The human brain
is the center of the human nervous system
. Enclosed in the cranium
, it has the same general structure as the brains of other mammals
, but is over three times as large as the brain of a typical mammal with an equivalent body size. Most of the expansion comes from the cerebral cortex
, a convoluted layer of neural tissue that covers the surface of the forebrain
. Especially expanded are the frontal lobes
, which are associated with executive functions
such as self-control, planning, reasoning, and abstract thought.
The portion of the brain devoted to vision is also greatly enlarged in human beings.
An electrochemical wave called an action potential travels along the axon of a neuron. When the wave reaches a synapse, it provokes release of a puff of neurotransmitter molecules, which bind to chemical receptor molecules located in the membrane of the target cell.