Every animal, from mammals to amphibians, has a brain. But the human brain is unique. It generates the ability to think, imagine, move and breathe. It weighs about 3 lbs. and tends to be slightly larger in men than in women; however, there is no correlation between intelligence and body size. There are two specific traits that distinguish humans from other animals: the ability to walk upright and extensive brain development. The brain has several main parts that work together to give people their unique abilities over other animals.
History
The 16th-century French philosopher Rene Descartes made great contributions to the fields of math, science and philosophy; however, he is also famous for his writings on the relationship between the mind, or brain, and body. Descartes was convinced that the body is a machine that follows physical properties, while the mind is a nonmaterial entity. Since Descartes’ time, scientists have learned a great deal about how the brain works from head trauma patients. Phineas Gage is one of the most famous of these patients. Gage had an iron rod pass completely through his skull in an accidental explosion while building the Rutland and Burlington railroad in Vermont in 1848. The tamping rod entered the base of his skull and exited out the top. Gage’s recovery was marked by a profound change in personality, which provided the first evidence--though not accepted until much later--of the link between the mind, emotions and the physical body--specifically, the brain. This case has since become acknowledged as a springboard for what is modern-day neurobiology.
Composition
The brain and spinal cord make up the central nervous system. The brain, spinal cord and peripheral nerves make up a complex, integrated information-processing and control system. The brain’s composition is about 40 percent white matter and 60 percent gray matter. The white matter consists of nerve cells, while bundles of long fibers that link the brain’s parts to each other, make up the gray matter. The brain contains about 100 billion nerves and two to four times as many glial cells, which provide the electrical and chemical reactions necessary for producing movement, thought and consciousness. Because the brain is very delicate, but has such an important role in survival, it requires several protective layers. Three layers, called the meninges, surround the brain. The deepest layer, the pia mater, envelops the brain’s surface. The next layer is the arachnoid mater and the outermost layer is the dura mater. The space between these two layers contains cerebrospinal fluid. This fluid absorbs shock from many different kinds of impact. The brain’s hardest and outermost protective layer is called the skull or cranium.
Structure
Because it is such a complex structure, scientists have divided the human brain into six major sections to make it easier to understand. The six regions are the cerebrum, diencephalon, midbrain, pons, cerebellum and medulla oblongata. The medulla, pons and midbrain constitute the brain stem; these are aptly named because they look like a stem for the rest of the brain. The medulla oblongata forms the lowest portion of the brain stem, the midbrain the uppermost and the pons lies between the two structures. The medulla attaches the brain to the spinal cord. The pons is a bridge-like structure that connects the cerebellum to the brain stem. The cerebellum is the second-largest part of the brain. The diencephalon is located between the cerebrum and the midbrain. It houses the thalamus, the hypothalamus and the posterior pituitary gland.
Function
The medulla performs sensory, motor and reflex functions such as heart rate, respiration and digestion. The pons contains reflex centers that help regulate breathing. The midbrain perceives pleasure and pain, and contains reflex centers from the eyes and ears to help maintain posture and to stay conscious and alert. The cerebellum programs and modifies movement by controlling skeletal muscles to maintain equilibrium. It also acts with the cerebral cortex to produce skilled movements and works below the conscious level to make movements smooth, steady, efficient and coordinated. The thalamus is a relay station for all kinds of sensory information, except possibly olfactory--including pain, temperature and touch--to the cerebrum. It also plays a role in feelings associated with pleasantness or unpleasantness. The hypothalamus is a small, but functionally powerful, area of the brain. It links the nervous system to the endocrine system and houses pleasure and reward centers that govern primary survival mechanisms such as hunger, thirst and reproduction. The pituitary gland secretes one hormone that controls water loss at the kidneys and another that stimulates uterine contraction, release of milk in females and stimulates prostate gland contraction in males.
Disorders
The brain is the nerve center of the body responsible for gathering, storing and retrieving sensory information and producing coordinated movement. When the brain is abnormally affected by internal or external forces, there is a marked deficit in performance directly associated with the afflicted area or areas. For example, meningitis--or inflammation of the meninges--is characterized by fever and chills, severe headache and stiff neck. Parkinson’s disease is a result of the loss of dopamine-producing brain cells, which result in a group of conditions that affect motor skills. The primary symptoms are uncontrollable shaking of the hands and other extremities and, as the disease progresses, it interferes in daily activities. Cerebral palsy is another disorder caused by abnormalities in the parts of the brain that control movement. Symptoms include lack of coordination and impaired gait. These conditions are but a few examples of how brain disorders result in impaired function. The brain is responsible for so many tasks that many disorders and conditions can adversely affect daily living activities.
References
- "The Human Body in Health and Disease"; Frederic H. Martini, Edwin F. Bartholomew, and Kathleen Welch; 2000
- "Descartes' Error: Emotion, Reason, and the Human Brain"; Antonio Damasio; 2000
- "Anatomy and Physiology: The Unity of Form and Function"; Eric Wise; 2004
- The National Institutes of Health: Meningitis
- The National Institutes of Health: Parkinson's Disease
