Corpus: Masseter muscle

The masseter muscle is a thick, skeletal muscle that belongs to the superficial muscles involved in mastication (chewing).

The masseter muscle is a thick, pennate muscle divided into two main parts: the superficial and deep portions. The superficial part originates from the anterior two-thirds of the zygomatic arch with a thick, tendinous aponeurosis. It runs obliquely in a backward and downward direction to attach to the masseteric tuberosity on the mandibular angle. The deep part originates from the lower edge of the posterior third of the zygomatic arch and runs vertically downward to attach to the mandibular ramus. The deep part is covered anteriorly by the superficial part and posteriorly by the parotid gland. Both the masseter muscle and the parotid gland are enveloped by a common fascia known as the fascia masseterica.

Some anatomical descriptions also include an additional part of the muscle that extends from the zygomatic process of the temporal bone to the posterior edge of the coronoid process of the mandible. This part is thought to contribute to the stabilization and retraction of the mandible. Between the masseter muscle and the buccinator muscle lies the buccal space, which houses the buccal fat pad (corpus adiposum buccae).

The masseter muscle is innervated by the masseteric nerve, a branch of the mandibular nerve, which is the third division of the trigeminal nerve (cranial nerve V).

The masseter muscle receives its blood supply from the masseteric artery, a branch of the maxillary artery. Venous drainage is provided by branches of the facial vein and retromandibular vein.

The primary function of the masseter muscle is to elevate the mandible, closing the jaw (adduction). Together with the medial pterygoid muscle, it forms a muscular sling that suspends the mandible. The masseter also contributes to protrusion (advancement) of the lower jaw and, when contracted unilaterally, aids in the grinding motion of the jaw (laterotrusion).

The masseter muscle is the most powerful muscle involved in chewing, providing about half of the total chewing force. Although the temporalis muscle generates more force in isolation, the masseter's biomechanical leverage during jaw closure makes it the strongest muscle in the human body relative to its size. Additionally, the movement of the masseter during chewing helps stimulate saliva secretion from the adjacent parotid gland by massaging the gland.

The masseter muscle, along with the temporalis and other muscles of mastication, develops from the mesenchyme of the first pharyngeal (branchial) arch.

Hypertrophy of the masseter muscle can occur on one or both sides, commonly seen in conditions like bruxism (teeth grinding).

1. ↑ Mezey SE, Müller-Gerbl M, Toranelli M, Türp JC. The human masseter muscle revisited: First description of its coronoid part. Ann Anat. 2022 Feb;240:151879. doi: 10.1016/j.aanat.2021.151879. Epub 2021 Dec 2. PMID: 34863910.