brain, spinal cord, and nerve disorders
Brain
Cerebrum
The cerebrum, the largest part of the brain, contains the following: The cerebral cortex:This convoluted layer of tissue forms the outer surface of the cerebrum. It consists of a thin layer of gray matter about one eighth of an inch (2 to 4 millimeters) thick. In adults, the cerebral cortex contains most of the nerve cells in the nervous system. White matter:White matter consists mainly of nerve fibers (axons) that connect the nerve cells in the cortex with one another, as well as with other parts of the brain and spinal cord. It also contains the support cells (oligodendrocytes) that make the myelin for the nerve cell fibers (to speed the conduction of impulses along nerve fibers). The white matter is located under the cortex. Subcortical structures:These structures are also located under ("sub-") the cortex—hence, their name. They include the basal ganglia, thalamus, hypothalamus, hippocampus, and the limbic system, which includes the amygdala, olfactory connections (structures that help transmit smell signals), and related structures. The cerebrum is divided into 2 halves—the left and right cerebral hemispheres. The hemispheres are connected by nerve fibers that form a bridge of white matter (called the corpus callosum) through the middle of the brain. Each hemisphere is further divided into lobes: Frontal lobe Parietal lobe Occipital lobe Temporal lobe Each lobe has specific functions, but for most activities, several areas of different lobes in both hemispheres must work together. Thefrontal lobeshave the following functions: Initiating many voluntary actions, ranging from looking toward an object of interest, to crossing a street, to relaxing the bladder to urinate Controlling learned motor skills, such as writing, playing musical instruments, and tying shoelaces Controlling complex intellectual processes, such as speech, thought, concentration, problem-solving, judgment, and planning for the future Controlling facial expressions and hand and arm gestures Coordinating expressions and gestures with mood and feelings Particular areas of the frontal lobes control specific movements, typically of the opposite side of the body. In most people, the left frontal lobe controls most of the functions involved in using language. Theparietal lobeshave the following functions: Interpreting sensory information from the rest of the body Controlling body and limb position Combining impressions of form, texture, and weight into general perceptions Influencing mathematical skills and language comprehension, as do adjacent areas of the temporal lobes Storing spatial memories that enable people to orient themselves in space (know where they are) and to maintain a sense of direction (know where they are going) Processing information that helps people know the position of their body parts Theoccipital lobeshave the following functions: Processing and interpreting vision and identifying the shapes of objects Enabling people to form visual memories Integrating visual perceptions with the spatial information provided by the adjacent parietal lobes Thetemporal lobeshave the following functions: Generating memory and emotions Processing immediate events into recent and long-term memory Storing and retrieving long-term memories Comprehending sounds and images, thus enabling people to recognize other people and objects and to integrate hearing and speech Subcortical structuresinclude large collections of nerve cells: The basal ganglia, which coordinate and smooth out movements The thalamus, which generally organizes sensory messages to and from the highest levels of the brain (cerebral cortex), providing an awareness of such sensations as pain, touch, and temperature The hypothalamus, which coordinates some of the more automatic functions of the body, such as control of sleep and wakefulness, maintenance of body temperature, regulation of appetite and thirst, and control of hormonal activity of the adjacent Overview of the Pituitary Gland None Thelimbic system,another subcortical structure, consists of structures and nerve fibers located deep within the cerebrum. The parts of the limbic system are the hypothalamus, the amygdala, the thalamus, mammillary bodies, and the hippocampus. This system connects the hypothalamus with other areas of the frontal and temporal lobes. The limbic system controls the experience and expression of emotions, motivation, memory, and learning, as well as some automatic functions of the body. By producing emotions (such as fear, anger, pleasure, and sadness), the limbic system enables people to behave in ways that help them communicate and survive physical and psychologic upsets. The hippocampus is also involved in the formation and retrieval of memories, and its connections through the limbic system help connect those memories to the emotions experienced when the memories form. Through the limbic system, memories that are emotionally charged are often easier to recall than those that are not. The limbic system also has input into other areas of the brain, such as the basal ganglia, that control intentional movements of the limbs. 