Cell , biological neuron

Figure 9-12. Biological neuron the dendrites receive the incoming information and send it to the cell body, The axon carries the information produced in the cell body to neighboring neurons.

The human brain is comprised of many millions of interconnected units, known individually as biological neurons. Each neuron consists of a cell to which is attached several dendrites (inputs) and a single axon (output). The axon connects to many other neurons via connection points called synapses. A synapse produces a chemical reaction in response to an input. The biological neuron fires if the sum of the synaptic reactions is sufficiently large. The brain is a complex network of sensory and motor neurons that provide a human being with the capacity to remember, think, learn and reason. 

The structural unit of artificial neural networks is the neuron, an abstraction of the biological neuron a typical biological neuron is shown in Fig. 44.1. Biological neurons consist of a cell body from which many branches (dendrites and axon) grow in various directions. Impulses (external or from other neurons) are received through the dendrites. In the cell body, these signals are sifted and integrated. 

Selkoe DJ (1998). The cell biology of APP and presenelin in Alzheimer s disease. Neuron, 16,... 

Heuser, J. E. Synaptic vesicle exocytosis revealed in quick-frozen frog NMJ treated with 4-aminopyridine and given a single electric shock. In W. M. Cowan and J. Ferrendelli (eds.), Approaches to the Cell Biology of Neurons. Bethesda, MD Society for Neuroscience, 1976, pp. 215-239. 

The adrenal medulla synthesizes two catecholamine hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine) (Figure 1.8). The ultimate biosynthetic precursor of both is the amino acid tyrosine. Subsequent to their synthesis, these hormones are stored in intracellular vesicles, and are released via exocytosis upon stimulation of the producer cells by neurons of the sympathetic nervous system. The catecholamine hormones induce their characteristic biological effects by binding to one of two classes of receptors, the a- and )S-adrenergic receptors. These receptors respond differently (often oppositely) to the catecholamines. 

The basic processing unit of an ANN (or its building block) is called perceptron [53]. This is a crude approximation to the biological neuron, the cell in the nervous system. It is a decision-making unit with several input connections and a single output, as sketched in Fig. 30.2. A signal xj which is delivered from input j is multiplied on arrival by a connection... 

Departments of Neurology, Pathology, and Cell Biology Center for Neurobiology and Behavior Center for Motor Neuron Biology and Diseases Columbia University New York, NY, USA... 

Figure 2 depicts the struetirre of RBF neural networks. RBF networks were introduced into the neural network literature by Broomhead and Lowe (1988). The RBF network model imitates the locally tuned response observed in biological neurons. Neurons with a locally tuned response characteristic can be found in several parts of the nervous system, for example, in cells in the visual cortex sensitive to bars oriented in a certain direction or other visual featirres within a small region of the visual field. These locally tuned neurons show the response characteristics bounded to a small range of the input space. The theoretical basis of the RBF approach lies in the field of interpolation of multivariate functions. The objective of... 

From a cell biological perspective, PrPc expressed from a neuron-specific enolase promoter could rescue granule cell degeneration but not a Dpl-specified leukoencephalopathy. In a reverse fashion, PrP expressed in trans from a myelin basic protein promoter could rescue leukoencephalopathy but not granule cell death [127]. 

Another important putative neurotransmitter is substance P. There are relatively well defined neuronal systems in the central nervous system that contain this 11-amino acid peptide. A group of Japanese scientists using recombinant DNA technology have been able to deduce the primary amino acid sequence of the precursor molecule. In this molecule they found the substance P sequence enclosed by pairs of basic residues. Of particular interest is the fact that the sequence for another biologically active amphibian peptide, kassinin, is also present in the precursor molecule. This sequence also is enclosed by pairs of basic residues. Thus while kassinin has yet to be found in brain, it can be predicted to be a naturally occurring neuropeptide. The use of cell biology techniques will clearly be of utmost importance as the mechanisms of neurotransmitter synthesis are unraveled. 

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