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The muscles of mastication, or chewing, are used to control the movements of the mandible, or jaw. The lateral pterygoid muscle is the major protractor, or opener, of the jaw. It has two heads, the upper and lower, known as the superior and inferior heads. When the lateral pterygoid muscle contracts, it opens the jaws by pulling the mandible downward and forward, and protrudes the mandible, causing the lower jaw to move forward. The lateral pterygoid muscle works in conjunction with other muscles involved in jaw movement, such as the masseter, temporalis, and medial pterygoid muscles.
| Characteristics | Values |
|---|---|
| Jaw elevators | Masseter, Temporalis, Medial pterygoid, Superior belly of lateral pterygoid |
| Jaw depressors | Inferior belly of lateral pterygoid, Anterior digastric, Geniohyoid, Mylohyoid |
| Jaw protrusion | Masseter, Medial pterygoid, Lateral pterygoid |
| Shape of Masseter | Quadrilateral |
| Consists of | Two portions, superficial and deep |
| Temporalis muscle | Elevates and retracts the jaw |
| Lateral pterygoid | Has a triangular shape with two heads, superior and inferior |
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What You'll Learn
Lateral pterygoid muscle
The lateral pterygoid muscle is a craniomandibular muscle with a crucial role in the inferior temporal region. It is one of the four muscles of mastication, along with the medial pterygoid, temporalis, and masseter muscles. These muscles act on the temporomandibular joint (TMJ) to enable chewing and biting. The lateral pterygoid muscle is the only one of these four muscles that participates in depressing the mandible (or opening the jaw).
The lateral pterygoid muscle is a two-headed, fan-shaped muscle located laterally in the infratemporal fossa of the skull. Its superior (upper) and inferior (lower) heads are separated by a small horizontal fissure. The superior head is formed by the most superomedial fibres of the muscle, which originate from the infratemporal crest of the greater wing of the sphenoid bone. The inferior head, which is much wider and three times larger than the superior head, originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone. Fibres from both heads converge to 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. The inferior fibres insert into the pterygoid fovea on the neck of the condyloid process of the mandible.
The lateral pterygoid muscle is supplied by the pterygoid branches of the maxillary artery and the lateral pterygoid nerve, a branch of the mandibular nerve (CN V3), itself a branch of the trigeminal nerve (CN V). The maxillary artery and buccal nerve pass through the split between the superior and inferior heads of the muscle. The muscle is also related to the mandibular ramus, temporalis tendon, and the masseter muscle on its lateral side, and the mandibular nerve, middle meningeal artery, the sphenomandibular ligament, and the upper part of the medial pterygoid muscle on its medial side.
The primary function of the lateral pterygoid muscle is to control the function of the jaw and temporomandibular joint. It does this by protruding and depressing the mandible when contracting bilaterally and rotating the mandible when contracting unilaterally. The unilateral contraction of the lateral pterygoid muscle with the ipsilateral medial pterygoid muscle results in lateral mandibular movement to the contralateral side. This movement is observable during functional and parafunctional lateral excursive movements, such as during a chewing stroke, masticating, and clenching.
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Masseter muscle
The masseter muscle is one of the four muscles of the masticatory apparatus, or the muscles of mastication (chewing). The word 'masseter' comes from the Greek 'masasthai', meaning 'to chew'. It is a powerful, thick, quadrilateral or quadrangular muscle with two divisions: superficial and deep. The superficial portion is the larger of the two, arising from the maxillary process of the zygomatic bone and the anterior two-thirds of the lower border of the zygomatic arch. Its fibres pass downwards and backwards, inserting into the angle and lower half of the lateral surface of the ramus of the mandible. The deep portion is smaller and is partly concealed by the superficial portion. It arises from the posterior third of the lower border and the whole of the medial surface of the zygomatic arch, with its fibres passing almost vertically downwards to insert into the upper half of the ramus of the mandible.
The masseter muscle is innervated by the masseteric nerve, a branch of the mandibular division (V3) of the trigeminal nerve. The trigeminal nerve carries both sensory and motor fibres. The masseter receives its blood supply from the masseteric artery, a branch of the maxillary artery, which in turn comes off the external carotid artery behind the neck of the mandible.
The masseter muscle's function is to elevate the mandible, causing a powerful closure of the jaw. The contraction of the superior part moves the mandible forward (protrusion). It also helps to stabilise the tension of the articular capsule of the temporomandibular joint. The masseter parallels the medial pterygoid muscle, but it is stronger and can cause protrusion. The masseter muscle can become enlarged in patients with bruxism (teeth-grinding) or those who constantly chew gum. This masseteric hypertrophy is usually bilateral but can be unilateral, and can cause asymmetry of the face.
The masseter muscle is easily palpated from the oral cavity along the cheek. It is a distinguishing feature of hystricognathous creatures such as mole-rats, where it passes partially through the infraorbital foramen and connects to the bone on the opposite side.
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Medial pterygoid muscle
The medial pterygoid muscle is a thick, quadrilateral-shaped muscle that connects the mandible with the maxilla, sphenoid, and palatine bones. It is one of the muscles of mastication (chewing) and is involved in controlling the movements of the mandible. The medial pterygoid muscle is located in the infratemporal fossa, lying deep to the masseter and temporalis muscles and medial to the lateral pterygoid muscle. Its outer surface is related to the inner surface of the mandible, from which it is separated by the lateral pterygoid muscle, the sphenomandibular ligament, the maxillary artery, and the mandibular nerve and its branches.
