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Brain

Brain

In the anatomy of animals, the brain, or encephalon (Greek for "in the head"), is the higher, supervisory center of the nervous system. The term 'brain' is typically used in connection with vertebrate nervous systems, and less often with regard to the nervous system of invertebrates. In the latter, neural control is performed by collections of ganglia. The brain is an extremely complex organ: the human brain is a collection of 100 billion neurons, each linked with up to 25,000 others. This huge number of interconnecting neurons, often referred to as a neural ensemble, is what makes the brain intelligent—enabling humans to analyze sensory signals, control the body, and think. In most animals, the brain is located in the head, close to the primary sensory apparatus and the mouth. Hippocrates considered the brain to be the seat of thought, while Aristotle believed it to be a cooling system for the blood. Today the study of the mind and brain consists of Neuroscience, the field of biology that studies the brain at its various levels of organization (from single neurons to functional systems such as visual system, auditory system, motor system and others); and psychology, the study of the cognition that arises from the neural function of the brain. Attempts have also been made to directly "read" the brain, which has been accomplished in a rudimentary manner through a brain-computer interface. In recent years, several institutions and bodies have undertaken research on recreating the neural structure of the brain with aim to produce human-like cognition and intelligence in computers. The brain controls and coordinates most movement, behavior and homeostatic body functions (such as heartbeat, blood pressure, fluid balance and body temperature). The brain is responsible for cognition, emotion, memory, motor learning and other kinds of learning. However, many behaviors, such as simple reflexes and basic locomotion, can be executed under spinal cord control alone.

The importance of the brain

The brain in animals

Three groups of animals, with some exceptions, have notably complex brains: the arthropods (insects and crustaceans), the cephalopods (octopuses, squid, and similar mollusks), and the craniates (vertebrates and their cousins). The brain of arthropods and cephalopods arises from twin parallel nerve cords that extend through the body of the animal. In arthropod, the brain consists of a central brain with three divisions and large optical lobes behind each eye for visual processing. eye The brain of craniates develops from the anterior section of a single dorsal nerve cord, which later becomes the spinal cord. In craniates, the brain is protected by the bones of the skull. In vertebrates, increasing complexity in the cerebral cortex correlates with height on the phylogenetic and evolutionary tree. Primitive vertebrates, like fish, reptiles, and amphibians have cortices with fewer than six layers of neurons, a structure known as allocortex (also named heterotypic cortex) (Martin, 1996). More complex vertebrates such as mammals have developed a six-layered neocortex (other terms: homotypic cortex, neocortex, neopallium), in addition to having some parts of the brain that are allocortex (Martin, 1996). In mammals, increasing convolutions of the brain, called gyri, are characteristic of animals with more advanced brains. These convolutions evolved to provide a larger surface area for a greater number of neurons, while keeping the volume of the brain compact enough to fit inside the skull.

The human brain

The structure of the human brain is different from that of other animals in several significant ways. These differences have allowed for many abilities over and above those of other animals, such as advanced cognitive skills. Human encephalization is especially pronounced in the neocortex, the most complex part of the cerebral cortex. The proportion of the human brain that is devoted to the neocortex—and the most advanced part within it, the prefrontal cortex—is larger than in all other animals. Humans enjoy unique neural capacities, but much of the human neuroarchitecture is shared with ancient species. Basic systems that alert the nervous system to stimulus, that sense events in the environment, and that monitor the condition of the body are similar to those of the most basic vertebrates. The neural circuitry underlying human consciousness includes both the advanced neocortex and protypical structures of the brain stem. The human brain also has a a million billion synaptic connections, making it one of the most densely connected network systems in the known universe; however, more complex structures may exist.

Pathology of the brain

The loss of function in the brain fulfills some definitions of death. Injuries to the brain tend to affect large areas of the organ, sometimes causing major deficits in intelligence, memory and control of the body. Head trauma, caused, for example, by vehicle and industrial accidents, is a leading cause of death in youth and middle age. In these cases, more damage is typically caused by resultant swelling (edema) than by the impact itself. Stroke, caused by the blockage of blood vessels in the brain, is another major cause of death from brain damage. Other problems in the brain can be more accurately classified as diseases rather than injuries. Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, motor neurone disease, and Huntington's disease, are caused by the gradual death of individual neurons, leading to decrements in movement control, memory, and cognition. Currently, only the symptoms of these diseases can be treated, but stem cell research may offer a cure. Mental illness, such as clinical depression, schizophrenia, bipolar disorder, and post-traumatic stress disorder, are brain diseases that impact on the personality and typically on other aspects of mental and somatic function. These disorders may be treated by psychiatric therapy, by pharmaceutical intervention, or by a combination of treatments; therapeutic effectiveness varies significantly among individuals. pharmaceutical Some infectious diseases affecting the brain are caused by viral and bacterial infection(s). Infection of the meninges, the membrane that covers the brain, can lead to meningitis. Bovine spongiform encephalopathy (also known as mad cow disease), is deadly in cattle and is linked to prions. Kuru is a similar prion-borne degenerative brain disease affecting humans. Both are linked to the ingestion of neural tissue, and may be an evolutionary defense against cannibalism. Viral or bacterial causes have been substantiated in multiple sclerosis, Parkinson's disease, Lyme disease, encephalopathy and encephalomyelitis. Some brain disorders are congenital. Tay-Sachs disease, Fragile X syndrome, Down syndrome, and Tourette syndrome are all linked to genetic and chromosomal errors. Malfunctions in the embryonic development of the brain can be caused by genetic factors, by drug use, and disease during a mother's pregnancy.

Other matters

Some philosophers consider that "brain" is synonymous with "mind", while others (such as strong AI theorists) believe that the mind is analogous to software and the brain to hardware. This issue—related to the mind-body problem—and many other issues, are the subjects of the area of the philosophy of mind. Questions asked in this field typically relate to the nature of consciousness and whether non-human animals are conscious beings. Computer scientists have produced computer systems called neural networks, loosely based on the structure of neuron connections in the brain. Artificial intelligence seeks to replicate brain function—although not necessarily brain mechanisms—but as yet is an immature science. Creating algorithms to mimic a biological brain is extremely difficult because the brain is not a static arrangement of circuits, but a network of vastly interconnected neurons that are constantly changing their connectivity and sensitivity. More recent work in both neuroscience and artificial intelligence models the brain using the mathematical tools of chaos theory and dynamical systems. Brain activity can be detected by electrodes, raising the possibility of "brain-computer interface". The reverse path has been demonstrated: brain implants have been used to generate artificial hearing and (crude and experimental) artificial vision for deaf and blind people; brain pacemakers are now commonly used to regulate brain activity in conditions such as Parkinson's disease. Both of these avenues of research are confronted with potentially serious ethical implications. For example, by placing electrodes in the brain and using a remote control, researchers have been able to remotely control the movements of a rat, combining commands of what to do with the stimulation of the brain pleasure centers. This raises the possibility of creating an electronically controlled biological "ratbot" that could be used in dangerous circumstances.

