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The Brain - Summary
This section is limited to a brief description of the gross structure of the brain, its major divisions, its composition, the cranial nerves, and how it's protected. The gross structure of brain consists of the forebrain, midbrain, and hindbrain. The brains functions are numerous and vary widely, and it's the main portion of the central nervous system (CNS).

It helps make sense of our world and all that happens around us. Everything that happens around us is brought in and received through the five senses of sight, smell, hearing, touch and taste, often many at the same time. The brain controls thoughts, memory and speech, arm and leg movements, and the function of many organs within the body. It also determines how people respond to stressful situations by regulating heart and breathing rates. The brain is an organized structure and is divided into many components that serve specific and important functions.

The highest mental and behavioral activities characteristic of humans are mediated by the cerebral hemispheres, in particular by the cerebral cortex. Important aspects of these functions are learning and language. In addition, there are association mechanisms for the integration of motor and sensory functions.

The brain is made up of two types of cells: neurons and glial cells. The neurons are responsible for sending and receiving nerve impulses or signals. Glial cells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and facilitate signal transmission in the nervous system. In the human brain, glial cells outnumber neurons by about 50 to 1.

The weight of the brain changes from birth through adulthood. At birth, the average brain weighs about 1 pound, and grows to about 2 pounds during childhood. The average weight of an adult brain is about 3 pounds. The brain has billions of neurons that receive, analyze, and store information about internal and external conditions. It's also the source of conscious and unconscious thoughts, moods, and emotions.

The brain burns about 11 calories an hour, just going about its business of keeping one alive and functioning in the world. Although it accounts for about 2% of body weight, it expends 20% of the body's energy.
How the Brain Works
The brain functions through a complex set neural circuits. Communication between neurons is both electrical and chemical and always travels from the dendrites of a neuron, through its soma, and out its axon to the dendrites of another neuron.

Dendrites of one neuron receive signals from the axons of other neurons through chemicals known as neurotransmitters. The neurotransmitters set off electrical charges in the dendrites, which then carry the signals electrochemically to the soma. The soma integrates the information, which is then transmitted electrochemically down the axon to its tip.

At the tip of the axon, small, bubble like structures called vesicles release neurotransmitters that carry the signal across the synapse, or gap, between two neurons. There are many types of neurotransmitters, including norepinephrine, dopamine, and serotonin. Neurotransmitters can be excitatory (they excite an electrochemical response in the dendrite receptors) or inhibitory (they block the response of the dendrite receptors).

Although the brain appears symmetrical, but how it functions is not. Each hemisphere is specialized and dominates the other in certain functions. Research has shown that hemispheric dominance is related to whether a person is predominantly right-handed or left-handed. In most right-handed people, the left hemisphere processes arithmetic, language, and speech. The right hemisphere interprets music, complex imagery, and spatial relationships and recognizes and expresses emotion. In left-handed people, the pattern of brain organization is more variable.

Hemispheric specialization has traditionally been studied in people who have sustained damage to the connections between the two hemispheres, as may occur with stroke in which an interruption of blood flow to an area of the brain that causes the death of nerve cells in that area. The division of functions between the two hemispheres has also been studied in people who have had to have the connection between the two hemispheres surgically cut in order to control severe epilepsy, a neurological disease characterized by convulsions and loss of consciousness.

Intelligence

Intelligence provides the means to utilize abstract ideas and implement reasoning in arguments to justify the things we do. The degree of intelligence in people is variable to a number of factors, such as genetics, environment, illness, and even diet.

It's important to distinguish that:
Knowledge is the accumulation and retention of information acquired through experience or education;
Intelligence is the ability to analyze and understand information to the persons advantages.

An illness or even a disease such as MS doesn't tend to have a direct impact on one's intelligence, but rather the side effects of the disease or medications may hinder or slow down the process. It's important to know that this in no way means that those with MS are any less intelligent or have less knowledge, they may simply have to find different ways to attain and maintain it.

Vision

The visual system of humans is one of the most advanced sensory systems in the body. More information is conveyed visually than by any other means. In addition to the structures of the eye itself, several cortical regions (collectively called primary visual and visual associative cortex) as well as the midbrain are involved in the visual system. Conscious processing of visual input occurs in the primary visual cortex, but reflexive responses (immediate and unconscious) occur at the superior colliculus in the midbrain. Associative cortical regions (specialized regions that can associate, or integrate, multiple inputs) in the parietal and frontal lobes along with parts of the temporal lobe are also involved in the processing of visual information and the establishment of visual memories.

Language

Language involves specialized cortical regions in a complex interaction that allows the brain to comprehend and communicate abstract ideas. The motor cortex initiates impulses that travel through the brain stem to produce audible sounds. Neighboring regions of motor cortex, called the supplemental motor cortex, are involved in sequencing and coordinating sounds. Broca's area of the frontal lobe is responsible for the sequencing of language elements for output. The comprehension of language is dependent upon Wernicke's area of the temporal lobe. Other cortical circuits connect these areas.

Memory

Memory is usually considered a diffusely stored associative process (puts together information from many different sources.) Although research has failed to identify specific sites in the brain as locations of individual memories, certain brain areas are critical for memory to function. Immediate recall (the ability to repeat short series of words or numbers immediately after hearing them) is thought to be located in the auditory associative cortex. Short-term memory (the ability to retain a limited amount of information for up to an hour) is located in the deep temporal lobe. Long-term memory probably involves exchanges between the medial temporal lobe, various cortical regions, and the midbrain.

The Autonomic Nervous System

The autonomic nervous system (ANS) regulates the life support systems of the body reflexively (without conscious direction.) It automatically controls the muscles of the heart, digestive system, and lungs; certain glands; and homeostasis (the equilibrium of the internal environment of the body.) The autonomic nervous system itself is controlled by nerve centers in the spinal cord and brain stem and is fine-tuned by regions higher in the brain, such as the midbrain and cortex. Reactions such as blushing indicate that cognitive, or thinking, centers of the brain are also involved in autonomic responses.
Brain Divisions
The brain presents three main divisions: forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). The forebrain in turn has two subdivisions, telencephalon (endbrain) and diencephalon (interbrain). The hindbrain likewise has two subdivisions, the metencephalon (afterbrain) and the myelencephalon (marrowbrain).

The forebrain is responsible for a variety of functions including receiving and processing sensory information, thinking, perceiving, producing and understanding language, and controlling motor function. The two major divisions of forebrain are the diencephalon and the telencephalon. The diencephalon contains structures such as the thalamus and hypothalamus which are responsible for such functions as motor control, relaying sensory information, and controlling autonomic functions. The telencephalon contains the largest part of the brain, the cerebral cortex. Most of the actual information processing in the brain takes place in the cerebral cortex.

The midbrain and the hindbrain together make up the brainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.

The hindbrain extends to the top of the spinal cord and is composed of the metencephalon and myelencephalon. The metencephalon contains structures such as the pons and cerebellum. These regions assists in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. The myelencephalon is composed of the medulla oblongata which is responsible for controlling such autonomic functions as breathing, heart rate, and digestion.