Allott Neurobiology & Behavior Text

8/13/2019 Allott Neurobiology & Behavior Text

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Option eurobiology and behaviourNeurobiology s the study of the nervous system of animals.Nervous systems are used in responses to stimuli. Behaviour s thepallern of responses in an animal. The simplest example of animalbehaviour s the reflex.

eflexes and reflexarcsAn example of a reflex takes place when a y ou ng rabbit tou ch es astinging n ellie p lant for the first t im e with the tip of ts nose. Therabbit s response to touching a nettle involves a series of neuronsthat are called a reflex arc.

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1 Nerve endings n the sk in of the rabbit s no se detect the paincaused y the stings. These cells are called pain receptors. Thepain receptors are nerve endings of sensory neurons.2 These sensory n eu ro ns carry impulses from the nose of therabbit to its central nervous system.3 The impulses travel to th e ends of t he sensory n eu ro ns w he rethere are synapses with relay neurons. Messages are passed tothe relay neurons y synaptic transmission.

4 The relay n eu ro ns have synapses with m otor n eu ro ns whichcarry impulses out of the central nervous system to muscles inthe rabbit s body.5 Messages are passed across synapses from motor neurons to

muscle fibres which contract n pull the rabbit s nose awayfrom the nettle. ts the cOlmeetions between sensory relay nmotor neurons that ensure the response s appropriate to thestimulus - this s known as co-ordination.

rThe pain withdrawal reflexAnother reflex arc is used toco ordinate the response to apain stimulus for example if wetouch a hot object with ourhand. This reflex action is calledthe pain withdrawal reflex and isco ordinated by the spinal cord.Figure shows the reflex arc forthe pain withdrawal reflex.

32igure Components of a reflex arc

greymatter

relayneuron

spinal cord

cell body ofsensory neuronin the dorsalroot ganglion

ventral root ofspinal nerve cell body of

motor neuron whitematter

spinalnerve

dorsal root ofspinal nerve

o receptorcells or nerveendingss nsin pain

effectormusclethat pulls handaway frompain whenit contracts

nelVe fibreof otorneuron

nerve fibreof sensoryneuron


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30 Option E Neurobiology and behaviourNatural selection and animal responsesThe survival chances of animals are greatly affected by theirbehavioural responses. Individuals with the best-adapted responsesare most likely to survive and produce offspring. U a response isgenetically determined, rather than learned, it can be inherited byoffspring. Responses should therefore change by natural selection,especially if the environment changes.Example 1 Migration in ylvi lric pillThe bird ylvi lric pill blackcap breeds duting thesummer in Germany and, until recently, migrated toSpain for winter. However, studies show that 10 ofblackcaps now migrate to the UK instead. To testwhether the change is genetically determined, eggswere collected from parents which had migrated tothe UK in the previous winter and from parents whohad ntigrated to Spain. The yowlg were reared andthe direction in which they ntigrated was recorded.Birds whose parents had ntigrated to the UK tendedto fly west, wherever they were reared, and birdswhose parents had migrated to Spain tended to flysouth-west. They therefore responded toenvironmental stimuli at the tin1e of ntigration in thesame way as their parents. In the 10 of birdsmigrating to the UK the response had changed.Warmer winters in the UK were probably the agent ofnatural selection that caused this change.

Example 2 Rejection of II IIIrISCailOrlIS eggsThe cuckoo ClIclIl l ls ailOrlIS lays single eggs in thenests of other bird species and then abandons them. Uthe strategy succeeds, the young cuckoo hatdles firstand is fed by its foster parents, whose own younghatch later and are pushed out of the nest by theyoung cuckoo. However, cuckoo eggs are sometimesidentified as foreign and removed from the nest.There is evidence that the egg rejection responsedevelops by natural selection in populations that aretargeted by cuckoos. Egg rejection is frequent inmany species that would be suitable for cuckoos touse to rear their YOlmg It is much less common inspecies that are W1sltitable for example because theylay their eggs in tree holes, which are inaccessible toegg-laying female cuckoos. Egg rejection behaviour ismudl less COlllillon in meadow pipits in Iceland,where there are no cuckoos, than in populations ofthe same species in Europe where there are cuckoos.

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er eption of stimuliStimuli are detected by receptors Some receptors are nerve endingsof sensory neurons e g pain receptors Others are special cellslocated in a sense organ Animals can detect a wide variety of stimuliusing different types of receptorHumans have the following types of receptor Mechanoreceptors perceive 111 velnents

Examples: mechanoreceptors ill the ear perceive sound vibrations alldmovements due to gravity; mechanareceptors in the skin perceive pressurechanges.o Chemoreceptors perceive chemical substances

Examples: chemareceptars ill the nose detect volatile chemieals in the airsmells ; chemoreceptors in the tongue perceive dissolved chemieals tastes .o Thermoreceptors perceive heat an d temperature

Examples: thermareceptors in the skin perceive heat and cold;thermo receptors in ti,e hypothalamus mallitar the tempemture theblood.

o Photoreceptors perceive electromagnetic radiation usually lightExamples: rod and cone cells ill the retilla the eye perceive light.

