Neurophysiology of the masticatory system
- Introduction :
The functioning of the masticatory system is very complex and it is currently impossible to describe these numerous basic neurophysiological mechanisms, or even to establish a rigorous analogy between the neurophysiological mechanisms of the organism in general and those of the masticatory system.
- Anatomy of the neuromuscular system:
Without the nervous system that triggers and regulates muscle activity, the function would never exist.
The neuromuscular system in fact represents an inseparable whole.
2.1. The nervous system:
2.1.1. Definition:
The nervous system is the set of anatomical structures ensuring the reception, integration and transmission of information coming from the environment or from the organism itself.
2.1.2. Organization:
We have a single nervous system formed by neurons in functional interaction, to facilitate the study we divide them however into large parts:
2.2. The central nervous system:
Composed of the brain and the spinal cord, the true axis of symmetry of the body.
2.2.1. Muscle tissue:
It is an organ with contractile properties, it is made of specialized cells that transform chemical energy into mechanical energy, the main source of energy comes from the breakdown of glucose. Skeletal muscle mainly contains thousands of muscle fibers between which we find connective tissue and blood vessels.
- The neurophysiological mechanism:
Perception: this is the phase of information acquisition by thousands of receptors.
Message integration : It analyzes and integrates information at the CNS level, then decides on a response.
The answer : It is the motor function represented by muscle contraction.
3.1. The chewing center:
Today, we accept the existence of a mastication center, located at the level of the central nervous system. This is assimilated to a real control center which composes the entire masticatory act, it includes 3 levels:
- Input stage: receives information, captured by the receptors in the form of nerve impulses directed by sensory flight.
- Integration stage:
This is the central generator where information is infiltrated, analyzed and finally activated or inhibited according to needs. It is at this level of the center that masticatory acts are developed according to the finesse of the desired adaptation and in order to give an adapted motor response.
- Output stage: last level of the masticatory center, it groups together the motor neurons which are the neurons of motor control.
3.2. Functional movements of the masticatory system:
3.2.1. Chewing:
a. Definition:
Chewing is the result of an extremely complex activity of the masticatory and digestive systems.
It includes a series of mandibular movements beginning with the introduction of food into the oral cavity and ending, after mechanical and physicochemical preparation, with the swallowing of the food bolus.
It is an acquired function that develops as soon as the temporary teeth appear.
b. Stages of chewing:
a. The incision:
The muscle movements being symmetrical, the movement takes place in the sagittal plane.
We observe the contraction of: – The deep masseters – The posterior temporals – The superior lateral pterygoids control the joint relationships.
b. Chewing itself:
Chewing movements are within the limit movements.
During a chewing cycle, muscle activities can be divided into 2 main phases:
→ Preparatory phase: This is a preparatory phase of remote opening and closing of the teeth with medium intensity muscle contractions.
→ Dento-dental phase: Subdivided into a dental cycle entry and a dental cycle exit. With high intensity muscle contractions.
3.2.2. Swallowing:
a. Definition:
It is the act by which the oral contents (saliva + liquid / bolus) are propelled from the mouth into the stomach. It follows chewing.
The total daily duration of chewing is about twenty minutes, but we swallow 500-2000 times/24h (LEHR), it increases during meals and decreases during sleep.
The consequences of poorly balanced swallowing are therefore very significant and certainly more dangerous than those of chewing.
b. Stages of swallowing:
- 1st time: oral time
It is voluntary, non-reflexive, conscious. Preparation of the food bolus requires sealing of the oral cavity with contraction of the orbicularis, the buccinator and the supra and subhyoid muscles, then the masticatory muscles.
- 2nd step: passage from the mouth to the pharynx:
Conscious but not voluntary. We are witnessing: Propulsion of the bolus towards the pharynx, anteroposterior sweeping movement of the tongue, very rapid respiratory inhibition.
- 3rd time: esophageal: Purely reflex, occurs one second after the start of swallowing, the mandible returns to its resting position. Breathing begins again and the organs of the oral cavity relax.
3.2.3. Phonation:
It is an essential act of human life, it allows communication between individuals. It is the first function to be developed at birth. It is represented by the child’s cry.
Phonation involves 3 levels: buccal, respiratory, glottic.
During the phonatory function, it is possible to study three types of contacts:
- Teeth – lips
- Teeth – tongue
- Teeth – teeth
GIBBS notes that the space used by a subject, when speaking:
Seen in a frontal plane, it is much narrower than that of mastication, there is almost no lateral displacement and a very small vertical movement that never reaches the PIM.
Viewed in a sagittal plane the anteroposterior space is notable, but vertical movement is limited.
- Conclusion :
Occlusion, like chewing or swallowing, results from mandibular movements , the latter are initiated and directed by the nervous system which, after analysis, transmits this information to the masticatory muscles .
Any dysfunction of the neuromuscular complex will cause a disturbance of mandibular movements and therefore occlusion, it is therefore important to define not only the anatomy of the muscles, but also the neurophysiology of the masticatory system in order to be able to diagnose any dysfunction.
Neurophysiology of the masticatory system
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