Maximus Gage
The jaw muscles are complex, with a unique internal architecture. They are capable of generating a range of force vectors, which allow for a variety of movements. Jaw movements are driven by jaw, face, and tongue muscles, and can be classified as voluntary, reflex, or rhythmical. The mandible rotates forward during opening, and the temporomandibular joint allows for lateral movement. Jaw-closing muscles are larger than jaw-opening muscles, as they do most of the work during chewing.
| Characteristics | Values |
|---|---|
| Internal architecture | Complex, with a feather-like internal architecture |
| Activation | The central nervous system (CNS) activates separate compartments with specific directions of muscle fibres |
| Movement | The jaw rotates around an instantaneous centre of rotation |
| Masticatory movements | Complex, consisting of jaw, face, and tongue movements |
| Mandible | Rotates forward during opening |
| Temporomandibular joint | Allows lateral movements |
| Jaw-opener muscles | Anterior digastric, mylohyoid, and inferior head of the lateral pterygoid |
| Jaw-closer muscles | Masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid |
| Muscle spindles | Only the jaw-closing muscles have muscle spindles |
| Speech production | More specialised for speed than force |
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What You'll Learn
- The internal architecture of the jaw muscles is complex, with a feather-like structure
- The central nervous system (CNS) activates motor units in different muscles to generate jaw movements
- The cortical masticatory area activates jaw muscles through corticobulbar bilateral projections
- Jaw movements are complex, consisting of jaw, face, and tongue movements that are driven by jaw, face, and tongue muscles
- Jaw-closing muscles are larger with more motor units as they do most of the work during chewing
The internal architecture of the jaw muscles is complex, with a feather-like structure
The jaw can be described as rotating around an instantaneous centre of rotation at any given time during jaw movements. Masticatory movements are complex, consisting of jaw, face, and tongue movements that are driven by jaw, face, and tongue muscles. Changes to the occlusion can have significant effects on the activity of the jaw muscles and the movement of the jaw joint.
In humans, the mandible rotates forward during opening, and the temporomandibular joint allows lateral movements. Muscles that depress the mandible and thus open the jaw include the anterior digastric, mylohyoid, and inferior head of the lateral pterygoid. Jaw-closer muscles consist of the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid. The jaw-closing muscles do most of the work of chewing during the closing powerstroke, so they are larger with more motor units.
Like the skeletal muscles, there is contralateral motor control of the lips, tongue, and jaw with ipsilateral innervation to many of the muscles. The ipsilateral pathway provides much more assistance in speech muscles, generating bilateral synergistic movements.
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The central nervous system (CNS) activates motor units in different muscles to generate jaw movements
The central nervous system (CNS) plays a crucial role in activating motor units in different muscles to generate jaw movements. The internal architecture of the jaw muscles is complex, with a feather-like structure. The CNS is capable of activating separate compartments within each jaw muscle, allowing for the generation of various force vectors (magnitude and direction) required for specific jaw movements. This activation of motor units by the CNS results in the classification of movements into three types: voluntary, reflex, and rhythmical.
Several parts of the CNS are involved in the generation of jaw movements. At the cortical level, masticatory muscle areas are specifically represented. Stimulation of the cortical masticatory area activates jaw muscles through corticobulbar bilateral projections to the trigeminal motor nuclei and brainstem reticular formation. Neurophysiological studies have shown that electrical and magnetic transcranial stimulation (TMS) applied over the facial area of the motor cortex (M1) can evoke motor potentials in the contralateral jaw-closing muscles during voluntary contraction. This occurs due to the activation of corticobulbar fibres projecting to the contralateral trigeminal nucleus.
The jaw can be described as rotating around an instantaneous centre of rotation during jaw movements. Masticatory movements are complex and consist of coordinated actions involving the jaw, face, and tongue muscles. Changes to the occlusion, or alignment of teeth, can significantly impact the activity of jaw muscles and the movement of the jaw joint. The mandible rotates forward during the opening of the jaw, and the temporomandibular joint enables lateral movements as well.
The muscles responsible for depressing the mandible and opening the jaw include the anterior digastric, mylohyoid, and inferior head of the lateral pterygoid. In contrast, the jaw-closing muscles consist of the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid. The jaw-closing muscles are larger and have more motor units because they perform most of the work during the closing powerstroke of chewing. Additionally, these muscles are the only ones endowed with muscle spindles.
