The Anatomy and Functions of Neurons

The existence of electrical potentials across cell membranes suggests that electrodes could be used to control in vivo processes as well as to monitor their activity. Indeed, in order to measure dopamine release, it was shown earlier in this report that electrodes can be used to stimulate the activity of neurons. This has been recognized by biologists for many years, and the use of local electrical stimulation has been used to probe the anatomy and function of neuronal circuits. 

Beltz BS (1999) The distribution and functional anatomy of amine containing neurons in decapod crustaceans. Microsc Res Tech 44 105-120... 

FIGURE 2.2 The anatomy of the neuron. Communication between two neurons occurs at the synapse. The presynaptic neuron produces and releases the neurotransmitter into the synaptic cleft. Four mechanisms (1 ) are important to understand the function of most neurotransmitter systems. The release of neurotransmitter can be modulated via presynaptic receptors (1). The amount of neurotransmitter in the synaptic cleft can be decreased by reuptake into the presynaptic neuron (2) or via enzymatic degradation. Neurotransmitter effects at the target neuron are relayed via fast-acting ion channel—coupled receptors (3) or via slower-acting G protein—coupled receptors (4). Down-stream effects of postsynaptic receptors include the phosphorylation (P) of nuclear proteins. 

The excitatory neurotransmitter glutamate is released upon depolarization by the corticostratial, corticosub-thalamic, subthalamic, and thalamocortical projection neurons. As such, these excitatory neurons are key players in the functional anatomy of the basal ganglia and the CSTC loops. While the activity of these neurons is likely to be important in TS, only limited data are available to evaluate their role in this disease. 

Okay, let s return to the anatomy lesson. At this point, you need only appreciate that your brain is composed of neurons and some supporting cells, called glia. If you were to extract a very small cube of brain tissue see Fig. i—i), you would find it densely packed with cells, blood vessels, and very little else. The neurons are organized into columns of cells and small gatherings, called nuclei or ganglia, which tend to be involved in related functions. For example, some ganglia control movement, some control body temperature, and some control your mood. 

The distinction between excitatory and inhibitory transmitters will now be outlined. As Fig. 7.3 indicates, some nerves, when stimulated, can inhibit and others stimulate. There is nothing in the chemical nature of the neurotransmitter that will indicate which of these functions its secretion will bring about that depends entirely on matters of anatomy, which adds to the burden of our memories For example, at the neuromuscular junction, and within autonomic ganglia, acetylcholine is an excitatory transmitter which depolarizes and hence fires neurons or causes muscle to contract. However, in the heart, acetylcholine is an inhibitory transmitter. 

The proposal that NO or its reactant products mediate toxicity in the brain remains controversial in part because of the use of non-selective agents such as those listed above that block NO formation in neuronal, glial, and vascular compartments. Nevertheless, a major area of research has been into the potential role of NO in neuronal excitotoxicity. Functional deficits following cerebral ischaemia are consistently reduced by blockers of NOS and in mutant mice deficient in NOS activity, infarct volumes were significantly smaller one to three days after cerebral artery occlusion, and the neurological deficits were less than those in normal mice. Changes in blood flow or vascular anatomy did not account for these differences. By contrast, infarct size in the mutant became larger... 

Unusually high levels of dysbindin-1 are found in neuronal and neuropil components of this brain area, which consists of the dentate gyrus (DG), hippocampus proper (i.e., cornu ammonis [CA] fields 1-3]), and the subiculum ( Figures 2.2-13c—d and O 2.2-14V). As in the case of the basal ganglia, an anatomical introduction clarifies the functional implications of dysbindin-1 found in the hippocampal formation ( Figures 2.2-13-2.2-18). For a detailed review of its anatomy, see Amaral and Lavenex (2007). 

Gerber, Stocker, Tanimura and Thum use Drosophila to elucidate the generation of behavior from olfactory and gustatory sensation. The functional anatomy of Drosophila olfactory receptor neurons is described both for mature flies and larvae, which emerge as simpler model system with fewer olfactory receptors and with attraction and repulsion as easily testable, behavioral outcomes. 

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