The biology of the brain

Despite the variance of the species in which the brain is found there are many common features in its cellular make-up, its structure and its function. On a cellular level, the brain is composed of two classes of cell, neurons and glia, both of which contain several different cell types which perform different functions. Interconnected neurons form neural networks (or neural ensembles). These networks are similar to man-made electrical circuits in that they contain circuit elements (neurons) connected by biological wires (nerve fibers). Of course, these do not form simple one-to-one electrical circuits (as is the case in many man-made circuits), neurons typically connect to at least a thousand other neurons. These highly specialized circuits make up systems which are the basis of perception, action and higher cognitive function. The brain contains anatomical and functional divides. In mammals, the most obvious partitioning of the brain is into the cerebrum (Latin for "brain", a large, anterior part that consists of two convoluted hemispheres and deep nuclei), cerebellum (Latin for "small brain", a smaller, structure behind the cerebrum with two rippled hemispheres and deep cerebellar nuclei), and brain stem (an elongated structure connecting the brain to the spinal cord). These parts are further divided into hemispheres, lobes, gyri, cortices, cytoarchitectonic and functional areas, nuclei, layers, fiber tracks and so forth. In summary, the chemical and electrical impulses continually passing through the cells of the brain produce all control, action and cognitive function in the body.

Histology

lobe Neurons, the cells that generate action potentials and convey them to other cells, constitute the chief class of brain cells. In each particular brain area, input (or afferent) neurons, output (or efferent) neurons and interneurons are typically found. Input neurons are recipients of projections from other brain areas. Output neurons project to the other areas. Interneurons are the neurons which do not leave the area. In addition to neurons, the brain contains glial cells in the proportion roughly 10 glial cells to every neuron; these are traditionally seen to perform supportive roles to neurons and fill out the space between them (hence its name, Greek for 'glue'). Most types of glia in the brain (and the rest of the central nervous system) are present in the entire nervous system, exceptions include oligodendrocytes which insulate neural axons (a role performed by Schwann cells in the peripheral nervous system). Oligosaccharides are the defining factor between white matter and grey matter in the brain—white matter is composed of myelinated (insulated) axons, whereas grey matter contains mostly cell soma, dendrites and unmyelinated portions of axons and glia and a smaller proportion of myelinated axons. In mammals, the brain also contains a certain amount of connective tissue called the meninges which is a system of membranes that separate the skull from the brain. The three-layered covering is made of, from the outside in, dura mater, arachnoid and pia mater (the latter two are connected and thus often considered as a single layer, the pia-arachnoid). Below the arachnoid is the subarachnoid space which contains cerebrospinal fluid which protects the nervous system. Blood vessels enter the central nervous system through the perivascular space above the pia mater. A blood-brain barrier protects the brain from unwanted substances that might enter it through the blood. The brain is suspended in cerebrospinal fluid, which circulates between layers of the meninges and through cavities in the brain called ventricles. It is important both chemically (metabolism) and mechanically (shock-prevention).

Anatomy

Although the histology of the brain is common to all those who have one, the structural anatomy is not. Apart from the general nature of the brain to order into lobes and suchforth, the lobes into which it has evolved are not common across the vertebrate/invertebrate divide. There are further dissimilarities within invertebrates, though vertebrates tend to share certain commonalities.

Invertebrates

In insects, the brain can be divided into four parts, the optical lobes, the protocerebrum, the deutocerebrum, and the tritocerebrum. The optical lobes are positioned behind each eye and process visual stimuli (Butler, 2000). The protocerebrum contains the mushroom bodies, which respond to smell, and the central body complex. The deutocerebrum includes the antennal lobes, which are similar to the mammalian olfactory bulb, and the mechanosensory neuropils which receive information from touch receptors on the head and antennae. The antennal lobes of flies and moths are quite complex. In cephalopods, the brain is divided into two regions: the supraesophageal mass and the subesophageal mass. These parts are divided by the animal's esophagus. The supra- and subesophageal masses are connected to each other on either side of the esophagus by the basal lobes and the dorsal magnocellular lobes. The large optic lobes are sometimes not considered to be part of the brain proper since the optic lobes anatomically separate from the brain and are joined to the brain by the optic stalks. However, the optic lobes perform much of the visual processing and can be functionally considered to be a part of the brain.

Vertebrates

In vertebrates, a gross division into three major parts is used: hindbrain (medulla oblongata and metencephalon), midbrain (mesencephalon) and forebrain (diencephalon and telencephalon). Varied taxonomies have been used by assorted schools at various times in history for the study of diverse species. An anterior part of the telencephalon called the cerebrum makes up the largest section of the mammalian brain and in humans, its surface has many deep fissures (sulci) and convolutions (gyri), giving a wrinkled appearance to the brain. In most vertebrates the metencephalon is the highest integration center in the brain, whereas in mammals this role has been adopted by the cerebrum. Behind (or in humans, below) the cerebrum is the cerebellum, a convoluted structure whose neural circuitry is often compared with crystal structure. Cerebellum participates in the control of movement. The cerebellum attaches to the hindbrain in a structure called the pons. The cerebrum and the cerebellum consist each of two halves (hemispheres). The corpus callosum connects the two hemispheres of the cerebrum. An outgrowth of the telencephalon called the olfactory bulb is a major structure in many animals, but in humans and other primates, it is relatively small. Vertebrate nervous systems are distinguished by encephalization and bilateral symmetry. Encephalization refers to the tendency for more complex organisms to gain a larger-size brains through evolutionary time. Larger vertebrates develop a complex of layered, networked and convoluted grey matter and white matter. Grey matter refers to tissue mostly comprised of neurons and can be found on the surface of cerebral cortex, as well as in clusters called nuclei deep within the brain. White matter refers to axons and their surrounding myelin insulation, which gives this tissue its white color. White matter is found in bundles of fibers known as tracts which connect the different parts of the brain. In modern species most closely related to the first vertebrates, brains are covered with gray matter that has a three-layer structure. Their brains also contain deep brain nucleus and fiber tracks forming the white matter. Most regions of the human cerebral cortex have six layers of neurons, a structure known as neocortex.

Brain Regions in Vertebrates

According to the hierarchy based on embryonic and evolutionary development, chordate brains are composed of the following regions:
- RHOMBENCEPHALON (Greek for "rhomboid brain")
  - Myelencephalon (Greek for "brain marrow", also called medulla oblongata which means "long marrow" in Latin)
  - Metencephalon (Greek for "after the brain"; also called hindbrain)
    - pons
    - cerebellum
- MESENCEPHALON (Greek for "middle brain", also called midbrain)
  - tectum
  - midbrain tegmentum
  - substantia nigra
  - crus cerebri (also called cerebral peduncles and pedunculus cerebri)
- PROSENCEPHALON
  - Diencephalon (Greek for "brain in between")
    - thalamus
    - hypothalamus (Greek for "under the thalamus")
    - pituitary gland
    - epithalamus
    - pineal gland
  - Telencephalon (Greek for "end brain", i.e. the most rostral part of the brain; also called forebrain)
    - TELENCEPHALON NUCLEI
      - putamen
      - caudate nucleus
      - putamen
      - globus pallidus
      - amygdala
    - CEREBRAL CORTEX
    - Archipallium (Greek for "first cloak", i.e. cortex that developed first; also called archeocortex)
      - hippocampus
    - Paleopallium (Greek for "ancient cloak"; also called "paleocortex")
      - priform(olfactory) cortex
      - parahippocampal gyrus
    - Neopallium (Greek for "new cloak"; also called "paleocortex"; also called neocortex and isocortex)
      - frontal lobe
      - temporal lobe
      - parietal lobe
      - occipital lobe
      - insula
      - cingulate cortex In addition, the brain is often subdivided into the following major parts:
- BRAINSTEM
  - Medulla
  - Pons
  - Midbrain
- CEREBELLUM
  - Cerebellar cortex
  - Cerebellar nuclei
- BASAL GANGLIA (some midbrain nuclei, such as substantia nigra are usually considered as basal ganglia)
  - Striatum (caudate nucleus and putamen)
  - Globus pallidus
- HIPPOCAMPUS
- AMYGDALA
- THALAMUS
- HYPOTHALAMUS
- CEREBRAL CORTEX Yet alternative classifications arrange brain areas into functional systems:
- Limbic system
- Sensory systems
  - Visual system
  - Olfactory system
  - Gustatory system
  - Auditory system
  - Somatosensory system
- Motor system
- Associative areas

