Dr. Maria Eller Isabel T. Collantes Oral Physiology
O : lower border of malar bone, Zygomatic arch & zygomatic process of maxilla R : Downward and Backward
I : Angle of mandible and inferior half of the lateral side of mandible
O : Internal surface of zygomatic arch I : Ramus of mandible and base of coronoid process
50 degree between 2 layers
Anterior bundle (vertical fibre) Action: Mandible elevator (Close jaws), crushing and chewing at C.O.
Inaction: Mandible depression (except Max. Opening and Opening against resistance)
Posterior bundle (Horizontal bundle) Action: Mand. retraction and positioner Inaction: Mand. depression and protrusion Action: Protrisive movement
Ant. and Post. deep temporal nerve
O : Pterygoid fossa and medial surf. of the lateral pterygoid plate I : Inf. + Post. border of ramus and angle of mand. R : Downward and Backward Rectangular shape at medial surface of ramus, synergistic with masseter muscle
N : Medial Pterygoid nerve
O: Wing of sphenoid and infratemporal crest
O: Lateral surf. of lateral pterygoid plate
Insertion of superior and inferior heads Ant. portion of the condylar neck (pterygoid fovea) Ant. surface of the articular capsule
Open the jaws, protrude and lateral movement with moving disk forward
Synergistic with elevator group of muscle for closing and clenching
Synergistic with suprahyoid group of muscle for opening jaw
As a result of a deliberate effort of will
Involves the trigeminal system
Horizontal axis of rotation Frontal (vertical) axis of rotation
Sagittal axis of rotation
Horizontal axis of rotation Frontal (vertical) axis of rotation
Sagittal axis of rotation
Around the horizontal axis ( hinge axis)
Around the frontal (vertical) axis
Continued left lateral border
Continued right lateral border
Continued right lateral border with protrusion
Left lateral superior border
Right lateral opening border
Activity of masticatory muscles during chewing reflected jaw-tracking devices and EMG duration of the chewing cycle
Variation is related to occlusal contact relation and musculoskeletal morphology
= opening + closing + power stroke
chewing sequence could be divided into
Start from static intercuspal position , where jaw movement pauses for 194 ms in chewing cycle, muscle activity begins in the ipsilateral inferior head of the lateral pterygoid muscle approximately half way through the period of tooth contact. Follow closely by the action of the contralateral inferior lateral pterygoid muscles.
Both superior and inferior head of the lateral pterygoid muscle are active during the opening phase.
Early in the opening phase, digastric muscles become active and remain until maximum opening position During the opening phase,
masseter, temporalis, medial pterygoid, and superior head of lateral pterygoid muscles are inactive .
At initiation of jaw closing the inferior heads of the lateral pterygoid muscle ceases their functioning and activity
initiated in the contralateral medial pterygoid muscle
During early closing, contralateral medial pterygoid muscle more active in wider strokes, ceases activity during the intercuspal phase.
contralateral medial pterygoid controls the upward and lateral positions of the mandible
The ipsilateral and contralateral medial pterygoid muscles are active in the onset of intercuspation when the chewing stroke is narrow, i.e., has a minimal lateral component
Activity increases in the anterior and posterior temporalis muscle, in the deep and superficial masseter muscles, and in the ipsilateral medial pterygoid muscle up to the peak 20 to 30 ms before the onset of the intercuspal position
anterior and posterior temporalis muscle, in the deep and superficial masseter muscles, and in the ipsilateral medial pterygoid muscle activity declines in activity at the onset of intercuspation .
There appears to be reciprocal action between the inferior head of the lateral pterygoid muscle and the medial pterygoid muscle in same subject.
In vertical affort (clenching in centric occlusion), most of the elevator muscles are activated maximally. In some subjects the medial pterygoid muscle activity is low. The variation between subjects related to occlusal contacts and musculoskeletal morphology.
The inferior head of the lateral pterygoid produces little activity or only 25 percent of maximum activity compared to the superior head.
Muscle activity decreases when only the incisors in contact slightly active during vertical effort with intercuspal clenching
more active during vertical incisive clenching.
Chewing is more obviously complicated than alternating jaw-opening and jaw-closing reflexes. Several models have been proposed to account for rhythmic jaw movements and sensory input interactions with proposed rhythm generators .
