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The human brain is the anteriormost part of the central nervous system in humans as well as the primary control center for the peripheral nervous system. more...

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The brain controls "lower" or involuntary activities such as heartbeat, respiration, and digestion - these are known as autonomic functions- as well as sensation, movement, and a variety of special senses. The brain also controls "higher" order, conscious activities, such as thought, reasoning, and abstraction. The human brain is generally regarded as more capable of these higher order activities than that of any other known species.

Overview

Human encephalization is especially pronounced in the neocortex, the most complex portion of the cerebral cortex. Singular among those of all animals, the human brain possesses the largest and most massive neocortex. Humans thus enjoy unique neural capacities despite the fact that much of the human neuroarchitecture resembles that of more primitive species. Basic systems that alert the nervous system to stimuli, sense events in the environment, and monitor and maintain the internal environment of the body (homeostasis) are similar in some ways to those of the most basic vertebrates. Human consciousness involves both the extended capacity of the modern neocortex in particular as well as profoundly developed prototypical structures of the brain stem. But the human brain is unique, in part, because it relies on some million billion synaptic connections, making it an extremely intricate and densely connected neural network.

Anatomy

The normal adult human brain typically weighs between 1 and 1.5 kg (3 lb) and has an average volume of 1,600 cm³. The mature human brain consumes some 20-25% of the energy used by the body, while the developing brain of an infant consumes around 60%. Such heavy energy usage generates large quantities of heat, which must be continually removed to prevent brain damage. An average male brain has approximately 4% more cells, more overall grey matter in the prefrontal lobe and 100 grams more brain tissue than an average female brain. Both sexes have similar brain weight to body weight ratios , though the differences in weight persist even when adjusted for relative body mass. The human brain varies in many interesting ways between the sexes and may be an example of sexual dimorphism within the species (see also Sex and intelligence). It should also be noted that because of these differences in brain development and function, correlation between weight and even grey-matter may be insignificant; much as comparing the weight of different home computers will give little useful information about their efficiency.

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