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: http://www.acsu.buffalo.edu/~wdmccall/ Style Will mix topics from Chapters 7 and 8. 03/01/05 RDN 803 W.D. McCall, Jr., Ph.D.

Topics to be Covered I. Properties of muscle II. Muscles of mandibular function III. Electromyography IV. Some trigeminal reflexes V. Selected dental controversies 03/01/05 RDN 803

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 03/01/05 RDN 803

The Length-Tension Experiment Set muscle length 2. Stimulate nerve to muscle 3. Record force 03/01/05 RDN 803

Tetanic force > twitch force Fast & slow fibers differ Features: Tetanic force > twitch force Fast & slow fibers differ Part of force is passive 03/01/05 RDN 803

The Force-Velocity Experiment 1. Set weight to lift 2. Stimulate muscle 3. Measure velocity 03/01/05 RDN 803

Feature: Faster is weaker 03/01/05 RDN 803

Delay from action potential to twitch Features: Delay from action potential to twitch More force from a shower of action potentials 03/01/05 RDN 803

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 03/01/05 RDN 803

II. Muscles of mandibular function Jaw closing muscles Masseter Temporalis Medial pterygoid Jaw opening muscles Anterior digastric Lateral pterygoid 03/01/05 RDN 803

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 03/01/05 RDN 803

03/01/05 RDN 803

03/01/05 RDN 803

Temporalis Origin: temporal fossa and temporal fascia Insertion: coronoid process of the mandible Innervation: temporal nerve Function: elevate mandible 03/01/05 RDN 803

03/01/05 RDN 803

03/01/05 RDN 803

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 03/01/05 RDN 803

03/01/05 RDN 803

03/01/05 RDN 803

Sphenoid 03/01/05 RDN 803

03/01/05 RDN 803

Origin of Medial Pterygoid 03/01/05 RDN 803

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 03/01/05 RDN 803

03/01/05 RDN 803

Origin of Lateral Pterygoid, Inferior head 03/01/05 RDN 803

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 03/01/05 RDN 803

Superior Head of Lateral Pterygoid 03/01/05 RDN 803

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 03/01/05 RDN 803

03/01/05 RDN 803

ANTERIOR DIGASTRIC 03/01/05 RDN 803

03/01/05 RDN 803

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 03/01/05 RDN 803

III. Electromyography Mechanism Electrodes Electronics Caveats Strengths 03/01/05 RDN 803

A. MECHANISM: Muscle Action Potentials Across membrane: 90 mV Extracellular: about 90 V EMG signal is attenuated at the skin by about 1000 03/01/05 RDN 803

B. ELECTRODES 03/01/05 RDN 803

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.) 03/01/05 RDN 803

Determinants of Muscle Force Item Seen in EMG? A. Recruitment Yes B. Frequency Yes C. Length No D. Velocity No 03/01/05 RDN 803

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. 03/01/05 RDN 803 W.D. McCall, Jr., Ph.D.

IV. Some trigeminal reflexes Jaw closing reflex Jaw opening reflex Blink reflex Tongue reflex Gagging Modulating influences 03/01/05 RDN 803

Postural Protective Cardiovascular Respiratory Digestive Humoral Types of Reflexes Postural Protective Cardiovascular Respiratory Digestive Humoral 03/01/05 RDN 803

The Jaw Jerk Reflex (Postural) R.M. Bradley, Figure 10-12 03/01/05 RDN 803

The Jaw Opening Reflex (Protective) R.M. Bradley, Figure 10-13 03/01/05 RDN 803

V. Selected Controversies Rest position: passive elasticity vs. active contraction Mastication: alternating reflexes vs. central pattern generator Electronic devices for TMD diagnosis 03/01/05 RDN 803

A. Rest position hypotheses 1. Passive elasticity 2. Active contraction a. Stretch reflex b. TMJ receptors c. Airway patency 03/01/05 RDN 803

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 03/01/05 RDN 803

Surface EMG,mV Vertical Jaw Opening, mm 03/01/05 RDN 803

B. Mastication hypotheses Alternating reflexes (Sherrington, 1917) Central pattern generator (Lund, 1971) Significance: part of the theme “Be skeptical and be critical” 03/01/05 RDN 803

C. Electronic devices for TMD diagnosis Hypotheses: Resting EMG greater in TMD patients (No convincing evidence) 2. Jaw position differs in TMD patients 03/01/05 RDN 803

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: http://www.acsu.buffalo.edu/~wdmccall/ 03/01/05 RDN 803