Structure of human brain and function

The human brain is a soft, gelatinous collection of gray and white matter

encased in the cranium and weighing about 1,400 grams (roughly three pounds)

in the adult. Estimates vary, but there may be 100 billion or more neurons in the

brain, and at least ten times this number of glial cells.As an indicator of the 

astonishing  degree of connectivity between cerebral neurons, each one 

makes contact with as  many as 10,000 others Interneurons, situated 

between afferent and efferent neurons, constitute by far the largest class 

of brain neurons, so that the great majority of the brain’s neuronal activity

is concerned with the processing and transfer of information that occur 

between sensory input and motor output In other words, a large quantity 

of nervous tissue lies interposed between the sensory and motor systems

 to elaborate the phenomena of behavior.

The brain is made up of the cerebrum, the brainstem, and the cerebellum

Most important for the higher functions is the cerebrum, which comprises

 the paired cerebral hemispheres and the diencephalon, the main 

components of which are the thalamus and hypothalamus. Why the 

hemispheres are paired, and why they have distinct functional 

affiliations in contrast to other paired organs in the body such as the 

lungs and kidneys, are not understood, but the distinct operations of 

the two cerebral hemispheres will be frequently emphasized in this book. 

The hemispheres are folded into ridges called gyri, and the grooves 

between these are known as sulci or fissures. These gross neuroanatomical 

features form the basis for the division of the hemispheres into four lobes: frontal,

temporal, parietal, and occipital.

The parcellation of the hemispheres into four lobes is somewhat arbitrary

but serves to produce convenient neuroanatomical landmarks that have important

functional affiliations. The image above gives a brief outline of some prominent

brain-behavior relationships, which will be developed in greater detail throughout

this book. The frontal lobes, largest and most anterior, provide the origin

of the motor system via the corticospinal tracts, mediate the production of language

and prosody, and organize the integrative capacities of motivation, comportment,

and executive function. The temporal lobes receive primary auditory

input, mediate comprehension of language and prosody, and, in concert with

the closely connected limbic system, subserve important aspects of memory

and emotion. The parietal lobes receive tactile input, mediate visuospatial competence,

and subserve reading and calculation skills. The occipital lobes, smallest

and most posterior, receive primary visual input and mediate perception of

visual material before further processing occurs in more anterior regions.

"Structure of human brain and function"