The brain consists of three functional regions, which developed at differing times over the course of human evolution. The newest and most complex area of the brain is the forebrain, which consists of the cerebrum and its underlying support tissues. The cerebrum dominates the human brain. Structurally, it accounts for approximately 85 percent of the total weight of the brain, according to the National Institute on Aging. Functionally, the cerebrum controls voluntary actions, perceptions and intellectual functions.
Voluntary Movement
"The Merck Manual for Healthcare Professionals" explains that the motor cortex in each of the frontal lobes of the cerebrum serves as the controlling site for all voluntary movement. Typing, walking, smiling, talking, playing a musical instrument and the myriad of other voluntary actions performed daily occur due to brain activity in the motor cortex. Interestingly, the motor cortex exhibits contralateral control. This means that the motor cortex on the right side of the brain controls the left side of the body, and vice versa. A stroke, brain tumor, or injury in the motor cortex region of the cerebrum results in weakness or paralysis on the opposite side of the body.
Sensation
Behind the motor cortex lies an area termed the sensory cortex, which is part of the parietal lobe of the cerebrum. The National Institute of Neurological Disorders and Stroke notes that the sensory cortex facilitates the perception, interpretation and understanding of touch, pressure and pain. Pressure interpretation permits graded force of muscular actions. For example, pressure perception controls the differentiation between gently holding a child's hand versus firmly grasping the handle of a shovel. Perceptive functions of the sensory cortex permit discrimination of varying textures and types of touch. The feel of the wind against the skin is easily distinguished from brushing against a passing stranger. Injury to the sensory cortex can lead to diminished or complete loss of sensation on the opposite side of the body.
Hearing
Dr. C. George Boeree of Shippensburg University points out that the auditory cortex of the temporal lobes receives input from the inner ear, which enables recognition and understanding of speech and sound. Identification of a specific person's voice, or picking out the sound of a French horn in an orchestra occurs through the activity of the auditory cortex. Damage to the auditory cortex often leads to an inability to understand spoken language.
Vision
The occipital lobes, located at the back of the head, are responsible for visual functions, explains "The Merck Manual for Healthcare Professionals." The left occipital lobe receives input from the right eye, and vice versa. The process of meaningful vision involves perceiving images and interpreting them. In looking at a flower, the brain first senses the visual image. A visual association function then transpires and recognition of the image as a flower occurs. Visual perception and association functions both occur within the occipital lobes. Damage to the occipital lobes may cause disturbances in visual perception or blindness.
References
- National Institute on Aging: Inside the Human Brain
- National Institute of Neurological Disorders and Stroke: Brain Basics
- Merck Manual for Healthcare Professionals: Function and Dysfunction of the Cerebral Lobes
- Shippensburg University: General Psychology, The Cerebrum
- University of Utah School of Medicine, Hyperbrain: The Cerebral Hemispheres
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