the spinal trigeminal nucleus, which is caudal to the pontine tegmentum in the medulla. The abducens nucleus controls abduction (outward rotation) of the eye. The facial motor nucleus and the superior salivary nucleus of the facial nerve are located within the pontine tegmentum. The facial motor nucleus serve motor control of the muscles of facial expression and the stapedius muscle of the ear, while the superior salivary nucleus controls the secretion of saliva and tears through parasympathetic innervation of structures including the lacrimal gland and the mucosal glands of the nose, palate, and pharynx. The facial solitary nucleus, which carries taste information from the anterior 2/3 of the tongue, is located caudal to the pontine tegmentum in the medulla. The superior vestibular nucleus, one of four vestibular nuclei, is located within the pons. The vestibular nuclei process information from the ear canals regarding the orientation and acceleration of the head. The remaining nuclei are located within the medulla. The two divisions of the cochlear nucleus, which process auditory input from the cochlea, lie on the border of the pons and the medulla. Some of the fibers from the cochlear nerve cross over in the pontine tegmentum, forming the trapezoid body, which is thought to help sound localisation. Functions of the mesopontine cholinergic system The pontine tegmentum contains two predominately cholinergic nuclei, the pedunculopontine nucleus (PPN) and the laterodorsal tegmental nucleus, which project widely throughout the brain. The PPN is involved in many functions, including arousal, attention, learning, reward, and voluntary limb movements and locomotion. While once thought important to the initiation of movement, recent research suggests a role in providing sensory feedback to the cerebral cortex. Recent research has discovered that the PPN is involved in the planning of movement, and that different networks of neurons in the PPN are switched on during real and imagined movement. It is also implicated in the generation and maintenance of REM sleep. In animal studies, lesions of the pontine tegmentum greatly reduce or even eliminate REM sleep. Injection of a cholinergic agonist (e.g. carbachol), into the pontine tegmentum produces a state of REM sleep in cats. PET studies seem to indicate that there is a correlation between blood flow in the pontine tegmentum and REM sleep Pontine waves, (PGO waves) or P-waves in rodents, are brain waves generated in the pontine tegmentum. They can be observed in mammals to precede the onset of