A2 Unit 5 Revision Cards

8/21/2019 A2 Unit 5 Revision Cards

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Jointsandmovementcontinued

Atajointthereis:

-tendon:joinsmuscletobone

-bone

-cartilage:absorbssynovialfluidandactsasshockabsorber

-padofcartilage:givesadditionalprotection

-fibrouscapsule:enclosesjoints

-muscle

-ligament:joinsbonetoboneandisstrongandflexible

-synovialmembrane:secretessynovialfluid

-synovialfluid:actsaslubricant

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Joints and movement

- muscles bring about movement at a joint

- muscles can only pull they cannot push so two muscles are needed to move a bone back and forth.

- a pair of muscles like these are called antagonistic.

- a muscle that contracts to cause extension of a joint is called an extensor

- a flexor contracts to reverse the movement

- the hip, knee and ankle joints are examples of synovial joints

- the bones that move in the joint are separated by a cavity filled with synovial fluid.

- the bones are held in position by ligaments that control and restrict movement.

-tendons attach muscles to the bones

- cartilage protects bones within joints.


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Insideamusclefibre

-eachmusclefibreismadeupofmyofibrils

-thesearemadeupofcontractileunitscalledsarcomeres

-thesarcomereismadeupoftwotypesofprotein,mainlyactin,andthickeronesmadefromthe

proteinmyosin.

-contractionsaremadebytheslidingoftheseproteinfilamentswithinthemusclesarcomeres.

-whereactinfilamentsappearontheirownthereisalightbandonthesarcomere.

-wherebothactinandmyosinfilamentsoccurthereisadarkband.

-thereonlymyosinfilamentsoccurthereisaintermediate-colouredband.

-whenthemusclecontractsthedarkbandoverlapstheintermediatebandshorteningthelength

ofthemuscleandthesarcomere.

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How do muscles work?

- muscle is made up of bundles of muscle fibres, each fibre is a single muscle cell

- each muscle cell is multinucleate (has more than one nucleus) this is because a single nucleus

could not effectively control the metabolism of such a long cell.

- Tendons connect muscle to bone

- the muscle is made up of bundles of muscle fibres. these are bound together by connective tissue.

- each muscle fibre is a single muscle cell surrounded by a cell surface membrane.

- Inside the muscle fibre is the cytoplasm containing mitochondria and the other organelles found

in a cell.

- Within each muscle fibre there are also numerous myofibrils, each is composed of repeated

contractile units called sarcomeres.


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Howthesarcomereshortenscontinued

-AnATPasemoleculeonthemyosinheadhydrolysestheATP,formingATPandPi.

-Thishydrolysiscausesachangeintheshapeofthemyosinhead.Itreturnstoitsupright

position.Thecyclestartsagain.

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How the sarcomere shortens

When a nerve impulse arrives at a neuromuscular junction calcium ions are released from the

sarcoplasmic reticulum. This moves the protein filaments in these steps:

- Ca2+ attaches to the troponin molecule, causing it to move.

- because of this the tropomyosin on the actin filament moves its position, exposing myosin binding

sites on the actin filaments.

- Myosin heads bind with myosin binding sites on the actin filament, forming cross-bridges.

- When the myosin head binds to the actin, ADP and Pi on the myosin head are released.

- the myosin changes shape, causing the myosin head to nod forward. This moves the filaments

and the actin moves over the myosin.

- An ATP molecule binds to the myosin head. this causes the myosin head to detach.


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Carbohydrateoxidation

InlowintensityexerciseenoughoxygenissuppliedtocellstoenableATPtoberegenerated

throughaerobicrespirationoffuels.

C6H12O6+6O2->6CO2+6H2O+energyreleased

-inaerobicrespirationthehydrogenstoredinglucoseisbroughttogetherwithoxygentoform

wateragain.

-thereisareleaseofenergythatcanbeusedtogenerateATP.

-glucoseandoxygenarenotbroughttogetherdirectlybecausethiswouldreleaselargeamounts

ofenergytooquicklyandcoulddamagethecell.

-glucoseissplitapartinaseriesofsmallsteps.Carbondioxideisreleasedasawasteproduct.

-hydrogenfromtheglucoseisreactedwithoxygentoreleaselargeamountsofenergyaswater

sformed.

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Releasing energy

The minimum energy requirement of the body at rest to fuel basic metabolic processes is called

your BMI.

Releasing energy:

- a series of enzyme-controlled reactions, known as respiration is linked to ATP synthesis.

- cells use the molecule ATP as an energy carrier molecule.

- ATP is created from ADP and inorganic phosphate (Pi)

- when one phosphate group is removed from the ATP by hydrolysis, ADP forms.

when removed the phosphate group becomes hydrated, a lot of energy is released as bonds form

between the water and phosphate.

ATP in water -> ADP in water + hydrated Pi + energy transferred


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Thelinkreaction

Ifoxygenisavailablethe3Cpyruvatecreatedattheendofglycolysispassesintothemitochondria.

Thereitiscompletelyoxidised,formingcarbondioxideandwater.

pyruvateis:

-decarboxylated(carbondioxideisreleasedasawasteproduct)

-dehydrogenated(twohydrogensareremovedandtakenupbythecoenzymeNAD)

The2carbonmoleculemadecombineswithcoenzymeAtoformacetylcoenzymeA(oracetyl

CoA)thetwohydrogensreleasedareinvolvedinATPformation.ThecoenzymeAcarriesthe2C

acetylgroupstotheKrebscycle.

-eachglucoseprovidestwopyruvatessothecycleturnstwiceperglucose.

-thehydrogensaretakenupbyhydrogenacceptors(FADandNADwhichthenbecomereduced

FADandreducedNAD)

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Glycolysis

The initial stages of carbohydrate breakdown occur in the cytoplasm, including the sarcoplasm of muscle cells.

- two phosphate groups are added to glucose from two ATP molecules, this increases its reactivity. It can now split into

two molecules of 3-carbon (3C) compounds.

- each intermediate 3C sugar is oxidised producing a 3-carbon compound, pyruvate.

- two hydrogen atoms atoms are removed during the reaction and taken up by the coenzyme NAD, a non-protein organic

molecule.

- phosphate from the intermediate compounds is transferred to ADP, creating ATP.

- this is called substrate level phosphorylation, because energy for the formation of ATP comes from the substrates ( the

intermediate compounds.)

- two ATP's are made, two pairs of hydrogen atoms and two molecules of 3-carbon pyruvate.


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TheKrebscyclecontinued

TheKrebscycletakesplaceinthemitochondrialmatrix,wheretheenzymesthatcatalysethereactionsarelocated.

-each2-carbonacetylCoAcombineswitha4-carboncompoundtocreateonewith6carbons.

-inacircularpathwayofreactionstheoriginal4-carboncompoundisrecreated.

Each2-carbonmoleculeenteringtheKrebscycleresultsintheproductionof:

-twocarbondioxidemolecules.

-onemoleculeofATPbysubstrate-levelphosphorylation.

-andfourpairsofhydrogenatoms,whicharetakenupbyhydrogenacceptors.

-fattyacidscanalsoberespiredtoreleaseenergy.

-fattyacidsarebrokendowngeneratingthesame2-carboncompoundwhichcanbeputintotheKrebscycleforoxidation.

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The Krebs cycle


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ATPsynthesisbychemiosmosis

howtheelectrontransportchainleadstoATPsynthesis:

-energyisreleasedaselectronspassalongtheelectrontransportchain

-thisenergyisusedtomovehydrogenionsfromthematrix,acrosstheinnermitochondrial

membrane,andintotheintermembranespace.

-thiscreatesasteepelectrochemicalgradientacrosstheinnermembrane

-makingtheintermembranespacemorepositivethanthematrix

-thehydrogenionsdiffusedowntheelectrochemicalgradientthroughhollowproteinchannelsin

stalkedparticlesonthemembrane

-asthehydrogenionspassthroughthechannelATPsynthesisiscatalysedbyATPaseineach

stalkedparticle

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The electron transport chain

- reduced coenzyme carries H+ and electron to electron transport chain on inner mitochondrial

membrane.

- Electrons pass from one electron carrier to the next in a series of redox reactions; the carrier is

reduced when it receives the electrons and oxidised when it passes them on.

- protons (H+) move across the inner mitochondrial membrane creating high H+ concentrationsin the intermembrane space.

- H+ diffuse back into the mitochondrial matrix down the electrochemical gradient.

- H+ diffusion allows ATPase to catalyse ATP synthesis.

-Electrons and H+ ions recombine to form hydrogen atoms which then combine with oxygen to

create water.

- if the supply of oxygen stops the electron transport chain and ATP synthesis stops.


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HowmuchATPisproduced?continued

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ATP synthesis by chemiosmosis continued

- the hydrogen ions cause a change in shape in the enzymes active site so the ADP can bind

- within the matrix the H+ and electrons re combine to form hydrogen atoms

- these combine with oxygen to form water

- the oxygen acts as the final carrier in the electron transport chain and is therefore reduced

- this method of synthesising ATP is known as oxidative phosphorylation

How much ATP is produced?

The maximum number of ATP's that can be made per glucose is 38

This is based on the assumption that:

- each reduced NAD that is reoxidised forms 3 ATP molecules

- each reduced FAD results in the production of two ATP molecules


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Anaerobicrespiration

Inexerciseoxygendemandinthecellsexceedssupply:

-withoutoxygentoacceptthehydrogenionsandelectronstheelectrontransportchaindoesnot

work:

-ThereducedNADcreatedduringglycolysis,thelinkreactionandthekrebscycleisnotoxidised.

-mostrespirationreactionscannotcontinue.

-itispossibletooxidisethereducedNADwithoutoxygen.

