Axons cytoskeleton

Myelin affects axonal structure. The presence of a myelin sheath affects the structure of the axon that it surrounds [5], presumably optimizing its properties for transmission of action potentials by saltatory conduction. Generally, one of the effects of myelin is to increase axonal diameter by inducing biochemical changes in components of the axonal cytoskeleton such as neurofilaments (see Ch. 8). The effects of myelin on axonal structure imply... 

Properties of slow transport suggest molecular mechanisms. Information about mechanisms of slow axonal transport is relatively limited. They are energy-dependent and require an intact axonal cytoskeleton. Indirect evidence suggests that MTs play a critical role, because transport of NFs can be pharmacologically uncoupled from MT transport without eliminating slow transport [33]. In contrast, all agents that disrupt MTs appear to block slow transport of all components. While this does not rule out a role for the MF cytoskeleton in slow transport movements, MTs appear to provide motive force for other elements of the cytoskeleton. 

The cytosol is the fluid compartment of the cell and contains the enzymes responsible for cellular metabolism together with free ribosomes concerned with local protein synthesis. In addition to these structures which are common to all cell types, the neuron also contains specific organelles which are unique to the nervous system. For example, the neuronal skeleton is responsible for monitoring the shape of the neuron. This is composed of several fibrous proteins that strengthen the axonal process and provide a structure for the location of specific membrane proteins. The axonal cytoskeleton has been divided into the internal cytoskeleton, which consists of microtubules linked to filaments along the length of the axon, which provides a track for the movement of vesicular material by fast axonal transport, and the cortical cytoskeleton. 

MS is an autoimmune disease that attacks the myelin sheath of oligodendrocytes around the neuronal axons. This allows the axonal cytoskeleton to be damaged, bringing about secondary axonal loss and persisting neurological dysfunction. The characteristic pathology is of a lesion or plaque in the CNS white matter, formed by inflammation and demyelination and these can be classified into active, chronic active, or chronic silent plaques [86]. 

Mab 22C10 hybridoma library mouse monoclonal Fujita et al. (1982) E 1 50 -I-I-+ L 1 50 +++ 1 500 + axonal cytoskeleton (only a portion of the synapse)... 

In erythrocytes and most other cells, the major structural link of plasma membranes to the cytoskeleton is mediated by interactions between ankyrin and various integral membrane proteins, including Cf/HCOj antiporters, sodium ion pumps and voltage-dependent sodium ion channels. Ankyrin also binds to the =100 nm, rod-shaped, antiparallel a(3 heterodimers of spectrin and thus secures the cytoskeleton to the plasma membrane. Spectrin dimers self-associate to form tetramers and further to form a polygonal network parallel to the plasma membrane (Fig. 2-9D). Neurons contain both spectrin I, also termed erythroid spectrin, and spectrin II, also termed fodrin. Spectrin II is found throughout neurons, including axons, and binds to microtubules, whereas spectrin I occurs only in the soma and dendrites. 

Throughout neurons and glia, enriched in growth cones and in membrane cytoskeleton Co-distributed with most MFs Enriched in membrane cytoskeleton Membrane cytoskeleton, distinct forms in axon, dendrite and nodes of Ranvier Growing neurites... 

Oblinger, M. M., Brady, S. T., McQuarrie, I. G. and Lasek, R. Differences in the protein composition of the axonally transported cytoskeleton in peripheral and central mammalian neurons. /. Neurosci. 7 453-462,1987. 

The cytoskeleton is found near the axonal membrane and consists of microfilaments linked internally to microtubules and the plasma membrane by a network of filamentous protein that includes the brain-specific protein fodrin. This protein forms attachment sites for integral membrane proteins either by means of the neuronal cell adhesion molecule (N-CAM) or indirectly by means of a specific protein called ankyrin in the case of the sodium channels. This may provide a means whereby the sodium channels are concentrated in the region of the nodes of Ranvier. Thus the cortical cytoskeleton plays a vital role in neuronal function by acting as an attachment site for various receptors and ion channels, but also for s)maptic vesicles at nerve terminals, thereby providing a mechanism for concentrating the vesicles prior to the release of the neurotransmitter. 

The neuronal cytoskeleton provides the axon with mechanical support and is directly involved in the transport of materials from the cell body towards the synapse (anterograde transport) and in the opposite direction (retrograde transport). Axons are generally covered (insulated) with a myelin sheath, which is formed by oligodendrocytes (in the CNS) or Schwann cells (PNS). 

One theory of the pathogenesis of Alzheimer s disease proposes that increased production or decreased secretion of the Ap peptides leads to accumulation of these peptides. A second theory proposes that an abnormal x-protein causes the formation of intracellular neurofibrillary tangles. x-Proteins are important in the maintenance of cytoskeleton function and axonal transport of proteins. Another theory is that Ap accumulation is a precipitating factor that is followed by the development of the x-enriched tangles in the dying neurons. 

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