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The muscles responsible for chewing, also known as mastication, are the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles work together to coordinate the movements needed for chewing and crushing food. The masseter muscle is the strongest muscle involved in mastication and is responsible for elevating the mandible and closing the jaw. The temporalis muscle is also one of the strongest muscles in the human body, generating significant biting force. The medial pterygoid and lateral pterygoid muscles work together to produce the sideways movement of the jaw needed for chewing food.
| Characteristics | Values |
|---|---|
| Muscle Name | Masseter |
| Muscle Type | Quadrangular, composed of two layers |
| Muscle Function | Elevates the lower jaw, assists in protrusion/forward movement of the lower jaw |
| Muscle Attachments | The superficial layer arises from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic arch |
| Innervation | Masseteric nerve, a branch of the mandibular nerve |
| Blood Supply | Masseteric artery, a branch of the maxillary artery |
| Hypertrophy Causes | Emotional stress, chronic clenching/grinding, repetitive habits like gum chewing |
| Hypertrophy Treatment | Splint therapy, behaviour therapy, botulinum toxin injection therapy, surgery |
| Other Chewing Muscles | Temporalis, Medial Pterygoid, Lateral Pterygoid |
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What You'll Learn
- Masseter muscle: a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible
- Temporalis muscle: a fan-shaped muscle with anterior fibres that help elevate the mandible
- Lateral pterygoid muscle: a triangular muscle with two heads that protracts the jaw
- Medial pterygoid muscle: a thick, rectangular muscle with two heads that assists in the elevation of the mandible
- Buccinator, suprahyoid, and infrahyoid muscles: accessory muscles that aid the primary muscles of mastication
Masseter muscle: a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible
The masseter muscle is one of the four muscles responsible for mastication, or the act of chewing. It is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. The masseter muscle helps to elevate the mandible and assist in the protrusion or forward movement of the lower jaw, enabling functions such as chewing and grinding.
The masseter muscle is composed of two layers: a larger, superficial layer and a smaller, deeper layer. The superficial portion of the masseter muscle originates from the temporal process of the zygomatic bone and the anterior two-thirds of the inferior border of the zygomatic arch. The deep portion of the masseter muscle originates from the entire surface of the zygomatic arch. The fibres of the superficial and deep portions converge as they insert along the angle and lateral surface of the mandibular ramus.
The masseter muscle is innervated by the mandibular division of the trigeminal nerve. Its blood supply is derived from the masseteric artery, a branch of the maxillary artery. The masseter muscle can become enlarged or hypertrophied due to various factors such as emotional stress, chronic clenching or grinding of the teeth, and repetitive habits such as chewing gum.
Treatment options for masseter muscle hypertrophy include conservative or non-surgical therapies such as splint therapy, behaviour therapy, and botulinum toxin injection therapy. In some cases, surgical procedures such as partial removal of the masseter muscle or liposuction may be considered. Singers often experience masseter tension, which can be relieved through transdermal massages or stretches as part of vocal warm-up routines.
The word "masseter" originates from the Greek word "masasthai," which means "to chew," reflecting its crucial role in the chewing or mastication process.
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Temporalis muscle: a fan-shaped muscle with anterior fibres that help elevate the mandible
The temporalis muscle is a fan-shaped muscle that is thin and broad, occupying most of the temporal fossa. Its origin point spans the entire surface of the fossa below the temporal line. The temporalis muscle is one of the four primary muscles of mastication (chewing food), along with the medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the rami of the mandible and function to move the jaw.
The temporalis muscle is divided into anterior, mid, and posterior parts. The anterior fibres run inferiorly in a vertical direction, while the mid fibres have an oblique orientation and the posterior fibres are directed horizontally. The 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.
The function of the anterior and mid fibres of the temporalis muscle is to elevate the mandible, while the posterior fibres function to retract the mandible. The contraction of the anterior fibres moves the mandible dorsocranially (elevation), while the contraction of the posterior fibres pulls the mandible backward (retrusion). In unison, these actions facilitate the closing of the mouth and the approximation of the teeth.
The temporalis muscle is the strongest muscle of the temporomandibular joint and the primary retractor of the mandible. It also contributes to side-to-side grinding movements of the jaw. The unilateral contraction of the temporalis muscle is important for the side-to-side movements of the jaw.
