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The muscles of mastication, also known as the masticatory muscles, are a group of four muscles that move the jaw in the temporomandibular joint (TMJ). These muscles are involved in movements such as protrusion, retraction, elevation, depression, and rotation of the mandible, enabling functions like chewing and grinding teeth. Unlike most facial muscles, they are innervated by the trigeminal nerve (CN V), specifically the mandibular branch (V3), which is both sensory and motor. The mandible is the only bone that moves during mastication and other activities such as talking.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 |
| Muscle names | Medial pterygoid, lateral pterygoid, temporalis, masseter |
| Muscle location | Temporal fossa (temporalis), cheek area (masseter), infratemporal fossa (medial and lateral pterygoids) |
| Function | Chewing, grinding teeth, elevation, depression, protrusion, retraction, rotation of the mandible |
| Innervation | Trigeminal nerve (cranial nerve V), specifically the mandibular branch (V3) |
| Embryological origin | First pharyngeal arch |
| Visibility | Deep but visible as they are not completely hidden by bone |
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What You'll Learn
The four primary muscles of mastication
The muscles of mastication, or masticatory muscles, are a group of four muscles that move the jaw in the temporomandibular joint (TMJ). These muscles enable functions such as chewing and grinding the teeth through movements like protrusion, retraction, elevation, depression, and rotation of the mandible.
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The role of the tongue and cheeks
The muscles of mastication, or masticatory muscles, are a group of four muscles that enable functions such as biting and chewing. These muscles are the temporalis, masseter, and medial and lateral pterygoids. They are attached to the mandible, or lower jaw, and work in opposition to the muscles responsible for opening the mouth, such as the geniohyoid, mylohyoid, and digastric muscles.
During mastication, the tongue and cheeks work together to move chewed food into the cheek pouch on one side. This creates a space beside the tongue into which food can be squeezed from the other cheek pouch by the buccinator muscle. This process is controlled by pressure receptors on the tongue and cheeks, as well as joint receptors around the temporomandibular joints. The tongue also plays a role in crushing food against the hard palate.
The tongue and cheeks are important in the development of mastication in early childhood. Their movements transform from synergistic and undifferentiated in infants to differentiated and refined in toddlers and young children, enabling functions such as biting, chewing, and bolus formation and propulsion. The development of the lips and tongue also plays a role in achieving mature mastication efficiency, although this occurs at different rates for each individual.
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The temporomandibular joint (TMJ)
The four mastication muscles that move the jaw in the TMJ are the medial and lateral pterygoid, temporalis, and masseter. The masseter is the most prominent masticatory muscle, and it works with the temporalis muscle to produce biting force. The pterygoid muscles enable the full range of lower jaw motion and control the articular disc's position in the TMJ.
Temporomandibular disorder (TMD) is a condition that arises when there is a problem with the TMJ and its associated muscles and bones. TMD can be caused by a variety of factors, including jaw injuries, joint disease, and arthritis. It is also believed that bruxism (tooth clenching or grinding) and head or neck muscle tension may contribute to TMD symptoms. TMD can be treated in several ways, including relaxation techniques, medication, and, in extreme cases, surgery.
The TMJ is innervated by the trigeminal nerve, and its muscles work in opposition to those responsible for opening the mouth. The TMJ is a crucial component of the skull, enabling essential functions such as chewing and speaking.
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The medial and lateral pterygoid muscles
The medial pterygoid muscle is a thick, quadrilateral-shaped muscle with two heads: a superficial head and a deep head. The smaller superficial head originates from the maxillary tuberosity and pyramidal process of the palatine bone. The larger deep head originates from the medial surface of the lateral pterygoid plate and the pyramidal process of the palatine bone. The medial pterygoid muscle has a triple function. Firstly, when contracted bilaterally with the lateral pterygoid muscle, it results in the protrusion of the mandible. Secondly, when contracted unilaterally with the lateral pterygoid muscle, it causes a lateral movement of the mandible towards the opposite side. Thirdly, it works together with the masseter and temporalis muscles to elevate the mandible.
The lateral pterygoid muscle is a short, two-headed muscle with a triangular shape. The smaller superior head arises from the infratemporal crest of the greater wing of the sphenoid bone, while the larger inferior head originates from the lateral surface of the lateral pterygoid plate. The fibres of both heads merge and insert on the pterygoid fovea on the neck of the mandible. The lateral pterygoid muscle is the only muscle in the head region with two different origins. Its primary function is to protrude and depress the mandible when contraction is bilateral. In unilateral contraction, the lateral pterygoid muscle moves the mandible medially, resulting in a 'side-to-side' movement of the jaw.
The pterygoid muscles receive their blood supply from branches of the maxillary artery, with the medial pterygoid muscle also receiving supply from the facial artery through its muscular branches. These muscles are innervated by branches of the mandibular division of the trigeminal nerve (CN V3).
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The masseter muscle
The word "masseter" comes from the Greek "masasthai", meaning "to chew". The masseter muscle's positioning is a distinguishing feature of hystricognathous creatures, such as mole-rats, and it also provides the tissue for acoustic fat bodies in toothed whales, which use them for echolocation.
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Frequently asked questions
Muscles of mastication, or masticatory muscles, are a group of four muscles that move the jaw in the temporomandibular joint (TMJ). They enable functions such as chewing and grinding teeth.
The four muscles of mastication are the medial pterygoid, lateral pterygoid, temporalis, and masseter.
The muscles of mastication enable the movement of the mandible, including protrusion, retraction, elevation, depression, and rotation. They work in opposition to the muscles responsible for opening the mouth.
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