-thepyruvatecreatedduringglycolysisisreducedtolactateandtheoxidisedformofNADis

regenerated.

-anaerobicrespirationpartiallybreaksdownglucosetomakeasmallamountofATP.

-thenetyieldisjust2ATPmoleculesperglucosemolecule.

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Rate of respiration

n small organisms the rate of respiration can be determined by measuring the uptake of oxygen using a respirometer.

- respiration is a series of enzyme-controlled reactions

- it is affected by enzyme concentration, substrate concentration, temperature and pH.

- the concentration also has a role in the control of respiration.

- ATP inhibits the enzyme in the first step of glycolysis.

The enzyme responsible for glucose phosphorylation can exist in two forms:

- in the presence of ATP the enzyme has a shape that makes it inactive so it cannot catalyse the reaction.

- as ATP is broken down the enzyme becomes an active form and catalyses the phosphorylation of glucose.

- this is end point inhibition: the end product inhibits an early step in the metabolic pathway which controls the whole precess.


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Gettingridoflactate

-mostlactateisconvertedbackintopyruvate.

-itisoxidiseddirectlytocarbondioxideandwaterviatheKrebscycleandreleasesenergytosynthesisATP.

-sooxygenuptakeisgreaterthannormalintherecoveryperiodafterexercise.

-thisoxygenrequirementiscalledtheoxygendebtorpost-exerciseoxygenconsumption.

-itisneededtofueltheoxidationoflactate.

-somelactatemayalsobeconvertedintoglycogenandstoredinthemuscleorliver.

Yeastcellscopedifferentlywithanaerobicconditions:

-theyreducepyruvatetoethanolandcarbondioxideusingthehydrogenfromreducedNAD.

-thisrecreatesoxidisedNADandallowsglycolysistocontinue.

-thisiscalledalcoholicfermentation.

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The effect of lactate bulid-up

The end product of anaerobic respiration is lactate:

- it builds up in the muscles and must be disposed of

- lactate forms lactic acid in solution so as lactate accumulates the pH of the cell falls inhibiting the

enzymes that catalyse the glycolysis reactions.

- enzymes function best over a narrow pH range.

- as hydrogen ions from the lactic acid accumulate in the cytoplasm they neutralise the negatively

charged groups in the active site of the enzyme.

- the attraction between charged groups on the substrate and in the active site will be affected.

- the substrate may no longer bind to the enzymes active site.


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Threeenergysystems

-Atthestartofexerciseaerobicrespirationcannotmeetthedemandsforenergybecausethe

supplyofoxygentothemusclesisinsufficient.

-thelungsandcirculationarenotdeliveringoxygenquicklyenoughandATPwillberegenerated

withoutusingoxygen.

-firsttheATP/PCsystemandthentheanaerobicrespirationsystemallowATPregeneration.

-inendurancetypeexerciseanincreasedbloodsupplytothemusclesensureshigheroxygen

supplytothemusclecells.

-aerobicrespirationcanregenerateATPasquicklyasitisbrokendown.

-thisallowstheexercisetobesustainedforlongperiods.

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Supplying instant energy

- at the start of exercise immediate regeneration of ATP is achieved using creatine phosphate (PC)

- this is a substance stored in muscles that can be hydrolysed to release energy.

- This energy can be used to regenerate ATP from ADP and phosphate, the phosphate is given

by the creatine phosphate.

- creatine phosphate breakdown starts as soon as exercise starts.

creatine phosphate -> creatine + Pi

ADP + Pi -> ATP

- the reactions do not require oxygen and provide energy for 6-10 seconds of intense exercise.

- this is known as the ATP/PC system its is used for regeneration of ATP.


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Cardiacoutputandstrokevolume

Cardiacoutput

thevolumeofbloodpumpedbytheheartinoneminute.

Cardiacoutputdependsonthevolumeofbloodejectedfromtheleftventricle(thestrokevolume)andtheheartrate:

Cardiacoutput(CO)=strokevolume(SV)xheartrate(HR)

Strokevolume

Isthevolumeofbloodpumpedoutoftheleftventricleeachtimetheventriclecontracts.

-howmuchbloodtheheartpumpsoutwitheachcontractionisdeterminedbyhowmuchbloodisfillingtheheart,thisis

thevolumeofbloodreturningtotheheartfromthebody.

-duringexercisethereisgreatermusclecontractionsomorebloodreturnstotheheartthisiscalledvenousreturn.

-indiastoleduringexercisetheheartfillswithalargervolumeofblood.

-theheartmuscleisstretchedtoagreaterextent,thisincreasesstrokevolumeandcardiacoutput.

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Peak performance

- being able to go for long periods of strenuous exercise depends on maintaining a constant supply

of ATP, and this depends on aerobic capacity: ability to take in/transport/use oxygen.

- VO2 is the volume of oxygen we consume per minute.

- VO2(max) is the maximum amount of oxygen we can consume per minute.

- cardiac output is the volume of blood pumped by the heart in a minute.

When running oxygen supply is maintained by:

increasing cardiac output

faster rate of breathing

deeper breathing


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Howdoestheheartbeat?

-theheartismyogenic;itcancontractwithoutexternalnervousstimulation.

-contractionofcardiacmuscleisinitiatedbysmallchangesintheelectricalchargeofcardiac

musclecells.

-whenthesecellshaveaslightpositivechargeontheoutsidetheyarepolarised.whenthischarge

isreversedtheyaredepolarised.

-thispolarityspreadsamongstthecellsandcausesthemtocontract.

-depolarisationstartsandthesinoatrialnode(SAN).

-theSANisasmallareaofspecialisedmusclefibreslocatedinthewalloftherightatriumbeneath

theopeningtothesuperiorvenacava.

-thesinoatrialnodeisalsoknownasthepacemaker.

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Heart rate

differences in resting heart rate are caused by:

different size

body size

genetic factors

- A larger heart usually has a lower resting hear rate.

- It will expel more blood with one beat and so does not have to beat as frequently to keep the

circulation of blood constant.

- Endurance training produces a lower resting heart rate

- this is because increase in size of the heart

- resulting from thickening of the muscle cell walls.


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Measuringelectricalactivity

-theelectricalactivitycanbedetectedanddisplayedonanelectrocardiogram(ECG).

-itisthemostcommontesttocheckforproblemswiththeheart.

-electrodesareattachedtotheperson'schestandlimbstorecordtheelectricalcurrentsproduced

duringthecardiaccycle.

-whenthereisachangeinpolarisationofthecardiacmuscle.

-thereisasmallelectricalcurrentthatcanbedetectedontheskinssurface.

-anECGisusuallyperformedwhenthepatientisatrest.

-butitisalsousedtodetectheartproblemsonlywhentheheartisworkinghard.

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How does the heart beat? continued

- the SAN generates an electrical impulse this spreads across the left and right atria causing them

to contract at the same time.

- the impulse then travels to some specialised cells called the atrioventricular node (AVN)

- the impulse is then sent to the ventricles after a delay of 0.13 seconds. this delay makes sure

the atria have fully contracted.

- the signal then reaches the purkyne fibres. these are large specialised muscle fibres that conduct

impulses to the apex of the ventricles.

- there are right and left bundles of fibres and these together are called the bundle of His.

- the purkyne fibres continue around each ventricle so the impulse makes the ventricles contract

from the apex upwards.

- this is so the blood is pushed upwards into the aorta and pulmonary artery.


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ECG

-aheartrateoflessthan60bpmisknownasbradycardia.

-aheartrateofmorethan100bpmisknownastachycardia.

-duringaperiodofischaemiatheheartmuscledoesnotreceivebloodduetoatherosclerosis

causingblockageofthecoronaryarteries.

-thiscausesthenormalelectricalactivityandrhythmofthehearttobedisrupted.

-andarrhythmiasiscausedwhichisirregularbeatingsoftheheartcausedbyelectrical

disturbances.anECGcanprovideinformationabout:

abnormalheartbeats

areasofdamage

inadequatebloodflow

-hypertrophiccardiomyopathy:isaninheritedconditioninwhichgenemutationscauseabnormally

thickwallsintheleftventricle.

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What does an ECG trace show us?

- P wave: depolarisation of the atria leading to atrial contraction (atrial systole)

- PR interval: the time taken for impulses to be conducted from the SAN across the atria to the

ventricles, through the AVN.

- QRS complex: the wave of depolarisation resulting in contraction of the ventricles (ventricular

systole).

- T wave: repolarisation (recovery) of the ventricles during the hearts relaxation phase (diastole).

- the ECG does not show atrial repolarisation because the signals generated are small and are

hidden by the QRS complex.

- you can work out the time for one complete cardiac cycle by: multiplying the the number of

squares between QRS complexes by 0.2 and then doing 60 divided by the answer.


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Hormonaleffectsonheartrate

-fear,excitementandshockcauseareleaseofthehormoneadrenalineintothebloodfromthe

adrenalglandslocatedabovethekidneys.

-adrenalinehasaneffectonthehearratesimilartostimulationbythesympatheticnerve.

-ithasdirectontheSANincreasingtheheartratetopreparethebodyforphysicaldemands.

-adrenalinealsocausesdilationofthearteriolessupplyingskeletalmuscles

-italsocausesconstrictionofarteriolesgoingtothedigestivesystemandothernon-essential

organs.

-thismaximisesbloodlowtotheactivemuscles.

-adrenalinecausesananticipatoryincreaseinhearratebeforethestartofarace.

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Nervous control of heart rate

- heart rate is under the control of the cardiovascular control centre located in the medulla of the

brain.

- nerves forming the part of the autonomic nervous system lead from the cardiovascular control

centre to the heart.

