HUMAN BRAIN AND ITS FUNCTIONS

Most brains exhibit a substantial distinction between the grey matter and white matter. Grey matter consists primarily of the cellbodies of the neurons, while white matter is comprised mostly of the fibers (axons) which connect neurons. The axons are surrounded by a fatty insulating sheath called myelin, giving the white matter its distinctive color. The outer layer of the brain is gray matter called cerebral cortex. Deep in the brain, compartments of white matter, gray matter and spaces filled with cerebrospinal fluid are found.

The brain innervates the head through cranial nerves, and it communicates with the spinal cord, which innervates the body through spinal nerves. Nervous fibers transmitting signals from the brain are called efferent fibers. The fibers transmitting signals to the brain are called afferent (or sensory) fibers. Nerves can be afferent, efferent or mixed (i.e., containing both types of fibers).

The brain is the site of reason and intelligence, which include such components as cognition, perception, attention, memory and emotion. The brain is also responsible for control of posture and movements. It makes possible cognitive, motor and other forms of learing. The brain can perform a variety of functions automatically, without the need for conscious awareness, such as coordination of sensory systems, walking, and homeostatic body functions such as heart rate, blood pressure, fluid balance, and body temperature.

Many functions are controlled by coordinated activity of the brain and spinal cord. Moreover, some behaviors such as simple reflexes and basic locomotion, can be executed under spinal cord control alone.

The study of the brain is known as neuroscience, a field of biology aimed at understanding the functions of the brain at every level, from the molecular up to the psychological. There is also a branch of psychology that deals with the anatomy and physiology of the brain, known as biological psychology. This field of study focuses on each individual part of the brain and how it affects behavior.