Brain Health Article

Function

The brain is the ultimate controller of the human body and performs functions with and without conscious thought. The brain enables the mind to conduct conscious thoughts and feelings. The brain allows human beings to respond to the environment. It also regulates functions without conscious thought such as digestion, blood pressure, balance, and sleep.

The brain allows one to interpret and respond to the stimuli given to the five senses: taste, touch, hearing, smell, and vision. The brain helps us learn to recognize a certain smell or remember how to ride a bike. The brain enables human communication. The brain contains regions devoted to speech production and speech comprehension. Certain regions of the brain are employed in reading, and writing. The brain is also involved in reproductive behavior and regulates the release of sex hormones. The hypothalamus in the brain tells the body when it is time to drink and when it is time to eat. The brain also regulates sleep and biological rhythms. The brain is likewise involved in generating emotions and largely determines personality.

It is within the cerebral cortex that impulses are received, analyzed, and answered. The body contains nerve cells that are specialized for detecting environmental events and other cells that are specialized for producing movement. Information in the form of light, sound waves, odors, tastes as well as contact with objects is gathered from the environment by specialized cells which are called sensory neurons. In response to this information, movements are performed by the contraction of muscles, which are controlled by motor neurons. Communication between sensory neurons and motor neurons is carried on by interneurons.

Specialized sensory cells of the ear called cells of Corti perceive sound waves and send corresponding impulses to the brain, where they reach the projector auditory center which is located in the superior temporal gyrus (field 41 of Brodmann). The cells of this center receive and analyze the separate impulses. Near this field 41 is located field 37, the associative auditory area, cells of which form one integral or complete auditory image of the object from the separate impulses sent by the neurons of field 41. If we destroy field 37, the person can hear sounds but cannot make sense out of them. For example, he or she can hear the speech sounds "p" and "e" and "n" but does not imagine a pen as a result of hearing these sounds. The parietal lobe contains a sensory area which is located in the post-central gyrus (fields 1, 2, 3 of Brodmann), and in the nearby part of the superior parietal lobulus (fields 5, 7 of Brodmann). In this area, impulses of general sensation such as touch, pain, pressure, and temperature are interpreted. The occipital lobe contains the visual region which is located in the area of the calcarine sulcus (field 17 of Brodmann) and an adjacent area (fields 18, 19, of Brodmann). In this visual area, the impulses arising from the retina of the eye are interpreted.

The frontal lobe contains the motor area (field 4 of Brodmann) with about 25,000 giant pyramidal neurons. It is located in the precentral gyrus, the superior frontal gyrus, and the paracentral lobulus. The uppermost part of the precentral gyrus together with the paracentral lobulus controls the movement of the legs. The hindmost part of the superior frontal gyrus controls the movement of the torso. The middle part of the precentral gyrus controls the movement of the arms, and the lowest part of the precentral gyrus controls the movement of the neck and head. The premotor area located in front of the motor area is responsible for coordination and integration of movements. If one suffers destruction of the back part of the middle frontal gyrus, one can still wiggle one's fingers, but one cannot write, although the movement of the corresponding muscles is normal, because writing requires a high degree of coordination and integration of hand and finger movements.

The brain controls the functions of the body that do not require conscious thought (the autonomic functions). Located in the medulla oblongata are the centers controlling digestion, breathing, the functioning of the heart, blood vessels, of the urinary system, and of the glands which produce saliva, tears, and sweat.

The sympathetic and parasympathetic nerves extending from these centers cause the arousal and inhibition of these systems. The sympathetic nerves speed up the heart, raise the blood pressure, dilate the pupils of the eyes, contract the sphincters of the hollow organs, and relax the longitudinal muscles. They prepare a person for crisis situations and they remain active during stress.

The parasympathetic nerves slow the heart, lower the blood pressure, constrict the pupils of the eyes, relax the sphincters of the hollow organs, and help promote the digestion and absorption of nutrients.