The medial pterygoid muscle has several functions, including elevating the mandible (closing the mouth), protruding the mandible, and assisting in mastication, especially when the maxillary and mandibular teeth are close together. It also helps in excursing the mandible, with unilateral contraction causing a rotation of the mandible and bilateral contraction resulting in elevation and protrusion. The muscle consists of two heads, superficial and deep, that work together to create a strong pull on the mandible.
The medial pterygoid muscle is innervated by the medial pterygoid nerve, a branch of the mandibular nerve (V3), which is itself a branch of the trigeminal nerve (V). It receives its blood supply primarily from the pterygoid and buccal branches of the maxillary artery, with contributions from the ascending palatine artery and muscular branches of the facial artery. The vascular supply to the medial pterygoid muscle can also, in some cases, come directly from a branch of the external carotid artery.
The medial pterygoid muscle is an important structure in the head and neck anatomy, and its function is crucial for chewing and jaw movement. Its synergy with other masticatory muscles, such as the lateral pterygoid, masseter, and temporal muscles, facilitates the complex movements of the jaw during chewing and speaking. Understanding the anatomy and function of the medial pterygoid muscle is valuable in clinical practice, especially in the diagnosis and treatment of conditions such as bruxism, which involves the abnormal functioning of these muscles.
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Temporalis muscle
The temporalis muscle, also known as the temporal muscle, is a thin, broad, fan-shaped muscle on each side of the head. It fills the temporal fossa, superior to the zygomatic arch, and covers much of the temporal bone. The zygomatic arch is the temporal region of the skull, located roughly at the level of the cheekbones. The temporal muscle is the most active postural muscle, maintaining the mandible in its rest position.
The temporalis muscle is one of the muscles of mastication, or chewing. It is the most powerful muscle of the temporomandibular joint. The muscle can be divided into two functional parts: the anterior and posterior. The anterior portion runs vertically, and its contraction results in the elevation of the mandible (closing the mouth). The posterior portion has fibres that run horizontally, and contraction of this portion results in retrusion of the mandible. The middle portion, where the fibres run in an oblique direction towards the inferior and anterior, is used for both elevation and retraction of the mandible. The unilateral contraction of the temporalis muscle is important for side-to-side movements of the jaw.
The temporalis muscle is covered by the temporal fascia, also known as the temporal aponeurosis. The muscle is accessible on the temples and can be seen and felt contracting while the jaw is clenching and unclenching. The muscle receives its blood supply from the deep temporal arteries, which anastomose with the middle temporal artery. The temporalis muscle is derived from the first pharyngeal arch in development.
The temporalis muscle is likely to be involved in jaw pain and headaches. Bruxism, the habitual grinding of teeth, typically while sleeping, and clenching of the jaw while stressed, can lead to overwork of the temporalis muscle and result in pain. A myotendinous rupture of the temporalis muscle can occur during a seizure due to extreme clenching of the jaw.
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Muscles of mastication
The muscles of mastication, or chewing, are a group of muscles that control the movements of the mandible, or jaw. They enhance the process of eating by assisting in grinding food and bringing the teeth together. The four main muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the rami of the mandible and function to move the jaw. The masseter muscle is the most powerful muscle of mastication.
The muscles of mastication can be divided into primary and secondary, or accessory, muscles. The primary muscles of mastication are responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint. The TMJ is a bilateral structure, meaning it is present on both sides of the body. The four cardinal mandibular movements of mastication are elevation, depression, protrusion, retraction, and side-to-side movement. Three out of the four main muscles are responsible for adduction of the mandible, and one helps in the abduction of the mandible.
The temporalis muscle is a fan-shaped muscle with anterior fibres that have a vertical orientation, mid fibres that have an oblique orientation, and posterior fibres that have a horizontal orientation. The origin of the temporalis muscle spans from the temporal fossa to the inferior temporal line of the lateral skull. The fibres of the temporalis muscle converge inferiorly, forming a tendon that exits the temporal fossa, passing underneath the zygomatic arch and inserting on the coronoid process of the mandible. The temporalis muscle is the most active postural muscle, maintaining the mandible in its rest position.
The medial pterygoid muscle has a quadrangular shape with two heads: deep and superficial. It is located inferiorly to the lateral pterygoid. The medial pterygoid assists in approximating the mandible to the maxillae. Acting with the lateral pterygoid, it protrudes the mandible. The lateral pterygoid muscle assists in opening the mouth by pulling forward the condyloid process of the mandible and the articular disc, while the body of the mandible is being depressed by the suprahyoid muscles. The lateral pterygoid also assists with protrusion and side-to-side movement of the mandible.
The masseter muscle is a rectangularly shaped muscle with three layers: superficial, deep, and intermediate. The superficial portion, the larger of the two, arises by a thick aponeurosis from the zygomatic process of the maxilla and from the anterior two-thirds of the lower border of the zygomatic arch. Its fibres pass downwards and backwards, inserting into the angle and lower one-half of the lateral surface of the ramus of the mandible. The deep portion is much smaller and is partly concealed by the superficial portion. Its fibres pass almost vertically downwards to be inserted into the lateral surfaces of the coronoid process and the upper one-half of the ramus of the mandible. The major function of the masseter muscle is to elevate the mandible and approximate the teeth.
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Frequently asked questions
The lateral pterygoid muscle is responsible for protruding the jaw.
The lateral pterygoid muscle is triangular in shape and has two heads, the superior and inferior.
The lateral pterygoid muscle has two main actions. Firstly, it opens the jaws by pulling the mandible downward and forward, which is important for activities like biting, chewing, and speaking. Secondly, it protrudes the mandible, causing the lower jaw to move forward.
