From the basilar artery are two posterior cerebral arteries. Medial pontine syndrome results from occlusion of paramedian branches of the basilar artery. Thus diagnosis of extraparenchymal cysts usually relies on signs like hydrocephalus or enhanced basilar meninges. In most adults, the PCA sources from the anterior portion of the basilar artery. The movement of the basilar membrane causes hair cell stereocilia movement. Patients with basilar skull fractures are especially likely to get meningitis. Brayton was killed instantly of basilar skull fracture. Irwin likely died instantly of a basilar skull fracture. Nerves that transmit information from different regions of the basilar membrane therefore encode frequency tonotopically. Hemotympanum is often the result of basilar skull fracture. He also sustained a fatal basilar skull fracture on impact. The CM is proportional to the displacement of the basilar membrane. Different frequencies of sound will cause vibrations in different location of the basilar membrane. This graph reflects the frequency selectivity and the tuning of the basilar membrane. Petty was killed instantly when he suffered a basilar skull fracture.