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Imagine the sliding filament model. In particular, make sure you know where each band/area lies, and what happens to the lengths of each as it contracts. Don't pass unless you know the different areas!
Ok, imagine another, slightly zoomed out diagram starting from the muscle fibre.
Two types of protein filament are involved in contraction. Which is which?
- The thin filaments are chiefly made of protein actin.
- The think filaments are bundles of the protein myosin.
Describe the structure of the thin & thick filaments that allow them to function in the sliding filament model.
- Thin filament: 2 strands of actin, coiled around each other. Tropomyosin (a rod-shaped protein) molecules coil around the actin. A troponin complex is attached to each tropomyosin. Each troponin consists of 3 polypeptides - one binds to actin, one to tropomyosin and one to calcium ions.
- The binding site for myosin head group on actin fibre is covered by this tropmyosin in normal relaxed times.
- Thick filament: Bundles of protein myosin. Each myosin molecule consists of tail and protruding globular heads. Each thick filament consists of many myosin molecules whose heads stick out from opposite ends of the filament.
- These globular heads are what binds to the binding sites on the actin during contraction.
1) What is the bond between the myosin head and the binding site on actin flimament called? 2) What is the movement of the filament called when it contracts?
- 1) cross-bridge
- 2) power stroke
Outline the steps that occur in the sliding filament model.
- 1. Binding sites on actin in resting muscles are blocked by tropomyosin (held in place by troponin). Myosin heads can't bind to actin binding site.
- 2. Action potential triggers influx of calcium ions. This happens because... depolarisation of sarcolemma spreads down the T-tubules to sarcoplasmic reticulum causing it to release stored calcium ions into sarcoplasm.
- 3. Calcium ions bind to troponin, causing it to change shape, which causes tropomyosin to move away from binding sites on actin.
- 4. This exposes the actin-myosin binding sites, allowing cross-bridges to form. This allows the power stroke to happen.
- 5. The head group then bends, causing the thin filament to be pulled along and so overlap more with the thick filament. This is the power stroke.
- ATP, which was attached to the myosin head, is used up and ADP and an inorganic phosphate is released.
- 6. When the myosin attaches to the binding sites in a cross-bridge, the molecules are in their most stable form. Energy from ATP required in order to break the cross-bridge connection and re-set the myosin head forwards.
- 7. The myosin head then reattaches to a different binding site further along actin filament and the cycle is repeated. The cycle will continue as long as calcium ions and ATP are present.
Outline briefly what happens after the excitation stops.
- 1. When muscle stops being stimulated, calcium ions leave their binding sites on troponin and are moved by active transport back into the sarcoplasmic reticulum, by carrier proteins on the membrane (This needs ATP too).
- 2. Troponin return to original shape, tropomyosin moves back, covering the binding sites, so cross-bridges can't form.
- 3. Actin filaments slide back to their relaxed position, which lengthens the sarcomere.
What is the role of ATP in muscular contraction?
It gets hydrolysed when the mysoin breaks off from the actin, which needs energy.
How is the supply of ATP maintained in muscles? (3)
- Aerobic respiration in cell mitochondria - level of ATP regeneration depends upon supply of oxygen to muscles and the availability of respiratory substrate (eg. glucose).
- Anaerobic respiration in muscle cell sarcoplasm - quite quick, but leads to production of lactate, which is toxic. Lactate enters the blood, where it leads to stimulation of increased blood supply to muscles. Remember how glycolysis produces pyruvate, and pyruvate converted to lactate by lactate fermentation.
- Transfer from creatine phosphate in muscle cell sarcoplasm - phosphate group from creatine phosphate can be transferred to ADP to form ATP very quickly by the action of enzyme creatine phosphotransferase. So ADP is phosphorylated.
- This system runs out after short burst. It is anaerobic, but does not produce any lactate.
Remember, muscle fibre is a ___. Myofibrils are ___. These are the bits concerned when we are looking at the sliding filament model. Instead of the endoplasmic reticulum, there is the ___ ___, and instead of plasma membrane, it's the ___.
- sarcoplasmic reticulum
List 3 uses of ATP in muscle cells.
- Contraction of sarcomeres in power stroke
- Protein synthesis
- Regeneration of creatine phosphate when muscle is at rest.
Responses to environmental stimuli in __ are coordinated by the ___ and ___ systems. The coordination of responses is mainly the result of __ activity. The ___ also regulates a number of ___ responses through the action of the ___ and its control on the __ gland.
What is the 'fight or flight' response?
The full range of coordinated responses of animals to situations of perceived danger. The combines nervous and hormonal response has dramatic effects on whole organism, making it ready for actions that lead to confrontation of the danger or escape from it.