Figure 4 shows the structure of the eye including th e retina wherethe photoreceptors are located

Option Neurobiology and behaviourigure 3 The Hermann grid Whatdo you perceive when you look atit What type of receptors are youusing

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:I Option E Neurobiology and behaviourod and stem cellsLight entering the eye is focused to form an image on theretina Figme 5 shows the cell types in the retina Twotypes of light sensitive cell detect the image and convert itinto nerve impulses These are the rod and cone cells Rodsare very sensitive to light so work well in dim lightconditions In bright light the pigment in them istemporarily bleached and they do not work. Rod cellsabsorb all the visible wavelengths of light and do notdistinguish between them so they give us black andwhite visionGroups of rod cells send impulses to the brain via a singleneuron so the brain cannot distinguish which rodabsorbed the light There is therefore less detail in imagestransmitted to the brain by rods than by the cones each ofwhich sends impulses to the brain via an individualnemon There are three types of cone which absorbdifferent ranges of wavelength of light They are namedaccording to the colour that they absorb most: red blue orgreen When any colour of light reaches the retina thered blue and green cones will each be stimulated by acertain amount By analysing the amount that each of thethree cone types are stimulated the colom of light can bevery precisely determined Cones are only stimulated bybright light and therefore the colour vision that they giveus does not work well in dim light.

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bipol rneuron

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l yer of pigmented ellsFigure 5 Rods and cones in the retina

Processing visual stimuliThe retina begins the task of processing the visual stimulithat are collected by the rods and cones and passed via thebipolar cells to the ganglion cells Each ganglion cell isstimulated when light falls on a small circular area of retinacalled the receptive Held There are two types of ganglioncelL In one type the ganglion is stimulated light falls onthe centre of the receptive field but tllis stimulation isreduced light also falls on the periphery In the othertype light falling on the periphery of the receptive fieldstimulates the ganglion cell but this stimulation is reduced light also falls on the centre Both types of ganglion cellare therefore more stimulated the edge of light/darkareas is wililin the receptive Held Tllis type of processing iscalled edge enhancement and it is the explanation of anoptical illusion called the Hermann gridContra lateral processing of visual stimuli means that someimpulses from the left eye pass to the right side of thebrain and vice versa This exchange happens in the opticclliasma shown in Figure The right side of the brainprocesses visual stimuli from the left side of the visual fieldnd vice vers

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Option Neurobiology and behaviour Perception of soundSound waves pass through the air. When they reachthe eardrum a thin sheet of tissue between theouter and middle ear they make it vibrate rapidly.There is a series of three tiny bones in the air filledmiddle ear which are in contact with each other.They form a connection between the eardrum andanother thin sheet of tissue the oval windowlocated between the middle and irmer ear. Thebones of the middle ear transmit vibrations from theeardrum to the oval wirIdow. They can also amplifythe sound by about twenty times. f sounds are tooloud muscles attached to the bones contract todamp down the vibrations and protect the ear.The cocWea is the part of the irmer ear that is usedfor hearing. t is a tubular coiled fluid filledstructure. Within the cochlea are membranes towhich sensory cells are attached. Each of these cellshas a bundle of hairs stretching from onemembrane to another. When vibrations are

transmitted from the oval window into the cochleathey stimulate particular hair cells by making theirhair bundles vibrate. Different hair cells resonateand therefore vibrate at different frequenciesallowirlg us to distinguish between soruIds of adifferent pitch. When a hair cell is stinllllated itsends an impulse to the brain across a synapse andalong a sensory neuron in the auditory nerve.The round window is another thin sheet of tissuelocated between the middle and irmer ear. f it didnot exist the oval window would not be able tovibrate because the incompressible fluid in thecochlea would prevent it from moving. When theoval window pushes the fluid in the cocWeainwards the round wirldow moves outwards andwhen the oval wirIdow moves outwards the roundwindow moves irlwards. n tltis way the ovalwindow is free to vibrate and to transmit vibrationsto the fluid in the cochlea.

muscle attached

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bones of skullI bones ofmiddle e r p rts of innere r on ernedwith balance

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cochlea

oval window

Figure 7 The structure of the ear

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Figure 8 Sensitivity of mammals tofrequencies of sound 325

