Brain

The central nervous system of vertebrates consists of a single spinal cord, which runs in a dorsal position along the back, and a highly developed brain. The brain is the dominant structure of the nervous system. It is the master controller of all body functions, and the analyzer and interpreter of complex information and behavior patterns. We can think of the brain as a powerful neural computer. The peripheral nervous system, composed of nerves that run to all parts of the body, transmits information to and from the central nervous system.

The vertebrate brain is divided into three main divisions: the forebrain, the midbrain, and the hindbrain. The hindbrain connects the brain to the spinal cord, and a portion of it, called the medulla oblongata, controls important body functions such as the breathing rate and the heart rate. Also in the hindbrain, the cerebellum controls balance. The forebrain consists of the cerebrum, thalamus, and hypothalamus. The forebrain controls, among other things, the sense of smell in vertebrates.

During the first few weeks of development, the brain of a vertebrate looks like a series of bulges in the neural tube. It is hard to see a difference when we examine the early embryonic brains of fish, amphibians, reptiles, birds, and mammals. As the brain develops, the bulges enlarge, and each type of vertebrate acquires its own specific adult brain that helps it survive in its environment. In the forebrain of fish, the olfactory (smell) sense is well developed, whereas the cerebrum serves merely as a relay station for impulses. In mammals, on the other hand, the olfactory division is included in the limbic system, which also controls emotions, and the cerebrum is highly developed, operating as a complex processing center for information. Optic lobes are well-developed in the midbrain of nonmammalian vertebrates, whereas in mammals the vision centers are mainly in the forebrain. In addition, a bird's cerebellum is large compared to the rest of its brain, since it controls coordination and balance in flying.