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The human body is a fascinating structure, with many muscles working in tandem to perform various functions. One such function is the opening of the mouth, which is made possible by the lateral pterygoid muscle. This muscle is the major protractor (opener) of the jaw, and it works in conjunction with other muscles to enable the full range of lower jaw motion. The masseter, temporalis, and medial pterygoid muscles also play a role in jaw movement, but their primary function is to assist in closing the mouth. These muscles are all controlled by the mandibular branch of the trigeminal nerve, allowing us to open our jaw, move it left and right, and close it with incredible force.
| Characteristics | Values |
|---|---|
| Main muscle that opens the mouth | Lateral pterygoid |
| Other muscles that help open the mouth | Masseter, temporalis, and medial pterygoid |
| Location of the masseter muscle | Runs from the side of the skull down to the bottom of the jawbone |
| Location of the temporalis muscle | Along the side of the skull |
| Location of the lateral pterygoid muscle | On the inner side of the mandible |
| Shape of the lateral pterygoid muscle | Triangular with two heads |
| Function of the lateral pterygoid muscle | Opener of the jaw, assists in side-to-side motion |
| Function of the medial pterygoid muscle | Elevates and closes the jaw, assists in mastication |
| Innervation | Mandibular branch of the trigeminal nerve |
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What You'll Learn
The lateral pterygoid muscle opens the mouth
The lateral pterygoid muscle is one of four masticatory muscles, along with the masseter, temporalis, and medial pterygoid muscles. These muscles control the movements of the mandible, or lower jaw. The lateral pterygoid muscle is responsible for opening the mouth, as well as deviation to either side, and anterior movement of the jaw. It is a short, thick muscle with two heads: the upper head and the lower head.
The upper head of the lateral pterygoid muscle originates on the infratemporal surface of the sphenoid bone, while the lower head originates on the lateral surface of the lateral pterygoid plate of the sphenoid bone. The insertion of both heads is on the fovea of the neck of the condyle of the mandible and on the articular disc. The lateral pterygoid muscle fibres converge inferiorly, forming a tendon that inserts into a depression on the neck of the condylar process of the mandible, along with the articular capsule and disc of the temporomandibular articulation.
The lateral pterygoid muscle is supplied by the pterygoid branches of the maxillary artery and the lateral pterygoid nerve, which is a branch of the mandibular nerve. It is located deep to the temporalis and masseter muscles, spanning between the sphenoid bone and the temporomandibular joint. The muscle belly is separated by a small horizontal fissure into two heads: the superior (upper) head and the inferior (lower) head. The superior head is formed by the most superomedial fibres of the muscle, while the inferior head is much wider and originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone.
The lateral pterygoid muscle contributes to the function of mastication by protruding and depressing the mandible when contracting bilaterally and by rotating the mandible when contracting unilaterally. Side-to-side movements of the jaw occur when the inferior head contracts unilaterally, rotating the mandibular condyle anteromedially. This movement occurs in synergy with the contraction of the ipsilateral medial pterygoid muscle, which swings the jaw to the opposite side.
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The masseter muscle closes the mouth
The masseter muscle is one of four muscles responsible for the action of mastication (chewing). It is a powerful muscle, with a quadrangular shape and two parts: deep and superficial. The masseter muscle is the most powerful muscle of mastication and is responsible for the elevation of the mandible, or jaw bone, bringing the teeth together in a chewing motion. This is achieved through the contraction of its superior part, which causes a powerful jaw closure.
The masseter muscle works in conjunction with two other jaw-closing muscles, the temporalis and the medial pterygoid. The temporalis muscle originates from the floor of the temporal fossa and inserts onto the coronoid process of the mandible. The medial pterygoid has a similar function to the masseter muscle, causing elevation and protrusion of the mandible. The masseter muscle is relatively well conserved across the human population and the animal kingdom.
The masseter muscle is innervated by the mandibular branch of the trigeminal nerve (CN V or V3). The mandibular nerve is both sensory and motor. The masseter reflex, or jaw-jerk reflex, involves placing a finger on the chin of a patient and striking the finger with a reflex hammer. This downward force can cause a reflex action in the masseter muscles, resulting in an elevation of the mandible.
The masseter muscle is a primary muscle of mastication and is one of the strongest muscles in the human body. It is responsible for the chewing movement of the mandible at the temporomandibular joint (TMJ). The superficial part of the masseter muscle functions to move the mandible or lower jaw forward, bringing the lower front teeth in front of the upper front teeth.