- there are two nerves going from the cardiovascular control centre to the heart

sympathetic nerve (accelerator)

vagus nerve which is a parasympathetic nerve (decelerator)

- stimulation of the SAN by the sympathetic nerve increases the heart rate whereas impulses from

the vagus nerve slow down the heart rate.

- the cardiovascular control centre detects accumulation of carbon dioxide and lactate in the blood,

reduction of oxygen, and increased temperature.

- mechanical activity in the muscles and joins is detected by sensory receptors in muscles, and

impulses are sent to the cardiovascular control centre.


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Thecontrolofbreathing

-Theventilationcentreinthemedullaoblongataofthebraincontrolsbreathing.

Inhalation

-theventilationcentresendsnerveimpulsesevery2-3secondstotheexternalintercostalmusclesanddiaphragmmuscles.

bothsetsofmusclescontractusinginhalation.

-wheninhalingtheexternalintercostalsanddiaphragmmusclesarealsoused.

Exhalation

-asthelungsinflatestretchreceptorsinthebronchiolesarestimulated.

-thestretchreceptorssendinhibitoryimpulsesbacktotheventilationcentre.

-impulsestothemusclesstopandthemusclesrelaxstoppinginhalationandallowingexhalation.

-exhalationiscausedbytheelasticrecoilofthelungsandgravityhelpingtolowertheribs.

-theinternalintercostalmusclesonlycontractduringdeepexhalation.

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Lung volumes

- the volume of air we breathe in and out at each breath is our tidal volume (at rest around 0.5 dm3).

- the maximum volume of air we can inhale and exhale is out vital capacity (most people 3-4 dm3).

- lung volumes can be measured using a spirometer.

- the volume of air taken into the lungs in one minute is the minute ventilation. This is calculated by:

minute ventilation = tidal volume x breathing rate


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Controllingbreathingduringexercise

whatcontrolsbreathing?:

-impulsesfromthemotorcortexhaveadirecteffectontheventilationcentrein

themedullaincreasingventilationsharply.

-ventilationisalsoincreasedinresponsetoimpulsesreachingtheventilation

centrefromstretchreceptorsintendonsandmusclesinvolvedinmovement.

-thevariouschemoreceptorssensitivetoCO2levelsandtochangesinblood

temperatureincreasethedepthandrateofbreathingviatheventilationcentre.

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Controlling breathing rate and depth

an important stimulus controlling the breathing rate and depth is the concentration of dissolved CO2

in the arterial blood. a small increase in CO2 concentration causes a large increase in ventilation:

- carbon dioxide dissolves in the blood plasma, making carbonic acid.

- carbonic acid dissociates into hydrogen ions and hydrogencarbonate ions, this lowers the pH

of the blood

CO2 + H2O H2CO3 H+ + HCO3-

- chemoreceptors sensitive to hydrogen ions are located in the ventilation centre of the medulla

oblongata. they detect a rise in H+ concentration.

- impulses are sent to other parts of the ventilation centre

- impulses are sent from the ventilation centre to stimulate the muscles involved in breathing.


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Fasttwitchfibres

-theyarespecialisedtoproducefastcontractions

-theATPusedinthesecontractionsisproducedalmostentirelyfromanaerobicglycolysis.

-thefasttwitchfibreshavefewmitochondria,highglycogencontent,andextensivesarcoplasmic

reticulum.

-theyalsohaveverylittlemyoglobinsotheyhavefewreservesofoxygenandfewassociated

capillaries.

-theyrelyonanaerobicrespirationwhichmeansthereisarapidbuildupoflactate,sothefast

twitchmusclefibresfatigueeasily

-withaerobictrainingfasttwitchfibrescantakeonsomeofthecharacteristicsofslowtwitchfibres

-forexampletheycouldhavemoremitochondriaallowingthemtouseaerobicrespirationreactions

whencontracting.

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Slow twitch fibres

- slow twitch fibres are specialised for slower sustained contraction

- they can cope with long periods of exercise to do this they carry out a lot of aerobic respiration

- they have many mitochondria and high concentrations of respiratory enzymes to carry out the

aerobic reactions.

- they also have a little sarcoplasmic reticulum and a low glycogen content.

- they also contain large amounts of the dark red pigment myoglobin.

- it has a high affinity for oxygen, and only releases it when the concentration of oxygen in the

cells falls very low.

- it acts as an oxygen carrier within muscle cells

- slow twitch fibres are associated with numerous capillaries to ensure a good oxygen supply.


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Temperaturecontrol

-thermoregulationisthecontrolofbodytemperature.

-ourbodystaysataround37degrees,thisallowsenzyme-controlledreactionstooccurata

reasonablerate.

-Atlowertemperaturesthereactionswouldoccurtooslowlyforthebodytoremainactive,and

athighertempstheenzymescoulddenature.

-inhumanstemperatureismaintainedbyanegativefeedbacksystem.

-thesysteminvolvesreceptorsthatdetectchangesinthebloodtemperature.thesereceptorsare

locatedinthehypothalamus.

-theyhypothalamusdetectschangesandturnsoneffectorswhenneededtoreturntonormtemp.

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Homeostasis

- homeostasis is the maintenance of a stable internal environment.

- this is partly achieved by maintaining stable conditions within the blood.

- in the blood the concentration of glucose, ions, carbon dioxide, water potential, pH and

temperature of the blood also needs to be kept within narrow limits.

- each condition that is controlled has a norm value or a set point that the homeostatic mechanisms

are trying to maintain.

- receptors are used to detect changes from the norm.

- these receptors are connected to a control mechanism which turns on or off effectors to bring

conditions back to the norm.


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Temperaturecontrol:Sweatandhairs

Sweat:

-sweatreleasedviathesweatductsevaporatestakingenergyfromtheskin

-sweatglandsarestimulatedbynervesfromthehypothalamus

Hairs:

-theyareraisedincoldweatherbycontractionsoftheerectormuscles.

-thisisareflexwehavenocontrolover.

-theaimistotrapalayerofairthatinsulatesthebody.

-althoughduetoourshortageinhairthisisbetterinothermammalsandbirdscomparedwith

humans.

-mostofuswearclothesforfurtherinsulation.

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Temperature control continued

Heat loss centre: stimulates - sweat glands to produce sweat.

inhibits - contraction of arterioles in skin (dilates capillaries in the skin)

- hair erector muscles (relax - hairs lie flat)

- liver (reduces metabolic rate)

- skeletal muscles (relax - no shivering)

Heat gain centre: Inhibits - sweat glands

stimulates - arterioles in the skin to constrict

- hair erector muscles to contract

- liver to raise metabolic rate

- skeletal muscles to contract in shivering


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Temperaturecontrol:Skin

whenwarm:

-constrictionofthearteriolesandshuntsiscontrolledbythehypothalamus.

-inwarmconditionstheshutvesselconstrictsandmusclesinthewallsofthearteriolesrelax.

-bloodflowsthroughthearteriolesmakingthemdilate.

-bloodflowsclosertothesurfacesomoreenergyislost.

-thisisknownasvasodilation.

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Temperature control: Skin

when cold:

- energy is lost from the blood flowing through the surface capillaries by radiation.

- in cold condition the muscles in the arteriole walls contract causing the arterioles to constrict

- this reduces the blood supply to the surface capillaries.

- blood is diverted through the shunt vessel which dilates as more blood goes through it.

- blood flows further from the skin surface so less energy is lost.

- this is known as vasoconstriction.


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Methodsofenergytransfer

Radiation:

-energycanberadiatedfromoneobjecttoanotherthroughair,orthrougha

vacuum,aselectromagneticradiation.

-ourbodiesareusuallywarmerthanthesurroundingenvironmentsoweradiate

energy.

Conduction:

-energylossbyconductioninvolvesdirectcontactbetweenobjects,andenergytransferfromonetotheother.

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How energy is transferred to and from the body

Energy transfer:

- sweat evaporation increases energy loss.

- evaporation from moist surfaces of lungs increases energy loss.

- arteriole vasoconstriction decreases blood flow to skin reducing energy loss by conduction,

convection and radiation.

- arteriole vasodilation increases blood flow to skin increasing energy loss by conduction,

convection and radiation.

- Hairs raised by contraction of erector muscles reduces energy loss by conduction, convection

and radiation.

- voluntary muscle contraction and involuntary shivering release energy, raising body temperature.


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Excessiveexerciseandimmunesuppression

-athletesengagedinheavytrainingprogrammesseemmorepronetoinfection

thannormal.

-upperrespiratorytractinfections(sorethroatandflu-likesymptoms)aremost

common.

-twomainfactorsthatcancontributetohigherinfectionrates:

increasedexposuretopathogensandsuppressedimmunitywithhardexericise

-somescientistsbelievethereisaU-shapedrelationshipbetweenriskofinfection

andamountofexercise.

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Methods of energy continued

Convection:

- air lying next to the skin will be warmed by the body

- as the air expands and rises it will be replaced by cooler air which is then warmed by the body.

- the energy loss by bulk movement of air is called convection.

Evaporation:

- energy is needed to convert water from liquid to vapour.

- the energy required to evaporate sweat is drawn from the body cooling it.

- in conditions with high humidity it is much harder to evaporate sweat.

- some animals pant to keep cool, by evaporation of water from gas exchange surfaces.


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Effectsofexericeonimmunitycontinued

Vigorousexercise:

-aftervigorousexercisethenumberofsomecellsintheimmunesystemfalls:

naturalkillercells

phagocytes

Bcells

Thelpercells

-thedecreaseinThelpercellsreducestheamountofcytokinesavailabletoactivatelymphocytes.

-thisthenreducestheamountofantibodybeingproduced.