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Does the world sound the same to any of the animals? g2 Which is the real world the one we perceive or the world perceived bythe bat?3 Animals also differ considerably in their visual perception Is what each

animal sees what is really there is it a construction of reality or is realitya false concept?

hinking out science perception and realityFigure 8 shows the frequency sensitivity of six land mammals The solid areashows where frequency sensitivity is best while the lines indicate howmuch louder other frequencies need to be in order to be heard


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m 3 Option Neurobiology and behaviourInnate behaviourS om e t yp es of a n i m a l b e h av i o ur develop whatever externalinlluences an animal experiences they develop independently ofth e environmental c o nt e xt . T h e y ar e genetically programmed an da re c al le d i n n a t e b e h a v i o u r . A n example is movement of ial ariaf latworms towards food. Other types of behaviour develop as a resulto f th e animal s experiences. They ar e examples of l e a r n e db e h a v i o u r. example is th e use by chimpanzees of narrow twigsto extract t erm ites from termite mounds. Figure 9 Woodlouse slater

Investigating biology: innate behaviour in invertebratesThe behaviour of invertebrate animals can be investigated by carefully designedexperiments. Two types of behaviour involving movement have been defined: Taxis is movement towards or away from a directional stimulus. An example

is movement of a woodlouse or slater Figure 9 away from light. Kinesis also involves movement as a response, but the direction of

movement is not influenced by the stimulus. Instead, the speed ofmovement or the number of t imes the animal turns is varied. An example isslower movement, with more frequent turning when woodlice are transferredfrom drier to more damp conditions.

Stages in designing an investigation:1 Place the animals in conditions that are similar to the natural habitat.2 Observe the behaviour and to see what stimuli affect movement.3 Choose one stimulus that appears to cause a taxis or kinesis.4 Devise an experiment to test responses to the stimulus.5 Ensure that other factors do not have an effect on the movement.6 Decide how you will measure the movement of the invertebrates.

Choice of invertebrate speciesMany different invertebrates canbe used in experiments.Planarian flatworms, woodlice,blowfly larvae, snails and beetlesare often used. Some speciescan be purchased from suppliersbut it is also possible to useinvertebrates from local habitats.These should be kept for a shorttime only, protected fromsuffering during the experimentsand then returned to theirhabitat. Endangered speciesshould not be used.

Figure 10 Testing chemotaxis

Unscented

w

Figure 10 shows apparatus that can be used to test the response ofinvertebrates to scents. The animals are placed in the syringe W a pump isattached to tube X to draw air gently through arms Yand ZThe apparatus was used to test whether woodlice were attracted to the smellof other members of their own species. Three species were tested. In eachcase air was drawn through a container of the woodl ice into one of the twoarms. This air was therefore scented with the woodlice. Unscented air wasdrawn into the other arm. The number of woodlice that moved from syringe Ainto each arm was counted. The results are shown in Table 2.

Suggest another method for encouraging the woodlice to move out of thesyringe and into one of the arms. [

f 2 Outline the trends shown by the data in the Table 2. [II 3 Tests show that the differences between the numbers collecting in each: arm are statistically significant chi-squared test . Deduce, with a reason,I the type of receptor that the woodlice must have. [ ]II 4 Discuss, in terms of survival and reproduction, theII possible reasons for the woodlice entering:II a the scented arm of the apparatus [2 Oniscus asellus 9II b the unscented arm of the apparatus. [ Porcellio scober I: Table 2 Armadillidium vulgare 55

f Data based questions: chemotaxis in woo li e

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earned behaviourLearned behaviour develops s a result of experience Althoughoffspring inherit the capacity to learn they do not inherit specificpatterns of behaviour Offspring eh ve in a similar way to theirparents in m ny cases ut only because they le rn behaviour patternsfrom them not because of the genes that they have inherited Forexample hum n offspring inherit the capacity to learn a language Thelanguage th t they le rn is usually that of their biological parents butnot i they are adopted by adults who speak a different languageBirdsong h s been investigated intensively in some species is partlyinn te nd partly learned All members of a bird species share inn teaspects of song allowing each individual to recognize other mem ersof the species The learned aspects introduce differences allowingindividuals to be recognized by their song nd in some speciesallowing mates to be chosen for the quality of their singingLearned behaviour h s adva11lages over innate behaviour allowsresponsiveness to change or variation in the environment Neweh viour patterns can spread quickly through a population This cangreatly improve chances of survival For example honeybees c n le nlfrom other bees in their colony how to find nectar sources They c nalso le rn to find a particular flower type by associating its colour withits scent The location nd type of flowers that is yielding the most und nt nectar changes over time ut bees can learn new locationsnd types of flower T J is would not be possible with innate behaviourAnimals le rn to avoid eating distasteful or poisonous plants oranimals; they learn to avoid touching plants or animals with stings;they learn to avoid predator attacks nd other dangers is possible tofind examples of ll of these patterns of learned behaviour throughoutthe world nd deduce how they increase chances of survival

