Basal Ganglia | Alveoli, Papillae, Transcendentalism, Cerebrum, Bronchi
The basal ganglia (or basal nuclei) are a group of nuclei in the brains of vertebrates, situated at the base of the forebrain and strongly connected with the cerebral cortex, thalamus and other areas. The basal ganglia are associated with a variety of functions, including motor control and learning. Currently popular theories implicate the basal ganglia primarily in action selection, that is, the decision of which of several possible behaviors to execute at a given time. Experimental studies show that the basal ganglia exert an inhibitory influence on a number of motor systems, and that a release of this inhibition permits a motor system to become active. The "behavior switching" that takes place within the basal ganglia is influenced by signals from many parts of the brain, including the prefrontal cortex, which is widely believed to play a key role in executive functions.
The main components of the basal ganglia are the striatum, pallidum, substantia nigra, and subthalamic nucleus. The largest component, the striatum, receives input from many brain areas but sends output only to other components of the basal ganglia. The pallidum receives its most important input from the striatum (either directly or indirectly), and sends inhibitory output to a number of motor-related areas, including the part of the thalamus that projects to the motor-related areas of the cortex. The substantia nigra consists of two parts, one that functions similarly to the pallidum, and another that provides the source of dopamine input to the striatum. The subthalamic nucleus receives input mainly from the striatum and cortex, and projects to the pallidum. Each of these areas has a complex internal anatomical and neurochemical organization.
The basal ganglia play a central role in a number of neurological conditions, including several movement disorders. The most notable are Parkinson’s disease, which involves degeneration of the dopamine-producing cells in the substantia nigra, and Huntington’s disease, which primarily involves damage to the striatum. Basal ganglia dysfunction is also implicated in some other disorders of behavior control such as Tourette’s syndrome and obsessive–compulsive disorder, although the neural mechanisms underlying these are not well understood.
The basal ganglia have a limbic sector whose components are assigned distinct names: the nucleus accumbens (NA), ventral pallidum, and ventral tegmental area (VTA). The VTA provides dopamine to the nucleus accumbens (ventral striatum) in the same way that the substantia nigra provides dopamine to the dorsal striatum. The VTA→NA dopaminergic projection has attracted a great deal of attention, because there is much evidence that it plays a central role in reward learning. A number of highly addictive drugs, including cocaine, amphetamines, and nicotine, are thought to work by increasing the efficacy of the VTA→NA dopamine signal. There is also evidence implicating overactivity of the VTA dopaminergic projection in schizophrenia.
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Tags: Basal Ganglia , alveoli, papillae, transcendentalism, cerebrum, bronchi
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