Sequencing and organization Language In general, the left hemisphere of the brain is responsible for language and speech and is called the "dominant" hemisphere. The right hemisphere plays a large part in interpreting visual information and spatial processing. In about one third of people who are left-handed, speech function may be located on the right side of the brain. Left-handed people may need special testing to determine if their speech center is on the left or right side prior to any surgery in that area.
The shape and size of the brain varies greatly between species, and identifying common features is often difficult.
Brain tissue in its natural The human brain is too soft to work with, but it can be hardened by immersion in alcohol or other fixativesand then sliced apart for examination of the interior.
Visually, the interior of the brain The human brain of areas of so-called grey matterwith a dark color, separated by areas of white matterwith a lighter color.
Further information can be gained by staining slices of brain tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations.
It is also possible to examine the microstructure of brain tissue using a microscope, and to trace the pattern of connections from one brain area to another.
When a pulse of electricity reaches a junction called a synapseit causes a neurotransmitter chemical to be released, which binds to receptors on other cells and thereby alters their electrical activity.
The brains of all species are composed primarily of two broad classes of cells: Glial cells also known as glia or neuroglia come in several types, and perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development.
Neurons, however, are usually considered the most important cells in the brain. The length of an axon can be extraordinary: Some neurons emit action potentials constantly, at rates of 10— per second, usually in irregular patterns; other neurons are quiet most of the time, but occasionally emit a burst of action potentials.
A single axon may make as many as several thousand synaptic connections with other cells. The neurotransmitter binds to receptor molecules in the membrane of the target cell. Shown is a pyramidal neuron from the hippocampus, stained for green fluorescent protein. Synapses are the key functional elements of the brain.
The human brain has been estimated to contain approximately trillion synapses;  even the brain of a fruit fly contains several million. A myelinated axon is wrapped in a fatty insulating sheath of myelinwhich serves to greatly increase the speed of signal propagation.
There are also unmyelinated axons. Myelin is white, making parts of the brain filled exclusively with nerve fibers appear as light-colored white matterin contrast to the darker-colored grey matter that marks areas with high densities of neuron cell bodies.
Evolution of the brain Generic bilaterian nervous system Nervous system of a generic bilaterian animal, in the form of a nerve cord with segmental enlargements, and a "brain" at the front. Except for a few primitive organisms such as sponges which have no nervous system  and cnidarians which have a nervous system consisting of a diffuse nerve net all living multicellular animals are bilateriansmeaning animals with a bilaterally symmetric body shape that is, left and right sides that are approximate mirror images of each other.
The brain is small and simple in some species, such as nematode worms; in other species, including vertebrates, it is the most complex organ in the body. It has not been definitively established whether the existence of these brainless species indicates that the earliest bilaterians lacked a brain, or whether their ancestors evolved in a way that led to the disappearance of a previously existing brain structure.
Invertebrates Fruit flies Drosophila have been extensively studied to gain insight into the role of genes in brain development.
This category includes tardigradesarthropodsmolluscsand numerous types of worms. The diversity of invertebrate body plans is matched by an equal diversity in brain structures.
Arthropods have a central brain, the supraesophageal ganglionwith three divisions and large optical lobes behind each eye for visual processing. Fruit flies Drosophilabecause of the large array of techniques available for studying their geneticshave been a natural subject for studying the role of genes in brain development.
The first biological clock genesfor example, were identified by examining Drosophila mutants that showed disrupted daily activity cycles. One of the advantages of working with this worm is that the body plan is very stereotyped: Each species has an equally long evolutionary historybut the brains of modern hagfishes, lampreyssharks, amphibians, reptiles, and mammals show a gradient of size and complexity that roughly follows the evolutionary sequence.
All of these brains contain the same set of basic anatomical components, but many are rudimentary in the hagfish, whereas in mammals the foremost part the telencephalon is greatly elaborated and expanded. The relationship between brain sizebody size and other variables has been studied across a wide range of vertebrate species.
As a rule, brain size increases with body size, but not in a simple linear proportion. In general, smaller animals tend to have larger brains, measured as a fraction of body size.
For mammals, the relationship between brain volume and body mass essentially follows a power law with an exponent of about 0. For example, primates have brains 5 to 10 times larger than the formula predicts.The brain constitutes only about 2 percent of the human body, yet it is responsible for all of the body's functions.
Learn about the parts of the human brain, as well as its unique defenses, like. The largest region of the human brain, our cerebrum controls higher brain functions such as language, logic, reasoning, and creativity. The cerebrum surrounds the diencephalon and is located superior to the cerebellum and brainstem.
The human brain is the center of the central nervous system in humans as well as the primary control center for the peripheral nervous system. The brain controls "lower" or involuntary activities. The human brain is the center of the central nervous system in humans as well as the primary control center for the peripheral nervous system.
The brain controls "lower" or involuntary activities. Life sized human brain model shows excellent detail of structures and is colored to highlight all parts and regions of the brain.
Left side has 34 call outs that are listed on included key, while the. The brain constitutes only about 2 percent of the human body, yet it is responsible for all of the body's functions. Learn about the parts of .