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The masseter, temporalis, medial pterygoid, and lateral pterygoid muscles are the four muscles that make up the muscles of mastication and are responsible for jaw movement. The masseter muscle is the most powerful muscle of mastication, and it is involved in the elevation and protraction of the mandible. The masseter, temporalis, and medial pterygoid muscles are responsible for closing the jaw, while the lateral pterygoid muscle is responsible for opening the jaw.
| Characteristics | Values |
|---|---|
| Muscles that close the jaw | Temporalis, Masseter, and Pterygoid |
| Masseter muscle origin | Zygomatic arch |
| Masseter muscle insertion | Angle and lateral surface of the mandibular ramus |
| Masseter muscle shape | Quadrangular |
| Masseter muscle divisions | Superficial and deep |
| Masseter muscle rigidity | Jaws of steel |
| Pterygoid muscles | Internal and external |
| Lateral pterygoid muscle origin | Greater wing of the sphenoid |
| Lateral pterygoid muscle insertion | Neck of the mandible |
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What You'll Learn
The masseter muscle
The masseter receives its motor innervation from the mandibular division of the trigeminal nerve, specifically the masseteric nerve, a branch of the mandibular nerve. The blood supply to the muscle is provided primarily by the masseteric artery, a branch of the maxillary artery, which comes off the external carotid artery behind the neck of the mandible.
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The temporalis muscle
Tension in the temporalis muscle can induce pain in the temporal area. This can be caused by bruxism, the habitual grinding of teeth, often during sleep, 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 medial pterygoid muscle
The deep head of the medial pterygoid muscle is larger and originates from the medial surface of the lateral plate of the pterygoid process and the pyramidal process of the palatine bone. The smaller superficial head originates from the maxillary tuberosity and pyramidal process of the palatine bone. The fibres of the two heads run posteroinferiorly and laterally, surrounding the lower fibres of the lateral pterygoid muscle. Together, they insert onto the triangular impression located on the medial surface of the mandible.
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The lateral pterygoid muscle
The primary function of the lateral pterygoid muscle is to control the function of the jaw and temporomandibular joint. It achieves 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 the chewing stroke, masticating, and clenching.
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The trigeminal nerve
The nerve branches into three main divisions: the ophthalmic (V1), maxillary (V2), and mandibular (V3) nerves. Each division is responsible for innervating specific regions of the face. The ophthalmic division (V1) provides sensory input to the forehead, scalp, upper eyelid, and parts of the nose. The maxillary division (V2) carries sensory signals from the midface, including the cheeks, upper lip, upper teeth, and nasal cavity. The mandibular division (V3) has both sensory and motor functions, innervating the lower lip, jaw, and teeth, and controlling the muscles involved in mastication (chewing). The trigeminal nerve also plays a role in swallowing by supporting the digastric muscle and mylohyoid muscle.
Damage to the trigeminal nerve can result in symptoms such as facial numbness or tingling, facial pain, corneal abrasions, vision issues, jaw muscle spasms or weakness, and difficulty chewing, speaking, or swallowing. Most of the suffering due to trigeminal nerve pain occurs as a result of common problems that can be readily diagnosed and treated effectively by trained practitioners.
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Frequently asked questions
The masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle is the most powerful muscle of mastication.
When the masseter contracts, it causes a powerful elevation of the mandible, causing the mouth to close.
