The main muscles involved are the masseter, temporalis and medial and lateral pterygoid muscles. The affected muscles include the temporalis, masseter, and pterygoid muscles. Polysomnography shows increased masseter and temporalis muscular activity during sleep. The ECMs were focussed on the masseter muscle and temporalis muscle. The "lateral surface" is smooth, and affords insertion to the temporalis and masseter muscles. In response, the masseter muscles will jerk the mandible upwards. In human anatomy, the masseter is one of the muscles of mastication. Botulinum toxin injections can be helpful for the blepharospasm and for masseter spasm. Likewise, treating the masseter muscle may damage the salivary glands superficial to this muscle. The "postero-inferior" or "zygomatic border" affords attachment by its rough edge to the masseter. The medial surface is concave, and affords attachment to the masseter. The fastest reflex recorded in humans happens within the masseter muscle or jaw muscle. Muscle rigidity in the masseter muscle causes intubation to be impossible. Hz produced deep masseter muscle relaxation and finger warming within six minutes. The masseter muscle on the skull was probably the main muscle used for biting down.