Overall view of locust flight

The overall picture we now have of the flight control system of the locust is of a series of intermeshed, overlapping neuronal loops (Fig. 7.8). It contains

Motor Neurons Locust

Figure 7.8 A flow diagram to show the relationships between some of the elements involved in generating the flight motor program in a locust. Some, but not all, of the thoracic interneurons included here are involved in generating the rhythm. Rhythmic input to motor neurons and interneurons is also derived from wing proprioceptors and brain neurons. As a result of the forward and rather irregular movement through the air, both the wind currents and the visual stimuli that the locust experiences are modified, so that the locust receives stimuli that are a combination of those caused by the external environment and those resulting from the locust's own movements.

Figure 7.8 A flow diagram to show the relationships between some of the elements involved in generating the flight motor program in a locust. Some, but not all, of the thoracic interneurons included here are involved in generating the rhythm. Rhythmic input to motor neurons and interneurons is also derived from wing proprioceptors and brain neurons. As a result of the forward and rather irregular movement through the air, both the wind currents and the visual stimuli that the locust experiences are modified, so that the locust receives stimuli that are a combination of those caused by the external environment and those resulting from the locust's own movements.

a surprisingly diverse array of different nerve cells. Many of them, including the proprioceptors and at least some of the wind-sensitive interneurons, are rhythmically active at the wing-beat rhythm. We must consider these neurons to be part of the flight generator itself because they are able to reset the flight rhythm in the same way as some of the thoracic interneurons. The flight generator is highly redundant - it contains many elements with similar or overlapping functions, none of which is indispensable to its normal operation. This redundancy brings the advantages, first, that the flight system is rugged and not easily perturbed, and, second, that the pattern produced is flexible and able to adapt rapidly to changing demands from the environment. Flight involves additional elements, not shown in Fig. 7.8. One of these is that the neurohormone octopamine is released into the haemolymph. Octopamine affects the contractile properties of muscle cells (Box 7.2) and increases the supply of fuel to muscles. In addition, it can affect the properties of some of the interneurons of the flight motor program generator, making them liable to fire spikes in cyclical bursts (Ramirez & Pearson, 1991), although it has not been demonstrated that octopamine is released within the central nervous system during flight.

A strong stimulus for flying is wind on the locust's head and, in the laboratory, flight ceases rapidly when wind stops. However, many rhythmical movements of animals are initiated by a brief stimulus and continue for some time after the stimulus finishes. Two quite different behaviours of this kind are examined below, both of which serve to take an animal away from a noxious stimulus. The first behaviour is escape swimming by the large nudibranch mollusc Tritonia to escape from starfish predators. The smell of starfish elicits fairly stereotyped movement patterns in many marine invertebrates and in Tritonia they consist of about four to seven cycles of alternate flexion of the body upwards and then downwards. The second example is swimming by young tadpoles of the frog Xenopus, which is elicited by touching the body surface.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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