The " THINKING " brain
 

     The main part of the brain are two halves of the cerebrum- the cerebral hemispheres..  They are the "thinking" parts of the brain, the sites of our conscious awareness, thoughts, feelings, ideas, and memories. 

     Each cerebral hemisphere has three main parts.  these are the outer layer or cerebral cortex of gray matter, the inner cerebral medulla of white matter, and the central curved lumps or lobes known together as basal ganglia.

     The cerebral hemispheres' wrinkled appearance is due to the folding of their surface into bulges called gyri and grooves called sulci.  Extra-deep grooves, called fissures, divide each hemisphere into main patches or lobes.  These are named the prefrontal, frontal, parietal, temporal, and occipital lobes, mostly after the names of the curves skull bones around them.

     The cortex is shiny, grayish pink in colour and about 0.16 inch (4 mm.) thick.  Its many folds and grooves give it a large total area.  Spread out flat, the cortex is the size of an office desks.  Its gray matter consists of 50 billion nerve cells, linked together by billions and trillions of dendrites.  They form a huge network with many pathways and routes for nerve signals.  Underneath the cortex, the white matter of the medulla is mainly the axons of these nerve cells, connecting them to the basal ganglia and other parts of the brain.

     The two cerebral hemispheres are linked by a "bridge", the corpus callosum.  This contains more than 200 million nerve fibers, known as commissural fibres.  The corpus callosum carries nerve signals between the hemispheres, so that each half of the brain knows what the other half is doing.