Posted by: Thixia | October 23, 2008

­­­­Diagram of Brain Mechanisms 6 of 7

Higher Brains

The cerebrum is the largest part of the human brain.  The cortex contains all of the centers that receive and interpret sensory information, initiate movement, analyze information, reason and experience emotions.  The centers for these tasks are located in different parts of the cortex.  Before we discuss what each part does, let’s look at the parts of the cerebrum. 

 

 

 

 

Gray Matter

The cerebrum contains gray matter (neurons with no myelin) and white matter (myelinated neurons that enter and leave the cortex). 

 

 

 

 

 

 

Major Parts of the Cerebral Cortex


The cortex dominates the exterior surface of the brain.  The surface area of the brain is about 233 to 465 square inches (1,500 to 2,000 cm2), which is about the size of one to two pages of a newspaper.  To fit this surface area within the skull, the cortex is folded, forming folds (gyri) and grooves (sulci).  Several large sulci divide the cortex into various lobes: the frontal lobe, parietal lobe, occipital lobe and temporal lobe.  Each lobe has a different function. 

 

 
Mouse over the part labels of the brain to see where those parts are located.


When viewed from above, a large groove (interhemispheric fissure) separates the brain into left and right halves.  The halves talk to each other through a tract of white-matter fibers called the corpus callosum.  Also, the right and left temporal lobes communicate through another tract of fibers near the rear of the brain called the anterior commissure. 

 

 

If you look at a cutaway view of the brain, you see that the cortical area above the corpus callosum is divided by a groove.  This groove is called the cingulate sulcus.  The area between that groove and the corpus callosum is called the cingulate gyrus, also referred to as the limbic system or limbic lobe.  Deep within the cerebrum lies the basal ganglia, amygdala and hippocampus. 

This ends our tour of the major structures of the cortex.  Now, let’s see what they do. 

 

Hard-wired

 

The brain is “hard-wired” with connections, much like a skyscraper or airplane is hard-wired with electrical wiring.  In the case of the brain, the connections are made by neurons that connect the sensory inputs and motor outputs with centers in the various lobes of the cortex.  There are also connections between these cortical centers and other parts of the brain. 

Several areas of the cerebrum have specialized functions:

*             Parietal lobe – The parietal lobe receives and processes all somatosensory input from the body (touch, pain). 

·       Fibers from the spinal cord are distributed by the thalamus to various parts of the parietal lobe. 

·       The connections form a map of the body’s surface on the parietal lobe.  This map is called a homunculus.  

·       The homunculus looks rather strange because the representation of each area is related to the number of sensory neuronal connections, not the physical size of the area. 

·       The rear of the parietal lobe (next to the temporal lobe) has a section called Wernicke’s area, which is important for understanding the sensory (auditory and visual) information associated with language.  Damage to this area of the brain produces what is called sensory aphasia, in which patients cannot understand language but can still produce sounds. 

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