hinking about science blue tits nd milk ottlesNewspaper articles recently reported that blue tits yanistesc eruleus hadstopped pecking through the aluminium caps of milk bottles delivered tothe doorsteps of houses to drink the cream. This type of behaviour wasobserved in the 1920s in Southampton England and then soon after 150kilometres away - far further than blue tits normally fly. Amateur bird-watchers followed the rapid spread of the behaviour in both blue tits andgreat tits across Europe to the Netherlands Sweden and Denmark. Germanoccupation of the Netherlands during the Second World War stoppeddeliveries of milk for eight years - five years longer than the life of a blue tit.However within months of the resumption of deliveries blue tits throughoutthe Netherlands were pecking through the bottle tops. In 1952 the journalNature reported Although no experimental analysis of the behaviourinvolved in the opening of milk bottles has yet been made furtherobservations in the field enable the discussion to be carried furtheMuch less milk is now delivered to doorsteps because milk in supermarketsis cheaper. Also skimmed milk without cream at the top has becomepopular with humans. This may explain why blue tits have not recently beenobserved pecking through bottle tops.

Option Neurobiology and behaviour

igure Blue tit pecking throughmilkbottle cap

What is the evidencefrom the observationsthat this is learnedrather than innate behaviour?2 How did the behaviour

increase the chance ofsurvival of the blue tits?3 How can we be certain this

behaviour pattern did notevolve y n tur l selection jhundreds of years ago?4 Why are scientists

sometimes suspicious ofevidence b sed on m teurobserv tions r ther th non numeric l d t fromcontrolled experiments?

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30 . Option E Neurobiology and behaviourLearned behaviourSeveral different types o f l ea rn in g h a ve been defined. On e of thesecalled conditioning wa s investigated b y th e Russian physiologist IvanPavlov using dogs.Pavlov inserted a tube through t he c he ek of hi s experimental animalsthat c ou ld b e u se d to collect saliva from th e mouth. He wa s then ableto give stimuli an d m e as u re t he volume of saliva secreted by th edogs. He found that saliva w as s ec re te d i n r es po ns e to th e sight orsmell of food. These types of stimulus t o w hi ch all dogs respondwithout learning are called unconditioned stimuli a nd t hesecretion of saliva that results is th e unconditioned re sponse .Pavlov observed after a w hi le t ha t t he dogs were starting to secretesaliva before they received t h e u n c on d it io n e d stimulus. Somethingelse had become a stimulus that allowed th e dogs to anticipate th earrival of food. He f ou nd th at th e dogs could learn to use a variety ofsignals in t hi s w ay including th e ringing of a bell th e H as hi ng o f alight a metronome ticking or a musical box playing. These ar eexamples of conditioned stimuli an d th e secretion of saliva thatthese stimuli elicit is th e conditioned re sponse .Conditioned responses a re u se d extensively in many animal sb e h av i ou r a n d ca n greatly increase survival chances. T he re a re othermore sophisticated types of learning which a ls o a id help animals tosurvive reproduce an d pass on their genes.

Figure 12 Pavlov s dogs

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Figure 13 Sonograms of birdsong

The sonograms in Figure 13 are a visual representation ofbirdsong with time on the x-axis and frequency or pitch on thev-axIs.I Compare sonograms Iand II which are from two populations

of white-crowned sparrows Zanatrichia leucophyrys . [2]2 Sonogram III is from a white-crowned sparrow that was

reared in a place where it could not hear anv other birdsong. Compare sonogram III with sonograrns I and II. [2Jb Discuss whether the song of white-crowned sparrows isinnate learned or due to both innatE factors and learning.

[3]3 In 1981 Martin Morton and Luis Baptista published a veryunusual discovery - a white-crowned sparrow had learned to

imitate the song of another species. Sonogram IV is from astrawberry finch Amandava amandava . Sonogram V isfrom a white-crowned sparrow that had been hand-reared bVitself until it was 46 davs old and then placed in an aviarywith other white-crowned sparrows and a strawberry finch. Compare sonogram Vwith sonogram IV. [2]b Compare sonogram Vwith sonograms I and II. [2Jc Suggest two reasons whV birds rarelv imitate otherspecies. [2]d Discuss whether Morton and Baptista s obseNation is

evidence for innate or learned development ofbirdsong. [2]I

I II Data based questions: birdsong inn te or le rned II IIII

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Neurotransmitters and synapsesThe basic principles of synaptic transmission were described inChapter 24 - an action potential in the pre-synaptic neuron causesrelease of neurotransmitter into the synaptic cleft, and an actionpotential is stimulated in the post-synaptic neuron when theneurotransmitter binds to receptors in its membrane Two additionalfeatures of synapses give a fuller understanding of the functions ofsyn pses

