05. The brain

The human brain [ 53 ] includes a forebrain [ 8 , 64 ] made of two hemispheres [ 224 ]  almost identical left and right (telencephalon [ 58 ]), and a diencephalon[ 41 , 51 ], a medial and single part that includes the thalamus and the hypothalamus [ 8 , 59 ].

1. Internal configuration:

The two cerebral hemispheres (most proeminent central nervous system organs [ 60 ]) are connected by commissural pathways, mainly the corpus callosum [ 37 , 61 , 62 ].

Each cerebral hemisphere is divided into two distinct regions : a peripheral part : The cortex (grey matter) [ 36 , 49 ] containing the bodies of the nerve cells, and a central part made of white matter that contains mainly axonal extensions of neurons and their myelin sheath[ 39 ].

Within each hemisphere, are patches of gray matter called: Basal ganglia [ 4 ]. These essentially comprise: The caudate nucleus [ 32 , 66 ], the putamen [ 32 , 51 ], the globus pallidus [ 32 ] and the claustrum [ 50 ].

 2. External configuration:

Each hemisphere is divided by deep fissures [ 91 ] that define lobes [ 224 ]:

• The first is the lateral sulcus, or Sylvian fissure [ 91 ], where lies the middle cerebral artery [ 38 ], it separate the frontal lobe from the temporal lobe.
• The second is the central sulcus, or fissure of Rolando [ 63 , 72 ], between the frontal lobe, and the parietal lobe.
• The third sulcus is the parieto-occipital sulcus [ 64 ], separating the occipital lobe from the parietal and temporal lobes.
• In addition, there is a fifth lobe, non-visible on the surface, the lobe of the insula [ 65 ], found by removing the Sylvian fissure.

In each lobe, there are less deep sulci, these structures delimit the gyri [ 66 ].