Function

Associative areas Vertebrate brains receive signals through nerves arriving from the sensors of the organism, interpret those signals and formulate reactions based on built-in programs and learned experiences. A similarly extensive nerve network delivers signals from a brain to control muscles throughout a body. Anatomically, the majority of afferent and efferent nerves (with the exception of cranial nerves) are connected to the spinal cord, which then transfers the signals to the brain. Sensory input is processed by the brain to recognize danger, find food, identify potential mates and perform more sophisticated functions. Visual, touch, and auditory sensory pathways of vertebrates are routed to specific nuclei of the thalamus and then to regions of the cerebral cortex that are specific to each sensory system: the visual system, the auditory system and the somatosensory system. Olfactory pathways are routed to the olfactory bulb, then to various parts of the olfactory system. Taste is routed through the brainstem and then to other portions of the gustatory system. To control movement, the brain has several parallel systems of muscle control. The motor system controls voluntary muscle movement, aided by motor areas of the cerebral cortex, the cerebellum and the basal ganglia — the system that eventually projects to the spinal cord. Nuclei in the brainstem control many involuntary muscle functions such as heartrate and breathing. In addition, many automatic acts (simple reflexes, locomotion) can be controlled by the spinal cord alone. Brains also produce hormones that can influence organs and glands elsewhere in a body - conversely, brains also react to hormones produced elsewhere in the body. In mammals, most of these hormones are released into the circulatory system by a structure called the pituitary gland. It is hypothesized that developed brains derive consciousness from interaction among numerous systems within the brain. Cognitive processing in mammals occurs in the cerebral cortex but relies on mid-brain and limbic functions as well, especially those of the thalamus and hippocampus. Among "younger" (in an evolutionary sense) vertebrates, advanced processing involves progressively rostral (forward) regions of the brain. Hormones, incoming sensory information, and cognitive processing performed by the brain determine the brain state. Stimulus from any source can trigger a general arousal process that focuses cortical operations to processing of the new information. Cognitive priorities are constantly shifted by a variety of factors, such as hunger, fatigue, beliefs, unfamiliar information or threats. The simplest dichotomy related to processing of threats is the fight-or-flight response mediated by the amygdala, among other structures.

The study of the brain

Fields of study

Several areas of science specifically study the brain. Neuroscience seeks to understand the nervous system, including the brain, from a biological perspective. Psychology seeks to understand behavior and the brain. The terms neurology and psychiatry usually refer to medical applications of neuroscience and psychology, respectively. Cognitive science seeks to unify neuroscience and psychology with other fields that concern themselves with the brain, such as computer science (in Artificial intelligence and similar fields) and philosophy.

Methods of observation

Each method for observing activity in the brain has its advantages and drawbacks. Electrophysiology, in which wire electrodes are implanted in the brain, allows scientists to record the electrical activity of individual neurons or fields of neurons, but since it requires invasive surgery, this is a technique usually reserved for lab animals. By placing electrodes on the scalp, electroencephalography (EEG) measures brain waves, which are the mass changes in electrical current from the cerebral cortex, but can only detect changes over large areas of the brain and very little sub-cortical activity. Functional magnetic resonance imaging (fMRI) measures changes in blood flow in the brain, but the activity of neurons is not directly measured, nor can it be distinguished whether this activity is inhibitory or excitatory. Similarly, a PET (Positron Emission Tomography) Scan, is able to monitor glucose intake in different areas within the brain which is correlated the level of activity in that region. Behavioral tests can measure symptoms of disease and mental performance, but only provide indirect measurements of brain function and may not be practical in all animals. Finally, post-mortem analysis of the brain allows for the study of anatomy and protein expression patterns, but is only possible after the human or animal is dead.

History

Ancient Greeks had differing views on the function of the brain. Hippocrates believed the brain to be the seat of intelligence, but Aristotle held that the brain was a cooling mechanism for the blood, while the heart was the seat of intelligence. He reasoned that humans are more rational than the beasts because they have a proportionally larger brain to cool their hot-bloodedness (Bear, 2001). During the Roman Empire, the anatomist Galen dissected the brains of sheep. He concluded that since the cerebellum was hard on touch, it must control the muscles, while since the cerebrum was soft, it must be where the senses were processed. Galen further theorized that the brain functioned by movement of fluids through the ventricles (Bear, 2001). In the Age of Reason, René Descartes espoused a fluid mechanical view of the brain similar to Galen's theories. However, Descartes thought that although this explanation was adequate to explain the brain functions of animals, the higher mental functions of humans were accomplished by the soul. This theoretical separation of the mind and brain became known as the mind-body problem (Bear, 2001). In the mid-1600s, however, great progress in describing the anatomy of the brain was achieved with the works of English anatomist Thomas Willis and Flemish anatomist Vesalius. They dispelled many of the notions of Galen and Descartes and discovered many facts about the macro structure of the brain of animals and humans. In the 1700s, Luigi Galvani showed that electrically stimulating the sciatic nerve of a dissected frog caused movement of the attached muscle. His experiments led scientists away from the fluid mechanical theory of the brain and toward an electrical theory. In the 19th century, Galvani's work led to the development of research in bioelectricity and to the discovery of the membrane potential and action potential by researchers such as Emil du Bois-Reymond. The scientists of the 1800s debated whether areas of the brain corresponded to specific functions or if the brain functioned as a whole (the "aggregate field theory"). Jean Pierre Flourens championed the aggregate field theory in opposition to the pseudoscience of phrenology, founded by Franz Joseph Gall. However, the work of Paul Pierre Broca, Karl Wernicke, and Korbinian Brodmann eventually helped to show that areas of the brain had specific functions, though some functions were repeated, an idea known as parallel distributed processing (Kandel, 2001). As the 20th century approached, the anatomical works of Santiago Ramon y Cajal and Camillo Golgi laid the foundation for the study of individual neurons in the brain. Charles Scott Sherrington and Edgar Douglas Adrian furthered the study of neurons with the new techniques of electrodes and the electroencephalogram (EEG). Neurotransmitters were discovered and investigated by a number of scientists, including Otto Loewi, Henry Hallett Dale, Arvid Carlsson and many others. Modern Neuroscience experiences rapid development. The scientists use a variety of approaches to study the brain at different levels — from the molecules to systems. Extensive knowledge has been accumulated about the electrophysiological properties of different types of neurons and their responsiveness to neurotransmitters. Recordings from the brain of awake, behaving animals pioneered by Edward Evarts help to decode neuronal firing during different behaviors and cognitive processes. Miguel Nicolelis introduce multielectrode recording techniques which led to creation of brain-computer interfaces. Rapidly developing brain imaging allows scientists to study the brain in living humans and animals in ways that their predecessors could not.

