RESPONDING TO THE ENVIRONMENT (behaviour and muscle contraction)

Muscle contraction
1. NEUROMUSCULAR JUNCTIONS
  1. this is where motor neurones terminate and info is transmitted from motor neurone to effector. this happens similarly to a synapse
  2. what happens:
    1. 1) action potential arrives at neuromuscular junction which causes vesicles with neurotransmitter inside, to fuse with presynaptic membrane and release acetylcholine into gap
      1. 2) acetyle choline binds to (nicotinic cholinergic) receptors on muscle membrane causing inflow of na+ ions which depolarises the sarcolemma (muscle fibre membrane)
        3) if threshold is reached, action potential is transmitted along the sarcolemme and down thet-tubules (t-system). these membranes have the same channel proteins and pumps as neurons.
        4) t system depolarisation leads to Ca2+ ions release from sarcoplasmic reticulum into sarcoplasm. Ca2+ ions act as second messengers to stimulate movement of muscle myofibrils.
        5) Ca2+ ions bind to protein actin in muscle, which leads to muscle contraction
        6) acetylcholinesterase in the gap rapidly breaks down acetylcholine so contraction only occurs when action potential arrives continuously
  3. synapses vs neuromusclular junction
    1. BOTH
      1. neurotransmitter acetylcholine located in vesicle is pre synaptic cytoplasm
      2. vesicles release acetylcholine into cleft on stimulation (arrival of ap)
      3. acetylcholine diffuses across gap and binds to post synaptic membrane receptor
      4. binding of neurotransmitter results in opening of channels and depolarisation of post synaptic membrane
      5. enzyme acetylcholinesterase present to break down acetylcholine into ethanoic acid and choline to avoid continual stimulation of post synaptic membrane
    2. SYNAPSE is neurone to neurone, NMJ is neurone to sarcomemre (muscle cell)
    3. SYNAPSE post synaptic stimulation leads to ap in postsynatic neurone, NMJ postsynpatic stimulation leads to depolarisation of sarcolemma and muscle contraction
    4. SYNAPSE have synaptic knob which is smooth and round, NMJ end plate has appearance of microvillia/ brush border and is flattened up to muscle cell
    5. SYNAPSE ca2+ ions diffuse into synaptic knob, NMJ ca2+ ions released from sarcoplasmic reticulum
2. elbow joint
  1. when arm goes down bicep relaxes an tricept contracts. when arm goes up bicep contracts and tricep relaxes.
  2. shoulder blade at the top, tendon joins muscles to bone. bicep on top/right of humerus and tricep on bottom/left. radius on palm side lower arm, ulna on top
  3. ELBOW
    1. in middle is synovial fluid which lubricates the joint
      1. next layer is synovial membrane which produces synovial fluid
        ligament surrounds the rest which holds bones together and prevents dislocation
    2. at end of bones is cartilage which pads wheres bones meet, reduces friction during movement and eases movement
3. types of muscle
4. GENERAL
  1. Length of sarcomere when muscle is relaxed=2.5um and contracted=2um
  2. THIN FILAMENTS
    1. made up of G/F actin which is a globular protein
    2. long chains of actin molecules: 2 chains of actin lie side by side and twist around one another
      1. actin chains are firmly anchored in Z lines
    3. TROPOMYOSIN
      1. rod shaped proteins hich forms long, thin molecules that lie in groove between 2 F/G actin chains
    4. TROPONIN
      1. globular protein that binds to actin chains at regular intervals
      2. composed of 3 polypeptides: 1 binds to actin, 1 to tropomyosin and 1 to ca2+ ions
  3. THICK FILAMENTS
    1. made up of bundles of myosin which is a fibrous protein
    2. many myosin molecules lie side by side
    3. each myosin molecules has a head and bundles are arranged so that half molecules heads are one end and half the other end
      1. where the tails meet forms the M line
  4. Z LINES: border of sarcomeres
  5. M LINES: middle of sarcomeres
  6. H ZONE: distance between ends of thin filaments, shortens during contraction as actin and myosin overlap increases
  7. I BAND: distance between thick filaments of one sarcomere and thick filaments of the subsequent sarcomere, shotens during contraction as actin slides over myosin
  8. A BAND: total length of thick filaments, stays the same on contraction as myosin length is unchanged
  9. overall sarcomere reduces in length on contraction as overlap increases and actin slides towards myosin, when relaxed sarcomere is longer
  10. striated muscles look stripey because I band has only actin microfilaments so appears light and A band has actin and myosin microfilaments so appears dark. filaments are arranged regularly giving stripey look.
