Spindle fibres

Changes in the interaction between sister chromatids, as opposed to changes in the activity of spindle fibres, is thought to trigger the sudden movement of chromatids... 

Figure 20.28 Diagrammatic representation of mitosis in a cell with a single pair of homologous chromosomes. In prophase, the chromatin condenses into chromosomes, each of which consists of a pair of chromatids that have been formed by replication during interphase, and the nuclear envelope disappears. In metaphase, each chromatid attaches to the spindle fibres (microtubules) at a centre point, the centromere. In anaphase, the two chromatids of each chromosome become detached from each other and move to opposite poles of the cell along the microtubules. In telophase, the chromatids have reached the poles. Two nuclear envelopes then form and enclose each new set of chromatids, now once again called chromosomes. The microtubules disappear and the chromosomes uncoil and re-form into the long chromatin threads. Finally the cell membrane is drawn inward by a band of microfilaments to form a complete constriction between the newly formed nuclei, and two new cells are formed. The process is called cytokinesis.

It is semisynthetic vinca alkaloid. It interferes with microtubules, in miotic spindle fibres leading to cell cycle arrest... 

The centrioles migrate to opposite poles of the cell and the mitotic spindle is formed, apparently joining the cell membrane through the centrioles to the centromere of each chromosome. Spindle fibres consist of one type of protein, tubulin, of molecular weight 60,000. It is the organisation of these molecules to form the mitotic spindle which is blocked by the drugs colchicine, colcemide, nocodazole, vincristine and vinblastine (Fig. 10.3) with the consequence that mitosis is arrested in metaphase. 

For mapping, BrdU is added to enhance chromosome elongation and banding for metaphase chromosomes and to help distinguish G1 from S and G2 phase nuclei in the case of interphase chromosomes. Treatment of the cells for a few minutes with hypotonic solutions to make them swell and exposure to low temperatures, thus interfering with the stability of spindle fibres, can improve the preparations. 

The unequal division of chromosomes during mitosis may sometimes occur (aneuploidization). This may be the result of exposure of the cell to agents which damage or disturb the spindle fibres or interfere in some way with the process of cell division. The result is a cell with more or less chromosomes than normal, which may or may not be viable. 

The spindle fibres are attached to the chromosomes at the centromere and align them on the equatorial plate. The spindle arrangement contains microtubules composed of the protein tubulin. Colchicine is a specific spindle poison, which binds to tubulin, and inhibits its polymerization. Consequently, colchicine blocks mitosis, causing polyploidy, the unequal partition of chromosomes and metaphase arrest. 

Mitosis phase (M phase). The spindle checkpoint ensures that all the chromosomes are correctly aligned on the spindle fibre prior to... 

Recently small fibrils known as microtubules have been shown to be present in the cytoplasm. During nuclear division these aggregate in parallel bundles radiating from the centriole and form the spindle fibres. Microtubules have also been isolated from cilia and flagella. They are composed of globular units having a molecular weight of 60000 and an amino acid composition which resembles that of the muscle protein actin. 

Amongst other specific effects of REE in animal systems is the inhibition of cell growth by the inhibition of spindle fibre orientations during cell division (Neldhuis 1982, Wolniak et al. 1980). For more detailed information on this and other effects of rare earths in animals the reader is referred to reviews by Mikkelson (1976) and Weiss (1974). 

Muscle spindles are composed of nuclear bag (dynamic) and chain (static) fibres known as intrafusal fibres and these are innervated by y motor neurones. Extrafusal fibres make up the muscle bulk and are innervated by a motor neurones. Stimulation of the muscle spindle leads to increased skeletal muscle contraction, which opposes the initial stretch and maintains the length of the fibre. This feedback loop oscillates at 10 Hz, which is the frequency of a physiological tremor. 

Fig. 3. Substructure of a spindle-shaped (a) and a feathered (b) skeletal muscle. The orientation of the myofibres and of the fatty septa arranged along the fibre bundles are indicated schematically.

Fig. 16. Single voxel STEAM spectra of the SOL muscle (top) and the TA muscle (bottom). Different fibre orientation in those muscles results in clearly different patterns of the lines in the spectra In SOL (feathered muscle with oblique fibres), IMCL and EMCL signals show lower frequency separation than in TA (spindle-shaped muscle) due to bulk susceptibility effects. Furthermore, in SOL the Cr2 doublet merges into one resonance, the Cr3 triplet is less resolved, and TAU is shifted towards TMA.

Smooth muscle is composed of spindle-shaped cells rather than fibres. It lacks striations since adjacent myofibrils are out of register. Power output is lower than that from skeletal muscle it is responsible for the gentler, involuntary movements including, for example, those that cause movement of the intestine and those that change the diameter of blood vessels. 

Nerves differ in their sensitivity to local anaesthetics. When lidocaine (lignocaine) is applied to a mixed peripheral nerve the onset of the block is in the order, vasodilatation (B fibres), loss of pain and temperature (C and A6 fibres), muscle spindle reflex (Ay fibres), motor and pressure (A(3 fibres) and large motor and proprioception (Aa fibres). This phenomenon is called differential block. There are other minor variations in this ranking order among the local anaesthetics. The basis of differential block is thought to be the result of variability in the sensitivity of different nerves to the same agent. 

Researchers have been dogged by the inability to delineate between myoactivity and neuroactivity, mainly because the isolation of individual tissues by dissection is extremely difficult. This obstruction precipitated the development of methods to generate dispersed muscle fibres, and these preparations provided the first visual information on individual muscle fibres and/or muscle fibre bundles three morphologically distinct fibre types were recorded from Schistosoma mansoni, frayed, spindle-shaped and crescent-shaped fibres (Day et al., 1993). Although the location of all three fibre types within the worm is not clear, it has been suggested that the frayed fibres originate from the longitudinal muscle layer. 

Fibrosarcoma is a mesenchymal tumour originating from fibroblasts it can therefore occur ubiquitously in the whole body. (12) It was first described by R.H. Jaefe in 1924. About 35 cases have been reported so far. This type of tumour has a firm consistency and contains cystic structures with focal necroses and haemorrhages. It possesses a fibrous pseudocapsule and consists of fascicu-larly arranged, spindle-like or fusiform tumour cells embedded in parallel collagen fibres. The non-epithelial stroma marker vimentin is overexpressed. These cells may exhibit marked polymorphism. Fibrosarcoma mainly occurs in men of advanced age. Therapy consists of tumour resection and adjuvant chemotherapy. (280,281)... 

About 90 per cent of the fibre is composed of cortical cells. When wool is treated cautiously with protein-degrading enzymes or is partially disintegrated by bacterial attack, bundles of elongated cells can be distinguished (see Fig. 5.7). Further degradation releases the individual cortical cells which arc spindle-shaped, and which can, by mechanical treatment, be... 

Composite yams in the WF series of yams were spun specifically for the purpose of this research by using a vertical hollow spindle covering machine of a type manufactured by the H H Arnold Company. This machine has been modified by World Fibre Inc, USA using a proprietary technique as described in the US Patent No. 6,413,636. ... 

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