Maximus Gage
The muscles responsible for opening the mouth are known as the muscles of mastication. These muscles are innervated by the mandibular division of the trigeminal nerve and are supplied with blood by the maxillary artery. The four main muscles of mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles work together to open and close the mouth by influencing the motion of the mandible, or jawbone.
| Characteristics | Values |
|---|---|
| Number of muscles of mastication | 4 |
| Names of muscles of mastication | Masseter, temporalis, medial pterygoid, lateral pterygoid |
| Muscles supplied by the trigeminal nerve | Masseter, pterygoids |
| Muscles involved in protrusion of the mandible | Masseter, medial pterygoid |
| Muscles involved in side-to-side movement | Medial pterygoid |
| Muscles involved in grinding movements | Temporalis |
| Muscles involved in the abduction of the mandible | Lateral pterygoid |
| Muscles involved in the depression of the mandible | Lateral pterygoid |
| Muscles involved in ingestive oromotor behaviors | Posterior belly of the digastric, orbicularis oris, buccinator, zygomatic |
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What You'll Learn
The masseter muscle
The masseter is one of the four primary muscles of mastication, which is the process of chewing. It is a powerful, thick, and rectangular muscle that originates from the zygomatic arch and inserts along the angle and lateral surface of the mandibular ramus. The masseter is primarily responsible for the elevation of the mandible, causing a powerful jaw closure, and some protraction of the mandible. The masseter muscle is innervated by the anterior division of the mandibular division (V3) of the trigeminal nerve, also known as the masseteric nerve. The blood supply to the masseter muscle is provided primarily by the masseteric artery, a branch of the maxillary artery, which was previously known as the internal maxillary artery.
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The temporalis muscle
Tension in the temporalis muscle can cause pain in the temporal area, and it is often involved in jaw pain and headaches. Bruxism, or the habitual grinding of teeth, can lead to overwork of the muscle and subsequent pain. A myotendinous rupture of the muscle can occur during a seizure due to extreme clenching of the jaw.
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The medial pterygoid muscle
The primary function of the medial pterygoid muscle is to produce movements of the mandible at the temporomandibular joint. Unilateral contraction of the medial pterygoid muscle causes a slight medial rotation of the mandible. When this occurs simultaneously with the contraction of the ipsilateral lateral pterygoid, it results in a noticeable movement where the same-sided part of the mandible swings anteriorly and medially. Bilateral contraction of the medial pterygoid muscle, on the other hand, elevates and protrudes the mandible, contributing to the closing of the mouth.
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The lateral pterygoid muscle
The inferior belly of the lateral pterygoid muscle is much wider than the superior belly, and it originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone. The fibres from both bellies converge and course posterolaterally in a predominantly horizontal plane. The superior fibres insert into the anteromedial part of the articular capsule and articular disc of the temporomandibular joint, while the inferior fibres insert into the pterygoid fovea on the neck of the condyloid process of the mandible.
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The digastricus muscle
The digastric muscle is comprised of two parts: the anterior and posterior bellies, joined by an intermediate tendon. The two bellies have different embryological origins and are supplied by different cranial nerves. The anterior belly is derived from the first brachial arch and is innervated via CN V, while the posterior belly originates from the second brachial arch and is innervated via CN VII. The intermediate tendon may be absent in some cases.
The posterior belly of the digastric muscle originates at the medial surface of the mastoid notch of the temporal bone. It travels anteroinferiorly towards the hyoid bone, piercing the stylohyoid muscle before attaching to the intermediate tendon. The anterior belly, on the other hand, originates from the digastric fossa of the lower border of the mandible near the midline. It extends posteroinferiorly from the mandible, joining with the intermediate tendon. The two bellies meet at the intermediate tendon, which perforates the stylohyoideus muscle.
The digastric muscle is involved in depressing the mandible when the hyoid bone is held in place by the infrahyoid muscles. The posterior belly is particularly important in swallowing and chewing. The digastric muscles are present in various animals, and specific attachment sites may vary. For example, in orangutans, the posterior digastric attaches to the mandible rather than the hyoid.
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Frequently asked questions
The muscles that open the mouth are the masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. Its major function is to elevate the mandible.
The temporalis muscle functions mainly as an elevator of the mandible. Its contraction also produces a retraction of the mandible, pulling the jaw backward.
The medial pterygoid muscle is a quadrangular muscle with two heads: deep and superficial. Its major functions are the elevation of the mandible and side-to-side movements during grinding and chewing.
The lateral pterygoid muscle is the only muscle that actively opposes the other muscles of mastication, allowing for depression of the mandible. Its contraction allows for the protraction of the mandible and the anterior motion of the temporomandibular joint, facilitating mouth opening.
