Neural pathways

In a classical neural pathway, such as that depicted in Fig. 1.3, neuron A must excite neuron B and at the same time inhibit neuron C in order to optimise the excitation of B. It could achieve this with one NT able to activate receptors linked to different events on B and C. Of course, neuron C would have other inputs, some of which would be excitatory and if the same NT was used it could activate the inhibitory mechanism on C as well. Also, the NT released from A might be able to stimulate as well as inhibit neuron C (Fig. 1.3(a)). Even the provision of separate receptors linked to excitation and inhibition would not overcome these problems since both would be accessible to the NT. One possible solution, used in the CNS, is to restrict the NT to the synapse at which it is released by structural barriers or rapid degradation. Also the inputs and receptors linked to excitation could be separated anatomically from those linked to inhibition and, in fact, there is electrophysiological and morphological evidence that excitatory synapses are mainly on dendrites and inhibitory ones on the soma of large neurons (Fig. 1.3(b)). Nevertheless, the problem of overlap would be eased if two NTs were released, one to activate only those receptors linked to excitation and another to evoke just inhibition, i.e. place the determinant of function partly back on the NT (Fig. 1.3(c)). This raises a different problem which has received much consideration. Can a neuron release more than one NT ... 

Of course, while the identification of these distinct systems may be useful there are many neural pathways that would not fit easily into one of them. Thus some inhibitory pathways, such as that from the caudate nucleus to substantia nigra, utilising GABA, are not intrinsic neurons. The dopamine pathway from the substantia nigra to striatum may start from a small nucleus but unlike other monoamine pathways it shows little ramification beyond its influence on the striatum. The object of the above classification is not to fit all neural pathways and mechanisms into a restricted number of functional categories but again to demonstrate that there are different forms of neurotransmission. 

The interactions between the endocrine and neural systems of the GIT are complex, include shared signaling molecules, and can be hard to separate. Therefore, it is likely that the influence(s) of some phytochemicals will cross over between neural and non-neural pathways. Corresponding with this, lumenal administration of capsaicin interacts with visceral neurons to increase GIT motility (Zittel et al., 2001 Topcu et al, 2002) and abrogates the decreased electrolyte and fluid secretion caused by piperine (Capasso et al., 2002). 

Pieper D. and Newman S. (1999). Neural pathway from the olfactory bulbs regulating tonic gonadotropin secretion. Neurosci Bio Behav Revs 23, 555-562. 

Mesocortical A neural pathway that connects the ventral tegmentum to the cortex, particularly the frontal lobes. It is one of the major dopamine pathways in the brain. 

A reflex response requires an intact neural pathway between the stimulated area and the responding muscle. This pathway is referred to as a reflex arc and includes the following components (see Figure 7.3) ... 

Dopamine A catecholamine neurotransmitter, involved in mesolimbic reward and other important neural pathways. 

Balfour DJK, Ridley DL (2000) The effects of nicotine on neural pathways implicated in depression a factor in nicotine addiction Pharmacol Biochem Behav 66 79-85 Balfour DJK, Birrell CE, Moran RJ, Benwell MEM (1996) Effects of acute D-CPPene on mesoac-cumbens dopamine responses to nicotine in the rat. Eur J Pharmacol 316 153-156 Balfour DJK, Wright AE, Benwell MEM, BirreU CE (2000) The putative role of extra-synaptic mesolimbic dopamine in the neurobiology of nicotine dependence. Behav Brain Res 113 73-83... 

The PNS contains afferent neural pathways that bring signals to the CNS and efferent neural pathways that conduct signals from the brain to the periphery. 

Afferent pathway a neural pathway leading from the periphery to the central nervous system. 

But the structure of the neuron leaves it well adapted to its purpose, namely, communication. Neurons provide the linkages to communicate from the outside environment to ourselves and again to the outside environment if we wish. The neural pathways can be simple, such as the two cell pathways that are activated when... 

From the accessory bulb, projections lead to the medial nuclei and posteri-omedial portion of the cortical nuclei of the amygdala. The amygdala in turn is connected to higher centers via the stria terminalis, and hypothalamic structures. Thus, the accessory olfactory system represents a neural pathway separate from the main olfactory system. Both project into absolutely different parts of the amygdaloids (Powers and Winans, 1975 Powers etal, 1979). 

Is there a hnal common neural pathway in delirium ... 

The biology of the monoamines is described in detail elsewhere. In simple terms, they facilitate transmission in neural pathways that originate in nuclei of the brainstem and have descending projections to the autonomic nervous system and widespread ascending projections to sites in the limbic system and cortex. These pathways modulate many aspects of behavioural function as well as anxiety responses. Of the three monoamines, the role of serotonin in anxiety is best understood, but the picture is complex as increased serotonergic activity may be anxiogenic or anxiolytic depending on the site of action (Bell and Nutt 1998). 

In addition to the integrated participation of the peripheral nerves, central neural pathways are involved in the process. These central mechanisms interact during normal sexual activity and require complex coordination between the autonomic nervous system and the somatic outflow at the level of the spinal cord. 

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