-physicalexerciseandpsychologicalstresscausesecretionofhormonessuchasadrenalineand

cortisol.

-bothofthesehormonesareknowntosuppresstheimmunesystem.

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Effects of exerice on immunity

- components of the non-specific and specific immune systems are effected by both moderate and excessive exercise.

Moderate exercise:

- increases the number of a lymphocyte called natural killer cells.

- they are found in the blood and lymph

- they are not like B and T cells because they do not use specific antigen recognition.

- they provide non-specific immunity against cells invaded by viruses and cancerous cells.

- they are sctivated by cytokines and interferons and they target cells that are non self

- they release the protein perforin which makes pores in the targeted cell membrane.


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Howcanmedicaltechnologyhelp?

Keyholesurgery:

-usingfibreopticsorminutevideocameras

-itispossibletorepairdamagedjointsortoremovediseasedorgansthroughsmallholes.

-keyholesurgeryonjointsisknownasarthroscopy.

-damagetothecruciateligamentsinthekneecanbetackledparticularywellwithkeyholesurgery.

Prostheses:

-isanartificialbodypartusedbysomeonewithadisabilitytoenablehimorhertoregainnear tonormalfunction.

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How are joints damaged by exercise

- professional athletes risk developing joint injuries bue to high forces the sport generates on their

joints.

- repeated forces on such joints of the knee can lead to wear or tear in the joint.

- knees are particularly susceptable to wear and tear injuries:

the articular cartilage covering the surfaces of the bones wears away and they grind on

eachother causing damage.

Patellar tendonitis occurs when the kneecap (patella) does not glide smoothly across the

femur due to damage of the articular cartilage on the femur.

the fluid sacs swell up with extra fluid, as a result they may push against other tissues in

the joint causing inflamtion.

sudden twisting or abrupt movement of the knee often result in damage to the ligaments.


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Hormones

-hormonesarechemicalmessengersthatarereleaseddirectlyintothebloodfromendocrineglands.

-mostareproducedeitherinaninactiveformorpackagedwithinsecretoryvesiclesbythegolgiapparatus.

-thevesiclesfusewiththecellsurfacemembranereleasingtheircontentbyexocytosis.

glandsandhormones:-

pituitarygland:hormone-growthhormone

-follicle-stimulatinghormone

-antidiuretichormone

Function-stimulatesgrowth

-controlestestesandovaries

-causesreabsoptionofwaterinkidneys

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Taking enough exercise

Advantages of doing exercise:

- increasing arterial vasodilartion lowers blood pressure (reduces the risk of CVD)

- increases the lovel of blood HDLs which transport cholesterol to the liver where it is broken down.

- reduces LDLs which are associated with the development of atherosclerosis.

- helps maintain a healthy weight.

- increased sensitivity of muscle cells to insulin improves blood glucose regulation, and reduces

the likelihood of getting type II diabetes.

- increases bone density and reduces its loss during old age.

- reduces the risk of getting some cancers

- improves mental well-being.


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Hormonescontinued

glandsandhormones:

Ovary:hormone-oestrogen

function-promotesdevelopmentofovaries

-promotesfemalesecondarysexualcharacteristics

testis:hormone-testosterone

function-promotesdevelopmentofmalesecondarysexualcharacteristics

-eachhormoneaffectsonlyspecifictargetcellsmodifyingtheiractivity

-hormonesarecarriedaroundbythebloodstream

-theyeitherentrthetargetcellsortheybindtocomplimentaryreceptormoleculesontheoutside

ofthecellmembranes.

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Hormones continued

glands and hormones:-

Thyroid gland: hormone - thyroxine

function - raises basal metabolic rate

Adrenal gland: hormone - arenaline

function - raises basal metaboic rate

- dilates blood vessels

- prepares the body for action

Pancreas: hormone - insulin

function - lowers blood glucose concentration


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Howtranscriptionfactorswork

Intranscriptiononlyoccurswhenthetranscriptioninitiationcomplexisformed.

Repressormolecules:

-proteinrepressormoleculescanattachtothetranscriptionfactors

-thispreventsthemfromformingthetranscriptoninitiationcomplex.

-sothegeneisswitchedoffandisnottranscribedwithinthecell.

Activatormolecules:

-activatormoleculesstimulatethebindingofthetranscriptioninitiatoncomplex.

-genesareswitchedonbysuccessfulformationandattachmentofthetranscriptioninitiation

complextothepromoterregion

-thetranscriptionfactorsattachtheRNApolymerasetothepromoterregion.

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How hormones affect cells

- peptide hormones are protein chains

- even though they are relatively small molecules they can not pass through cell membranes easily

because they are charged

- they bind to a receptor on the cell membrane

- this receptor activates another molecule in the cytoplasm called a second messenger

- the second messenger brings about chemical changes in the cell by affecting gene transcription

- steroid hormones are formed from lipids and have complex ring structures.

- the hormone- receptor complex functions as a transcription factor, switching enzyme synthesis

on or off.


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Hormonesusedtoenhanceperformancecontinued

Creatine:

-isnotbanned

-itisconsideredtobeanutritionsupplement

-itisaminoacidderived

-itisnaturallyfoundinmeatandfish

-onceingesteditisabsorbedandunchangedandcarriedinthebloodtotissues

-itisalsosynthesisedinthebodyfromtheaminoacidsglycineandarginine

-somesideeffectsincludediarrhoea,nausea,vomiting,highbloodpressure,kidneydamageand

musclecramps.

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Hormones used to enhance performance

Erythropoietin:

- is a peptide hormone produced naturally by the kidneys

- it stimulates the formation of new red blood cells in bone marrow

- it can be made using DNA technology and is used to treat anaemia

- if you have too much it can make the body produce too many red blood cells and can cause heart attack and stroke.

Testosterone:

- is a steroid hormone

- produced in the testes by males and in the adrenal glands in males and females

- testosterone is in a group of male hormones called androgens

- it causes the development of the male sexual organs

- testosterone binds to androgen receptors


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Nervoussystemcontinued

ThePeripheralnervoussystemisdividedinto:

Autonomicnervoussystem:

involuntary

stimulatessmoothmuscle,cardiacmuscleandglands

Somaticnervoussystem:

voluntary

stimulatesskeletalmuscle

Autonomicnervoussystemisdividedinto:

Sympatheticnervoussystem:

preparesbodyfor'fight'or'flight'responses

Parasympatheticnervoussystem:

preparesbodyfor'restanddigest'

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Nervous system

The nervous system is divided into:

The central nervous system:

Brain spinal cord

Peripheral nervous system:

sensory nerves - carrying sensory information from the receptors to the

CNS motor nerves - carrying the motor commands from the CNS to the effectors


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Neuronescontinued

Relayneurone:

thecellbodyisinthemiddleoftheaxon

theyarefoundmostlywithintheCNS

theycanhavealargenumberofconnectionswithothernervecells

theyarealsoknownasconnectorneuronesandasinterneurones

Myelinsheath:

isafattyinsulatinglayeraroundtheaxon

madeofschwanncellswrappedaroundtheaxon

iteffectshowfastnerveimpulsespassalongtheaxon

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Neurones

There are two types of main extensions from the cell body of a neurone:

dendrites that conduct impulses towards the cell body

the axon which transmits impulses away from the cell body

Motor neurone:

cell body is at the end of the neurone

its situated within the CNS

it conducts impulses from the CNS to effectors (muscles or glands)

they are also known as effector neurones

sensory neurones:

cell body is attached to the middle of the axon

they carry impulses from sensory cells to the CNS


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Thepupilreflex

Howdothemusclesoftheirisrespondtolight?:

theiriscontrolsthesizeofthepupil

itcontainsapairofantagonisticmuscles;radicalandcircularmuscles

thesearebothcontrolledbytheautonomicnervoussystem

theradicalmusclesarecontrolledbysympatheticreflex

thecircularbyparasympatheticreflex

Pupilconstricted:

radialmusclesrelax

circularmusclescontract

Pupildilated:

radialmusclescontract

circularmusclesrelax

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Reflex arcs

nerve impulses follow routes or pathways through the nervous system. These pathways are called

reflex arcs and are responsible for our reflexes.

An example is a reflex arc allowing withdrawal of the arm:

Receptors detect a stimulus and generate a nerve impulse

sensory neurones conduct a nerve impulse to the CNS along a sensory pathway sensory neurones enter the spinal cord through the dorsal route

sensory neurone forms a synapse with a relay neurone

relay neurone forms a synapse with a motor neurone that leaves the spinal cord through

the ventral route

motor neurone carries impulses to an effector which produces a response

in this case the bicep contracts to raise the arm away from the flame


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Therestingpotential

1.Na+/K+pumpcreatesconcentrationgradientsacrossthemembrane

2.K+diffuseoutofthecelldowntheK+concentrationgradientmakingtheoutsideofthe

membranepositiveandtheinsidenegative

3.theelectricalgradientwillpullbackK+intothecell

4.at-70mVpotentialdifferencethetwogradientscounteracteachotherandthereisnonet

movementofK+

Whyistheaxonrestingpotential=70mV?

therearetwoforcesinvolvedinthemovementoftheK+ions:

theconcentrationgradientgeneratedbytheNa+/K+pump

theelectricalgradientduetothedifferenceinchargeonthetwosidesofthemembrane

resultingfromK+diffusion

theelectricalgradientbalancesoutthechemicalgradientandthereisnonetmovementofK+so

asteadystateexists.