3 Option Neurobiology and behaviour

_

Splus IPS More than one pre-synaptic neuron can form a synapse with thesame post-synaptic neuron see Figure 14). Sometimes there arehundreds of pre-synaptic neurons Usually a single release ofneurotransmitter from one of the pre-synaptic neuron isinsufficient to trigger an action potential. Either one pre-synapticneuron must repeatedly release neurotransmitter, or severaldifferent pre-synaptic neurons must release neurotransmittertogether. The additive effect from multiple releases ofneurotransmitter is called summation

Neurotransmit ters that stimulate action potentials in the post-synaptic neuron are called excitatory. Some neurotransmittershave a different effect - they inhibit action potentials. Neuronsonly release one type of neurotransmitter. Pre-synaptic neuronstherefore either excite or inhibit post-synaptic transmission - theycannot do both.

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action potentialactionpotential

Where there are many synapses between pre-synaptic neurons and apost-synaptic neuron there can be interaction between the activitiesof the excitatory and inhibitory neurons Figure 15). Whether a post-synaptic action potential is excited or not is a summation of theeffects of all of these neurons This is the basis of decision-makingprocesses i n the central nervous system.

Psychoactive drugsThe brain has many synapses, perhaps as many as 1016 in children.These synapses vary in their organization and use a wide variety ofneurotransmitters. Over a hundred different brain neurotransmittersare known Psychoactive drugs affect the brain and personallty byaltering the functioning of some of these synapses. Some drugs areexcitatory, because they increase post-synaptic transmission. Othersare inhibitory because they decrease it.

Figure 14 Excitatory post-synapticpotentials EPSP , inhibitory post-synaptic potentials IPSP

nerve endingsof pre synaptic neuronsformingsynapses

Figure 15 Multiple synapsesExamples of excitatory drugsI Nicotine contained in

cigarettes and other forms oftobacco, derived from theplant Nicotiana tabacum.

2 Cocaine derived from theleaves of a Peruvian plant,Etythroxylon coca.

3 Amphetamines a group ofcompounds that aresynthesized artificially.

Examples of inhibitory drugsI Benzodiazepines a group of

compounds including Valiumthat are synthesized artifiCially.

2 Alcohol in the form ofethanol, which is obtained byusing yeast to ferment sugar.

3 TetrahydrocannabinolTHC) obtained from theleaves of the Cannabis sativaplant. Figure 16 Micrograph of brain tissue 3 9


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a Option Neurobiology and behaviourCocaineCocaine acts at synapses that use dopamine as aneurotransmitter. binds to dopamine reuptaketransporters which are membrane proteins thatpump dopamine back into the pre synaptic neuronBecause cocaine blocks these transportersdopamine builds up in the synaptic cleft and thepost synaptic neuron is continuously excited.Cocaine is therefore an excitatory psychoactivedrug. Synapses that use dopamine are part of whatis known as the reward pathway that gives uspleasurable feelings during certain activities.Cocaine gives feelings of euphoria that are notrelated to any particular activity. Excitatory drugscan also work by mimicking excitatoryneurotransmitters for example heroin mimicsendorphins

Tetrahydrocannabinol THeTHC binds to cannabinoid receptors in pre synapticmembranes Binding inhibits the release ofneurotransmitters that cause excitation of postsynaptic neurons THC is therefore an inhibitorypsychoactive drug. Cannabinoid receptors arefound in synapses in various parts of the brainincluding the cerebellum hippocampus andcerebral hemispheres. Sevcral naturally occurringor endogenous cannabinoids have been discovered.They are an lUllIsual example of rctrogradesignalling as they are released by the post synapticneuron and convey a message to the prc synapticneuron People have reportcd a wide variety offeelings due to THe. The main eUects are disruptionof psydlOmotor behaviour short term memoryinlpairment intoxication and stimulation ofappetite.

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Drug addiction - the causesThe American Psychiatric Association has defined addiction as:a chrollically relapsil1g disorder that is characterized by three maillelemellts:

a) compulsioll to seek alld take the drugb) loss cOl1trol l limitillg illtake alldc) emergel1ce a mgative emotiollal state whell access to the

drug is prevelltedOnly certain drugs cause addiction and usually repeated useover a prolonged period of time is needed. With a few drugsaddiction can develop more rapidly. Some people seem muchmore vulnerable to addiction than others. Also addiction ismore prevalent in some parts of society than others. Thecauses of addiction are clearly not simple and three areas needto be considered.1 Dopamine secretion is associated feelings of well being

and pleasure. Many addictive drugs including opiatescocaine nicotine and alcohol affect dopamine secretingsynapses.

