Q. A 52 year-old man presents to your clinic with symptoms of worsened memory, gait ataxia (trouble walking), and difficulty knowing when he has to urinate and difficulty fully voiding. On exam, you appreciate a "magnetic gait." You are concerned about the possibility of normal pressure hydrocephalus, so you send him for a non-contrast head CT. The head CT ultimately does show enlarged ventricles. The cilia of what type of cell helps to circulate cerebrospinal fluid?