Chapter 1

ANIMAL BEHAVIOR

Introduction

Warm-up' or facilitation

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.

• At a behavioural 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).

• Sherrington was able 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'.

2.5

• In complex behaviour, 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'.

Inhibition

• Inhibition• Inhibition operates 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

• Muscles are commonly 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

• Inhibition of the 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'

The role of inhibition in complex behaviour is superficially less obvious

• The role of 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.

• 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.

Reflex Rebound in dust-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.

The Winged AphidsMutual inhibition between the systems controlling flights and those controlling settling

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.

•

• activation of the settling system may temporarily inhibit the expression of the flight system but, at the same time, gradually lower the threshold for flight.

Feedback control

Stand at ease

Feedback control_ to Maintain 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',

Examp 2• animals maintain 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.

Feed back &

Hom

eoStasis

• the end result 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 &

Hom

eoStasis

• Open Loop Model 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

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),

• Close Loop Model• 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

• Applying the Close 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.

• Figure 1.10, represents a typical muscle on the limb of a mammal, involved in maintaining posture.

• —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.

• There are differences in complexity and these often require different types of approach. • what sort of questions about

behaviour we are trying to answer.