2 Genetic predisposition is the increased chance ofdeveloping an addiction that some people have because oftheir genes. One example is the gene DRD that codes forthe dopamine receptor protein. There are multiple alleles ofthis gene and a recent study showed that people with oneor more copies of the Al allele consumed less alcohol thanthose homozygous for the A2 aIIele.3 Social factors affect drug use and addiction. Culturaltraditions are very important and help to explain whydifferent drugs cause problems in different parts of theworld. Peer pressure poverty and social deprivationtraumatic life experiences and mental health problems mayalso contribute.

Figure 7 Wineand other alcoholic drinkscontain ethanol which an addidive drug Somescientists who advise on drug addiction regardproblems due to alcohol addidion to be greaterthan other less socially acceptable drugs


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pituit rygl nd

he human br inThe re h a s been intense research into the structure an d function ofth e hum a n brain. Figure 18 sho ws t h e main structures. Medulla o b lo n g ata controls

automatic and homeostaticactivities such as swallowingdigestion vomiting breathing an dheart activity.

Cereb ellu m co-ordinatesullconscious functions such asmovement an d balance.

H y p o t h a l a m u s maintainshomeostasis co-ordinating th enervous and endocrine systenlSsynthesising t h e h o rm o ne s secretedby th e posterior pituitary an dreleasing factors that regulate th esecretion of hormones by th eanterior pituitary.

Pituitary gland th e posterior lobestores an d releases hormonesproduced by th e hypothalamus an dt h e a nt eri or lobe produces an dsecretes hormones that regulatemany body functions.

Cerebral hemispheres act as th eintegrating centre for high complexfunctions such as learning memoryand emotions.

Figure iagram of the brainlesion studies and animal experimentationLesion studies gave th e first useful information about brainfunctions. Fo r example in the 19th century after t he d ea th of apatient who could only say t he w or d Tan th e French neurologistCharcot found a single large tumour damaging t he l ow er left side ofth e patient s brain. He deduced that this part of th e brain is invoivedwith speech. Another famous case involved Phineas Gage wh osuffered severe damage to th e frontal lobes of his brain in 1848when a large m et al p in passed through his skull. Th e lesion radicallyaltered his personality an d capacity for social interaction.Many lesions du e to tumours or accidental damage have beeninvestigated bu t rather than wait for these fortuitous opportunitiessome neuroscientists have perfonned experi nents on aninlalsincluding primates. Removal of parts of th e skull gives access to th ebrain an d allows experimental procedures to be performed. Theeffect on th e animal can be observed as long as th e animal is stillalive. These experiments therefore involve vivisection. Therc ar ewidespread objections to them because of th e suffering they ma ycause to th e animal an d because at th e e nd the animal is oftensacrificed.

Option Neurobiology and behaviour m

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Option Neurobiology and behaviourunctional magnetic resonance imagingMagnetic resonance imaging MRI) a v er y usefu l technique forstudying the internal structure of the body and for finding tumoursand other conditions in patients.A specialized version of MRI, called functional magnetic resonanceimaging fMRI) has been developed, which allows the parts of thebrain that are activated by specific thought processes to be identified.Active parts of the brain receive increased blood flow, which fMRIrecords. The experimental subject placed in the scalUler and ahigh-resolution scan of the brain taken. A series of low-resolutionscans then taken while the subject being given a stimulus. Thesescans show which parts of the brain are activated during the responseto the stimulus.The three iInages in Figure 20 were obtaiIled from an fMRIexperiment where experiInental subjects watched a mov in g tar get ona scr een and moved a cur so r to follow it. This task cau sed thecerebellum to be strongly activated because it coordinates eye andhand movements

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igur fMRI scans

ain and painkillersPain receptors iIl the Skill and other parts of the body detect StiIllUlisuch as the chemical substances in a bee s sting, excessive heat froma flame or the puncturing of sk in b y a h yp od er mic need le. Thesereceptors are the nerve endings of sensory neurons and they conveyimpulses to the central nervous system. When iInpulses reachsensory areas of the cerebral cortex we experience the sensation ofpa in. At ti me s i t necessary to block feelings of pain and the bo dyuses natural paink illers to do this. O ne gr ou p, called end or ph in s, areoligopeptides that are secreted by the pituitary gland. They bind toreceptors in synapses in the pathways used iIl the perception of pain.This blocks synaptic transmission and prevents the pain being felt.