The brain as a food

Like most other internal organs, the brain can serve as nourishment. For example, in the Southern United States canned pork brain in gravy can be purchased for consumption as food. This form of brain is often fried with scrambled egg to produce the famous "Eggs n' Brains". The brain of animals also features in the cuisine of France such as in the dish tête de veau, or head of calf. Although it might consist only of the outer meat of the skull and jaw, the full meal includes the brain, tongue and glands (the latter form being the favorite food of president Jacques Chirac). Similar delicacies from around the world include Mexican tacos de sesos (tacos made with cattle brain) and squirrel brain in the US South. The Anyang tribe of Cameroon practiced a tradition in which a new chief would consume the brain of a hunted gorilla while another senior member of the tribe would eat the heart. Consuming the brain and other nerve tissue of animals is not without its risks. The first problem is that the brain is made up of 60% fat due to the myelin (which by itself is 70% fat) insulating the axons of neurons and glia. As an example, a 5 oz. (0.14 kg) can of "Pork Brains in Milk Gravy", a single serving, contains 3500 milligrams of cholesterol, 1170% of our recommended daily intake. More importantly, humans can contract fatal transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease and other (prion diseases), as well as Bovine Spongiform Encephalopathy (colloquially known as "mad cow" disease) through the consumption of the infected nerve tissue of cattle and other animals - However, "there is no evidence that people can get mad cow disease from eating muscle meat". Another prion disease called kuru has been traced to a mourning ritual among the Fore people of Papua New Guinea in which those close to the dead would eat their brain to create a sense of immortality. Some archaeological evidence suggests that the mourning rituals of European neanderthals also involved the consumption of the brain. The practice of eating another human's brain has been depicted by Hollywood in Hannibal (film) and countless zombie movies. It is not only humans who eat the brains of other animals. The two species of chimpanzee, though generally vegetarian, are known to eat the brains of monkeys to obtain fat in their diet.

External links


- [http://www.stanford.edu/group/hopes/basics/braintut/ab0.html Brain Tutorial]
- [http://brainmuseum.org/ Comparative Mammalian Brain Collection]
- [http://www.rmcybernetics.com/science/cybernetics/ai_vision_perception_brain.htm RMCybernetics - The Brain and Artificial Intelligence]
- [http://braininfo.rprc.washington.edu BrainInfo for Neuroanatomy]
- [http://faculty.washington.edu/chudler/neurok.html Neuroscience for kids]
- [http://3dscience.com/advancedsearch.asp?stS=brain&cboMatch=Any&selectcategory=0&txtMinPrice=&txtMaxPrice= Free Brain Medical Clip Art].
- [http://purl.net/net/neurowiki neuroscience wiki]
- [http://www.brainmaps.org/ BrainMaps.org], interactive high-resolution digital brain atlas based on scanned images of serial sections of both primate and non-primate brains

Related topics


- A/S ratio
- Avian pallium
- Brain damage
- Brain-computer interface
- Coma
- Human brain
- Persistent vegetative state
- Regions in the human brain
- The Memory-Prediction Framework
- Metastability in the brain
- Neuroendocrinology
- Traumatic brain injury

References


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Notes

The following are the sources for individual facts, statistics and information included in the article:
- Statistic from page 161 of Basic Histology: Text and Atlas, 10th ed. by L.C. Junqueira, and J. Carneiro.
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- Category:Central nervous system Category:Cerebrum ja:脳 ko:뇌 simple:Brain th:สมอง

Animal

:For the Muppet Show character, see Animal (Muppet). For the professional wrestler, see Joseph Laurinaitis.

    - Porifera (sponges)
    - Ctenophora (comb jellies)
    - Cnidaria (coral, jellyfish, anenomes)
    - Placozoa (trichoplax)
- Subregnum Bilateria (bilateral symmetry)
    - Acoelomorpha (basal)
    - Orthonectida (flatworms, echinoderms, etc.)
  - Rhombozoa (dicyemids)
  - Myxozoa (slime animals)
  - Superphylum Deuterostomia (blastopore becomes anus)
    - Chordata (vertebrates, etc.)
    - Hemichordata (acorn worms)
    - Echinodermata (starfish, urchins)
    - Chaetognatha (arrow worms)
  - Superphylum Ecdysozoa (shed exoskeleton)
    - Kinorhyncha (mud dragons)
    - Loricifera
    - Priapulida (priapulid worms)
    - Nematoda (roundworms)
    - Nematomorpha (horsehair worms)
    - Onychophora (velvet worms)
    - Tardigrada (water bears)
    - Arthropoda (insects, etc.)
  - Superphylum Platyzoa
    - Platyhelminthes (flatworms)
    - Gastrotricha (gastrotrichs)
    - Rotifera (rotifers)
    - Acanthocephala (acanthocephalans)
    - Gnathostomulida (jaw worms)
    - Micrognathozoa (limnognathia)
    - Cycliophora (pandora)
  - Superphylum Lophotrochozoa (trochophore larvae / lophophores)
    - Sipuncula (peanut worms)
    - Nemertea (ribbon worms)
    - Phoronida (horseshoe worms)
    - Ectoprocta (moss animals)
    - Entoprocta (goblet worms)
    - Brachiopoda (brachipods)
    - Mollusca (mollusks)
    - Annelida (segmented worms) Animals are a major group of organisms, classified as the kingdom Animalia or Metazoa. In general they are multicellular, capable of locomotion and responsive to their environment, and feed by consuming other organisms. Their body plan becomes fixed as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on. Along with sponges, gastropods, emus, dolphins and all other animals, Homo sapiens sapiens meet all the criteria above for membership in the group of organisms known as animals and they do not meet the criteria of the other groups. Some humans often consider themselves separate from animals, not on the grounds of biology, but through the use of "other contexts". Whilst self-delusion may be a unique characteristic of the human species it is not cause for exclusion from the Kingdom Animalia. The name animal comes from the Latin word animal, of which animalia is the plural, and ultimately from anima, meaning vital breath or soul.

Characteristics

Aristotle divided the living world between animals and plants, and this was followed by Carolus Linnaeus in the first hierarchical classification. Since then biologists have begun emphasizing evolutionary relationships, and so these groups have been restricted somewhat. For instance, microscopic protozoa were originally considered animals because they move, but are now treated separately. Kingdom Animalia has several characteristics that set it apart from other living things. First, animals are eukaryotic. This separates them from the Kingdom Monera. Second, animals are multicellular, which separates them from Kingdom Protista. Third, they are heterotrophic, setting them apart from Kingdom Plantae and several plant-like protists. Finally, Kingdom Animalia consists of organisms without cell walls, which makes it unique compared to Kingdom Plantae, algae, and Kingdom Fungi.

Structure

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and a nervous system, which sends and processes signals. There is also typically an internal digestive chamber, with one or two openings. Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general. All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. During development it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible. In contrast, other multicellular organisms like plants and fungi have cells held in place by cell walls, so develop by progressive growth. Also, unique to animal cells are the following intercellular junctions: tight junctions, gap junctions, and desmosomes.

Reproduction and development

Nearly all animals undergo some form of sexual reproduction. Adults are diploid or occasionally polyploid. They have a few specialized reproductive cells, which undergo meiosis to produce smaller motile spermatozoa or larger non-motile ova. These fuse to form zygotes, which develop into new individuals. Many animals are also capable of asexual reproduction. This may take place through parthenogenesis, where fertile eggs are produced without mating, or in some cases through fragmentation. A zygote initially develops into a hollow sphere, called a blastula, which undergoes rearrangement and differentiation. In sponges, blastula larvae swim to a new location and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber, and two separate germ layers - an external ectoderm and an internal endoderm. In most cases, a mesoderm also develops between them. These germ layers then differentiate to form tissues and organs. Animals grow by indirectly using the energy of sunlight. Plants use this energy to turn air into simple sugars using a process known as photosynthesis. These sugars are then used as the building blocks which allow the plant to grow. When animals eat these plants (or eat other animals which have eaten plants), the sugars produced by the plant are used by the animal. They are either used directly to help the animal grow, or broken down, releasing stored solar energy, and giving the animal the energy required for motion. This process is known as glycolysis.

