The human brain has the same general structure as the brains of other mammals, but is over five times as large as the "average brain" of a mammal with the same 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 involved in executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the brain devoted to vision is also greatly enlarged in humans, and some regions of the human brain, such as those devoted to language, have no clear counterparts in the brains of other animals.

Human brain evolution, from the earliest shrewlike mammals through primates to hominids, is marked by a steady increase in encephalization, or the ratio of brain to body size. The human brain has been estimated to contain 50-100 billion neurons, of which about 10 billion are cortical pyramidal cells. These cells pass signals to each other via around 100 trillion synaptic connections.

In spite of the fact that it is protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood-brain barrier, the delicate nature of the human brain makes it susceptible to many types of damage and disease. The most common forms of physical damage are closed head injuries, caused by a blow to the head, stroke, caused by interruption of the brain's blood supply, and poisoning, caused by a wide variety of chemicals that can act as neurotoxins. Infection of the brain is rare because of the barriers that protect it, but is very serious when it occurs. More common are genetically based diseases, such as Parkinson's disease, multiple sclerosis, and many others. A number of psychiatric conditions, such as schizophrenia and depression, are widely thought to be caused at least partially by brain disfunctions, although the nature of the brain anomalies are not very well understood.

The brain of all vertebrates develops from three swellings at the anterior end of the neural canal of the embryo. From front to back these develop into the

• forebrain (also known as the prosencephalon)
• midbrain (mesencephalon)
• hindbrain (rhombencephalon)

The forebrain is the largest part of the brain, most of which is made up of the cerebrum. Other important structures found in the forebrain include the thalamus, the hypothalamus and the limbic system.

The cerebrum is divided into two cerebral hemispheres connected by a mass of white matter known as the corpus callosum. Each hemisphere is divided into four lobes frontal, parietal, occipital and temporal. The surface of each hemisphere is made up of grey matter known as the cerebral cortex and is highly folded to increase the cortical surface area available within the confines of the skull. The cortex controls perception, memory, and all higher cognitive functions, including the ability to concentrate reason and think in abstract form.

Beneath the cortex is white matter, within which a number of nuclei (grey matter), known as the basal nuclei are found. The basal nuclei receive information from the cortex to regulate skeletal movement and other higher motor functions.

The thalamus functions to relay sensory information to the cerebral cortex and the hypothalamus regulates visceral functions, such as temperature, reproductive functions, eating, sleeping and the display of emotion. The limbic system describes a collection of structures within the forebrain, including the amygdala hippocampus. Also known as the ‘emotional brain’, the limbic system is important in the formation of memories and in controlling emotions, decisions, motivation and learning.

Thalamus - A main sensory relay and integrative center connecting with many areas of the brain, including the cerebral cortex.

Hypothalamus - The master control of the autonomic nervous system, parasympathetic and sympathetic. This system stimulates and controls structures such as the heart, most glands and smooth muscles. In effect, this system allows your systems to excite and relax, as needed. This system integrates the autonomic and endocrine functions with behavior.

Hippocampus - This area of the brain, apart from its other functions, is primarily responsible for short term memory.

Basal Ganglia - Made up of the caudate nucleus, globus pallid us and putaman, the basal ganglia is primarily but not exclusively esponsible for crude motor movements. Injury to this area leads to rigidity, hypotonic, and Parkinson's and Huntington's diseases. In addition the basal ganglion houses the amygdale, which mediates inborn and acquired emotional responses. It appears to be involved in mediating both conscious and unconscious emotional feelings. It connects, among other places, into the prefrontal lobe.

Pineal Body - A gland-like body which is primarily responsible for melotonin biosynthesis.

Corpus Callosum - A great network or connection of fibers that links the two cerebral hemispheres. Right and left, together.

Cerebellum - Primarily responsible for regulating muscle tone, for integrating the motor and sensory pathways, and for balance/spatial awareness