5. SLIDING FILAMENT THEORY
  1. in presence of ATP, thin actin filaments slide towards the M line along the thick myosin filaments. This is the sliding filament model and explains why H ZONE and I BANDS shorten by A band does not during contraction
    1. the filaments dont change size, they just overlap
      1. energy is provided by splitting of ATP caused by ATPase in the myosin cross bridge head. The cross bridges can also attach to actin
  2. Binding sites in resting muscles:
    1. for myosin and actin to slide past eachother, the myosin head must bind to the actin-myosin binding site on the actin filament
      1. in a resting muscle, the actin-myosin binding site is bloacked by tropomyosin which means myofilaments cant slide past eachother because myosin head cant bind to actin filaments
    2. 1) Arrival of action potential
      1. when ap from motor neurone stimulates muscle cell, sarcolemma is depolarised. depolarisation spreads down t tubules to sarcoplamsic reticulum where ca2+ ions are released from into sarcoplasm. influx of ca2+ ions stimulate muscle contraction
        ca2+ ions bind to troponin causing it to change shpe. this pulls attached tropomyosin out of the actin-myosin binding site on the actin filament
        this exposes binding site so allows myosin head to bind. the bond formed when myosin head binds to actin filament is called an actin-myosin cross bridge
      2. 2) Movement of actin filament
        ca2+ ions also activate enzyme ATPase which breaks down ATP into ADP + Pi to provide energy for contraction
        energy released from ATP moves myosin head to the side which pulls the actin filament along in a rowing action
        3) Breaking of the cross bridge
        ATP provides energy to also break cross bridge so myosin head detached from actin filament after it moved
        myosin head then returns to starting position and reattaches to different binding sie further along the actin filament
        new cross bridge is formed and cycle is repeated. many cross bridges rapidly form and break pulling actin filament along which shortens the sarcomere causing muscle to contract
        as long as ca2+ is present and bound to troponin, cycle will continue
        4) Returning to resting state
        when muscle stops being stimulated, ca2+ ions leave binding sites on troponin molecules are are moved by active transport back into sarcoplasmic reticulum (needs ATP)
        the troponin molecules return to their original shape, pulling attached tropomyosin molecule with them so tropomyosin now blocks the actin-myosin binding sites again
        mucle now cant contract as no myosin heads are attached to actin filaments so there are noa-m cross bridges
        actin filaments slide back to relaxed position lengthening sarcomere
Behaviour
1. = an organisms response to changes in its external environment, these responses help organisms survive and reproduce. Behaviour is influenced by genes and environment.
2. INNATE BEHAVIOUR
  1. behaviour organisms do instinctively
  2. genetically determined
  3. requires no thought or learning, respond straight away
    1. eg new born babies instinctively suckle from their mothers
  4. not influenced by environment
  5. inherited from parents
  6. it is stereotyped= always carried out in the same way and by all indiciduals in a species
  7. Escape Reflexes
    1. the organism moves away from potential danger
    2. eg cockroaches run away when threat of being squashed
  8. Tactic Responses (TAXIS)
    1. directional movement in response to a stimulus
    2. direction of stimulus affects response
    3. eg woodlice move away from light source, keep safe from predators
  9. Kinetic Responses (KINESIS)
    1. non-directional (random) movement in response to a stimulus
    2. intensity of stimulus affects the response
    3. eg woodlice under low humidity move from dry air to more humid air and stay put as this reduces water loss so improves chances of survival
  10. complex example: bee waggle dance
    1. a display used by worker honey bees to communicate the direction and distance of a food source to other worker bees this helps bees find food source
3. LEARNED BEHAVIOUR
  1. Habituation
    1. = a reduced response to an unimportant stimulus after repeated exposure over time
    2. an unimportant stimulus is a change that isnt threatening or rewarding
    3. an animal quickly learns to reduce or stop response to unimportant stimulus so it doesnt waste time and energy responding to unimportant things
    4. however animals remain alert to unfamiliar stimuli
    5. eg living near busy road, noise of traffic wont keep u awake at night as you stop responding to noise so sleep through it but an unfamiliar noise lik ea car crash will wake you up
  2. Classical Conditioning
    1. = learning to respond naturally to a stimulus that doesnt normally cause that response (association)
    2. before conditioning a natural stimulus (unconditioned stimulus) can cause natural response (uncondtioned response)