Origin and fossil record

Animals are generally considered to have evolved from flagellate protozoa. Their closest living relatives are the choanoflagellates, collared flagellates that have the same structure as certain sponge cells do. Molecular studies place them in a supergroup called the opisthokonts, which also include the fungi and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal sperm, whereas other eukaryotes tend to have anterior flagella. The first fossils that might represent animals appear towards the end of the Precambrian, around 600 million years ago, and are known as the Vendian biota. These are difficult to relate to later fossils, however. Some may represent precursors of modern phyla, but they may be separate groups, and it is possible they are not really animals at all. Aside from them, most animal phyla with known phyla make a more or less simultaneous appearance during the Cambrian period, about 570 million years ago. It is still disputed whether this event, called the Cambrian explosion, represents a rapid divergence between different groups or a change in conditions that made fossilization possible.

Groups of animals

The sponges (Porifera) diverged from other animals early. As mentioned, they lack the complex organization found in most other phyla. Their cells are differentiated, but not organized into distinct tissues. Sponges are sessile and typically feed by drawing in water through pores all over the body, which is supported by a skeleton typically divided into spicules. The extinct Archaeocyatha, which have fused skeletons, may represent sponges or a separate phylum. Among the eumetazoan phyla, two are radially symmetric and have digestive chambers with a single opening, which serves as both the mouth and the anus. These are the Cnidaria, which include anemones, corals, and jellyfish, and the Ctenophora or comb jellies. Both have distinct tissues, but they are not organized into organs. There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, these animals are sometimes called diploblastic. The tiny phylum Placozoa is similar, but individuals do not have a permanent digestive chamber. The remaining animals form a monophyletic group called the Bilateria. For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i.e. all three germ layers are well-developed, and tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is also an internal body cavity called a coelom or pseudocoelom. There are exceptions to each of these characteristics, however - for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures. Genetic studies have considerably changed our understanding of the relationships within the Bilateria. Most appear to belong to four major lineages: # Deuterostomes # Ecdysozoa # Platyzoa # Lophotrochozoa In addition to these, there are a few small groups of bilaterians with relatively similar structure that appear to have diverged before these major groups. These include the Acoelomorpha, Rhombozoa, and Orthonectida. The Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well.

Deuterostomes

Deuterostomes differ from the other Bilateria, called protostomes, in several ways. In both cases there is a complete digestive tract. However, in protostomes the initial opening (the archenteron) develops into the mouth, and an anus forms separately. In deuterostomes this is reversed. In most protostomes cells simply fill in the interior of the gastrula to form the mesoderm, called schizocoelous development, but in deuterostomes it forms through evagination of the endoderm, called enterocoelic pouching. Deuterostomes also have a dorsal, rather than a ventral, nerve chord and their embryos undergo different cleavage. All this suggests the deuterostomes and protostomes are separate, monophyletic lineages. The main phyla of deuterostomes are the Echinodermata and Chordata. The former are radially symmetric and exclusively marine, such as sea stars, sea urchins, and sea cucumbers. The latter are dominated by the vertebrates, animals with backbones. These include fish, amphibians, reptiles, birds, and mammals. In addition to these, the deuterostomes also include the Hemichordata or acorn worms. Although they are not especially prominent today, the important fossil graptolites may belong to this group. The Chaetognatha or arrow worms may also be deuterostomes, but this is less certain.

Ecdysozoa

The Ecdysozoa are protostomes, named after the common trait of growth by moulting or ecdysis. The largest animal phylum belongs here, the Arthropoda, including insects, spiders, crabs, and their kin. All these organisms have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. The ecdysozoans also include the Nematoda or roundworms, the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water. A number are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, which are visible to the unaided eye, and the Kinorhyncha, Priapulida, and Loricifera, which are all microscopic. These groups have a reduced coelom, called a pseudocoelom. The remaining two groups of protostomes are sometimes grouped together as the Spiralia, since in both embryos develop with spiral cleavage.

Platyzoa

The Platyzoa include the phylum Platyhelminthes, the flatworms. These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors. A number of parasites are included in this group, such as the flukes and tapeworms. Flatworms lack a coelom, as do their closest relatives, the microscopic Gastrotricha. The other platyzoan phyla are microscopic and pseudocoelomate. The most prominent are the Rotifera or rotifers, which are common in aqueous environments. They also include the Acanthocephala or spiny-headed worms, the Gnathostomulida, Micrognathozoa, and possibly the Cycliophora. These groups share the presence of complex jaws, from which they are called the Gnathifera.

Lophotrochozoa

The Lophotrochozoa include two of the most successful animal phyla, the Mollusca and Annelida. The former includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and leeches. These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods, because they are both segmented. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla. The Lophotrochozoa also include the Nemertea or ribbon worms, the Sipuncula, and several phyla that have a fan of cilia around the mouth, called a lophophore. These were traditionally grouped together as the lophophorates, but it now appears they are paraphyletic, some closer to the Nemertea and some to the Mollusca and Annelida. They include the Brachiopoda or lamp shells, which are prominent in the fossil record, the Entoprocta, the Phoronida, and possibly the Ectoprocta or moss animals.

History of classification

In Linnaeus' original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, whereas the various other forms have been separated out. The above lists represent our current understanding of the group, though there is some variation from source to source.

Usage of the word animal

In everyday usage animal refers to any member of the animal kingdom that is not a human being, and sometimes excludes insects (although including such arthropods as crabs). This confusion stems primarily from the familiarity with zoo animals, farm animals and pets, not from an analytical distinction between insects, humans and the rest of the animal kingdom.

Examples

Some well-known types of animals, listed by their common names:
- alpaca, ant, antelope, badger, bat, bear, bee, beetle, bird, bison, butterfly, cat, chicken, cockroach, coral, cow, deer, dinosaur, dog, dolphin, earthworm, elephant, elk, fish, fly, fox, frog, giraffe, goat, gorilla, hippopotamus, horse, human, iguana, jellyfish, kangaroo, lion, lizard, llama, lynx, monkey, mouse, nightingale, octopus, owl, ox, parrot, penguin, pig, quail, rabbit, rat, rhinoceros, salamander, scorpion, seahorse, shark, sheep, sloth, snake, spider, squid, starfish, tiger, turtle, urial, vole, whale, wolf, yak, zebra

See also


- Altruism in animals
- Amphibian
- Animal intelligence
- Animal locomotion
- Animal rights
- Biblical terms
  - Clean animals
  - Unclean animals
- Biology
- Biota
- Bird
- Fish
- Insect
- Mammal
- Macrofossil
- Prehistoric life
- Reptile
- Zoology
- Zoo

