Alternative Models Of Excitability

Two distinct stable steady states and a stable limit cycle coexist for a given parameter regime). The greatest advantage of the model has come from an expanded version, which includes a third variable that describes the dynamics of intracellular Ca2+, and by adding a Ca2+-dependent K+ current. This three-variable system can simulate a variety of bursting behaviors. The simplicity of this model and its rich dynamical repertoire make it an excellent choice for nonlinear dynamical analyses of...

The Cerebral Vasculature

Blood vessels form an extremely rich network in the central nervous system, particularly in the cerebral cortex and subcortical gray masses, whereas the white matter is less densely vascularized (Fig. 1.21) (Duvernoy et al., 1981). The vascular bed is supplied by perforating arteries that arise from a relatively small number of large, peripheral arterial trunks. The main trunks give off smaller cerebral arteries whose branches penetrate the subarachnoidal space, where they divide into many...

Molecular Motors In The Nervous System

Until 1985, knowledge of molecular motors in vertebrate cells of any type was restricted to myosins and flagellar dyneins. Myosins had been identified in nervous tissue, but their functions were uncertain. Because the preponderance of evidence indicated that fast axonal transport was microtubule-based, there was considerable interest in dyneins in cell cytoplasm. Despite a number of studies, no evidence for a functional cytoplasmic dynein emerged. Worse yet, the characteristic properties of...

Building And Maintaining Nervous System Cells

Passant Synapse

The functional architecture of neurons comprises many specializations in cytoskeletal and membranous components. Each of these specializations is dynamic, constantly changing and being renewed at a rate determined by the local environment and cellular metabolism. The processes of axonal transport represent a key to understanding neuronal dynamics and provide a basis for exploring neuronal development, regeneration, and neuropathology. Recent advances are important sources of insight into the...

Hepatic Encephalopathy Is A Disorder Of Astrocyte Function Resulting In A N E U R O P S Y C H I At R I C Syndrome

Brain Leucine Glutamate Flux Astrocyte

Hepatic encephalopathy is observed in patients with severe liver failure. The disease can be in one of two forms an acute form, called fulminant hepatic failure, and (2) a chronic form, portosystemic encephalopathy (Plum and Hindfeld, 1976). The neuropsychiatric symptoms of fulminant hepatic failure are delirium, coma, and seizures associated with acute toxic or viral hepatic failure. Patients having portosystemic encephalopathy may present personality changes, episodic confusion, or stupor,...

T

FIGURE 2.6 Mechanisms of vesicle targeting and docking in the synaptic terminal. The synaptic counterpart of v-SNARE is synaptobrevin (also known as vesicle-associated membrane protein), and syntaxin corresponds to the t-SNARE. SNAP-25 is an accessory protein that binds to syntaxin. Synaptotagmin is believed to be the Ca2+-sensitive regulatory protein in the complex that binds to syntaxin. The neurexins appear to have a role in conferring Ca2+ sensitivity to these interactions. Exocytosis of...

The Astrocyteneuron Metabolic Unit

From a strictly energetic viewpoint, the brain can be seen as an almost exclusive glucose-processing machine producing H2O and CO2. However, the metabolism of glucose in the brain is temporally, spatially, and functionally specified. Thus, glucose metabolism increases with exquisite spatiotemporal precision in register with neuronal activity. The site of this increase is not the neuronal cell body rather, it is the neuropil, where presy-naptic terminals, postsynaptic elements, and astrocytes...

Nissl Substance

Axon Hillock Microtubules

It is interesting that Nissl recognized the composite nature of the substance named for him, although he could not have resolved either of its components. The preceding quote and the following discussion of the Nissl substance appeared in L. Sanford, M. D. Palay, and G. E. Palade 1955 . The fine structure of neurons. J. Biophys. Biochem. Cytol. 88, 69-88. As imaged in the electron microscope, the crowded cytoplasm of the neuron contrasts sharply with the relatively open cytoplasm of many other...

Inherited Peripheral Neuropathies

Reactive Microglia

The peripheral myelin protein-22 PMP22 is a very hydrophobic glycoprotein and is highly expressed in compact PNS myelin. It has been mapped to the previously defined Tr locus on mouse chromosome 11. Comparison of marker genes on mouse chromosome 11 and human chromosome 17 revealed that PMP22 was also a candidate gene for the most common form of autosomal-dominant demyelinating hereditary peripheral neuropathy in humans, Charcot-Marie-Tooth disease type 1A CMT1A . Indeed, the entire PMP22 gene...

The Neuron

Pyramidal Cells And Purkinje Cells

Neurons are highly polarized cells, meaning that they develop, in the course of maturation, distinct subcellular domains that subserve different functions. Morphologically, in a typical neuron, three major regions can be defined 1 the cell body, or perikaryon, which contains the nucleus and the major cytoplasmic organelles 2 a variable number of den-drites, which emanate from the perikaryon and ramify over a certain volume of gray matter and which differ in size and shape, depending on the...