Logan Steele
The muscles of mastication are a group of muscles responsible for the movement of the mandible at the temporomandibular joint (TMJ). They enable us to chew, grind food, and approximate our teeth. There are four main muscles of mastication: the masseter, the temporalis, and the medial and lateral pterygoids. These muscles originate from the surface of the skull and attach onto the rami of the mandible at the TMJ. The tongue, which is made up of eight interwoven muscles, also plays a role in closing the mouth by moving food towards the teeth and the throat.
| Characteristics | Values |
|---|---|
| Muscles Involved | Masseter, Temporalis, Pterygoid Medialis, Pterygoid Lateralis, Digastric, Mylohyoid, Tongue, Cheeks |
| Muscle Structure | The Masseter is a powerful, superficial quadrangular muscle with two divisions: superficial and deep. |
| Muscle Function | The Masseter, Temporalis, and Pterygoid Medialis are responsible for elevating the mandible and closing the mouth. The Pterygoid Lateralis and Digastric open the mouth by depressing and protracting the mandible. |
| Innervation | The muscles of mastication are innervated by the mandibular branch of the trigeminal nerve (CN V or CN V3). |
| Blood Supply | The Masseter receives blood supply from the masseteric artery, a branch of the internal maxillary artery. |
| Muscle Spindles | There are muscle spindles within the lingual muscles, and mesencephalic trigeminal neurons innervate muscle spindles in jaw-closer muscles. |
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What You'll Learn
The masseter muscle
Singers often experience various kinds of masseter tension, which can be treated with transdermal massages or stretches as part of their vocal warm-up routine. The masseter muscle is also important in the study of hystricognathous creatures, such as mole-rats, where it passes partially through the infraorbital foramen and connects to the bone on the opposite side. In toothed whales, the masseter muscle has become redundant due to a shift from chewing to swallowing, but it still provides tissue for acoustic fat bodies used for echolocation.
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The temporalis muscle
Tension in the temporalis muscle can cause pain in the temporal area. This can be caused by bruxism, the habitual grinding of teeth, often while sleeping, and clenching of the jaw while stressed. A myotendinous rupture of the temporalis muscle can occur during a seizure due to extreme clenching of the jaw. The temporalis muscle may be used in reconstructive surgery of the mouth.
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The pterygoid muscles
The lateral pterygoid is a short, two-headed muscle, located in the infratemporal fossa of the skull. The smaller superior head arises from the infratemporal crest of the greater wing of the sphenoid bone, while the larger inferior head arises from the lateral surface of the lateral pterygoid plate. The lateral pterygoid muscle is supplied by the lateral pterygoid nerve, a branch of the mandibular nerve (CN V3), itself a branch of the trigeminal nerve (CN V). The primary function of the lateral pterygoid muscle is to pull the head of the condyle out of the mandibular fossa along the articular eminence to protrude the mandible. A unilateral action of the lateral pterygoid muscle causes contralateral excursion, usually performed in concert with the medial pterygoids. When working independently, they can move the mandible from side to side.
The medial pterygoid muscle is a thick quadrilateral muscle that arises by two heads, a superficial 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 plate of the pterygoid process and the pyramidal process of the palatine bone. The medial pterygoid muscle is supplied by the medial pterygoid nerve, a branch of the mandibular nerve, itself a branch of the trigeminal nerve (V). The medial pterygoid muscle has functions including elevating the mandible (closing the mouth), protruding the mandible, and excursing the mandible (contralateral excursion occurs with unilateral contraction).
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The tongue
There are two groups of muscles associated with the tongue: the intrinsic muscles and the extrinsic muscles. The intrinsic muscles comprise the core of the tongue and are placed within it. They are responsible for altering the shape of the tongue, which is essential for tongue rolling, and they facilitate speech, eating, and swallowing. There are four paired intrinsic muscles: the superior longitudinal, inferior longitudinal, transverse, and vertical muscles of the tongue. These muscles are named based on the direction in which they travel. The motor innervation to the intrinsic muscles is via the hypoglossal nerve (CN XII).
The extrinsic muscles of the tongue originate from structures outside the tongue and insert into it. They are responsible for altering the position of the tongue. There are four pairs of extrinsic muscles: the genioglossus, hyoglossus, styloglossus, and palatoglossus. The genioglossus muscle is a large, thick muscle that contributes significantly to the shape of the tongue. It arises from the mandibular symphysis and inserts into the body of the hyoid bone and the entire length of the tongue. It is responsible for protrusion (sticking the tongue out) and depression of the tongue. The hyoglossus muscle is located in the floor of the oral cavity, immediately lateral to the geniohyoid. It arises from the hyoid bone and inserts into the lateral aspect of the tongue, and it is responsible for depression and retraction of the tongue. The styloglossus is a thin, paired muscle located on either side of the oropharynx. It originates from the styloid process of the temporal bone and inserts into the lateral aspect of the tongue, and it is responsible for retraction and elevation of the tongue. The palatoglossus muscle is associated with the soft palate and is innervated by the vagus nerve (CN X).
The lingual reflexes play important protective roles, such as protecting the tongue from the teeth during chewing. The tongue, along with the muscles of the cheeks, also contributes to ingestive oromotor behaviors, such as positioning food within the mouth and forming a seal to facilitate suckling or drinking.
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The buccinator and zygomatic muscles
The buccinator muscle is a thin, quadrilateral facial muscle that is the main component of the cheek. It is part of the buccolabial group of facial muscles, which also includes the levator labii superioris alaeque nasi, levator labii superioris, zygomaticus major, zygomaticus minor, levator anguli oris, risorius, depressor labii inferioris, mentalis, orbicularis oris, incisivus superior, and inferior muscles. The buccinator has several origin points, which form the basis for subdividing the muscle fibres into superior, inferior, and posterior parts. This muscle provides the cheek with structure and tightness.
The three parts of the buccinator converge towards the angle of the mouth and fill the space between the upper and lower jaws. At the angle of the mouth, the buccinator fibres interlace with other muscles that attach at the same site, including the orbicularis oris, risorius, depressor anguli oris, and zygomaticus major. Together, these muscles form a dense fibromuscular mass called the modiolus. The buccinator is innervated by the buccal branches of the facial nerve (CN VII) and vascularized mainly by the buccal branch of the maxillary artery, with contributions from the facial artery.
The function of the buccinator muscle is to compress the cheek against the molar teeth and prevent them from being bitten during mastication. It also helps to keep a bolus of food in the centre of the oral cavity and prevents it from escaping into the oral vestibule. The buccinator is important for playing wind instruments or whistling, as it allows air from the inflated vestibule to be blown out by compressing the cheeks.
The zygomaticus major and minor muscles are part of the buccolabial group of facial muscles and are involved in smiling and elevating and everting the upper lip.
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Frequently asked questions
The masseter muscle is one of the four muscles responsible for the action of mastication (chewing). When the masseter contracts, it causes powerful elevation of the mandible, causing the mouth to close.
The other three muscles are the temporalis, medial pterygoid, and lateral pterygoid.
The temporalis muscle fibres converge to form a tendon that exits the temporal fossa, passing underneath the zygomatic arch and inserting on the coronoid process of the mandible. It assists the masseter muscle in closing the mouth.
The medial pterygoid and lateral pterygoid muscles originate from two heads each and insert along the medial surface of the mandibular ramus. Their contraction causes elevation and protrusion of the mandible, assisting in closing the mouth.