References

External links


- [http://www.animool.com/animals/index.jsp Animals Search Engine]
- [http://www.wikianimals.com wikianimals.com] - Documenting the animal kingdom
- [http://tolweb.org/tree?group=Animals&contgroup=Eukaryotes Tree of Life]
- [http://www.arkive.org A Multimedia Database of Various UK or Endangered Species]
- [http://freepages.genealogy.rootsweb.com/~wakefield/animals.html Animals and Birds Names] - Large table of words: animal, collective, male, female, young, & home
- [http://www273.pair.com/med/words/animal_adjectives.htm English Animal Adjectives]
- [http://www.georgetown.edu/faculty/ballc/animals/animals.html Sounds of the World's Animals] - animal sounds in many languages
- [http://www.findsounds.com/ FindSounds - Search the Web for Sounds] - sound files including animal sound files
- [http://www.australianfauna.com/ Australian Animals]
- [http://www.animalreviews.com AnimalReviews] - animals reviewed and evaluated
- [http://animals.timduru.org/ The animal photo archive] - Photos of animals
- [http://www.wildlife-photo.org Photo gallery of animals pictures from the entire world.]
- [http://www.wildlife-photo.org/birds_list.htm Birds Name Check List in Latin, English, Russian and Hebrew.]
- [http://www.wildanimalsonline.com Wild Animals Online] - an online encyclopedia of wild animals - facts, photos Category:Animals zh-min-nan:Tōng-bu̍t ko:동물 ms:Haiwan ja:動物 simple:Animal th:สัตว์





Invertebrate

Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. It therefore includes all animals except vertebrates (fish, reptiles, amphibians, birds and mammals). Lamarck divided these animals into two groups, the Insecta and the Vermes, but nowadays, they are classified into over 30 phyla, from simple organisms such as sponges and flatworms to complex animals such as arthropods and mollusks. Since invertebrates include all animals except a certain group, invertebrates form a paraphyletic group, but, despite not forming a "natural group" (that is, monophyletic), "invertebrate" is still a widely used term. It is not uncommon for books entitled "Invertebrate Zoology" to be found. This reflects the bias in society and also in zoology towards larger, more complex animals that are more closely related to humans. Thus, there are relatively many scientists studying (and relatively much funding available for the study of) birds, mammals, reptiles, and so on, but far fewer scientists studying invertebrates, even though invertebrates include 97% of all animal species. For a full list of animals considered to be invertebrates, see animal. All the listed phyla are invertebrates along with two of the three subphyla in Phylum Chordata: Urochordata and Cephalochordata. These two, plus all the other known invertebrates, have only one cluster of Hox genes, while the vertebrates have duplicated their original cluster more than once.

External links


- [http://reference.allrefer.com/encyclopedia/categories/invertz.html Invertebrate Zoology]
- [http://digitalcommons.unl.edu/onlinedictinvertzoology/ Online Dictionary of Invertebrate Zoology]
- [http://www.goliathus.cz/en/museum-homepage-0.html Online museum] of many invertebrates, provided by [http://www.goliathus.cz/ goliathus.cz]. Category:Animals ms:Invertebrata ja:無脊椎動物

Ganglia

The term ganglia may refer to:
- multiple clusters of neurons; see ganglion.
- a scalable distributed monitoring system for high-performance computing systems; see Ganglia (software) [http://ganglia.sourceforge.net].
- A cybergrind band Gånglîå

Neuron

Neurons (also spelled neurones or called nerve cells) are the primary cells of the nervous system. In vertebrates, they are found in the brain, the spinal cord and in the nerves and ganglia of the peripheral nervous system.

Classes

There are three classes of neurons: afferent neurons, efferent neurons, and interneurons.
- Afferent neurons convey information from tissues and organs into the central nervous system.
- Efferent neurons transmit signals from the central nervous system to the effector cells.
- Interneurons connect neurons within the central nervous system. Structural classification
- Pseudounipolar- single dendrite longer than single axon
- Bipolar - single axon and single dendrite equal length
- Multipolar - more than two dendrites
  - Golgi I- pyramidal cell
  - Golgi II- granule (stellate) cell

Anatomy and histology

Golgi II Many highly specialized types of neurons exist, and these differ widely in appearance. Characteristically, neurons are highly asymmetric in shape. Neurons consist of:
- The dendrite, a short, branching arbour of cellular extensions. Each neuron has very many dendrites with profuse dendritic branches. These structures form the main information receiving network for the neuron.
- The soma, or cell-body, the relatively large central part of the cell between the dendrites and the axon.
- The axon, a much finer, cable-like projection which may extend tens, hundreds, or even tens of thousands of times the diameter of the soma in length. This is the structure which carries nerve signals away from the neuron. Neurons have only one axon, but this axon may - and usually will - undergo extensive branching, enabling communication with many target cells. Axons and dendrites in the central nervous system are typically only about a micrometre thick, while some of those in the peripheral nervous system are much thicker. The soma is usually about 25 micrometres in diameter and not much larger than the cell nucleus it contains. The axon of a human motoneuron can be over a metre long, reaching from the base of the spine to the toes, while giraffes have single axons running along the whole length of their necks, several feet in length. Much of what we currently know about axonal transport comes from studying the squid neuron, an ideal neuron for research due to it's relatively immense size (0.5 - 1 millimetres thick, several centimetres long).

Connectivity

Neurons communicate with one another and to other cells through synapses, where the axon tip of one cell impinges upon a dendrite or soma of another, or less commonly to an axon. Neurons of the cortex in mammals, such as the Purkinje cells, can have over 1000 dendrites each, enabling connections with tens of thousands of other cells.

Adaptations to carrying action potentials

The narrow cross-section of axons and dendrites lessens the metabolic expense of carrying action potentials, although thicker axons convey the impulses more rapidly, generally speaking. Many neurons have insulating sheaths of myelin around their axons. The sheaths are formed by glial cells: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. The sheath enables the action potentials to travel faster than in unmyelinated axons of the same diameter whilst simultaneously spending less energy to "recharge" the action potential after. The myelin sheath in peripheral nerves normally runs along the axon in sections about 1 mm long, punctuated by unsheathed nodes of Ranvier. Multiple sclerosis is a neurological disorder which results from abnormal demyelination of peripheral nerves. Neurons with demyelinated axons do not conduct electrical signals properly. Neurons and glia make up the two chief cell types of the central nervous system. There are far more glial cells than neurons, and recent experimental results have suggested that glial cells play a vital role in information processing among neurons. It has been estimated that Glial cells outnumber neurons by as many as 50:1.

Histology and internal structure

Nerve cell bodies stained with basophilic dyes will show numerous microscopic clumps of Nissl substance (named after German psychiatrist and neuropathologist Franz Nissl, 1860–1919), which consists of rough endoplasmic reticulum and associated ribosomes. The prominence of the Nissl substance can be explained by the fact that nerve cells are metabolically very active, and hence are involved in large numbers of protein synthesis. The cell body of a neuron is supported by a complex meshwork of structural proteins called neurofilaments, which are assembled into larger neurofibrils. Some neurons also contain pigment granules, such as neuromelanin (a brownish-black pigment, byproduct of synthesis of catecholamines) and lipofuscin (yellowish-brown pigment that accumulates with age).

Neurons of the brain

The nematode worm (Caenorhabditis elegans) has 302 neurons. Scientists have mapped all of the nematode's neurons. As a result, such worms are ideal candidates for neurobiological experiments and tests. The human brain has about 100 billion (10^) neurons and 100 trillion (10^) connections (synapses) between them.