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The temporalis muscle retracts the jaw
The temporalis muscle is a fan-shaped muscle with anterior, mid, and posterior fibres. The function of the temporalis muscle depends on the direction of its fibres. While the anterior and mid fibres help in elevating the mandible, the posterior fibres aid in retracting the mandible. The temporalis muscle is a powerful muscle of the temporomandibular joint. It is located in the temporal region of the head and is accessible on the temples. It is one of the muscles of mastication (chewing). It is a major component of the human masticatory system, along with the muscles of mastication, supporting the ligaments, maxilla, mandible, and teeth. The temporalis muscle is derived from the first pharyngeal arch in development. It is also known as the temporal muscle.
The masseter muscle is a powerful muscle that helps in the elevation of the mandible, leading to mouth closure. The medial pterygoid muscle is responsible for closing and lateral movements of the mandible. The lateral pterygoid muscle functions as the main depressor muscle, leading to the opening of the jaw. The mandibular nerve is the largest and most inferior division of the trigeminal nerve. The temporalis muscle receives innervation by deep temporal branches of the mandibular nerve. 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.
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The medial pterygoid muscle elevates the jaw
The medial pterygoid muscle is a thick, quadrilateral muscle of the face, with two heads: a superficial head and a deep head. The deep head forms the bulk of the muscle. The muscle is supplied by the mandibular branch of the trigeminal nerve (V).
The medial pterygoid muscle is responsible for several actions, including elevating the mandible (closing the mouth). This action is achieved through the bilateral contraction of the muscle, which also results in protrusion of the mandible. The protrusion occurs as the muscle pulls the mandible forward. This movement is important for chewing.
Unilateral contraction of the medial pterygoid muscle causes a slight medial rotation of the mandible. When this unilateral contraction occurs in conjunction with the contraction of the ipsilateral lateral pterygoid, the same-sided part of the mandible swings anteriorly and medially. Alternating contractions of the medial and lateral pterygoids cause side-to-side movements of the mandible.
The medial pterygoid muscle is located in the infratemporal fossa of the skull, lying deep to the masseter and temporalis muscles. The outer surface of the muscle lies against the inner surface of the mandible, from which it is separated by the lateral pterygoid muscle, sphenomandibular ligament, maxillary artery, mandibular nerve, and its lingual and inferior alveolar branches. The medial pterygoid is susceptible to injury during inferior alveolar nerve block due to its proximity to the nerve.
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The digastric, mylohyoid, and geniohyoid muscles depress the jaw
The human mouth is a complex system of muscles, bones, and ligaments that work together to facilitate essential functions such as chewing, swallowing, and speaking. The mandible, or lower jaw, plays a crucial role in these processes, and its movement is influenced by various muscles.
One group of muscles that contribute to mandibular movement is the accessory muscles of mastication. These muscles, including the digastric, mylohyoid, and geniohyoid muscles, work in coordination to depress the jaw and facilitate opening the mouth.
The digastric muscle, for instance, has two bellies: the anterior belly and the posterior belly. The anterior belly originates from the mandible, while the posterior belly originates from the mastoid notch, a groove in the temporal bone. Both bellies insert on the hyoid bone, which is a small, U-shaped bone located below the mandible. When the digastric muscle contracts, it can cause depression of the mandible, especially when the hyoid bone is locked in place by the strap muscles.
The mylohyoid muscle, a flat and triangular-shaped muscle, is another accessory muscle of mastication. It originates from the mylohyoid line of the mandible and inserts on the hyoid bone. This muscle is crucial for depressing the mandible, especially when other muscles stabilize the hyoid bone. Additionally, the mylohyoid muscle forms the floor of the oral cavity, creating a muscular base for the mouth opening.
The geniohyoid muscle is the third muscle in this group and is responsible for depressing the mandible. It originates from the mental spine of the mandible and inserts on the hyoid bone. Contraction of the geniohyoid muscle not only depresses the mandible but also elevates and protrudes the hyoid bone forward.
These three muscles, along with other accessory muscles of mastication, assist in jaw opening by coordinating their movements through attachments to the hyoid bone. This complex interplay of muscles allows for seamless mandibular movement during essential functions such as chewing, swallowing, and speaking.
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Frequently asked questions
The lateral pterygoid muscle is the only muscle responsible for opening the jaw.
The lateral pterygoid also assists in the side-to-side movement of the jaw. It is also the major protractor of the jaw.
Yes, there are three muscles dedicated to closing the jaw: the masseter, the temporalis, and the medial pterygoid.
