Chapter 1 - Brain structures and functions

Abstract

The human brain is the most complex organ in the body. It coordinates everything that we see, hear, evaluate, and distinguish. Nearly 97% of the body’s nervous tissue is contained within the adult human brain. The four brain regions are the cerebral hemispheres, diencephalon, brainstem, and the cerebellum. There is a unique distribution of gray and white matter throughout the brain. The gray matter is made up of short, nonmyelinated neurons and neuron cell bodies. The white matter consists of mostly myelinated and some nonmyelinated axons. The brain weighs approximately 1600g (3.5 pounds) in men, and 1450g (3.2 pounds) in women. The difference in brain sizes is proportional to body size, not intelligence. The brain is part of the nervous system, which is the main controlling and communicating system of the body, along with the spinal cord, receptors in complex sensory organs such as the eye and ear, and the nerves, which link to other body systems. Nervous tissue makes up the organs of the nervous system while supporting blood vessels and connective tissues. The basic structural and functional units of the nervous system are the neurons, used for intercellular communication and transmission. Nervous tissue also contains neuroglia (glial cells), which are essential for the survival and function of neurons, preserving the physical and biochemical structures. Glial cells include microglia and macroglia. Think of nerves as electrical wires where the bare copper is covered by a plastic sheet to decrease waste of energy and to increase the electrical conduct. Axons are similar to the bare copper that is covered by myelin sheath in order to increase the electrical conduction.