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The cortical masticatory area activates jaw muscles through corticobulbar bilateral projections
Neurophysiological studies in healthy humans have shown that both electrical and magnetic transcranial stimulation (TMS) applied over the facial area of the motor cortex (M1) evoke motor potentials in the contralateral jaw-closing muscles during voluntary contraction. This is due to the activation of corticobulbar fibres projecting to the contralateral trigeminal nucleus.
The internal architecture of the jaw muscles is complex, with many exhibiting a complex pennate (feather-like) internal architecture. The central nervous system (CNS) is capable of activating separate compartments with specific directions of muscle fibres within each of the jaw muscles. This means that each jaw muscle can generate a range of force vectors (magnitude and direction) required for a particular jaw movement.
The CNS activates motor units in different muscles to generate movements, which can be classified as voluntary, reflex, and rhythmical. Many parts of the CNS participate in the generation of jaw movements.
Masticatory movements are complex and consist of jaw, face, and tongue movements that are driven by jaw, face, and tongue muscles. Changes to the occlusion can have significant effects on the activity of the jaw muscles and the movement of the jaw joint.
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Jaw movements are complex, consisting of jaw, face, and tongue movements that are driven by jaw, face, and tongue muscles
The mandible rotates forward during jaw opening, and the temporomandibular joint enables lateral movements. Muscles responsible for depressing the mandible and opening the jaw include the anterior digastric, mylohyoid, and inferior head of the lateral pterygoid. In contrast, the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid are responsible for closing the jaw. The jaw-closing muscles are larger and have more motor units because they bear the brunt of the work during the closing powerstroke of chewing.
Neurophysiological studies have revealed that electrical and magnetic transcranial stimulation (TMS) applied over the facial area of the motor cortex (M1) can evoke motor potentials in the contralateral jaw-closing muscles during voluntary contraction. This occurs due to the activation of corticobulbar fibres projecting to the contralateral trigeminal nucleus. At the cortical level, masticatory muscle areas are specifically represented, and stimulation of the cortical masticatory area is believed to activate jaw muscles through corticobulbar bilateral projections, possibly mediating the initiation and control of jaw movements.
Speech muscles, including those involved in jaw movements, are specialised for speed and precise coordination of movement sequences. They exhibit different kinematics and force features at slow rates compared to normal and fast rates. The lips, tongue, and jaw also demonstrate contralateral motor control with ipsilateral innervation, contributing to bilateral synergistic movements.
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Jaw-closing muscles are larger with more motor units as they do most of the work during chewing
The internal architecture of the jaw muscles is complex, with many exhibiting a complex pennate (feather-like) internal architecture. Jaw movements are driven by jaw, face and tongue muscles. The jaw can be described as rotating around an instantaneous centre of rotation.
The jaw-closing muscles are larger with more motor units as they do most of the work during chewing. These muscles consist of the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid. The muscles of mastication show specialisations indicative of their specific roles during chewing. For example, only the jaw-closing muscles are endowed with muscle spindles.
At the cortical level, masticatory muscle areas are specifically represented. According to previous evidence in animals, stimulation of the cortical masticatory area activates jaw muscles through corticobulbar bilateral projections to the trigeminal motor nuclei and brainstem reticular formation. Neurophysiological studies in healthy humans showed that both electrical and magnetic transcranial stimulation (TMS) applied over the facial area of the motor cortex (M1) evoke motor potentials in the contralateral jaw-closing muscles during voluntary contraction due to the activation of corticobulbar fibres projecting to the contralateral trigeminal nucleus.
The central nervous system (CNS) appears capable of activating separate compartments with specific directions of muscle fibres. This means that each jaw muscle is capable of generating a range of force vectors (magnitude and direction) required for a particular jaw movement. In the generation of any desired movement, the CNS activates motor units in different muscles. Movements are classified into voluntary, reflex, and rhythmical.
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Frequently asked questions
The internal architecture of jaw muscles is complex, with many exhibiting a complex pennate (feather-like) internal architecture.
The central nervous system (CNS) activates motor units in different muscles to generate any desired movement. The jaw can be described as rotating around an instantaneous centre of rotation.
Muscles that depress the mandible and thus open the jaw include the anterior digastric, mylohyoid, and inferior head of the lateral pterygoid.
Jaw-closer muscles consist of the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid.