igur fMRI scan of n om triosisp n


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ymp thetic nd p r symp thetic controlTh e peripheral nervous system comprises all of th e nerves outside th ecemral nervous system. t is divided i nt o t wo parts: th e voluntary an dth e autonomic nervous systems. Unconscious processes ar e controlledby th e autonomic nervous system, which is itself divided im osympathetic an d parasympathetic systems. These often have contraryeffects on an unconscious process. For example, parasympatheticnerves cause an increase in blood flow to th e gu t wall when th e gu t isactive. Sympathetic nerves cause a decrease in blood low, duringfasting or when blood is needed elsewhere, for example in musclesduring vigorous exercise.Th e heart rate an d size of th e p up il a re also under autonomic control. Impulses are transmitted to th e heart s p a ce m ak e r b y t he medulla

oblongata. Impulses carried by th e sympathetic system cause th eheart rate to speed up; impulses canied by th e parasympatheticsystem cause it t o s lo w down.

Muscle fibres in th e iris control th e size o f th e pupil. Impulsescarried to radial muscle fibres by neurons of th e sympathetic systemcause t he m to contract an d dilate th e pupil; impulses carried tocircular muscle fibres by neurons of th e parasympathetic systemcause th e pupil to constrict.

The pupil reflexT he p up il reflex occurs when bright light shines into th e eye. Photoreceptor cells in th e retina perceive th e bright light, causing

impulses to be se m t o th e brain in neurons of th e optic nerve. Th e medulla oblongata brain stem) processes these impulses,

which results in impulses being transmitted via neurons of th eparasympathetic syste m t o th e circular muscle fibres i n t he iris.

This causes const rict ion of th e pupil, so th e amOWll of lightentering th e eye is reduced a nd t he eye is protected from damage.

Doctors sometimes u se t he pupil reflex to te st a patient s brainfundion. A light is shone i nt o e ac h eye. f th e pupils do no tconstrict, th e medulla oblongata is probably damaged. f this an dother tests of brain stem function ar e repeated an d fail to shownonnaI activity, th e patient is said to have suffered brain death. tma y be possible to sustain activity in other parts of th e patient sbody on a life support machine, bu t recovery is extremely unlikely.

RITI L CONSIDERATIONS medical definitions of death

Option Neurobiology and behaviour aa

igur 22 Eye: dilated pupil

igur Eye: constricted pupil

Which of these standards: a is possible in practiceb is most appropriate for

ethical or other reasons.2 Some would argue that whatdefines a person is higher

brain function this is so isit possible, or reasonable, todistinguish between the deathof the body and the death of aperson?3 Supporters of euthanasiamight argue for a quality of lifestandard.Why is this definitionproblematic? Discuss theethical issues associated witheuthanasia.

For legal and ethical reasons, it is often necessary to clearly define when a human life has ended. For example, aperson may have expressed a wish that once dead, their healthy organs may be used for organ transplants. Humandeath can be established by several different criteria1 The biological standard: cessation of life of the whole organism.2 The cardiopulmonary standard: when the heart and lungs cease to function. This standard is problematic todaybecause heart and lung function can often be maintained indefinitely through artificial means.3 The whole-brain standard: if all parts of the brain including the brain stem are non-functional. The pupil reflex isone way to check if the brain stem is non-functional. Patients have survived for years with only the brain stem

functioning - known as a permanent vegetative state.4 The higher brain standard: death is considered to have occurred if the cerebral hemispheres have ceased tofunction, even if the brain stem is functioning and allowing homeostasis to continue. 333


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m 3 Option E Neurobiology and behaviourSocial organisationHoneybees ar e on e of th e best known of social organisms. They livei n col on ies o f thousands of bees co-operating to give th e colony as aw ho le th e colony th e best chance of survival. Individual bees cannotsurvive unless th e colony survives. The colony is l ike a s up er -organism with natural s el ecti on act in g at t hi s l ev el rather than at th elevel of th e individual b ee s i n it.There ar e three castes of honeybee:o Queens - fertile females on e only pe r colony who lays eggs.o Drones - fertile males several hundred pe r colony whose only

role is to search for virgin females a nd m at e w it h them.o W or ke rs - i nf er ti le fe male s thousands who carry ou t all th e tasks