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Inside a resting axon

all cells have a potential difference across their surface membrane

the inside of the axon is more negative then he outside so the membrane is said to be

polarised

the value of -70 mV is known as resting potential

Why is there a potential difference?:

the uneven distribution of ions across the cell surface membrane is achieves by the action

of sodium-potassium pumps

they carry Na+ out of the cell

and carry K+ into the cell

these pumps act against the concentration gradients

and are driven by energy supplied by hydrolysis of ATP

the organic anions are large and stay within the cell

so chloride ions move out of the cell to help balance the charge


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Whatcausesanactionpotential?

1.Depolarisation

whenaneuroneisstimulatedsomedepolarisationoccurs

thischangeinthepotentialdifferencechangestheshapeoftheNa+gate

thisopenssomeofthevoltage-dependentsodiumionchannels

astheNa+ionsflowindepolarisationincreasestriggeringmoregatestoopen

theopeningofmoregatesincreasesdepolarisationfurther

thisisanexampleofpositivefeedback

thereisahigherconcentrationofNa+ionsoutsideoftheaxon

soNa+ionsflowrapidlyinwardsthroughtheopenvoltage-dependentNa+channels

causingabuild-upofpositivechargesinsidethisreversesthepolarityofthemembrane

thepotentialdifferenceacrossthemembranereaches+40mV

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What happens when a nerve is stimulated?

- if an electrical current above the threshold level is applied to the membrane it causes a massive

change in the potential difference

- the potential difference across the membrane is locally reversed

- this makes the inside of the axon positive and the outside negative

- this is known as depolarisation

- the potential difference becomes +40 mV for a very short time

- it then returns to its resting potential so more impulses can be conducted

- this is known as repolarisation

- the large change in voltage across the membrane is known as an action potential


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Howistheimpulsepassedalonganaxon?

-whenaneuroneisstimulatedittriggersasequenceofactionpotentialsalongthelengthoftheaxon

-atrestingpotentialthereisapositivechargeontheoutsidewithhighNa+concentrationandanegativechargeinside

withahighconcentrationofK+ions

-whenstimulatedvoltage-dependentNa+ionsopenandNa+ionsflowintotheaxondepolarisingthemembrane

-theNa+ionsmovetotheareainthemembranewherechangeiscausingtheelectricalchargetochange

-thechangeinpotentialdifferenceinthemembranenexttothefirstactionpotentialcausesasecondactionpotential

-atthesiteofthefirstactionpotentialtheNa+channelscloseandtheK+channelsopen

-K+ionsleavetheaxonrepolarisingthemembraneanditbecomeshyperpolarised

-athirdactionpotentialisstartedbythesecondone

atthesiteofthefirstactionpotentialK+ionsdiffusebackintotheaxonrestoringrestingpotential

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What causes an action potential? continued

2. Repolarisation

the voltage-dependent Na+ channels close

and the permeability of the membrane to Na+ ions decreases

voltage-dependent K+ channels open due to the depolarisation of the membrane

because of this K+ channels open due to the depolarisation of the membrane

K+ ions move out of the axon down the electrochemical gradient because they areattracted by the negative charge outside of the cell

as K+ ions move out of the cell the inside of the cell becomes more negative than the

outside

3. Restoring the resting potential

the membrane is now very permeable to K+ ions and more ions move out

making the potential difference more negative than the normal resting potential, this is

called hyperpolarisation of the membrane the resting potential is back by closing K+ channels and opening Na+


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Howdoesanervousimpulsepassbetweencells

-wheretwoneuronesmeetisknownasasynapse

-thecellsdonottouchthereisagapknownasasynapticcelft

-thesynapticcleftseparatesthepresynapticmembranewhichtheimpulsearrivesatfromthe

postsynapticmembraneoftheothercell

-anerveimpulsecannotjumpacrossthegap

-inthecytoplasmattheendofthepresynapticneuronetherearesynapticvesicles

-thesesynapticvesiclescontainachemicalcalledaneurotransmitter

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Speed of conduction

- the speed of nervous conduction is in part determined by the diameter of the axon

- in general the wider the diameter the faster the impulse travels

- the myelin sheath acts as an electrical insulator along the axon

- it prevents any flow of ions across the membrane

- gaps known as nodes of Ranvier occur in the myelin sheath at regular intervals

- in these gaps is the only place where depolarisation can occur

- the impulse jumps from gap to gap making depolarisaion quicker

- this is called saltatory conduction


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Nerveimpulses

Therearethreestagesleadingtothenerveimpulsepassingalongthepostsynapticneurone:

neurotransmitterrelease

stimulationofthepostsynapticmembrane

inactivationoftheneurotransmitter

Neurotransmitterrelease:

thepresynapticmembraneisdepolarisedbyanactionpotential,channelsinthe

membraneopenincreasingpermeabilitytoCa2+ions

Ca2+ionconcentrationisgreateroutsidethecellsotheydiffuseintothecell

theincreasedCa2+concentrationcausessynapticvesiclescontainingacetylcholineto

fusewiththepresynapticmembrane

thiscausestheircontentstobereleasedintothesynapticcleftbyexocytosis

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How does the synapse transmit an impulse?

1. An action potential arrives at the presynaptic neurone

2. the membrane depolarises. Ca2+ ion channels open and Ca2+ ions enter the neurone

3. Ca2+ ions cause synaptic vesicles containing neurotransmitter to fuse with the presynaptic

membrane

4. Neurotransmitter is released into the synaptic cleft

5. Neurotransmitter binds with the receptors on the postsynaptic membrane. Cation channels

open. Na+ ions flow through the channels.

6. membrane depolarises and initiates an action potential

7. when released the neurotransmitter will be taken up across the presynaptic membrane (whole

or after being broken down), or it can diffuse away and be broken down


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Controlandcoordination

Synapseshavetworoles:

controlofnervepathwaysallowingflexibilityofresponse

integrationofinformationfromdifferentneuronesallowingacoordinatedresponse

Twofactorsthataffectthelikelihoodthatapostsynapticmembranewilldepolarise:

thetypeofsynapse

thenumberofimpulsesreceived

-somesynapseshelpstimulateanactionpotential

-othersareinhibitoryandmakeitlesslikelythatdepolarisationwilloccur

-apostsynapticcellhasmanyinhibitoryandexcitatorysynapses

-isanactionpotentialismadeornotdependsonthebalanceofthesynapses

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Nerve impulses continued

stimulation of the postsynaptic membrane:

embedded in the postsynaptic membrane are specific receptor proteins

these proteins have a binding site that have a complimentary shape to part of the

acetylcholine molecule

the ecetylcholine molecule binds to the receptor changing the shape of the protein

this opens the cation channels and makes the membrane permeable to Na+ ions the flow of Na+ ions across the postsynaptic membrane causes depolarisation

an action potential is produced

inactivation of the neurotransmitter:

an enzyme called acetylcholinesterase breaks down the acetylcholine so that it cannot

bind to receptors

some of the products from the breakdown are then reabsorbed by the presynaptic

membrane and are used again


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Inhibitorysynapses

-inhibitorysynapsesmakeitlesslielythatanactionpotentialwillresultinthepostsynapticcell

-theneurotransmittersfromthesesynapsesopenschannelsforCl-ionsandK+ionsinthe

postsynapticmembrane

-theseionsthenmovethroughthechannelsdowntheirdiffusiongradients.

-Cl-ionsmoveintothecellcarryingnegativechargeandK+ionswillmoveoutcarryingapositive

charge

-thisresultsinagreaterpotentialdifferenceacrossthemembraneastheinsidebecomesmore

negativethanusual(-90mV)

-thismakesdepolarisaionlesslikelyasmoreexcitatorysynapseswillbeneededtodepolarise

themembrane

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Excitatory synapses

- Excitatory synapses make the postsynaptic membrane more permeable to Na+ ions

- more than one of these is needed to provide sufficient depolarisation each impulse adds to the

effect of another this is called summation

There are two types of summation:

Spatial summation -

- here the impulses are from different synapses, usually from different neurones.

Temporal summation -

- in this case several impulses arrive at a synapse having traveled along a single neurone one

after the other.

- their combined release of neurotransmitter generates an action potential in the postsynaptic

membrane.


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Receptors

-stimuliaredetectedbyreceptorcellsthatsendelectricalimpulsestothecentralnervoussystem.

-sometypesofreceptorcellsaregroupedtogetherintosenseorgans

Differenttypesofreceptors

Chemoreceptors:

stimulated-bychemicals

examplesofrole-taste,smellandregulationofchemicalconcentrationsintheblood.

Mechanoreceptors:

stimulatedby-forcesthatstretch,compressormovethesensor

examplesorrole-balance,touchandhealing

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Coordination in plants

- plants use chemicals to coordinate growth these chemicals can be called plant growth regulators or plant growth

substances

- plants have phototropism (bending of plants towards a light source)

- there is a chemical in the tip that travels down the coleoptile (a plant) it was found that this chemical is an auxin called

indoleacetic acid

- when the tip of a plant is removed and placed on some agar jelly and then placed back on top of the plant, it started to

grow again showing the chemical had diffused through the agar jelly

- auxins are synthesised in actively growing plant tissues (known as meristems) such as shoot tips etc

- they bind with receptors on the plasma membranes in the zone of shoot elongation

- by doing this the auxins produce second messenger signal molecules that bring about changes in gene expression

- an increased potentail difference across the membrane enhances uptake of ions into the cell

- this causes uptake of water by osmosis causing cell elongation


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Thestructureoftheeye

Conjunctiva-protectsthecornea

cornea-bendslight

lens-focuseslightonretina

iris-controlsamountoflightenteringtheeye

sclera-protectivelayer

blindspot-nolight-sensitivecellswhereopticnerveleavestheeye

yellowspot(fovea)-mostsensitivepartoftheretinalocatedinthemaculathecentralareaoftheretina

retina-containslight-sensitivecells

vitreoushumour-transparentjelly

choroid-blacklayerpreventsinternalreflectionoflight

ciliarymuscle-altersthicknessoflensforfocusing

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Receptors continued

Photoreceptors:

stimulated by - light

examples of role - sight

Thermoreceptors:

stimulated by - heat or cold

examples of role - temperature control and awareness of changes in the surrounding temperature

- all of the receptors except for photoreceptors work in the same way

- at rest the cell surface membrane has a negative resting potential, stimulation of the receptor causes depolarisation

- when the depolarisation goes above the threshold level it triggers an action potential

- it is either relayed across the synapse using neurotransmitters or passed directly down the axon of the sensory nerve


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Howdoeslioghtstimulatephotorecertorcells?