See also


- Artificial neuron
- F wave
- Neural oscillations
- Mirror neuron
- Neuroscience

External links


- [http://primate-brain.org High-Resolution Cytoarchitectural Primate Brain Atlases]
- [http://purl.net/net/neurowiki NeuroWiki], a wiki website for Neuroscience related topics.
- [http://ccdb.ucsd.edu/CCDB/index.shtml Cell Centered Database] UC San Diego images of neurons. Category:Neuroscience Category:Neurons ja:ニューロン simple:Neuron

Neural ensemble

Neural ensemble is a population of brain cells involved in a particular neural computation. Neuronal ensembles encode information in the way similar to the principle of Wikipedia operation - multiple edits by many participants. Neuroscientists have discovered that individual neurons are very noisy. For example, by examining the activity of only a single neuron in the visual cortex, it is very difficult to reconstruct the visual scene that the owner of the brain is looking at. (However, the existence of neurons specialized to detect specific objects - the so-called grandmother neurons - has been postulated.) Like a single Wikipedia participant, an individual neuron does not 'know' everything and is likely to make mistakes. This problem is solved by the brain having billions of neurons. Information processing by the brain is population processing, and it is also distributed - in many cases each neuron knows a little bit about everything, and the more neurons participate in a job, the more precise the information encoding. The emergence of specific neural assemblies is thought to provide the functional elements of brain activity that execute the basic operations of informational processing (see Fingelkurts An.A. and Fingelkurts Al.A., 2004; 2005). In the 1980s, Apostolos Georgopoulos and his colleagues Richard Kettner and Andrew Schwartz formulated a population vector hypothesis to explain how populations of motor cortex neurons encode movement direction. This hypothesis was based on the observation that individual neurons tended to discharge more for movements in particular directions, the so-called preferred directions for individual neurons. In the population vector model, individual neurons 'vote' for their preferred directions using their firing rate. The final vote is calculated by vectorial summation of individual preferred directions weighted by neuronal rates. This model proved to be successful in description of motor-cortex encoding of reach direction, and it was also capable to predict new effects. For example, Georgopoulos' population vector accurately described mental rotations made by the monkeys that were trained to translate locations of visual stimuli into spatially shifted locations of reach targets. After the techniques of multielectrode recordings were introduced (Miguel Nicolelis being the most notable proponet of this methodology), the task of real-time decoding of information from large neuronal ensembles became feasible. A series of studies that Nicolelis conducted with John Chapin, Johan Wessberg, Mark Laubach, Jose Carmena, Mikhail Lebedev, Sidarta Ribeiro and other colleagues showed that activity of large neural ensembles is predictive of behavioral state, intended direction of movement and movement parameters. This work made possible creation of brain-machine interfaces - electronic devices that read movement intentions from the brain and translate them into movements of artificial actuators. Carmena et al. (2003) built a brain-machine interface allowed a monkey to control reaching and grasping movements by a robotic arm, and Lebedev et al. (2005) argued that brain networks reorganize to create a new representation of the robotic appendage in addition to the representation of the animal's own limbs. Interestingly, individual neurons in the population can contribute information about different parameters. For example, Miguel Nicolelis and colleagues reported that individual neurons simultaneously encoded arm position, velocity and hand gripping force. Mikhail Lebedev, Steven Wise and their colleagues reported prefrontal cortex neurons that simultaneously recorded spatial locations that the monkeys attended to and those that they stored in short-term memory. Both attended and remembered locations could be decoded when these neurons were considered as population. How many neurons are needed to obtain an accurate read-out from the population activity? To address this question, Mark Laubach in Nicolelis lab used neuron-dropping analysis. In this analysis, he measured neuronal read-out quality as a function of the number of neurons in the population. Read-out quality increased with the number of neurons -- initially very notably, but then substantially larger neuronal quantities were needed to improve the read-out. What about the role of experts? Are a few experts better than mass action of many contributors? Neuroscientists found that, indeed, some neurons provide better information than the others, and selection of such expert neurons improves signal to noise ratio in neuronal signals. However, the basic principle holds: large neuronal populations do better than single neurons.

See also


- Attention versus memory in prefrontal cortex

References


- Carmena JM, Lebedev MA, Crist RE, O'Doherty JE, Santucci DM, Dimitrov DF, Patil PG, Henriquez CS, Nicolelis MA (2003) Learning to control a brain-machine interface for reaching and grasping by primates. PLoS Biol. 1:E42.
- Georgopoulos AP, Lurito JT, Petrides M, Schwartz AB, Massey JT (1989) Mental rotation of the neuronal population vector. Science 243: 234-236.
- Georgopoulos AP, Kettner RE, Schwartz AB. (1988) Primate motor cortex and free arm movements to visual targets in three-dimensional space. II. Coding of the direction of movement by a neuronal population. J Neurosci. 8: 2928-2937.
- Fingelkurts An.A., Fingelkurts Al.A. (2004) Making complexity simpler: Multivariability and metastability in the brain // International Journal of Neuroscience. 114(7): 843-862. Url: http://www.bm-science.com/team/art30.pdf
- Fingelkurts An.A., Fingelkurts Al.A., Kähkönen S.A. (2005) Functional connectivity in the brain – is it an elusive concept? // Neuroscience & Biobehavioral Reviews. 28(8): 827-836. Url: http://www.bm-science.com/team/art33.pdf
- Laubach M, Wessberg J, Nicolelis MA (2000) Cortical ensemble activity increasingly predicts behaviour outcomes during learning of a motor task. Nature 405: 567-571.
- Lebedev MA, Carmena JM, O'Doherty JE, Zacksenhouse M, Henriquez CS, Principe JC, Nicolelis MA (2005) Cortical ensemble adaptation to represent velocity of an artificial actuator controlled by a brain-machine interface. J Neurosci. 25: 4681-4693.
- Nicolelis MA, Ribeiro S (2002) Multielectrode recordings: the next steps. Curr Opin Neurobiol. 12: 602-606.
- Wessberg J, Stambaugh CR, Kralik JD, Beck PD, Laubach M, Chapin JK, Kim J, Biggs SJ, Srinivasan MA, Nicolelis MA (2000) Real-time prediction of hand trajectory by ensembles of cortical neurons in primates. Nature 408: 361-365. Category:Neuroscience Category:Neurology

Hippocrates

Hippocrates of Kos (c. 460 BC–c. 380 BC) was an ancient Greek physician. He has been called "the father of medicine", and is commonly regarded as one of the most outstanding figures in medicine of all time. He was a physician trained at the Dream temple of Kos, and may have been a pupil of Herodicus. Writings attributed to him (Corpus hippocraticum, or "Hippocratic writings") rejected the superstition and magic of primitive "medicine" and laid the foundations of medicine as a branch of science. Little is actually known about Hippocrates's personal life, but some of his medical achievements were documented by such people as Plato and Aristotle.

Writings

Aristotle The Hippocratic writings introduced patient confidentiality, a practice which is still in use today. This was described under the Hippocratic Oath and other treatises. Hippocrates recommended that physicians record their findings and their medicinal methods, so that these records may be passed down and employed by other physicians. Other Hippocratic writings associated personality traits with the relative abundance of the four humours in the body: phlegm, yellow bile, black bile, and blood, and was a major influence on Galen and later on medieval medicine. The Hippocratic Corpus is a collection of about sixty treatises, most written between 430 BC and AD 200. They are actually a group of texts written by several different people holding several different viewpoints erroneously grouped under the name of Hippocrates, perhaps at the Library of Alexandria. None of the texts included in the Corpus can be considered to have been written by Hippocrates himself, and one of them at least was written by his son-in-law Polybus. The best known of the Hippocratic writings is the Hippocratic Oath; however, this text was most likely not written by Hippocrates himself. A famous, time-honoured medical rule ascribed to Hippocrates is Primum non nocere ("first, do no harm"); another one is Ars longa, vita brevis ("art is long, and life short").

