Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content ++ INTRODUCTION + To those I address, it is unnecessary to go farther, than to indicate that the nerves treated of in these papers are the instruments of expression, from the smile upon the infant’s cheek to the last agony of life. —Sir Charles Bell (1774–1842) ++ I. V CRANIAL NERVE MOTOR FUNCTION: CHEWING ++ A. Functional anatomy of chewing ++ Motor-wise, cranial nerve (CrN) V only chews. Its motor axons innervate all and, for clinical purposes, only the chewing muscles: masseter, temporal, and lateral and medial pterygoids. CrN V conveys no efferents to glands or smooth muscle and no special sensory afferents (Table 2-7). Jaw closure Place your fingertips about 2 cm above and in front of the angle of your mandible. Bite hard and relax several times. The muscle felt, the masseter, is the easiest of the chewing muscle to palpate. The other jaw-closing muscles are the temporalis muscles that originate in the temporal fossa and insert on the mandible and the medial pterygoid muscle. Lateral jaw movement: Move your jaw from side to side. Chewing requires not only jaw closure but also a lateral, grinding action and jaw opening, caused by the lateral pterygoid muscles. In Fig. 6-1 notice that the lateral pterygoid muscle originates from the skull base and inserts near the mandibular condyle. Because the skull base is fixed, only the mandible moves when the pterygoids contract. Equal contractions of right and left pterygoids pull the mandible straightforward (Fig. 6-1). If only the right lateral pterygoid muscle contracts, the mandibular tip moves to the ❒ right/❒ left. left If the patient (Pt) can move the jaw to the right but not to the left, the lateral pterygoid muscle on the ❒ right/❒ left is paralyzed. right As a second action, the lateral pterygoid muscles act to open the jaw because they insert on the neck of the mandible (Fig. 6-2). If the Pt’s mandible moves forward and down in the midline on jaw opening, both _______________________________ muscles have contracted equally. lateral pterygoid If the left lateral pterygoid muscle contracts, the tip of the mandible moves not only to the ❒ right/❒ left but also ❒ up/❒ down. right; down Name the two major actions of the lateral pterygoid muscles. ____________________________________________________________ Lateral movement and opening of the jaw The remaining mandibular muscles innervated by CrN V all close the jaw. Name these muscles. ____________________________________________________________ Masseter, temporal, and medial pterygoid ++ FIGURE 6-1. Innervation and action of the lateral pterygoid muscles. If both muscles contract equally, the tip of the mandible moves straight forward. If one muscle contracts, the tip moves forward and to the opposite side. Study the vector diagram (arrows between the muscles). Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) ++ FIGURE 6-2. (A) Action of lateral pterygoid muscles to depress the tip of the mandible when the patient ... GET ACCESS TO THIS RESOURCE Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth Get Free Access Through Your Institution Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. What is MyAccess? Create a FREE MyAccess profile to: Use this site remotely Bookmark your favorite content Track your self-assessment progress and more!