-inbothrodsandconesaphotochemicalpigmentabsorbsthelightresultinginachemicalchange

-inrodsthemoleculeisapurplishmigmentcalledrhodopsin

-rodscontainanouterandinnersegmentthesecontainthemanylayersofflattenedvesicles

-therhodopsinmoleculesarelocatedinthemembranesofthesevesicles

hereidrewapictureofthestructureofrodsandconeswithintheretinabecauseicouldnotfind

anappropriateonefromtheinternet.

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Photoreceptors

- the human retina contains two types of photoreceptor cells sensitive to light, these are rods and

cones

-cones allow colour vision in bright light

- rods only give black and white vision but work in dim light and bright light

- in the centre of the retina there are only cones but over the remainder of the retina rods outnumber

cones

- the rods and cones synapse with bipolar neurone cells

- which in turn synapse with ganglion neurones

- whose axons together make up the optic nerve

- light hitting the retina has to pass through the layers of neurones before reaching the rods and

cones


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Intherodcells:light

-whenlightfallsontherhodopsinmolecule,itbreaksdownintoretinalandopsinnon-proteinand

proteincomponents,theopsinactivatesaseriesofmembrane-boundreactions

-thesereactionsendinhydrolysisofamoleculeattachedtothecationchannelintheouter

segment

-thebreakdownofthismoleculeresultsintheclosingofthecationchannels

-theentryofNa+intotheroddecreaseswhiletheinnersegmentcontinuestopumpNa+out

-thismakestheinsideofthecellmorenegativeandbecauseofthisitbecomeshyperpolarised

andthereleaseofglutamatestops

-thelackofglutamateresultsindepolarisationofthebipolarcellwithwhichtherodsynapses

-theneuronesthatmakeuptheopticnervearealsodepolarisedandrespondbyproducingan

actionpotential

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In the rod cells: dark

Dark:

- sodium ions flow into the outer segment through non-specific cation channels

- the sodium ions move down the concentration gradient into they inner segment where pumps

transport them back out of the cell

- this movement of Na+ produces a slight depolarisation of the cell

- the potential difference across the membrane is about -40 mV

- this slight depolarisation triggers the release of a neurotransmitter thought to be glutamate from

the rod cells

- the rods release this neurotransmitter continuously

- the neurotransmitter binds to the bipolar cell stopping it depolarising


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Phytochromestriggergermination

-phytochromeswerediscoveredthroughgerminationexperiments

-theyusedseedsthathavethinseedcoatsandfewfoodreserves

-onesthatdonotgerminateinthedarkandonlygerminatewhencloseenoughtothesoilsurface

-thefindingstheyproducedwherethatredlightiseffectiveattriggeringgermination,whilefar-

redlightseemstoinhibitgermination

-whenlettuceseedsareexposedtoredlightPrisconvertedtoPfrstimulatingresponsesthat

leadtogermination

-whentheyarekeptinthedarknoPrisconvertedtoPfr

-becauseofthistheseedsdonotgerminatebecausethereisnopresenceofPfr

-whenexposedtofar-redlightPfrisconvertedbacktoPrinhibitinggermination

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Phytochromes - plant photoreceptors

- a phytochrome molecule consists of a protein component bonded to a non-protein light-absorbing pigment molecule.

- the five phytochromes differ in their protein component

- the non-protein component exists in two forms which are different isomers:

Pr - phytochrome red; absorbs red light

Pfr - phytochrome far-red; absorbs far-red light

- these two isomers are photoreversible but plants synthesise phytochromes in the Pr form

- absorption of red light converts Pr into Pft, absorption of far red light converts Pfr back into Pr

- in sunlight Pr is converted into Pfr and Pfr is converted into Pr

- the former reaction dominates in sunlight because more red than far-red light is absorbed

- therefore Pfr accumulates in the light

- and in the dark any Pfr present is slowly converted to Pr


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Phytochromeandgreening

-onceashoothasbrokenthroughsoilintosunlighttheplantunsergoesbigchangesinbothitsformandbiochemistry

-thesechangesarecalledgreening

-onceinthelightphytochromespromotethedevelopmentofprimaryleaves,leafunrollingandtheproductionofpigments

-theycanalsoinhibitcertainprocessessuchaselongationofinternodes

Howdophytochromeswhichprocessesonoroff?

-exposuretolightcausesphytochromemoleculestochangefromoneformtoanotherbringingaboutachangeinchape

-thephytochromesmaythenbindtoproteinsordisruptthebindingofaproteincomplex

-thesesignalproteinsmayactastranscriptionfactorsoractivatetranscriptionfactorsthatbindtoDNAtoallowtranscription

oflightregulatedgenes

-thetranscriptionandtranslationofproteinsresultintheplantsresponsetolight

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Photoperiods, flowering and phytochromes

- the photoperiod is the environmental cue that determines the of flowering

- the ratio of Pr to Pfr in a plant enables it to determine the length of day and night

- long nights give time for Pfr to convert back to Pr so that all phytochrome will be Pr

- summer nights may not be long enough though so some Pfr may still be present in the morning

- long-day plant:

only flower when day length exceeds a critical value

flower when the period of uninterrupted darkness is less them 12 hours

they need Pfr to stimulate flowering

- short-day plants:

tend to flower in spring or autumn when the period of uninterrupted darkness is greater than 12 hours

they need long hours of drakness in order to convert all Pfr present back into Pr

Pfr inhibits flowering in shot-day plants


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Thebrain

Thecerebralhemispheres:

-thetopofthebrainiscalledthecortexitismadeofmainlynervecellbodies,synapsesand

dendrites

-thisouterlayerofthebrainisknownasthegreymatter

-thecortexisthelargestregionofthebrain,andisdividedintoleftandrightcerebralhemispheres

-eachhemisphereiscomposedoffourregionscalled:

frontallobe

parietallobe

occipitallobe

temporallobe

-thetwocerebralhemispheresareconnectedbyabroadbandofwhitematter(nerveaxons)

calledthecorpuscallosum.

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Plants detect other environmental clues

Gravity:

- more than a short distance under the soil surface light cannot be the cue for the shoot to grow upwards and the root

to grow donwards

- the stimulus for this is gravity and the response ensures that developing shoots reach the light while roots grow in the soil

Touch and mechanical stress:

- some plants are sensitive to touch and mechanical stress

- it is thought that mechanical stimulus (such as rubbing the plant stem) activates signal molecules whose end result is

the activation of genes that control growth

- some plants have leaves that move rapidly in response to mechanical stimulation

- the mechanism is that when touched speciaslised cells lose potassium ions

- water follows by osmosis and the cells become flaccid so no longer support the leaf and keep it upright


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Thebraincontinued

Occipitallobe(visualcortex):

-concernedwithprocessinginformationfromtheeyes,includingvision,colour,shaperecognition

andperspective

Temporallobe:

-concernedwithprocessingauditoryinformation,i.e.hearing,soundrecognitionandspeech(left

temporallobe).itisalsoinvolvedinmemory.

Andthecerebellum.

Thestructureslyingdirectlybelowthecorpuscallosumare:

Thethalamus-responsibleforroutingalltheincomingsensoryinformationtothecorrectpartof

thebrain,viatheaxonsofthewhitematter.

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The brain continued

Frontal lobe:

- is concerned with the higher brain functions such as decision making, reasoning, planning and

consciousness of emotions, it is also concerned with forming associations and ideas

- it includes the primary motor cortex which has neurones that connect directly to the spinal cord

and brain stem and from there to the muscles

- it sends infomation to the body via the motor neurones to carry out movements

- the motor cortex also stores information about how to carry out different movements

Parietal lobe:

- concerned with orientation, movement, sensation, calculation, some types of recognition and

memory


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Thecerebellumandbrainstem

-thebrainstemissituatedatthetopofthespinalcolumnanditextendsfromthemidbraintothemedullaoblongata

Corpuscallosum-

whitemattermademainlyofaxonsandithaswhitemyelinsheaths

itprovidesconnectionsbetweenthecortexandthebrainandthestructuresbelow

italsoformsconnectionsbetweenthetwohemispheresofthecortex

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The brain continued

The hypothalamus - contains the thermoregulatory centre so it monitors such things as core body

temperature and initiates action to put it back to normal.

- it also acts as a endocrine gland which secretes hormones such as antidiuretic hormone

- it connects directly to the pituitary gland, which in turn secretes other hormones

The hippocampus: - is involved in laying down long-term memory

The basal ganglia - is a collection of neurones that lie deep within each hemisphere

- they are responsible for selecting and initiating stored programmes for movement.


