Ever what exactly comprises the human brain? For a chemical composition check here. But for right now let's talk about the physical parts of the brain. The brain isn't just one big gelatinous organ. Its actually made up of several different parts, that each evolved one after the other, ever since the first nerves cells were created. In this section we'll talk about the brain's different parts and where they are located. To learn more about the functions of each part of the brain you can check out Brain Parts Function.

First let's divide the brain into three basic units: the Forebrain, the Midbrain, and the Hindbrain (shown below).

The hindbrain includes the upper part of the spinal cord, the brain stem, and a wrinkled ball of tissue called the Cerebellum. The uppermost part of the brainstem is the midbrain. The forebrain is the largest and most highly developed part of the human brain: it consists primarily of the Cerebrum and the structures hidden beneath it. When people see pictures of the brain it is usually the cerebrum that they notice. The cerebrum sits at the topmost part of the brain.

The cerebrum itself is split into two halves (hemispheres) by a deep fissure. Despite the split, the two cerebral hemispheres communicate with each other through a thick tract of nerve fibers that lies at the base of this fissure. This neural highway is called the Corpus Callosum and is about 1 cm wide and 10 cm long.

The Cerebral Cortex

Coating the surface of the cerebrum and the cerebellum is a vital layer of tissue about 3.4mm thick or the thickness of a short stack of two or three dimes. That's what's called the Cortex, from the Latin word for bark. When people talk about "gray matter" in the brain they are talking about this thin rind. The cortex is gray because nerves in this area lack the insulation that makes most other parts of the brain appear to be white.

The Geography of Thought

Each cerebral hemisphere can be divided into sections, or lobes, each of which specializes in different functions. To understand each lobe and its specialty we will take a tour of the cerebral hemispheres, starting with the two Frontal Lobes, which lie directly behind the forehead. In the rearmost portion of each frontal lobe is the Premotor and Primary Motor Cortex. Just beside the motor area but only on the left hemisphere is where Broca's area resides.

The two sections directly behind the frontal lobes are called the Parietal Lobes. The forward parts of these lobes, just behind the motor cortexes, are the Primary Somatosensory Cortex.

At the very back of the cerebrum are the Occipital Lobes. At the very back of the Occipital Lobes is where the Primary Visual Cortex is located.

The last lobes on our tour of the cerebral hemispheres are the Temporal Lobes, which lie in front of the visual areas and nest under the parietal and frontal lobes. This is where the Primary Auditory Cortex lies and on the left hemisphere where Wernicke's area is too.

The Inner Brain

Deep within the brain, hidden from view, lie structures that are the gatekeepers between the spinal cord and the cerebral hemispheres. Like the lobes in the cerebral hemispheres, the structures described below come in pairs: each is duplicated in the opposite half of the brain. The Hypothalamus, about the size of a pearl, directs a multitude of important functions. Near the hypothalamus lies the Thalamus, a major clearinghouse for information going to and from the spinal cord and the cerebrum. An arching tract of nerve cells leads from the hypothalamus and the thalamus to the Hippocampus. The Basal Ganglia are clusters of nerve cells surrounding the thalamus.