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Evolution Of Behaviour
1) The document discusses various concepts in animal behavior including warm-up effects, inhibition, feedback control, and reflex rebound. 2) Warm-up effects refer to behaviors that increase in intensity over time without a change in stimulus, due to summation of nerve signals. Inhibition operates at all levels of the nervous system to prevent conflicting behaviors. 3) Feedback control is important for maintaining homeostasis, exemplified by standing posture which is monitored and corrected. Both open and closed loop models of behavior are described.
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Evolution Of Behaviour
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- 3. Warm-up' or facilitation •Sherrington found that some reflexes do not appear at full strength at first but, with no change in the stimulus, their intensity increases over a few seconds. • Neurons, as we saw, show synaptic facilitation, each successive PSP being larger than the one before.
- 4. • At abehavioural level,Hinde (1954) found that chaffinches show a similar type of 'warm-up' effect • The bird's response to the owl is to give a mobbing call. (Fig. 1.7).
- 5. • Sherrington wasable to show that 'warm-up1 in some reflexes is due summation of stimuli that come to evoke a response from more and more nerve fibers, producing a stronger contraction. He called this phenomenon 'motor recruitment'.
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- 7. • In complexbehaviour, not only a change in the intensity of response but in the nature of the behaviour as well. • Sherrington (1917) provides an excellent example from what he calls the cat's 'pinna reflex'.
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- 9. • Inhibition • Inhibitionoperates at every level within the nervous system. As we have seen, nerve cells can actively inhibit each others' transmission of information. • Prevention of one activity's occurrence while another is in progress constitutes inhibition at behavioural level. • Inhibition is just as important for coordination of behaviour as excitation
- 10. • Muscles arecommonly arranged in antagonistic pairs, • Mutual inhibition: to alternate flexion and extension of the limbs- • it is not only antagonists on same limb that inhibit each other, but that muscles located on opposite limbs also have antagonistic effects during locomotion. • When flexors of one limb r contracting, flexors of opposite limb inhibited. Reciprocal inhibition
- 11. • Inhibition ofthe scratch reflex by the flexion reflex. The stimulus denoted on line A invokes the scratch reflex, but this response is inhibited when the stimulus on line B evokes the flexion reflex. • The moment B is removed the scratch reflex returns, and much more vigorously than before—an instance of‘ reflex-rebound'
- 12. The role ofinhibition in complex behaviour is superficially less obvious
- 13. • The roleof inhibition in complex behaviour is superficially less obvious than that of excitation. • We stimulate an animal and the conspicuous result is it makes a response. • But in so doing it has made a swift transition that requires inhibition of its behaviour prior to the stimulus and of other behaviour that it may be stimulated to perform at the same time.
- 14. • reflexes 'competing'for the final common pathway, i.e. the muscles whose action is common to several different reflexes. • analogous, fighting, feeding and sleeping competing for the control of the animal's musculature.. • Such systems are incompatible, only one behaviour can occur at a time.
- 15. Reflex Rebound indust-bath • Vestergaard (1980) found that if laying hens are kept on wire so that they have no substrate to dust-bath, when eventually given access to litter they start dustbathing quickly • It is possible that the system controlling dustbathing shows something akin to reflex rebound.
- 16. The Winged Aphids Mutualinhibition between the systems controlling flights and those controlling settling
- 17. Kennedy, • Winged Aphids,alternates between periods of flight and settling /feeding on leaves. • If aphid settles on an ‘old leaf—,it does not stay long and soon takes off but flies relatively weakly and soon settles again. • settled on a young shoot, it stays for a long period but, when it takes off, flies vigorously and for a long time.
- 18. • activation ofthe settling system may temporarily inhibit the expression of the flight system but, at the same time, gradually lower the threshold for flight.
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- 20. Feedback control_ toMaintain Homeostasis Commonly, reflex or complex behaviour consists of a steady output of some activity that has to be held at a given level. Exmp 1 'stand at ease',
- 21. Examp 2 • animalsmaintain a very constant body weight and eat and drink sufficient for their needs at regular intervals. do not overeat. • In times of scarcity, they consume more when the chance arises. Feedback& HomeoStasis
- 22. • the endresult of behavior(posture and balance whilst standing; state of nutrition) is monitored • When it deviates, control mechanisms correct the imbalance and bring the end result back to the set value again. Feedback& HomeoStasis
- 24. • Open LoopModel of Reflex • It has no monitor and input coming to behavioral system(BS) is interacted and we get the output(response). • Even if the output is subjected to some disturbances it is not going to effect the the BS
- 25. Strike of Mantis,open loop • No time to modify a swift movement. • The mantis orientates its body( involve feedback control) but, once aimed, the strike is an all-or- none movement. • If the fly moves , it will hit the wrong place • (without feedback),
- 27. • Close LoopModel • Any alteration in out put feeds back to the input to affect the behavior system and thus changes the out put. • Thus out put is adjusted proportional to the feed back. • This model works in slow and precise movements
- 28. • Applying theClose Loop Mechanism shown in Figure to STAND at EASE. • The output (state of tension in the muscle) is affected by a disturbance (being stretched by other muscles) • muscle spindle, records the change and feeds back to change the input (motor nerve) and restore the original output.
- 29. • Figure 1.10,represents a typical muscle on the limb of a mammal, involved in maintaining posture.
- 30. • —excitation, inhibition,summation, facilitation and feedback control • common to many levels. neurons, reflexes and more complex behavior share many basic properties • in many cases, very different concepts. • It is often possible to break down complex into smaller units.
- 31. • There aredifferences in complexity and these often require different types of approach. • what sort of questions about behaviour we are trying to answer.
