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29 Cards in this Set
- Front
- Back
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How do organisms increase thier chances of survival?
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By responding to changes in their environment
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What is a tropism?
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A response to a directional stimuli that can maintain the roots and shoots of flowering plants in a favourable environment
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What is a taxes?
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A simple response whose direction is determined by the direction of the stimulus
E.g. moving towards a favourable stimulus or away from an unfavourable stimulus |
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What is a kinesis?
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A response whereby the more unpleasant the stimulus, the more rapidly the organism moves and the more rapidly it changes direction.
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What do taxes and kinesis achieve for an organism?
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Keeps the organism in a favourable environment
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Outline the reflex arc
SRS.IMER |
Stimulus, receptor, sensory neurone, intermediate neurone, motor neurone, effector, response
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What is the importance of reflexes? (3)
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Involuntary - brain not overloaded
Protect from harmful stimuli Fast with short pathway |
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What part of the brain is responsible for heart rate?
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Medulla oblongata, split into two sections
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What is the role of the sympathetic NS in controlling HR?
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Sympathetic stimulates effectors --> Speeds up an activity (fight or flight)
Antagonistic with parasympathetic |
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What is the role of the parasympathetic NS in controlling HR?
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Inhibits effectors --> Slows down an activity (rest and digest)
Antagonistic with sympathetic |
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When blood pressure is higher than normal...
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Pressure receptors transmit an impulse to DECREASE HR
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When blood pressure is lower than normal...
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Pressure receptors transmit an impulse to INCREASE HR
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What is produced when a pacinian corpuscle is stimulated?
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A generator potential
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What kind of stimulus does the pacinian corpuscle respond to?
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Mechanical
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What is a transducer, how is the pacinian corpuscle one?
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A transducer converts one type of energy into another.
E.g. PC converts mechanical impulses into a nervous impulse (known as the generator potential) |
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How do nerves stimulate their target cells?
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They secrete neurotransmitters onto them
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What are three characteristics of nervous impulses?
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Rapid, short lived, localised
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How do hormones reach their target cells?
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Via the blood
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What are the three characteristics of hormones?
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Slow, long-lasting, widespread
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Name two chemical mediators:
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Prostaglandins and histamines
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What areas to chemical mediators effect?
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Cells in the immediate vicinity
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What is the importance of the refractory period?
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APs are propagated in one direction only
Discrete impulses (new AP cannot be formed behind the first one) Limits the number of APs |
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What factors affect the speed of conduction?
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Myelination
Axon diameter Temperature |
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What is saltatory conduction?
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A nerve impulse along a MYELINATED axon in which the AP JUMPS from one node of Ranvier to another
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Outline the all-or-nothing principle
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A threshold value is required to stimulate an AP - if it isn't reached no AP occurs, if it is reached, one AP occurs - regardless of power of stimulus
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How does an organism perceive the size of a stimulus? (2)
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The number of impulses passing in a given time
Different neurones have different threshold values |
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What is unidirectionality?
Think! |
SYNAPSES can only pass impulses in one direction
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What is temporal summation?
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When a SINGLE presynaptic neurone releases neurotransmitter many times over a short period - total amount exceeds the threshold value of postsynaptic neurone --> AP
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What is spatial summation?
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When MANY presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone --> AP
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