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Theeffectsofstrokes

-braindamagecausedbyastrokecancauseproblemswithspeaking,understandingspeech,

readingandwriting

-lesionsinsmallcorticalareaintheintheleftfrontallobewereresponsiblefordeficitsinlanguage

production

-somepatientscanrecoversomeabilitiesafterastrokeshowingthepotentialofneuronesto

changeinstructureandfunction

-thischangeisknownasneuralplasticity

-thestructureofthebrainremainsflexibleeveninlaterlifeandcanrespondtochangesintheenvironment

-brainstructureandfunctioningisaffectedbybothnatureandnurture

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The cerebellum and brain stem continued

Cerebellum:

responsible for balance

coordinates movement as it is being carried out, receiving information from the primary

motor cortex, muscles and joints.

constantly checks whether the motor programme being used is the correct one, e.g.

referring to incoming information about posture and external circumstances

Midbrain:

relays information to the cerebral hemispheres, including auditory information to the

temporal lobe, and visual information to the occipital lobe

Medulla oblongata:

regulates those body processes that we do not consciously control, such as heat rate,

breathing, and blood pressure.


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Brainimaging

Magneticresonanceimaging(MRI):

-usesamagneticfieldandradiowavestodetectsofttissues

-whenplacedinamagneticfieldthenucleiofatomslineupwiththedirectionofthemagneticfiels

-inanMRIscannerthemagneticfieldrunsdownthecentreofthetubeinwhichthepatientlies

-anothermagneticfieldissuperimposedonthiswhichcomesfromthemagneticcomponentofhighfrequencyradiowaves

-thecombinedfieldscausethedirectionandfrequencyofspinofthehydrogennucleitochangetakingenergyfromthe

radiowaves

-whentheradiowavesareturnedoffthehydrogennucleireturntotheiroriginalalignmentandreleasetheenergythey

absorbed

-thisenergyisdetectedandasignalissenttoacomputerwhichanalysesittoproduceanimage

-itisusedinthediagnosisoftumors,strokes,braininjuriesandinfectionsofthebrainandspine

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Brain imaging

CT scans: (Computerised Axial Tomography)

- use narrow-beam X-rays rotated around the patient to pass through the tissue from different

angles

- each narrow beam is reduced in strength depending on the density of the tissue in its path

- the x-rays are detected and are used to produce an image of a thin slice of the brain on a computer

screen in which the different sort tissues can be distinguished

- they only give frozen pictures

they look at the structures in the brain and can detect brain disease and monitor the tissue of the

brain over the course of an illness

- they do not use harmful x-rays


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Fromtheeyetothebrain

-theaxonsoftheganglioncellsthatmakeuptheopticnervepassoutoftheeyeandextendto

severalpartsofthebrain

-itextendstopartofthethalamus

-andthenimpulsesarethensentalongotherneuronestotheprimaryvisualcortexwherethe

informationisthenprocessed

-beforereachingthethalamussomeoftheneuronesineachopticnervebranchofftothemidbrain

-heretheyconnecttomotorneuronesinvolvedincontrollingthepupilreflexandmovementof

theeye

-audiosignalsalsoarriveatthemidbrainsowecanquicklyturnoureyesinthedirectionofa

visualorauditorystimulus

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Brain imaging

Functional magnetic resonance imaging (fMRI):

- fMRI is used to look at the functions of the different areas of the brain by following the uptake

of oxygen in active brain areas

- it works because the deoxyhaemoglobin absorbs the radio wave signal where as

oxyhaemoglobin does not

- increased neural activity requires an increased demand for oxygen and because of this increase

in blood flow

- there is a large increase in oxyhaemoglobin levels in the enhanced blood flow so less signal is

absorbed

- the less radio signal there is absorbed the higher the level of activity in a particular area

- active areas of the brain 'light up'


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Axongrowth

-axonsoftheneuronsfromtheretinagrowtothethalamuswheretheyformsynapseswith

neuronesinthethalamus

-axonsfromthesethalamusneuronsgrowtowardsthevisualcortexintheoccipitallobe

-thevisualcortexismadeofcolumnsofcells,axonsfromthethalamussynapsewithinthese

columnsofcells

-columnsofcellsreceivestimulationfromthesameareaoftheretinaintheleftandrighteye

-itusedtobethoughtthatthesecolumnofcellsinthevisualcortexwereformedduringacritical

periodforvisualdevelopment,itisnowfoundnottobethecase

-periodsoftimeduringpostnataldevelopmenthavebeenidentifiedwhenthenervoussystem

mustobtainspecificexperiencestodevelopproperly

-theseareknownascriticalperiods,criticalwindowsorsensitiveperiods

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Visual development

- the human nervous system begins to develop after conception

- by the 21st day the neural tube has formed the front part of the neural tube goes on to develop

into the brain where the rest of it develops into the spinal cord

- there is no large increase in the number of brain cells after birth but there is a large increase

in brain size

- this increase in brain size is due to the elongation of axons, myelination and the development

of synapses

- once neurones have stopped dividing the immature neurones migrate to their final position and

start to wire themselves

- axons lengthen and synapse with the cell bodies of other neurones

- neurones must make the correct connections in order for a function such as vision to work properly


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Studiesofnewbornanimals

-inonestudyonegroupofnewbornmonkeyswereraisedinthedarkfor3tosixmonthsand

anotherexposedtolightbutnottopatterns

-whentheywerereturnedtothenormalworldbothgroupshaddifficultywithobjectdiscrimination

andpatternrecognition

HubelandWiesel:

-theyraisedmonkeysfrombirthtosixmonthsdeprivingthemofanylightstimulusinoneeye,

thisisknownasmonoculardeprivation

-after6monthstheeyewasexposedtolightanditwasclearthatthemonkeywasblindinthelight-deprivedeye

-retinalcellsinthedeprivedeyedidrespondtothelightstimulibutthecellsinthevisualcortex

didnotrespondtoanyvisualinputfromthedeprivedeye

-deprivationinadultshadnoeffect

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Evidence for a critical period in visual developme

Medical observations:

- a young boy who had a eye infection had his eyes bandages for two weeks and when it was removed he had permanently

impaired vision

- some people are born with cataracts, which is a clouding of the lens which affects the amount of light entering the retina

- they can have permanent impairment of their ability to perceive shape of form, including difficulties in face recognition

- but elderly people who develop cataracts in later life and have them for several years have normal vision after they are

removed

Research:

- research is conducted on just a few types of animals so a lot of information is available about them they are known as

animal models

- most animal models are easy to obtain, easy to breed, have short life cycles and a small adult size

- for example mice are used extensively in the study of cancer and disease


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Makingsenseofwhatwesee

-neuronesinthevisualcortexarealvetorespondtotheinformationfromtheretina

-individualneuronesinthecolumnsofcellsrespondindifferentwaystotheinformationfromthe

retinaandtodifferentcharacteristicsoftheobjectbeingviewed

-someneuronescalledsimplecellsrespondtobardoflight

-otherscalledcomplexcellsrespondtoedges,slitsorbarsoflightthatmove,otherstotheangle

oftheedgeandotherstocontours,movementororientation

-visualperceptioninvolvesknowledgeandexperienceasthebraininterpretsthesensory

informationreceivedfromtheretina

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What happens during the critical period?

In the visual cortex:

- overlapping columns in the visual cortex are present at birth

- in a normal adult the critical period produces the distinctive pattern of columns for the left and right eye

- columns that receive input from a light-deprived eye become much narrower

Explanation:

- columns with axons from the light-deprived eye are narrower than those receiving light stimulation

- dendrites and synapses from the light-stimulated eye take up more territory in the visual cortex

- this suggests that light stimulation is needed for the refinement of the columns and full development of the visual cortex

- axons compete for target cells in the visual cortex

- every time a neurone fires onto a target cell the synapses of another neurone sharing the target cell are weakened and

they release less neurotransmitter


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Cross-culturalstudies

-peoplefromdifferentculturesmaynotsharethesamebeliefsandtheymayshowdifferent

behaviours

Carpenteredworldhypothesis:

-thosewholiveinaworlddominatedbystraightlinesandrightanglesperceivedepthcuesvery

differentlyfromthosewholiveina'circularculture'

-whensurroundedbybuildingswithrightanglecornersunconsciouslyfromanearlyagetendto

interpretimageswithacuteandobtuseanglesasrightangles

-peoplewholivein'circularculture'withfewstraightlinesorrightanglecorners

-theyhavehavelittleexperienceofinterpretingacuteandobtuseanglesontheretinaas

representationsofrightangles

-studiesshowthemtoberarelyfooledbyopticalillusions

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Depth perception

Close objects:

- for close objects we depend on the presence of cells in the visual cortex that obtain information from both eyes at once

- the visual field is seen from two different angles

- the cells in the visual cortex let us compare the view from one eye with that from the other

- this is called stereoscopic vision and allows relative position of objects to be perceived

Distant objects:

- for far objects the images on our two retinas are very similar, so visual cues and past experiences are used with interpreting

the images

- overlaps of objects and changes of colour also help in judging depth

- for example when a car drives away we perceive it as moving further away not getting smaller


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Learningandmemory

-thenervoussystemchangeswithchangesoccurringinournetworkofneurones,oftenbythe

modificationofsynapses

-italsochangeswhenchangesinthesynapsesthatunderpinlearningandmemorychanges

-memoryislocatedindifferentpartsofthecortexwithdifferentsitesforshortandlong-term

memory

-differenttypesofmemoryarecontrolledbydifferentpartsofthebrain

Howmemoriesarestored:

-inthebraineveryneuroneconnectswithmanyotherneuronestomakeupacomplexnetwork

thepatternofconnections

thestrengthofsynapses

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Studies with newborn babies

The visual cliff:

- babies are encouraged to crawl across a table made of glass or perspex, below which is a visual

cliff

- patterns placed below the glass create the appearance of a steep drop

- if the perception of depth is innate then babies shout be aware of the drop even if they have not

previously experienced this stimulus themselves

- young babies were reluctant to crawl over the 'cliff' even when their mothers encouraged them

- the experiment was repeated with animals that can walk as soon as they are born (e.g. chicks)