These reflexes perform useful functions when the body is in movement and during chewing but their characteristics change during the two situations .
Cyclic jaw movements are largely centrally programmed and require little in the way of proprioceptive control loop.
mouth is not merely a motor organ, but also a sensory perceptual system.
A simple jaw-opening reflex (JOR) can be evoked experimentally by a brisk tap to a tooth by noxious stimulation of the tooth pulp, facial skin, and widespread area in the oral cavity. By stimulation of low-threshold afferents in the lips or oral mucosa
by light tactile stimulation of the peroral region in a fetus
The jaw-opening reflex and the trigemino-neck reflexes are considered to protect the orofacial region against sudden contact with an unforeseen object when the body is in motion. to protect the soft tissues and lips against being bitten during jaw closure
To against being damaged due to excessive occlusal forces if the teeth encounter a hard object.
So called Jaw-jerk reflex usually initiated experimentally by tapping on the chin. Postural or antigravity reflex of jaw-closing muscles. During locomotion the stretch reflex probably helps to maintain position of the mandible relative to the maxilla
postural stability of the mandible
The reflex is activated when muscles that elevate the mandible are stretched activate muscle spindle afferents conveyed through monosynaptic connections with the motoneurons of the trigeminal motor nucleus,
results in the jaw-closing reflex
Sensory feed back from the periphery may modulate the reflex and other afferent pathways reticular formation in brain stem
V sensory nucleus in brain stem
Simple jaw-opening and jaw-closing reflexes are adapted to perform useful functions in two different situations , they cannot continue to act the same way during mastication. during movement of the whole body during movements of the jaw
normal rhythmic jaw movements can take place without being interrupted by low threshold reflexes evoked by innocuous stimulation of the lips, teeth, and mucosa during chewing.
The low-threshold input that can be evoked the JOR must be suppressed to allow normal jaw movements to occur during chewing.
The synaptic transmission at the terminals of low-threshold primary afferents appears to be tonically reduced by presynaptic depolarization during chewing.
During jaw closure the amplitude of the JOR increases so that a strong stimulus in the periphery can interrupt jaw closure to avoid damage to the tissues if they are trapped between the teeth.
The protective potential of the JOR occurs in those phases pf chewing when injury is likely to occur.
Neuronal networks located in the brain are capable of generating rhythmic activity in trigeminal motor systems without peripheral feed back .
The site for the masticatory rhythm generator or central pattern generator (CPG) appears to be in the brain stem reticular formations (RF).
The CPG may modulate directly and indirectly the trigeminal motoneuron pool. Rhythmic jaw movement (RJM) influence and are influenced by orofacial afferents has a differential effect on the excitability of effector neurons
influences how information is transmitted.
Descending influence on RJM from cortical sites occurs. Input may activate the trigeminal motor pool during the initial phases of preparing and positioning of the food .
Such inputs also activate the CPG which modulated descending inputs from the motor cortex, and acts directly on the motor pool to drive RJM.
Peripheral input contributions to RJM are influences via the central motor program either by modulation of motoneuronal excitability (stretch reflex)
by modulation of reflex circuits at the level of primary afferents or interneurons .
sensory feed back from peripheral organ
CPG :Central Pattern Generator neuron in brain stem
During the jaw-opening phase of mastication, rhythmic inhibition occurs to inhibit the stretch reflex. This postsynaptic hyperpolarization appears to be responsible for the phasic inhibition of the stretch reflex during jaw-opening motoneuron pool is inhibited during chewing.
The muscle spindle feedback is mainly controlled by cyclical changes in the membrane potential of jaw-closing motoneurons.
neuron circuits are modulated at the level of primary afferent or interneurons.
modulation of sensory transmission occur through neurons in the trigeminal main sensory nucleus in the subnucleus oralis , and in the intertrigeminal area which lies between the sensory and motor nuclei.
During the masticaory cycle the excitability of the jaw-opening reflex interneurons is inhibited which receive inputs from low-threshold mechanosensitive fields in the face or oral cavity,. most of the neuron with high threshold fields are very excitable during fast and slow jaw closing and relatively unexcitable during jaw opening.
Modulation of sensory transmission through the subnucleus caudalis is not phase modulated.