Portal:Neuroscience/Featured article archive
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[edit] October 15, 2006
Chemical synapses are specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands. A chemical synapse between a motor neuron and a muscle cell is called a neuromuscular junction.
Chemical synapses allow the neurons of the central nervous system to form interconnected neural circuits. They are thus crucial to the biological computations that underlie perception and thought. They also provide the means through which the nervous system connects to and controls the other systems of the body.
The human brain contains a huge number of chemical synapses, with young children having about 1,000 trillion. This number declines with age, stabilizing by adulthood. Estimates for an adult vary from 100 to 500 trillion synapses.
The word "synapse" comes from "synaptein" which Sir Charles Scott Sherrington and his colleagues coined from the Greek "syn-" meaning "together" and "haptein" meaning "to clasp". Chemical synapses are not the only type of biological synapse: electrical and immunological synapses exist as well. Without a qualifier, however, "synapse" by itself most commonly refers to a chemical synapse.
[edit] September 16, 2006
The cerebellum (Latin: "little brain") is a region of the brain that plays an important role in the integration of sensory perception and motor output. Many neural pathways link the cerebellum with the motor cortex—which sends information to the muscles causing them to move—and the spinocerebellar tract—which provides feedback on the position of the body in space (proprioception). The cerebellum integrates these pathways, using the constant feedback on body position to fine-tune motor movements.
Because of this 'updating' function of the cerebellum, lesions within it are not so debilitating as to cause paralysis, but rather present as feedback deficits resulting in disorders in fine movement, equilibrium, posture, and motor learning. Initial observations by physiologists during the 18th century indicated that patients with cerebellar damage show problems with motor coordination and movement. Research into cerebellar function during the early to mid 19th century was done via lesion and ablation studies in animals. Research physiologists noted that such lesions led to animals with strange movements, awkward gait, and muscular weakness. These observations and studies led to the conclusion that the cerebellum was a motor control structure. However, modern research shows that the cerebellum has a broader role in a number of key cognitive functions, including attention and the processing of language, music, and other sensory temporal stimuli.
[edit] September 09, 2006
Lysergic acid diethylamide, commonly called LSD, or LSD-25, is a semisynthetic psychedelic drug. The short form LSD comes from the German "Lysergsäure-diethylamid".
The effects of LSD can vary greatly, depending on factors such as previous experiences, state of mind and environment, as well as dose strength. Generally, LSD causes expansion and altered experience of senses, emotions, memories, time, and awareness for 8 to 14 hours. In addition, LSD may produce visual effects such as moving geometric patterns, "trails" behind moving objects, and brilliant colors. LSD does not produce hallucinations in the strict sense but instead illusions and vivid daydream-like fantasies, in which ordinary objects and experiences can take on entirely different appearances or meanings. At higher doses it can cause synesthesia. The drug experience sometimes spurs long-term or even permanent changes in a user's personality and life perspective.
[edit] August 25, 2006
Long-term potentiation (LTP) is the long-lasting enhancement in efficacy of the synapse between two neurons. Though its biological mechanisms have not yet been fully determined, LTP is believed to contribute to synaptic plasticity in living animals, providing the foundation for a highly adaptable nervous system. Most neuroscientific learning theories regard long-term potentiation and its opposing process, long-term depression, as the cellular basis of learning and memory.
Experimentally, a series of short, high-frequency electric stimulations to a nerve cell synapse can strengthen, or potentiate, that synapse for minutes to hours. In living cells, LTP occurs naturally and can last from hours to days, months, and years.
LTP was discovered in the mammalian hippocampus by Terje Lømo in 1966 and has remained a popular subject of neuroscientific research since. Most modern LTP studies seek to better understand its biology, while other research aims to develop drugs that exploit these biological mechanisms to treat neurodegenerative diseases such as Parkinson's and Alzheimer's disease.
[edit] August 18, 2006
Visual cortex is the term applied to both the primary visual cortex (also known as striate cortex or "V1") and upstream visual cortical areas also known as extrastriate cortical areas (V2, V3, V4, V5).
The primary visual cortex, V1, is the koniocortex (sensory type) located in and around the calcarine fissure in the occipital lobe. It is the one that receives information directly from the lateral geniculate nucleus.To this have been added later as many as thirty interconnected (secondary or tertiary) visual areas. At the present time there is fair agreement for only 3 of these areas, V2, V3 and MT (aka V5).
The first cortical visual area, transmits information to two primary pathways, called the ventral stream and the dorsal stream:
- The ventral stream begins with V1, goes through Visual area V2, then through Visual area V4, and to the inferior temporal lobe. The ventral stream, sometimes called the "What Pathway", is associated with form recognition and object representation. It is also associated with storage of long-term memory.
- The dorsal stream begins with V1, goes through Visual area V2, then to Visual area V3, Visual area MT (also known as V5) and to the inferior parietal lobule. The dorsal stream, sometimes called the "Where Pathway" or the "How Pathway", is associated with motion, representation of object locations, and control of the eyes and arms, especially when visual information is used to guide saccades or reaching.