Editor's Notes
- #5 Counting the number of calls given "by a chaffinch in successive 10s periods after the owl is shown to it indicates that it begins by calling at a relatively low rate and that the maximum calling rate is not reached for about 2.5 min, after which it gradually declines
- #8 Repeated tactile .stimulation to the cat's car first causes it to be laid back. If stimulation persists, the ear is fluttered; thirdly the cat shakes its head and when all else fails to remove irritation, it brings its hind leg up and scratches
- #10 Inhibition operates at every level within the nervous system. As we have seen, nerve cells can actively inhibit each others' transmission of information. Similarly, prevention of one activity's occurrence while another is in progress constitutes inhibition at behavioural level. In many ways, inhibition is just as important for coordination of behaviour as excitation Muscles are commonly arranged in antagonistic pairs, Mutual inhibition allows them to take the lead in turn during limb movements, and to alternate flexion and extension of the limbs- Sherrington found that it is not only antagonists on die same limb that inhibit each other, but that muscles located on opposite limbs also have antagonistic effects during locomotion. When die flexors of one limb arc contracting, die flexors of die opposite limb arc inhibited. Reciprocal inhibition of this type is one of the basic integrating mechanisms
- #15 In an analogous, systems controlling patterns of complex behaviour like fighting, feeding and sleeping competing for the control of the animal's musculature.. Such systems are obviously incompatible in sense that only one behaviour can occur at a time. When animal starts feeding, other behaviour must be inhibited for the time being.
- #16 We observe that when a particular type of complex behaviour, e.g. courtship, has not been elicited for some time, it has a lowered threshold and is performed with high intensity when it is, at last, evoked. and dustbath in very much longer session than hens kept all the time on litter.
- #18 In an elegant series of experiments, Kennedy was able to exclude any simple explanation for this relationship based on physical exhaustion during flight and recovery after resting and feeding on a young leaf. He suggested that there is mutual inhibition
- #21 feedback control loop (plural feed·back con·trol loops) noun connection from output to input: the connection or path that forms an electrical loop from the output to the input of a feedback circuit Very commonly, reflex or complex behaviour consists of a steady output of some activity that has to be held at a given level. When we 'stand at ease', our body is evenly balanced over the pelvic girdle and easily corrects for any slight jostling we may receive. To do so, the muscles of the legs and back must be held at a constant level of tension and, if shifted away from this level, they must correct to bring the body upright again. Analogously, under normal circumstances animals maintain a very constant body weight and eat and drink sufficient for their needs at regular intervals. If a surplus is available they do not overeat. In times of scarcity, they spend a higher proportion of their time in feeding and consume more when the chance arises to replace any deficit.
- #22 Analogously, under normal circumstances animals maintain a very constant body weight and eat and drink sufficient for their needs at regular intervals. If a surplus is available they do not overeat. In times of scarcity, they consume more when the chance arises to replace any deficit. these examples SHOW behaviour acting as homeostatic. In the first case, this was achieved through reflex systems controlling the leg and trunk muscles; in the second case it was achieved by a series of more complex systems regulating the search for food, feeding and satiation.
- #23 In both cases the operation requires that the end result of behavior(posture and balance whilst standing; state of nutrition) is monitored in some way. When it deviates from a set value a signal is sent to the control mechanisms to correct the imbalance and bring the end result back to the set value again. This idea is shown diagrammatically in Figure on next slide. It is disscused in more detail in chapter 4.
- #25 e.g simple reflexes like, flexion reflexes, touching hot or cold.
- #26 No time to modify a swift movement. The mantis orientates its body slowly and precisely ( involve feedback control) but, once aimed, the strike is an all-or-none movement. If the fly moves after the strike is initiated, it will hit the wrong place without feedback, So, despite the many levels at which the be- The mantis moves towards a fly and orientates its body slowly and precisely (operations that certainly involve feedback control) but, once aimed, the strike is an all-or-nothing movement. If the fly moves after the strike is initiated, this makes no difference to the form of the movement and the mantis strikes in the wrong place. Such behaviour, which occurs without feedback, is said to be under 'open-loop' control (as opposed to the 'closed-loop' control of a homeosta-tic system).
- #29 This is a simplified picture of the real situation, which in fact includes other regulatory mechanisms allowing for very fine graded control over the muscle contractions involved both in the maintenance of posture and in movements, but it serves to illustrate the reality of feedback control at a reflex level.
- #30 The homeostatic control of posture is understood at a neurophysiological level. In some cases we know the paths of the neurons. Motor neurons that have their cell bodies in the ventral horn of the spinal cord run to the muscle and it is their activity that determines the tension developed by the muscle. In parallel with every skeletal muscle, and embedded within its fibers so that they contract and relax it, are muscle spindles. These are specialized sense organs for recording the degree of tension in the muscle. Their sensory nerves run back to the spinal cord and, entering through the dorsal root, synapse with the motor neurons to the muscle. Thus a loop that forms the basis of the stretch reflex is closed. When a muscle is stretched by the contraction of its antagonists, the muscle spindles are also stretched and their sensory fibres increase their rate of firing, stimulating the motor neurons so that the muscle contracts.
- #31 —excitation, inhibition, summation, facilitation and feedback control—that appear to be common to many different levels. Studying single neurons and studying the behaviour of whole animals may require very different techniques and, in many cases, very different concepts. Nevertheless, as we have seen, neurons, reflexes and more complex behavior share many basic properties. It is often possible to break down complex behaviour patterns into smaller units, some of which are immediately equitable with reflexes. However, we cannot always explain behavioral observations using reflex terminology nor is there any point in trying to do so in many cases. There are differences in complexity and these often require different types of approach. Which we choose may well depend on what sort of questions about behaviour we are trying to answer. We must now turn to consider what these might be.