3. Record
force
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Features:
1. Tetanic force >
twitch force
2. Fast & slow fibers
differ
3. Part of force is
passive
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The Force-Velocity Experiment
1. Set weight to lift
2. Stimulate muscle
3. Measure
velocity
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Feature:
Faster is weaker
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Features:
1. Delay from action potential to twitch
2. More force from a shower of action potentials
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Determinants of Muscle Force
1.
2.
3.
4.
5.
6.
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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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II. Muscles of mandibular function
A.
Jaw closing muscles
1.
2.
3.
B.
Masseter
Temporalis
Medial pterygoid
Jaw opening muscles
1.
2.
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Anterior digastric
Lateral pterygoid
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Origin:
Masseter
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
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Temporalis
Origin:
temporal fossa and
temporal fascia
Insertion:
coronoid process of
the mandible
Innervation:
temporal nerve
Function:
elevate mandible
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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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Sphenoid
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Origin of
Medial
Pterygoid
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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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Origin of
Lateral
Pterygoid,
Inferior
head
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Lateral Pterygoid -- Superior Head
Origin:
infratemporal fossa of
greater sphenoid wing
Insertion:
anterior neck of the
mandible
Innervation:
branch of masseteric
or buccal nerve
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Function:
pull condyle and disk
along the eminence 26
Superior
Head of
Lateral
Pterygoid
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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
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Function:
Lower
mandible, raise hyoid28
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ANTERIOR DIGASTRIC
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THE BIG PICTURE
FUNCTION EXAMPLE NEURAL CIRCUIT
LOCATION
Protection
Jaw jerk,
Reflex
Jaw opening,
Gagging
Brain stem
Rhythmic
activity
Chewing,
Breathing,
Walking
Brain stem
Complex
function
Speech
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Pattern generator
Cortex
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III. Electromyography
A.
B.
C.
D.
E.
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Mechanism
Electrodes
Electronics
Caveats
Strengths
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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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B. ELECTRODES
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Caveats
A.
B.
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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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Determinants of Muscle Force
Item
A.
B.
C.
D.
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Seen in EMG?
Recruitment
Frequency
Length
Velocity
Yes
Yes
No
No
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Strengths of Electromyography
A. Know precisely when muscle is active.
B. Know roughly how active.
C. Insight into activity of motor neuron.
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IV. Some trigeminal reflexes
A.
B.
Jaw closing reflex
Jaw opening reflex
C.
D.
E.
F.
Blink reflex
Tongue reflex
Gagging
Modulating influences
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Types of Reflexes
1. Postural
2. Protective
3.
4.
5.
6.
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Cardiovascular
Respiratory
Digestive
Humoral
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The Jaw Jerk Reflex (Postural)
R.M. Bradley, Figure 10-12
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The Jaw Opening Reflex (Protective)
R.M. Bradley, Figure 10-13
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V. Selected Controversies
A.
Rest position: passive elasticity vs.
active contraction
B. Mastication: alternating reflexes vs.
central pattern generator
C. Electronic devices for TMD diagnosis
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A. Rest position hypotheses
1. Passive elasticity
2. Active contraction
a. Stretch reflex
b. TMJ receptors
c. Airway patency
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Rest Position: Evidence
Passive Elasticity
Stretch reflex
Length-tension curve
Negative EMG search
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Sleep in chair
MN inhibition in sleep
Positive needle EMG
Positive surface EMG
45
Surface EMG,V
Vertical Jaw Opening, mm
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B. Mastication hypotheses
A.
Hypotheses
1.
2.
B.
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Alternating reflexes (Sherrington, 1917)
Central pattern generator (Lund, 1971)
Significance:
part of the theme
“Be skeptical and be critical”
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C. Electronic devices for TMD diagnosis
Hypotheses:
1. Resting EMG greater in TMD patients
(No convincing evidence)
2. Jaw position differs in TMD patients
(No convincing evidence)
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Summary
I.
II.
III.
IV.
V.
Properties of muscle
Muscles of mandibular function
Electromyography
Two trigeminal reflexes
Selected dental controversies
These slides are available at:
http://www.acsu.buffalo.edu/~wdmccall/
03/01/05
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