Explain how the 'fight or flight' response is coordinated by the nervous and endocrine systems.
- When we take in a threatening stimuli (such as sight of lion running at you), then this response it initiated.
- Brain (I think hypothalamus - CHECK) activates the sympathetic nervous system.Sympathetic n.s not only activates various target organs, it also triggers release of hormone adrenaline and noradrenaline from the adrenal medulla.
- Hypothalamus also releases corticotropin-releasing factor (CRF) into pituitary gland, stimulating release of hormone adreno-corticotropic hormone (ACTH) from anterior pituitary gland. This hormone stimulates release of various corticosteroid hormones from the adrenal cortex (outer parts of adrenal glands). Some of these help body resist stressors.
Between the sympathetic nervous system and the endocrine system, the 'fight or flight' response is brought about. For example, what physiological changes? (9)
- Increased heart rate and blood pressure
- Pupils dilate
- Arterioles to digestive system and skin are constricted whilst those to the muscles and liver are dilated, so more blood is supplied there.
- Blood glucose conc increases.
- Metabolic rate increases.
- Hair stand up - to make animal look bigger, scaring the threat away.
- Endorphins (natural painkillers) are released in brain.
- Sweat production increases - heat needs to be removed.
- Breathing rate and depth increase - CO2 removed faster and increased supply of oxygen.
What is innate behaviour?
- Any animal response that occurs without the need for learning.
- It is an inherited response (genetically determined reflexes), similar in all members of the same species and is always performed in the same way in response to the same stimulus.
Quickly list the main differences between innate and learned behaviour. (3)
- Innate: Genetically determined - environment has no impact, passed onto offspring. Learned: Determined by genetic make-up and environmental influences, can't be passed on but may be taught to offspring.
- I: Rigid and inflexible; L: Can be altered by experience.
- I: Patterns of behaviour the same in all members of a species (stereotyped). L: Considerable variety between members of species.
- Also, learned behaviour form the basis of all intelligent and intellectual activity.
What is the advantage of innate behaviour to an organism?
Organisms can respond in the right way (in a way that increases chance of survival - remember this has been inherited so it must be good), and quickly - because no learning is needed.
Why does the short life span of invertabrates mean that innate responses are more important to their survival thatn learned responses?
- Because their short lifespan gives them little time to learn survival skills, whereas innate behaviour can be put to use from the beginning of life, as it is carried in the DNA.
- Learning also takes place usually, by following a parent, but because of the short life span and the solitary lives of these invertabrates, they will not be able to learn with a parent.
List the 3 examples of innate behaviour I need to know. What type of organism are these 3 important in to help them survive?
- Escape reflexes
- Kineses (singular; kinesis)
- Taxes (singluar; taxis)
Describe escape relex in an invertabrate.
- A fast, autonomic response to avoid/escape predators.
- Earthworms withdraw underground in response to vibrations on the ground, sensed by touch receptors. The longitudinal muscles contract to make the body shorten too.
Describe kineses with an example.
- Innate behaviour where the rate of movement increases when the organism is in unfavourable conditions.
- The behaviour is non-directional - response is just to change the rate of movement overall in relation to the intensity of the stimulation, not in any particular direction.
- Eg. Woodlice avoid predation and drying out by living in dark, damp areas. When placed in dry/bright conditions, woodlice will move around rapidly and randomly until they are in more suitable conditions (damper and darker), when they will move slowly or even stop moving.
Describe taxes with an example.
- A directional orientation response. The direction of movement is described in relation to the stimulus which triggers the behavioural response.
- So, positive phototaxis is towards, negative phototaxis is away from, light stimulus.
- Eg. A nematode (worm) have chemoreceptors that sense the chemical signals in the air. It moves its head side to side to compare signal strengths before moving its body towards or away from the chemical.
The linking together of a series of __ behaviours gives some __ behaviour patterns in invertabtrates. Give an example.
- The waggle dance by worker honey bees to communicate direction and distance of a food source to other worker bees.
Explain the meaning of the term 'leaned behaviour'. (SPEC)
Behaviour which shows adaptation/change in response to experience.
What are the 6 different types of learned behaviours we need to know about?
- Classical conditioning
- Operant conditioning
- Latent (exploratory) learning
- Insight learning
- Habituation: Reduced response to an unimportant stimulus after repeated exposure to the stimulus results in neither a reward nor a punishment.
- It avoids wasting energy responding to unimportant stimuli.
- Involves young animals becoming associated with (imprinting on) another organism - usually the parent.
