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Until recently, most scientists thought that complex behaviors (behaviors that arise through the various integrated behaviors and coordinated movement of the various muscles respectively) were generated through the interfacing reflex arcs. It was assumed that each reflex arc received a single sensation and controlled a single muscle (or a pair of antagonistic muscle as in the hand withdrawal reflex). Learned behavior, for example, rats in a maze to find such a reflection of the reflex circuits were thought to be the result of chaining. This model of acceptable behavior is dominated by scientists in the majority of this century.

Insect Flight

The idea that complex behavior was a chain of reflexes was refuted by Donald Wilson's research at Stanford University in the 1960s. Wilson was working on circuits that made the grasshopper fly. This was a good candidate for reflex chains. 

A group of flying muscles will lift the wings; After a while, the tension receptors in another group would be stimulated to initiate contractions that would lower the wings. When the wings went down, the stress receptors in the uplifting muscle group would be stimulated with increasing strain and after a while the ıla lifting reflex would be activated. Hareket Then the wings would be lifted up and this time the receptors in the lowering muscle group would be warned and they would start the un download reflex aşağı and so on forever he would continue.
Following the circuit, Wilson discovered the necessary stress receptors and cut the nerves from the receptors to the thoracic ganglia. Wilson hoped the behavior would be removed by deactivating the initiating elements. But the grasshopper almost surprised her by maintaining her normal flight. Still, the operation had an impact.
The speed of the flapping of the wings has fallen slightly and coordination has been impaired to some extent. However, the behavior was continuing. Subsequent investigations revealed that another circuit is responsible for maintaining the ability of the grasshopper to fly without stress receptors . This was a circuit that produced commands to fly, without the need for any external stimulation from an engine program and strain receptors in the thoracic ganglia. Of course, this was normally set.
Since the discovery of Wilson, it has been found that many complex, rhythmic or sequential behaviors, which have been thoroughly studied in vertebrates and invertebrates, have been performed by some specialized independent circuits. These circuits regulate muscle movements in the correct sequence and in the right timing. No complex behavior on reflex chains is known. The list of behaviors controlled by the motor programs includes feeding, walking, swimming, itching, sounding, nesting, attacking, courtship and mating behavior.

Nutrition in Aplysia

As research techniques developed, attention was focused on cell neurophysiological mapping of circuits responsible for complex cases. Most of the well-understood engine program networks today include rhythmic and repetitive movements, as we have seen in the displacement movement. Due to the practical need, research focuses on behaviors that last for even minutes or even hours. Thus, scientists can find enough time to find two cells in the same circuit, to determine the nature of the connection between them, to record their activity at the same time, and finally to mark them (usually by dye injection). Naturally, the more cells there are in the circuit, and the more detailed the relationship between them, the longer it takes to map and understand the circuit.
A good example of an almost completely mapped behavior is the circuit that controls feeding in Aplysia. This circuit identifies four steps in the flow of information - difference, forward, processing and response - in the context of a relatively complex behavior. Aplysia, which is fed on algae, contains chemosensitive tentacles that detect potential nutrients. The impulses from these receptors are transmitted to the brain of Aplysia for analysis. If the fragrance processing network decides that the animal is in contact with a suitable food (the molluscs can learn the smell of the food), it sends signals to the interneurons that control the feeding behavior. These interneurons, however, also receive feeding signals from other parts of the brain. For example, avoidance can prevent feeding, so that if the animal is in danger, low priority activities such as nutrition are stopped. A motor program is activated when feeding is continued. As with many invertebrate behavior, the central nervous system only stops inhibiting a suitable circuit in a ganglion.
Nutrition is controlled by 22 muscle, six motor neurons. These motor neurons are also coordinated by two antagonistic groups of tern commander veren interneurons, including protrusors and retractors. The protrusion and retractor muscles are analogue to extensor and filament muscles, respectively. Protraktor interneurons, in three or four seconds, rhythmic impulses themselves. The signals coming out of these cells activate the muscles that open the mouth and lower the belli teeth pozisyon to lower the position of the food. These cells also inhibit retractor motor neurons and their command interneurons.
When the rhythmic cycle of protraktor interneurons bring them to the silent phase, they stop inhibiting the retractor interneurons. These cells, which are continuously impulse-free when there is no inhibition, activate the retractor motor neurons at this stage and inhibit the protractor muscles. They change the contractile sequence of the muscles to bite and close the mouth.
The feeding circuit of Alpysia exhibits three basic characteristics of a typical engine program:
1. The program is operated by an independent circuit that coordinates the movement of various muscles.
2.It automatically adjusts the behavior automatically by using sensory feedback. In this example, it extends and reinforces the opening phase when appropriate.
3. The brain is directly under centralized control. In Aplysia, the brain enters information from cells with chemical sensitivity and iy hunger ”receptors, and activates this motor program when necessary. Similarly, when other behaviors are required (eg, escape from a hunter starfish), it can hamper brain-feeding behavior. The brain can also change the behavior rate; it may extend or shorten the cycle time when necessary.
The strategy of using two groups of command cells, such as Aplysia's protractors and retractors, is called reciprocal inhibition. This method is seen as the organized way of apparently all rhythmic behaviors. The motor programs also perform non-rhythmic behaviors such as swallowing, laughing. The strategy to regulate much more complex behaviors, such as the construction of a birdhouse or a cat's silent approach to a mouse, chasing it, catching it, killing it, and eating it requires the establishment of a number of separate engine programs and the formation of high-level circuits to coordinate them. It is the greatest achievement of modern neurophysiology to understand that the behavior of an organism is accomplished by groups of neurons that interact with each other, similar to those in Alplysia.

Source: poxox blogs

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