    3. if neutral stimulus coincides with unconditioned stimulus enough times, eventually neutral stimulus (now conditioned stimulus) will on its own cause the same response as the uncondtioned stimulus (condtioned response)
    4. eg in dogs: uncondtioned stimulus= food, unconditioned response= salivation; if a bell is rung immediately before dogs given food, dog will salivate to sound of bell. neutral stimulus= bell, is associated with unconditoned stimulus = food, triggers salivation (unconditoned), bell by itself= conditioned stimulus trigger conditioned response= salivation
  3. Operant Conditioning
    1. =learning to associate particular response with a reward or punishment (reinforcement)
    2. when in same sitaution several times, animal will work out which response gets reward or punishment
    3. the response must be rewarded or punished stright away, this reinforces behaviour so animal is more likely to repeat behaviour if it is rewarded
    4. eg rat put in a cage with choice of leves, pressing one lever rewarded rat with food and the rat was repeatedly put in same cge so learned which level to press to get the reward
  4. Latent Learning
    1. =hidden learning
    2. an animal doesnt immediately show its learned something
    3. it involves repetedly doing the same task
    4. animal only shows it's learned something when its rewarded or punished
    5. eg three groups of rats put in same maze repeatedly
      1. group 1 were reinforced with reward each time they reached the end, they quickly learned their way around the maze
      2. group 2 were not reinforced (no reward) and continued to plod around maze and took ages to reach the end
      3. group 3 were only rewarded from 11th time they did the maze, after this they vert qickly reached the end with hardly any errors. the rats had been learning the maze all along without any reinforcement but they didnt show their learning until there was a reward
  5. Insight Learning
    1. =solving a problem by working out a solution using previous experience
    2. solving problems by insight is quicker than by trial and error as actions are planned and worked out
    3. eg chimpanzees put in play area with sticks, clubs and boxes. bunches of bananas were hung out of reach. chimps used previous experience of playing with objects to work out a soltuion: they piled up boxes to reach banaanas and used the sticks and clubs to knock them down
  6. =behaviour influenced by environment and is modified as a result of experience
  7. it is not sterotyped, it varies in different individuals in the same species
  8. allows animals to respond to changin conditions
4. IMPRINTING
  1. =combination of learned behaviour and innate behaviour
    1. eg animal learns to recognise its parents and instinctively follows them
  2. a newly born animal has an innate instinct to follow the first moving object it sees (usually mother or father) who provide warmth, shelter and food (helping suvivl)
    1. but the animal has no innate instinct of what its parents look like- need to learn this.
      1. once learned imprinting is fixed and irreversible, use later in life to identify mates from same species
  3. only happens during critical period (soon after birth)
  4. Lorenz- ducklings followed mother and him (2 gorups, first moving object)
5. UNDERSTANDING HUMAN BEHAVIOUR
  1. animals behaviour depends of structure of brain (neurotransmitters, synapses, receptors etc)
  2. dopamine receptor D4
    1. dopamine= neurotransmitter
      1. can affect mood and behaviour
      2. 5 different receptors for dopamine (d1-d5)
        effects of dopamine vary depending on which receptor it binds to
        each receptor is coded for by a different gene
    2. D4 receptor protein is coded for by the DRD4 gene
      1. too many d4 receptors linked to abnormal behaviour eg schizophrenia -disorder effects thinking, perception, memory and emotions
        evidence for this link: -drugs that stimualte dopamine receptors are given to healthy people, causes abnormal behaviour -drugs that block D4 receptors reduce symptoms in schizophrenics -people with schizophrenia have higher density of D4 receptors in brain -one drug used to treat schiz binds to D4 receptors better than it binds to other dopamine receptors
        link between D4 receptor and abnormal behvaiour helps us understand roel of D4 in normal behaviour as it is involed in thinking , perception, memory and emotions
6. SOCIAL BEHAVIOUR IN PRIMATES
  1. SB= behaviour involving members of large groups nteracting with eachother
  2. primates=baboons, apes, humans
  3. social behaviours have advantages
    1. Baboons live in groups of around 50, + large group is more efficeient at hunting for food, communicate good food sources
    2. Hireachy of adult males, + prevents fighting as males know rank in order
    3. Groom eachother, +hygeinic and reinforce bonds between members of group

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RESPONDING TO THE ENVIRONMENT (behaviour and muscle contraction)

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