Dr. Maria Eller Isabel T. Collantes

Oral Physiology

Masseter muscle

Temporalis muscle

Medial pterygoid muscle

Lateral pterygoid muscle

Superficial layer

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

Deep layer

O : Internal surface of zygomatic arch

R : Downward (vertical)

I : Ramus of mandible and base of coronoid process

50 degree between 2 layers

3 bundlesAnterior 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

Intermediate bundleAction: Protrisive movement

Nerve supplyNerve supply

Ant. and Post. deep Ant. and Post. deep temporal nervetemporal 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

N : Medial Pterygoid nerve

Rectangular shape at medial surface of ramus, synergistic with masseter muscle

Superior head

O: Wing of sphenoid and infratemporal crest

R: Downward and Backward

Inferior head

O: Lateral surf. of lateral pterygoid plate

R: Upward and backward

Insertion of superior and inferior heads

Ant. portion of the condylar neck (pterygoid fovea)

Ant. surface of the articular capsule

Ant. Border of the diskFunction Open the jaws, protrude

and lateral movement with moving disk forward

Superior head Synergistic with elevator group of muscle for closing and clenching

Inferior head Synergistic with suprahyoid group of muscle for opening jaw

Nerve supplyLateral pterygoid nerve

Voluntary Movements As a result of a deliberate effort of will

Reflex Sensory input

Cylical Movements Involves the trigeminal system

Rotational movement Horizontal axis of rotation Frontal (vertical) axis of rotation Sagittal axis of rotation

Translational movement

Rotational movement Horizontal axis of rotation Frontal (vertical) axis of rotation Sagittal axis of rotation

Translational movement

Around the horizontal axis (hinge axis)

Around the frontal (vertical) axis

Around the sagittal axis

Posterior open border Anterior open border Superior contact border Functional movements

Left lateral border Continued left lateral border

with protrusion Right lateral border Continued right lateral border

with protrusion Functional movements

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

amplitude onset timing duration of the chewing cycle

Variation is related to occlusal contact relation and musculoskeletal morphology

- 1 chewing cycle = opening + closing + power stroke

- chewing sequence = numerous chewing cycle

- chewing sequence could be divided into- preparatory series- reduction series- pre-swallow series

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 musclemore 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 whenless posterior teeth only the incisors in contact

The digastric muscle slightly active during vertical effort with intercuspal clenching

more active during vertical incisive clenching.

Nociceptor Trigeminal nu.

Tactile Motor nu. of V

Proprioceptive Mesencephalic nu.

Primary NeuronsPrimary Neurons

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

as well as 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 mucosaby 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 pathwaysreticular formation in brain stemV 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.

Coordination betweensensory feed back from peripheral organCPG :Central Pattern Generator neuron in

brain stemhigher center jaw reflexes

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 inhibitedwhich 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.