- Imprinting only occurs in a sensitive period (also known as receptive period). [eg. 36hrs in gosling]
- Important in helping the young learn skills from the parents. Eg. Flight in birds
Describe classical conditioning.
- When an animal learns to respond automatically to a stimulus that doesn't usually cause that response.
- 1. A natural stimulus (unconditioned stimulus) causes a reflex action (unconditioned response) - eg. dog salivates when there is a smell of food.
- 2. If another unrelated stimulus is associated/coincides with an unconditioned stimulus enough times, eventually this other stimulus alone will cause the response.
- 3. Here, the associated stimulus is called the conditioned stimulus, and the response is the conditioned response. Eg. bell ringing - conditioned stimulus; salivate - conditioned stimulus.
- This type of learning is passive and involuntary.
Describe operant conditioning.
- Learning to associate a particular response/operation (hence operant) with a reward or a punishment.
- The reward or punishment (called reinforcers) should be given straight away.
- This leads, over time, to an increased frequency of actions that give leads to the reward.
- This type of learning is active and to an extent voluntary.
- Often called trial and error learning.
Describe latent learning.
- 'Hidden' learning - an animal doesn't show it has learnt, until it is placed in a situation where reward/punishment is introduced.
- Eg. A rat runs around randomly around a maze many times. Here, it has no incentive to do anything, so movement is random and doesn't get any quicker at finishing the maze. But when reward is introduced, it learns to get the end faster than a mouse which had no previous experience of the maze. The rat had learned the pattern of the maze even when there was no reward in doing so.
Describe insight learning.
- The highest form of learning. Based on the ability to think and reason in order to solve problems that do not resemble simple fixed, reflex responses or the need for repeated trial and error.
- The animal solves the problem by working out a solution using information from experience - like a box can be stood on.
- Once solved, the solution to the problem is remembered.
What is social behaviour?
That of organisms of a particular species living together in groups with relatively defined roles for each member of the group.
Give the advantages of social behaviour in primates (remember, you're going to use mountain gorillas as the example). (7)
- Knowledge and protection of food sources is shared with the group.
- Greater ability to detect and fight off predators is achieved by group members working together.
- Learned behaviour can be passed on. Insight learning, perhaps of just one individual, can be copied by all the other individuals and generations. Cultural learning.
- Female gorillas only give birth to one (or very few) infants at a time, so maternal care and group protection enhances survival rate of the young. Remember, in primates, there is an extended care of the young.
- The young learn by observing other members of the group and playing with them.
- The hierarchy in groups (groups called a troop - usually 10-15 members) prevent wasting energy fighting, as each know their place in society. Also, members know their role, so efficiency too.
- Grooming - increased hygiene and reinforce social bonds.
What is the specific example we need to know about human behaviour?
Dopamine receptor DRD4
What is dopamine and its usual role? There are different type of dopamine ___, but the one we need to learn about is ___.
- Dopamine is a neurotransmitter in the brain.
- It is involved in the autonomic nervous system, and when given this drug, it increases activity of sympathetic neurones.
Abnormally low levels of dopamine is associated with ___ ___. To treat this, dopamine levels are increased resulting from treatment. Raised dopamine levels is sometimes linked to what?
- Parkinson's disease
- Raised dopamine levels is sometimes linked to schizophrenia and other mental health conditions.
- Also noted that patients with Parkinson's who are treated with more dopamine are prone to behavioural changes such as compulsive gambling.
The range of activities affected by dopamine is partly due to the __ and __ of dopamine __. There are __ different dopamine __ from __ to ___.These are all coded by the __ genes.
- number and variation
- receptors (dopamine binding to different dopamine receptors causes different cellular responses).
- DRD1 to DRD5
Binding dopamine to its receptor is involved in a number of processes such as what? Dopamine receptor __ __ are used to treat ___.
- For example, control of motivation and learning, and is linked to regulatory effects on other neurotransmitter release.
- targeted drugs
- psychosis (mental health condition characterised by impaired grasp on reality and disorder of perception etc.).
Give 2 examples of conditions that DRD4 receptor seems to contribute to.
- A particular variant of the DRD4 dopamine receptor has been shown to be more frequent in individuals suffering from attention-deficit hyperactivity disorder (ADHD).
- Particular variants of the DRD4 receptor gene are implicated in increased likelihood of addictive behaviours, such as smoking and gambling.
Human behaviours are very complex. But the correlation between certain behaviour and DRD4 receptors show what?
- That human behaviour is, most likely, influenced in some form by genetic makeup and physiology in the brain.
- The complex human behaviour is, however, most definitely caused by a combination of environmental causes and genetic causes.