Hindbrain: Pons Varolii, Cerebellum and Medulla Oblongata

c. Hind brain : The hindbrain, the posterior region of the brain, is made of the pons varolii, the cerebellum and the medulla oblongata. The pons varolii appears as a rounded bulge on the underside of the brain stem (which itself is made of midbrain, pons and medulla, and continues on into the spinal cord); it carries a cross-band of nerve fibres linking the cerebrum, the cerebellar lobes, the medulla oblongata and the spinal cord, and it also holds several nuclei.

The cerebellum is the brain's second-largest part, made of two lateral hemispheres joined by a central vermis; it is mostly white matter topped by a thin grey-matter cortex, and its white matter's tree-like branching pattern, visible in section, is called the arbor vitae. Its surface, like the cerebrum's, is convoluted (gyri and sulci), with over 30 million neurons in its cortex, and three pairs of myelinated cerebellar peduncles connect it to the rest of the CNS. The cerebellum is an important regulatory centre for neuromuscular activity, maintaining equilibrium, posture, balance, orientation and muscle tone, moderating voluntary movements, and controlling rapid coordinated activities such as walking, running and speaking -- all of its own outputs are involuntary, though early learning of a skilled movement may still involve it.

The medulla oblongata is the posterior, conical part of the brain continuing directly into the spinal cord, with inner grey matter and outer white matter; because it controls vital involuntary functions -- heartbeat, respiration, vasomotor activity and peristalsis -- as well as non-vital reflexes such as coughing, sneezing, swallowing, vomiting and yawning, injury to the medulla can prove fatal. Its internal cavity, the fourth ventricle (metacoel), carries the posterior choroid plexuses that secrete CSF, draining through three openings -- a pair of lateral foramina of Luschka and a median foramen of Magendie.