Works

Of these works, none can be demonstrably credited to Hippocrates, but they are considered to form the Corpus Hippocraticum:
- Aphorisms
- Instruments Of Reduction
- Of The Epidemics
- On Airs, Waters, And Places
- On Ancient Medicine
- On Fistulae
- On Fractures
- On Hemorrhoids
- On Injuries Of The Head
- On Regimen In Acute Diseases
- On The Articulations
- On The Sacred Disease
- On The Surgery
- On Ulcers
- The Book Of Prognostics
- The Law
- The Oath

The "portrait" of Hippocrates

The purely conventional iconography of Greek poets and philosophers were set in the "portrait" busts, (illustration, above right), produced in series to decorate the villas of the Roman cultured class. The changing careers of these idealized "character" images have been studied by Paul Zanker, The Mask of Socrates: The Image of the Intellectual in Antiquity, translated by Alan Shapiro. Berkeley: University of California Press, 1996. [ ISBN 0-520-20105-1]. See [http://ccat.sas.upenn.edu/bmcr/1996/96.08.04.html review in Bryn Mawr Classical Review].

See also


- Hippocratic face
- Hippocratic fingers (clubbing)
- Medical astrology
- Hippocratic bench

External links


- [http://etext.library.adelaide.edu.au/aut/hippocrates.html Online version of works]]
- [http://classics.mit.edu/Browse/browse-Hippocrates.html Translations of Hippocratic texts in English]
- [http://194.254.96.6/FMPro?-DB=livanc.fp3&-Format=livanc-rech.htm&cote=
- &-max=1000&-Find Texts in Greek]
- Aphorisms available at [http://sources.wikipedia.org/wiki/Aphorisms WikiSource]
- [http://www.healthvoices.com/blog/hippocrates/2005/10/24/what_would_hippocrates_do What Would Hippocrates Do?] Category:460 BC births Category:380 BC deaths Category:Ancient Greeks Category:Classical Humanists Category:History of ancient medicine ja:ヒポクラテス simple:Hippocrates

Aristotle

by Lysippos. Louvre Museum.]] Aristotle (Greek: Αριστοτέλης Aristotelēs; 384 BC – March 7, 322 BC) was an ancient Greek philosopher, student of Plato and teacher of Alexander the Great. He wrote many books about physics, poetry, zoology, logic, rhetoric, government, and biology. Aristotle, along with Plato and Socrates, is generally considered one of the most influential ancient Greek philosophers in Western thought. Among them they transformed Presocratic Greek philosophy into the foundations of Western philosophy as we know it. The writings of Plato and Aristotle form the core of Ancient philosophy. Aristotle placed much more value on knowledge gained from the senses and would correspondingly be better classed among modern empiricists (see materialism and empiricism). He also achieved a "grounding" of dialectic in the Topics by allowing interlocutors to begin from commonly held beliefs (Endoxa); his goal being non-contradiction rather than Truth. He set the stage for what would eventually develop into the scientific method centuries later. Although he wrote dialogues early in his career, no more than fragments of these have survived. The works of Aristotle that still exist today are in treatise form and were, for the most part, unpublished texts. These were probably lecture notes or texts used by his students, and were almost certainly revised repeatedly over the course of years. As a result, these works tend to be eclectic, dense and difficult to read. Among the most important ones are Physics, Metaphysics, Nicomachean Ethics, Politics, De Anima (On the Soul) and Poetics. Their works, although connected in many fundamental ways, are very different in both style and substance. Aristotle is known for being one of the few figures in history who studied almost every subject possible at the time. In science, Aristotle studied anatomy, astronomy, embryology, geography, geology, meteorology, physics, and zoology. In philosophy, Aristotle wrote on aesthetics, economics, ethics, government, metaphysics, politics, psychology, rhetoric and theology. He also dealt with education, foreign customs, literature and poetry. His combined works practically comprise an encyclopedia of Greek knowledge.

Biography

Early life and studies at the Academy

encyclopedia.]] Aristotle was born at Stageira, a colony of Andros on the Macedonian peninsula of Chalcidice in 384 BC. His father, Nicomachus, was court physician to King Amyntas III of Macedon. It is believed that Aristotle's ancestors held this position under various kings of Macedonia. As such, Aristotle's early education would probably have consisted of instruction in medicine and biology from his father. About his mother, Phaestis, little is known. It is known that she died early in Aristotle's life. When Nicomachus also died, in Aristotle's tenth year, he was left an orphan and placed under the guardianship of his uncle, Proxenus of Atarneus. He taught Aristotle Greek, rhetoric, and poetry (O'Connor et al., 2004). Aristotle was probably influenced by his father's medical knowledge; when he went to Athens at the age of 18, he was likely already trained in the investigation of natural phenomena. From the age of 18 to 37 Aristotle remained in Athens as a pupil of Plato and distinguished himself at the Academy. The relations between Plato and Aristotle have formed the subject of various legends, many of which depict Aristotle unfavourably. No doubt there were divergences of opinion between Plato, who took his stand on sublime, idealistic principles, and Aristotle, who even at that time showed a preference for the investigation of the facts and laws of the physical world. It is also probable that Plato suggested that Aristotle needed restraining rather than encouragement, but not that there was an open breach of friendship. In fact, Aristotle's conduct after the death of Plato, his continued association with Xenocrates and other Platonists, and his allusions in his writings to Plato's doctrines prove that while there were conflicts of opinion between Plato and Aristotle, there was no lack of cordial appreciation or mutual forbearance. Besides this, the legends that reflect Aristotle unfavourably are traceable to the Epicureans, who were known as slanderers. If such legends were circulated widely by patristic writers such as Justin Martyr and Gregory Nazianzen, the reason lies in the exaggerated esteem Aristotle was held in by the early Christian heretics, not in any well-grounded historical tradition.

Aristotle as philosopher and tutor

After the death of Plato (347 BC), Aristotle was considered as the next head of the Academy, a post that was eventually awarded to Plato's nephew. Aristotle then went with Xenocrates to the court of Hermias, ruler of Atarneus in Asia Minor, and married his niece and adopted daughter, Pythia. In 344 BC, Hermias was murdered in a rebellion, and Aristotle went with his family to Mytilene. It is also reported that he stopped on Lesbos and briefly conducted biological research. Then, one or two years later, he was summoned to Pella, the Macedonian capital, by King Philip II of Macedon to become the tutor of Alexander the Great, who was then 13. Plutarch wrote that Aristotle not only imparted to Alexander a knowledge of ethics and politics, but also of the most profound secrets of philosophy. We have much proof that Alexander profited by contact with the philosopher, and that Aristotle made prudent and beneficial use of his influence over the young prince (although Bertrand Russell disputes this). Due to this influence, Alexander provided Aristotle with ample means for the acquisition of books and the pursuit of his scientific investigation. It is possible that Aristotle also participated in the education of Alexander's boyhood friends, which may have included for example Hephaestion and Harpalus. Aristotle maintained a long correspondence with Hephaestion, eventually collected into a book, unfortunately now lost. According to sources such as Plutarch and Diogenes, Philip had Aristotle's hometown of Stageira burned during the 340s BC, and Aristotle successfully requested that Alexander rebuild it. During his tutorship of Alexander, Aristotle was reportedly considered a second time for leadership of the Academy; his companion Xenocrates was selected instead.

Founder and master of the Lyceum

In about 335 BC, Alexander departed for his Asiatic campaign, and Aristotle, who had served as an informal adviser (more or less) since Alexander ascended the Macedonian throne, returned to Athens and opened his own school of philosophy. He may, as Aulus Gellius says, have conducted a school of rhetoric during his former residence in Athens; but now, following Plato's example, he gave regular instruction in philosophy in a gymnasium dedicated to Apollo Lyceios, from which his school has come to be known as the Ly