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Lateral pterygoid muscle: a triangular muscle with two heads that protracts the jaw
The lateral pterygoid muscle is a craniomandibular muscle with a triangular shape and two heads, the superior and inferior. The inferior belly is three times larger than the superior belly. It is the major protractor of the mandible, or jaw, and is the only muscle of mastication that assists in depressing the mandible (opening the jaw). The lateral pterygoid is active during mastication and mandibular movements, including protrusion (forward movement of the mandible), abduction (depression of the mandible), and mediotrusion (mandibular condyle movement towards the midline).
The lateral pterygoid muscle works particularly during speaking, singing, and clenching. It is also active during functional and parafunctional lateral excursive movements, such as the chewing stroke, masticating, and clenching. When both bellies of the lateral pterygoid muscle contract bilaterally, the mandible travels anteriorly (protrusion). The unilateral contraction of the lateral pterygoid muscle with the ipsilateral medial pterygoid muscle results in lateral mandibular movement to the contralateral side.
The lateral pterygoid muscle is the only muscle of mastication with horizontally arranged fibres. It is analogous to the temporalis muscle, which is fan-shaped and exhibits a continuous range of anteroposterior movements, while the lateral pterygoid muscle exhibits a range of mediolateral and superoinferior movements. The origin of both the bellies of the lateral pterygoid muscle is medial to their insertions. This means that the wide opening of the mandible may temporarily result in the mandible undergoing distortion in the transverse plane.
The lateral pterygoid muscle also plays a crucial role in controlling the function of the jaw and temporomandibular joint, as well as in generating the horizontal forces required during mastication and parafunctional activities.
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Medial pterygoid muscle: a thick, rectangular muscle with two heads that assists in the elevation of the mandible
The medial pterygoid muscle is a thick, rectangular 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 of the sphenoid bone. 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. The outer surface of the medial pterygoid muscle is in contact with 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 is one of the four muscles of mastication, along with the lateral pterygoid, masseter, and temporalis muscles. These muscles are responsible for the chewing movement of the mandible at the temporomandibular joint, enhancing the process of eating and assisting in grinding food. The medial pterygoid muscle assists in the elevation of the mandible, with unilateral contraction causing a slight medial rotation of the mandible and bilateral contraction resulting in elevation and protrusion of the mandible. The combination of bilateral contraction of the medial pterygoid and lateral pterygoid muscles leads to the protrusion of the mandible.
The medial pterygoid muscle is innervated by the medial pterygoid branch of the mandibular division of the trigeminal nerve (CN V3). Its blood supply is derived from the pterygoid branches of the maxillary artery. The medial pterygoid muscle can sometimes be injured during an inferior alveolar nerve block due to its proximity to the nerve.
The medial pterygoid muscle also plays a role in closing the mouth. When pronouncing certain words or sounds that require closing the jaw, such as the "m" sound, the medial pterygoid muscle contracts to facilitate this movement.
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Buccinator, suprahyoid, and infrahyoid muscles: accessory muscles that aid the primary muscles of mastication
The masseter muscle is the strongest muscle involved in the act of chewing, or mastication. Mastication involves the adduction and lateral motion of the jaw bone, which is facilitated by four bilateral muscles in the face. The masseter muscle is the most powerful of these four muscles and is responsible for raising the lower jaw.
In addition to the four primary muscles of mastication, there are several accessory muscles that aid in the act of chewing. These include the buccinator, suprahyoid, and infrahyoid muscles.
The buccinator muscle is a thin, quadrilateral muscle occupying the interval between the maxilla and mandible at the side of the face. It forms the anterior part of the cheek or the lateral wall of the oral cavity. The muscle fibres converge toward the angle of the mouth, with the upper and lower fibres continuing forward into the corresponding lip.
The suprahyoid muscles are a group of four muscles located superior to the hyoid bone in the neck. They act to elevate the hyoid bone, which is involved in swallowing. The arterial supply to these muscles is via branches of the facial artery, occipital artery, and lingual artery.
The infrahyoid muscles are also a group of four muscles, located inferiorly to the hyoid bone in the neck. They can be divided into two groups: the superficial plane, which includes the omohyoid and sternohyoid muscles, and the deep plane, which includes the sternothyroid and thyrohyoid muscles. The arterial supply to the infrahyoid muscles is via the superior and inferior thyroid arteries.
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Frequently asked questions
The masseter muscle is the most powerful muscle for chewing. It is quadrangular in shape and has two parts: deep and superficial.
The masseter muscle's main function is to elevate the mandible, approximate the teeth, and assist in mastication.
The other chewing muscles are the temporalis, medial pterygoid, and lateral pterygoid muscles.
Overworking the masseter muscle can lead to pain or hypertrophy of the muscle. Masseter hypertrophy causes the jaw to appear wide and the face rectangular, which can cause psychological distress.