needed in th e colony including foraging for food an d rearinglarvae

Often worker bees give up their lives while defending th e colony.They also help in rearing larvae though they do not usuallythemselves breed. Both these actions ca n be regarded as altruistic. Instudies of animal behaviour altruism is defined as actions thatincrease another individual s lifetime number of offspring at a cost toone s own survival an d reproduction.ltru smThe evolution of altruism is an interesting conundrum: i naturalseJection involves a struggle for existence in which th e winnersreproduce an d pass on their alleles to their offspring naturalselection should always act against altruism. is easier to understandth e evolution of co-operation - a group of animals who help eachother in some wa y may be more successful in th e overall struggle forexistence than animals that do not an d all o f them will increase theirchance of reproduction. Of course there are cases where cheating ormanipulation b y s om e individuals disrupts these relationships. Truealtruism always seems to involve animals that are genetically relatedw it h n at u ra l selection operating at th e leve l of alleles. In a honeybeecolony th e offspring that a worker helps to rear will usually be he rsiblings an d shaTe some of he r alleles. In fact because of t he wa y inwhich gender is determined in honeybees female siblings will onaverage share 75 p er c en t of their alleles. th e larvae that a workerrears become either queens or drones they will h av e t he chance ofreproducing an d passing o n s om e of the worker s alleles to bees inth e colony or another colony. This explains wh y workers toil so hardto ensure th e survival of th e colony - their alleles perish or survivewith it. Over mil li on s of y ears o f evolution an y colonies w he re t heworker bees did no t act altruistically to defend th e colony an d rearthe y ou ng will have died ou t a nd t he alleles that m ad e t he workersact non-altruistically will have disappeared too.

igur Naked mole ratsHeterocepho/us glober are socialmammals They live in undergroundcolonies of about 80 individuals Onlyone female reproduces but three othercastes help her: frequent workersinfrequent workers and non workersEach of these castes has different roles inthe colony

igur 5 Vampire bats living in groupsshare blood If a member of the groupfails to feed for several nights it is givenblood by another member of the groupThis happens even if the bats are notgenetically related so is regarded asaltruism ll the bats are vulnerable tostarvation if they fail to feed so theybenefit from this system of blood sharing

33 4


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30 Option Neurobiology and behaviour EaIII

Figure 26 Crab diet investigation

Foraging behaviourForaging is searching for food. Animals must decide what type of prey tosearch for and how to find it Studies have shown that animals tend tochoose the prey that gives the highest rate of energy relllm. For example,the shore crab Carcil1l1S II/omas prefers to eat mussels of intermeruate size,when presented in an aquarium with equal numbers of each size. AsFigure 26 shows, these give the highest energy yield per second of timespent breaking open the shells. For most animals, the availability of foodvaries over both space and time. Foraging behaviour may therefore need tochange, to optimize food intake at any moment Evidence for this has comefrom sturues of the bluegill sunfish Lepo lI is II/acrocilirus , which feed onsmall invertebrates, including Dapill1ia. Figure 27 shows how theconswnption of Dapill1ia of clifferent sizes changes as prey density increases.011 low prey intermediate nigh prey S sm llo E density prey density density mediumco0 l large0

0 S M l M l 0 S M lSize of prey

Figure 27 Sunfish prey size at different prey densities

a 1 1.5

1.0ol

0.5

bl 9 500 40@ SO.l 20

r1 0 2 0 3 0 4 0ize of mussel em

1 0 1 5 2-0 2 S 3-0ize of mussel/em

Rhythmical behaviourMany animal species show rhythmical variations inactivity. These can be over an annual cycle. Forexample, mate selection and mating in red deerCell/lls elaplws occurs in the aullmm As a result,calves are born in the spring, when most food isavailable. On the Great Barrier Reefmost speciesspawn together over just one or two nights, soonalter the full moon in November each year. This givesthe highest possible concentration of sperm and eggs,raising the chance of fertilization and reducing thechance of predation. Rhythmical behaviour patternscan also follow daily cycles, for example, diurnalsleep arld nocturnal activity in hamsters.

Exaggerated traitsSome species have behaviour patterns oranatomical features that seem to us to beexaggerated, for example the tail feathers of thepeacock. Darwin explained this by mate selection.In the case of the peacock, if female peahens prefermales with longer, more spectacularly coloured tailfeathers, such tails will develop by natural selection.Exaggerated traitsmay be preferred when selectinga mate because they indicate fitness. a peacockcan survive with the encumbrance of its tailfeathers, it is probably well adapted in olber waysand is therefore a good mate to moose

IData-based questions: rhythmi l eh viourp tterns IIAstudy was done of the flight behaviour of 6 :serotine bats Eptesicus serotinus , using radio sumis Itransmitters attached to the bats. Each line 4 I I :indicates the timing and length of a flight 2 I I I1 Outline the rhythmical behaviour pattern of the midnight 24 III \: : I :

bats in autumn. [3] Ii j I I I I2 a) Compare the behaviour of the bats in 22 1II 1 I \ :summer and autumn. [3] 2 r \ :b Suggest reasons for the differences in suns t , IIIII ll \ :behaviour. [2J 11 II3 Discuss whether the behaviour of the serotine 1600 Ibats shows any rhythmical variation. [2] spring summer utumn II Figure 28 Flight behaviour in serotine bats : 335

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