- they too refused to cross the cliff


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Seaslugsandhabituationcontinued

-seaslugsarehabituatedtowaves,habituationisatypeoflearning

-sothegillwithdrawswhensiphonisstimulatedbutafterafewminutesofrepeatedstimulation

thesiphonnolongerwithdraws

-habituationallowsanimalstoignoreunimportantstimuli

-thisissothatlimitedsensory,attentionandmemoryresourcescanbeconcentratedinmore

threateningorrewardingstimuli

Howhabituationisachieved:

-withrepeatedstimulationCa2+channelsbecomelessresponsivesolessCa2+crossesthe

presynapticmembrane

-thereforelessneurotransmitterisreleased

-thereislessdepolarisationofthepostsynapticmembranesonoactionpotentialistriggeredin

themotorneurone

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Sea slugs and habituation

- there are no fundamental differences between the nerve cells and synapses of humans and

animals such as sea slugs

- but sea slugs have less neurones so their neurobiology is much simpler than that of humans

- sea slugs also have large accessible neurones so those involved in particular behaviors can be

identified

- sea slugs behaviour can be modified by learning and the effects on neurones and synapses

studied

- the sea slug breathes through a gill located in a cavity on the upper side of its body

- water is expelled through a siphon tube at one end on the cavity

- if the siphon is touched the gill is withdrawn into the cavity, this is a protective reflex action


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Ethicsofusinganimalsinmedicalresearch

Theimportanceofconsent:

Acceptingthatanimalshaverightswecouldonlyuseanimalsthatconsentedtoparticipateinmedicalexperiments,just

likeweonlyusehumansifthatgivetheirconsent.

Animalwelfareratherthananimalrights:

Awidespreadbeliefisthathumansshouldtreatanimalsaswellaspossible.NocountryintheEuropeanUnionisallowed

tousevertebratesinmedicalexperimentsistherearenon-animalalternatives.

Animalsufferingandexperienceofpleasure:

boththeanimalrightsapproachandtheanimalwelfareapporachassumethatanimalscansufferandexperiencepleasures.

Autilitarianapproachtotheuseofanimals:

Utilitarianismisthebeliefthattherightcourseofactionisonethatmaximisestheamountofoverallhappinessorpleasure

intheworld.Autilitarianframeworkallowscertainanimalstobeusedinmedicalexperimentsprovidedtheoverallexpected

benifitsaregreaterthantheoverallexpectedharms.

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Sensitisation

What is happening during sensitisation?:

- sensitisation is the opposite of habituation, it happens when an animal develops an enhanced

response to a stimulus

-in sea slugs if a predator attacks it becomes sensitised to other changes in its environment and

responds strongly to them

sensitisation: (a shock to the tail enhances the gill withdrawal due to the water jet)

impulse due to electric shock to tail

serotonin released

greater calcium ion uptake

impulse passes along sensory neurone

more neurotransmitter released

greater depolarisation

higher frequency of action potentials

enhanced gill withdrawal response


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Treatmentforparkinsonsdisease

-slowingthelossofdopaminefromthebrainbyusingdrugssuchasselegiline.Thedruginhibits

theenzymemonoamineoxidasewhichbreaksdowndopamineinthebrain.

-AdrugcalledL-dopacanbegiven.OnceinthebrainL-dopaisconvertedintodopamine,

increasingtheconcentrationofdopamine.

-theuseofdopamineagonists.Theyaredrugsthatactivatethedopaminereceptordirectly,they

bindtodopaminereceptorsatsynapsesandtriggeractionpotentials.

-genetherapycanbeused.genesforproteinsthatincreasedopamineproductionandthat

promotethegrowthandsurvivalofnervecellsareinsertedintothebrain.celltherapyinwhichthe

proteinsthemselvesareinjectedisalsobeingtrialled.

-Newsurgicalapproachesarebeingtrialled,someofwhicharegeneratingencouragingresults.

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Dopamine and Parkinson's disease

- dopamine is a neurotransmitter secreted by neurones, included many located in part of the

midbrain

- these neurones normally release dopamine in the motor cortex

- Parkinson's patient motor cortexes receive little dopamine and there is a loss of control of

muscular movements

- the main symptoms of the disease are:

stiffness of muscles

tremor of the muscles

slowness of movement

poor balance

walking problems

depression

difficulties with speech and breathing


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Howdrugsaffectsynaptictransmission

Theeffectofecstasy:

-effectsthinking,moodandmemoryandcanalsocauseanxietyandalteredperceptions.Itsmost

desirableeffectisthatitprovidesfeelingsofemotionalwarmthandempathy.

-therearefivedifferentstagesinsynaptictransmissionthatcanbeaffectedbydrugs:

neurotransmittersynthesisandstorage

neurotransmitterrelease

neurotransmitter-receptorbinding

neurotransmitterreuptake

neurotransmitterbreakdown

-short-termeffectsincludechangesinbehaviourandbrainchemistry,sweating,drymouth,

increasedheartrate,fatigue,musclespasmsandhypothermia.

-long-termeffectsincludechangesinbehaviourandbrainstructure

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Depression

- neurones that secrete serotonin are stimulated in the brain stem. a lack of serotonin has been linked to depression.

- Their axons extend to the cortex, the cerebellum and the spinal cord, targetinga a huge area of the brain.

- depression is a multifactorial condition; several genes my be involved but so my environmental factors.

- a gene called 5-HTT is known to influence our susceptibility to depression, people with the 'short' version of the 5-HTT

gene are more likely to develop depression after a stressful life event.

- when someone is depressed, fewer never impulses than normal are transmitted abound the brain, which may cause low

levels of neurotransmitters to be produced.

- serotonin binding sites are more numerous than normal when depressed to make up for the low levels of the molecule.

Drug treatment for depression:(SSRI and Prozac)

- the drugs inhibit the reuptake of serotonin from synaptic clefts

- this type of drug is called a Serotonin Reuptake Inhibitor (SSRI) so it blocks the only uptake of serotonin.


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Bettertreatments

-thedecipheringofthebasesequenceinthehumangenomeaspartoftheHumanGenome

Project(HGP)meanswearenowgettingabetterunderstandingofthewaygenescontrolourphenotype

-agenomeisalltheDNAofaorganism(orspecies),includingthegenesthatcarrytheinformation

formakingtheproteinsrequiredbytheorganism(orspecies)

-theseproteinshelpdetermineallthecharacteristicsoftheorganismfromindividualbiochemical

pathwaystoitsoverallappearance

-In1977FredSangerthefirstDNAsequencingprocess

-DNAisusedasatemplatetoreplicateasetofDNAfragments,eachdifferinginlenthbyonebase

-thefragmentsareareseparatedaccordingtosizeusinggelelectrophoresisandthebaseatthe

endofeachfragmentisidentified

-thisallowsthesequenceofbasesinthewholeDNAchaintobedetermined

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How drugs affect synaptic transmission

How ecstasy affects synapses:

- ecstasy increases the concentration of serotonin in the synaptic cleft

- it does this by binding to molecules in the presynaptic membrane that are responsible for

transporting the serotonin back into the cytoplasm

- this prevents its removal from the synaptic cleft

- the drug may also cause the transporting molecules to work in reverse, further increasing the

amount of serotonin outside the cell

- these higher levels of serotonin bring about the mood changes seen in users of the drug

- there is growing evidence of long-term effects including insomnia, depression and other

psychological problems


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Usinggeneticallymodifiedorganismstoproducedr

-ithasbeenpossibletogeneticallymodifynon-humanorganismstoproducespecifichuman

proteins,suchasthehumangrowthhormone,insulinandcollagen

-theartificialintroductionofgeneticmaterialfromanotherorganismthroughgeneticmodification

producesatransgenicorgeneticallymodifiedorganism(GMO)

-geneticmodificationisalsoknownasgeneticengineeringorgeneticmanipulationorrecombinant

DNAtechnology

Modifyingorganisms:

-thefirstsuccessingeneticengineeringwaswithbacteria

-bacteriacontainsimpleDNAstructures,plasmids,whichcanbetransferredfromonecellto

another

-usingrestrictionenzymes,thecircularplasmidcanbecut,andusinganothersetofenzymesa

pieceofDNAfromanotherspeciescanbeinsertedin

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Human Genome Project

Issues with the Human Genome Project:

- testing for generic predisposition has many implications

- who should decide about the use of generic predisposition tests, and on whom should they be

used?

- making and keeping records of individual genotypes raises acute problems of confidentiality

- many medical treatments made possible through the development of genetic technologies will

initially be very expensive

- restricted availability of many medical treatments will add considerably to the problems faced by

the health services in deciding who is eligible for the treatments


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Geneticallymodifiedplants

-forcenturiesfarmershavepickedoutthehardestandmostprolificplantsfromtheircropsand

havesavedtheseedsfromtheseplantsforsowingthefollowingyear

-becauseofthiscropshavesteadilyimproved,thisiscalledartificialselection

-geneticengineersintroducenewgeneswithallelesfordesiredcharacteristicsintoaplantsDNA

resultingingeneticallymodifiedplants

-Genesareinsertedintoplantcells.thiscanbedoneby:

abacteriumthatinfectsmanyspeciesofplant.Whenthebacteriainvadetheplantcells

genesfromplasmidDNAbecomeincorporatedintothechromosomesoftheplantcellsMinutepelletsthatareconvertedwithDNAcarryingthedesiredgenesareshotintothe

plantcellsusingaparticlegun.

virusesaresometimesused.TheyinfectcellsbyinsertingtheirDNAorRNA.Theycan

beusedtotransferthenewgenesintothecell.

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Modifying organisms

- an example of how bacteria can be used for

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