Brain and Behavior

The Major Structures of the Brain

What is the triune model?

In 1964, Paul D. MacLean (1913–2007) divided the brain into three general regions, the reptilian, palio-mammalian, and neo-mammalian, which he believed to correspond with different periods of evolution. The neo-mammalian region of the brain refers to the neocortex, which includes the frontal lobe and most cortical regions. These parts of the brain are most developed in more complex and evolutionarily younger mammals, such as primates. The paleo-mammalian region incorporates the limbic system, which is found in all mammals. The reptilian area of the brain refers to the brain stem and the cerebellum, phylogenetically ancient regions that are found in some of the most ancient and primitive species (e.g., reptiles). Although MacLean’s triune model has been criticized as overly simplistic, it does provide a useful way for non-specialists to picture the brain.

What is a neuron?

A neuron is a brain cell, the basic building block of the brain. The entire brain is actually a huge network of interlocking, interacting neurons. There are about one hundred billion neurons in the human brain and several times that amount of glial and other smaller cells that support neuronal function. A neuron is composed of a cell body, an axon, and a profusion of branching dendrites.


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