Neural axons

Utility Stimulation of Neural Axons in Nerve Cells in the Treatment of Parkinson s disease... 

The axcn is a c5doplasmic continuation of the cell body specialized for the electrical conduction of neural signals. The axcn may be Icng—to a yard in length in humans—or short, dependir upon the neuron s position and flmcfion. The cell membranes of the neural axon transmit neural signals via changes in action potentials that sweep down the membrane. 

The MAP called t (tau) is found in neuronal tissue. Phosphorylation of t dissociates i from microtubules, destabilizing the microtubules. Hyperphosphorylation of t has a much more dramatic effect, resulting in the formation of tangles of t-filaments in neural axons, one of the major cellular symptoms of Alzheimer s disease. 

LH/FSH-RH is formed in the hypothalamus, particularly in the basal-ventral area, but the precise location of its origin remains to be elucidated. By the use of immunohistochemical techniques, LH/FSH-RH has been found in the arcuate nucleus and in the median eminence (PI). Electron microscopy studies revealed that some neural axons of the median eminence contain immunopositive LH/FSH-RH (P4). Norepinephrine appears to be the most important neurotransmitter regulating LH/FSH-RH biosynthesis. From this origin, LH/FSH-RH is transported, presumably by axonal flow, to the median eminence, where it is stored. It is secreted into the hypothalamic-pituitary portal system to reach the anterior pituitary gland, where it binds to membrane receptors on the LH- and FSH-producing cells. It has been shown that LH/FSH-RH induces ultrastructural changes in the gonadotropin-pro-... 

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. 

Fig. 4.6(a) Migration of LHRH neurocrine cells prenatal transportation along the track of extra-bulbar VN axons (caudal branch). CB, cribriform plate FB, forebrain cell types, TAG-1, transient axonal surface glycoprotein and N-CAM, neural cell adhesion molecule (from Yoshida et al, 1995). 

Yoshihara Y Kawasaki M., Tamada A., Fujita H., et al. (1997). OCAM a new member of the neural cell adhesion molecule family related to zone-to-zone projection of olfactory and vomeronasal axons. J Neurosci 17, 5830-5842. 

As its name implies, the neurohypophysis is derived embryonically from nervous tissue. It is essentially an outgrowth of the hypothalamus and is composed of bundles of axons, or neural tracts, of neurosecretory cells originating in two hypothalamic nuclei. These neurons are referred to as neurosecretory cells because they generate action potentials as well as synthesize hormones. The cell bodies of the neurosecretory cells in the supraoptic nuclei produce primarily antidiuretic hormone (ADH) and the cell bodies of the paraventricular nuclei produce primarily oxytocin. These hormones are then transported down the axons to the neurohypophysis and stored in membrane-bound vesicles in the neuron terminals. Much like neurotransmitters, the hormones are released in response to the arrival of action potentials at the neuron terminal. 

Cell adhesion molecules (CAMs) play critical roles in all facets of nervous system development and maintenance. Important phenomena in which CAMs are involved include initial formation of the neural tube and the neural crest, migration of all neurons and glial cells, axonal outgrowth and guidance, target selection, synaptic stabilization and plasticity, myelination and nerve regeneration after injury (see Chs 4,24,28-30 and 53). Adhesion molecules interact with each other and with nonadhesive cell-surface and/or cytoplasmic molecules, and, in the two... 

FIGURE 7-6 Neural cell adhesion molecule (NCAM) carries different levels of polysialic acid. (A) NCAM is depicted on a growing axon, without polysialic acid. Under these conditions, NCAM and LI molecules interact homophilically and axons fasciculate. (B) NCAM carries polysialic acid (PSA), and NCAM and LI molecules are far apart and cannot, therefore, interact. Growing axons do not fasciculate under these circumstances. 

Walsh, F. S. and Doherty, P. Neural cell adhesion molecules of the immunoglobulin superfamily role in axon growth and guidance. Annu. Rev. Cell. Dev. Biol. 13 425-456, 1997. 

Adcock, K. H., Brown, D. J., Shearer, M. C., Shewan, D., Schachner, M., Smith, G. M., Geller, H. M. and Fawcett, J. W. Axon behavior at Schwann cell-astrocyte boundaries manipulation of axonal signaling pathways and the neural adhesion molecule LI can enable axons to cross. Eur. /. Neurosci. 20 1425-1435, 2004. 

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