which part of the cns is made up of the midbrain
Midbrain The midbrain or mesencephalon (from the Greek mesos, middle, and enkephalos, brain[1]) is a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.[2]
Central canal Throughout the cervical and thoracic regions the central canal is situated in the anterior third of the spinal cord; in the lumbar enlargement it is near the middle, and in the conus medullaris it approaches the posterior surface. It is filled with cerebrospinal fluid, and lined by ciliated, columnar epithelium, outside of which is an encircling band of gelatinous substance, the substantia gelatinosa centralis (or central gelatinous substance of spinal cord). This gelatinous substance consists mainly of neuroglia, but contains a few nerve cells and fibers; it is traversed by processes from the deep ends of the columnar ciliated cells which line the central canal.