Anatomy & Physiology I and II

Anatomy & Physiology Study Guide The cuspids , or canines, are conical, with a sharp ridgeline and a pointed tip. They are used for tearing or slashing. Cuspids have a single root. • Bicuspids , or premolars, have flattened crowns with prominent ridges. They crush, mash, and grind. Bicuspids have one or two roots. • Molars have very large, flattened crowns with prominent ridges adapted for crushing and grinding. Molars typically have three or more roots. Masticatio The muscles of mastication allow you to open or close your jaw and move it from side to side. Making chewing a complex process that involves any combination of mandibular elevation/depression, protraction/retraction, and medial/lateral movement. During mastication, the body will force food from the oral cavity to the vestibule and back, crossing and recrossing the occlusal surfaces . This movement results in part from the action of the muscles of mastication, but control would be impossible without the aid of the muscles of the cheeks, lips, and tongue. Once the material is shredded or torn to a satisfactory consistency and has been moistened with salivary secretions, the tongue begins compacting the debris into a moist, cohesive bolus that can be swallowed relatively easily. 23.6 The Pharynx The pharynx serves as the standard passageway for solid food, liquids, and air. Food passes typically through the oropharynx and laryngopharynx (all parts of the larynx) on its way to the esophagus. Deep to the lamina propria lies a dense layer of elastic fibers, bound to the underlying skeletal muscles. The pharyngeal constrictor muscles push the bolus toward the esophagus. The palatopharyngeus and stylopharyngeus muscles elevate the larynx. The palatal muscles elevate the soft palate and adjacent portions of the pharyngeal wall. 23.7 The Esophagus The esophagus is a hollow muscular tube innervated by parasympathetic and sympathetic fibers from the esophageal plexus to transfer solid foods and liquids to the stomach. It consists of three layers: mucosal, submucosal, and muscularis. The esophagus plunges toward the thoracic cavity posterior to the trachea and passes inferiorly along the dorsal wall of the mediastinum. It enters the abdominopelvic cavity through an opening in the diaphragm (the esophageal hiatus), and then the esophagus then empties into the stomach. The circular muscle layer of the esophagus typically prevents air from entering the esophagus if it is relaxed. A comparable zone at the inferior end of the esophagus usually remains in a state of active contraction. This condition prevents the backflow of materials from the stomach into the esophagus. ©2018 Achieve Test Prep Page 317 of 367 •