Dictionary of Human Evolution and Biology

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Brain Metabolism

Sum of the synthetic and degradative chemical activities that occur in the brain. An adult human brain weighs about 1.5 kg (3-3.5 lbs) and is composed of an estimated 100 billion neurons. Over 200 known neuropeptides facilitate neurotransmission. The high metabolic rate of the human brain requires that it receive about 20% of the total resting cardiac output although it accounts for only 2% of the total body mass; interruption of this flow for 10 seconds results in unconsciousness. These vascular needs are supplied by the paired internal carotid and vertebral arteries that unite at the cerebral arterial circle. The hominid, and especially human, brain generates excess heat that must be transferred to other tissues, and its thermoregulation and homeostasis is of ongoing concern to human biologists.

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