The Midbrain and Hindbrain

Below the forebrain lie the midbrain and the hindbrain, structures that are older in evolutionary terms and control many of the body's essential, largely automatic functions.

The midbrain is a short segment of the brain lying between the thalamus/hypothalamus above and the pons below. Although small, it acts as an important relay and reflex centre — it processes and relays visual and auditory information and coordinates certain reflexes associated with sight and hearing, such as reflex movements of the eyes and head in response to visual or auditory stimuli, and it also contains a canal (the cerebral aqueduct) connecting the fluid-filled spaces of the forebrain and hindbrain.

The hindbrain consists of three parts: the pons, the medulla oblongata and the cerebellum. The pons ('bridge' in Latin) lies just below the midbrain and, true to its name, acts as a bridge relaying signals between the cerebrum above and the cerebellum and spinal cord below; along with the medulla, it also contributes to the regulation of the rate and pattern of breathing. The medulla oblongata is the lowest part of the brain, directly continuous with the spinal cord below it, and despite its small size it houses vital centres that control essential involuntary functions — the rhythm and depth of respiration, cardiovascular reflexes that adjust heart rate and blood vessel diameter, the secretion of digestive (gastric) juices, and reflexes such as swallowing and vomiting. Because these functions are constant and essential for survival, the medulla is one of the most critical parts of the entire brain, and damage to it is frequently life-threatening. The midbrain, pons and medulla together are grouped under a single collective name, the brainstem, which forms the essential connecting stalk between the forebrain and the spinal cord and through which almost all information travelling between the brain and the rest of the body must pass. …