Nervous And Chemical Integration

are very closely associated by tight junctions, forming the blood-brain barrier (Carlson et al, 2000; Kretzschmar and Pflugfelder, 2002). This barrier is critical in isolating the nervous system from the hemolymph whose composition is both highly variable and inappropriate for neuronal function (see Chapter 17, Section 4). However, the barrier itself creates two potential problems, namely, obtaining adequate supplies of oxygen and nutrients for the neural elements. The former is solved by having tracheae running deeply into the ganglia, the latter by the ability of the perineural cells to transfer materials between the hemolymph and neurons. In addition, they secrete the neural lamella, a protective sheath that contains collagen fibrils and mucopolysaccharide. The lamella is freely permeable, enabling the perineural cells to accumulate nutrients from the hemolymph. The inner glial cells occur among the perikarya into which they extend fingerlike extensions of their cytoplasm, the trophospongium (Figure 13.3A). The function of these cells is to transport nutrients from perineural cells to the perikarya. Once in the perikarya, nutrients are transported to their site of use by cytoplasmic streaming.

Wrapped around each axon or groups of smaller axons are other glial (Schwann) cells (Figure 13.3B), These cells effectively isolate axons from the hemolymph in which they are bathed, However, in contrast to the situation in vertebrates, the glial cells are not compacted to form a myelin sheath but rather are loosely wound around the axons, Further, in insect nerves there are no distinct nodes of Ranvier (the regions between adjacent glial cells); hence, saltatory conduction of impulses does not occur (Section 2.3).

FIGURE 13.3. (A) Cell body of motor neuron showing trophospongium; and (B) cross-section through axons and surrounding Schwann cells. [A, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author. B, after J. E. Treherne, and Y. Pichon, 1972, The insect blood-brain barrier, Adv. Insect Physiol. 9:257-313.By permission of Academic Press Ltd., London, and the authors.]

FIGURE 13.3. (A) Cell body of motor neuron showing trophospongium; and (B) cross-section through axons and surrounding Schwann cells. [A, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author. B, after J. E. Treherne, and Y. Pichon, 1972, The insect blood-brain barrier, Adv. Insect Physiol. 9:257-313.By permission of Academic Press Ltd., London, and the authors.]

Structurally, the nervous system may be divided into (1) the central nervous system and its peripheral nerves and (2) the visceral nervous system.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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