Birds have a similar basic plan to their nervous system as the rest of the vertebrates. The central nervous system is made up of a brain, a spinal chord and nerves. The brain is situated inside the skull and connected to one end of the spinal chord which as its name suggests runs down the centre of the spinal column. Neurones come in two sorts, sensory and motor. They carry the messages to the brain that the bird uses to build up and maintain its image of the world.
Motor neurones transmit messages the other way - from the brain to the muscles.
The brain of a bird weighs about 10 times as much as a brain of a reptile of the same weight, but slightly less than that of a mammal of the same weight. However, there is considerable variation between birds of similar size. For birds weighing in at around 85g, brain weight varies from 0.73g for a Quail to 2.7g for a Great Spotted Woodpecker. There is therefore quite a range in the intelligence of birds, with game birds at the bottom of the list and Woodpeckers, Owls and Parrots at the top. A bird's brain is different to a mammalian brain in that the complex folds found in the cerebral cortex of mammals are missing and the cerebral cortex itself is much smaller proportionally than in mammals.