ALBERT

Notes: Summary Mammalian muscle spindles consist of the capsule, two types of muscle fibres and their efferent and afferent nerves. The cells of the capsule are flat endothelial like cells of perineural origin closely interlocked with each other and covered on both sides by a basement membrane. They contain a large number of cytopemptic vesicles. The viscous (v. Brzezinski, 1961) spindle room substance appears filamentous in the electron microscope. Each intrafusal muscle fibre is enclosed in a tube of endomysial cells, which is open towards both spindle poles. The thicker fibres (nuclear bag fibres) traverse the capsule at both poles and insert in the extrafusal connective tissue. The thinner fibres (nuclear chain fibres) are accompanied by elastic fibres and fixed in the capsule at both ends of the spindle. The M-line is absent in nuclear bag fibres, but clearly visible in nuclear chain fibres. These contain more sarcoplasmic organells and a better developed T-system than the nuclear bag fibres. Satellite cells are more numerous in intrafusal muscle fibres than in extrafusal ones. Most frequently they are associated with nuclear bag fibres and more often they occur in man than in rat. The myotube regions of both fibres are sparsely supplied with myofibrils. Besides chains of axially arranged nuclei large Golgi fields and vesicles with a central core are seen. Leptomeric fibrils sometimes connect in these regions myofibrils, or different parts of the plasmalemma or myofibrils with the plasmalemma. In nuclear bag fibres the chain of nuclei of the myotube region is widened by a cluster of nuclei filling the nuclear bag and further reducing the number of myofibrils. The sensory endings (initial fibres) wind around the myotube regions and nuclear bags of the muscle fibres, thereby forming the „annulospiralige Endigung“. The axon of the ending, which is not covered by a Schwann-cell, runs between the basement membrane and the plasmalemma of the muscle fibre. It contains a great number of mitochondria and is fixed by desmosomes to the plasmalemma. The sensory endings are obviously stimulated by a stretch of the adjacent intrafusal muscle fibres. The stretch is supposed to be most effective in myotube regions with few myofibrils. Mechanical distortion of the receptor membrane or a transmitter substance released or changes in the ional distribution within the gap between plasmalemma and axolemma may cause the initiation of generator potentials. Assuming two different receptor systems in the muscle spindle, the following hypotheses are proposed: 1. A transverse lateral pressure from contracting or stretched extrafusal muscle fibres compresses the capsule whereby nuclear chain fibres and elastic fibres are stretched and the nerve endings are stimulated (pressoreceptor, Bridgman and Eldred, 1965). As soon as the pressure in the spindle room is diminished by release of fluid into the extrafusal tissue, the nuclear chain fibres shorten with the elastic fibres, even when the stretch or contraction of the extrafusal muscle fibres continues (adaptation). After relaxation of the extrafusal fibres the spindle room is filled up again by fluid transport across the capsule cells by cytopempsis. 2. Since nuclear bag fibres are attached to the extrafusal tissue, a stretch of the total muscle causes a stretch of the nuclear bag fibres and a stimulation of their sensory endings. This lasts as long as the muscle is stretched (tensoreceptor). 3. The sensitivity of both receptor systems can be adjusted by varying the stiffness of the polar regions of the intrafusal muscle fibres by graded non-propagated contractions.

Notes: Die Belastung von kontinuierlichen Filtrierapparaten, wie Vakuumfiltern und Zentrifugen, läßt sich durch Voreindicken des Zulaufgutes herabsetzen; durch vorherige Abstoßung eines Teiles der Begleitflüssigkeit läßt sich also die erforderliche Filterfläche verringern. Als Voreindicker hat sich das Kasteneindickfilter bewährt. Das automatisch gesteuerte Vakuumfilter ohne rotierende Teile taucht dabei mit der gesamten Filterfläche in die einzudickende Suspension ein. Auch die Kombination eines Vakuumdrehfilters und einer Filterzentrifuge ist von Vorteil, da auf dem Drehfilter eine bessere Kuchenauswaschung erreicht wird als in der Zentrifuge, während die Zentrifuge eine geringere Restfeuchtigkeit des Kuchens erreichen läßt. Aus den gleichen Gründen wird der thermische Trockenprozeß verbessert, wenn ihm Drehfilter und Zentrifuge in Kombination vorgeschaltet sind. Allgemein bieten die Kombinationsmöglichkeiten verschiedener Apparate zur Trennung fest-flüssiger Systeme Möglichkeiten zur Wirtschaftlichkeitssteigerung, wie an einigen Beispielen gezeigt wird.