Masseter muscle is partly concealed, anteriorly, by the superficial portion. Posteriorly, it is covered by the parotid gland. Along with the other three muscles of mastication (temporalis, medial pterygoid, and lateral pterygoid), the masseter is innervated by the anterior division of the mandibular division (V3) of the trigeminal nerve. The innervation pathway is: gyrus precentralis > genu capsula interna > nucleus motorius nervi trigemini > nervus trigeminus > nervus mandibularis > musculus masseter. The action of the muscle during bilateral contraction of the entire muscle is to elevate the mandible, raising the lower jaw. Elevation of the mandible occurs during the closing
In vitro muscle testing the level which ensures maximal motor unit recruitment. The servomotor can be programmed to maintain a given force while allowing the muscle to change length, vice versa, or the muscle may be subject to more complex testing, such as in work loops. When pennate muscles are used, sonomicrometry is often used to accurately determine fiber length during the test. "In vitro" muscle testing can be done on any scale of muscle organization - entire groups of muscles (provided they share a common insertion or origin, as in the human quadriceps), a single muscle, a "bundle" of muscle fibers, a single