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42 Cards in this Set
- Front
- Back
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What are the differences between the transmission of hormones and nerves?
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Chemical/electrical
Bloodstream/neurones slow/rapid (amplitude-modulated/frequency-modulated) |
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What are the differences between hormonal and nervous responses?
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Slow/fast
Widespread (although only target organs respond)/localised long-lasting/short-lived |
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What are the 2 types of hormones?
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Peptides - amino acids (water soluble)
Steroids - lipid (lipid soluble) |
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What are chemical mediators?
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Substances that have an effect on surrounding cells without travelling in the blood
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What is histamine and describe its function/mode of action?
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A local chemical mediator
released by mast cells and released following allergen/injury; causes allergy inflammation/mucus/swelling/itching |
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What is prostaglandis and describe its function/mode of action?
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A local chemical mediator (lipid compounds)
Found in cell membrane; dilation and constriction of blood vessels/contraction of smooth muscle/inflammation (by changing permeability of capillaries)/blood pressure/pain neurotransmitters |
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Describe the mode of action of water-soluble hormones (peptides)
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Bind to specific membrane receptor;
cause formation of second messenger; changes activity of specific enzyme; (binding activates adenyl cyclase to convery ATP into cyclic AMP - 2nd messenger) |
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Describe the mode of action of steroid hormones
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Bind to a receptor in cytoplasm;
complex binds to DNA and alters gene expression |
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Why is plant growth factors a more correct term than plant hormones? (3)
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Act on cells that produce them
Produced throughout the plant Affect growth |
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What is the function/mode of action of IAA?
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Causes cells to elongate
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Explain shoot/root geotropism/phototropism in terms of plant growth factors
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IAA diffuses from tip of the shoot Shoot:IAA accumulates on underside of shoot High conc of IAA stimulates growth (through elongation) IAA accumulates on the dark side and stimulates growth Root: IAA accumulates on underside of root High conc of IAA inhibits growth |
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What is a neurone?
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A nerve cell (a specialised elongated cell)
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What are the features of neurones?
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1. cell body - nucleus and RER for proteins/neurotransmitters
2. axon - single fibre carrying away from cell body 3. dendrites - take impulses towards cell body 4. Schwann cell - surround axon and provide electrical insulation. ALSO carry out phagocytosis and regenerate nerves 5. Myelin sheath - membranes of Schwann 6. Nodes of Ranvier - unmyelinated parts |
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What is the difference between a nerve and a neurone?
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Nerve - bundle of axons surrounded by connective tissue
neurone - a single nerve cell |
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Describe the difference in structure between a sensory neurone and a motor neurone
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Sensory = one axon and one dendron
Motor - one axon and many dendrites |
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What is a nerve impulse?
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A self-propagating wave of depolarisation that spreads along the axon membrane
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What is the advantage of a lograithmic scale?
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Allows a large range of y values to fit
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Suggest how a plant growth factor can be used as a weed-killer
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Absorbed more by weeds than other plants
High conc causes rapid growth and excessive elongation and death May not be broken down easily |
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Describe how the resting potential is established in an axon and maintained.
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Membrane is polarised (negative inside and positive outside)
Sodium-potassium pump pumps out sodium ions faster than K+ pumped in/3 for 2 membrane more permeable to potassium ions potassium ions diffuse out 50* faster |
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What is the resting potential?
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-70mV
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Describe the events that produce an action potential
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polarised axon membrane;
stimulus causes some voltage gated sodium ion channels to open; sodium ions DIFFUSE into the axon; causing depolarisation; If stimulus is of threshold; positive feedback causes more (and eventually all) sodium ion channels to open; adjacent region of axon stimulated and impulse propagated; all-or nothing |
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Explain why intensity of a stimulus has to be conveyed by frequency of impulses
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all-or-nothing
Below TSI, no impulse Above TSI - max impulse |
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Explain how pressure on the Pacinian corpuscle produces an action potential
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Pressure defroms layers of lamellae
Causes stretch-mediated sodium channels to open Sodium ions diffuse into axon causing depolarisation increased pressure opens more channels |
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Why can sodium and potassium ions only cross the axon through proteins?
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Charged, polar particles cant pass through hydrophobic fatty acid tails of phospholipid bilayer
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Why is it important that the resting potential is established?
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Allows depolarisation to occur quickly
As chemical/electrical gradient set up |
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Describe the process of repolarisaiton
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potassium ion channels open and potassium ions diffuse out due to due to reversed electrical gradient
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What are the 2 different refractory periods? Why is the refractory period important?
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absolute - no impulse created as potassium channels open, and hyperpolarisation
relative - another impulse but greater threshold; ensures action potentials are discrete; limits the number of action potentials; ensures unidrectional propagation |
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What increases the speed of impulse transmission?
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Higher temp = faster diffusion of ions/opening of gates
myelination - insulates nerve, saltatory conduction, impulses jump between permeable nodes of Ranvier (larger local circuits) Larger axon diameter = less leakage of ion and easier to maintain membrane potentials (less resistance to movement of ions) |
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The rate of ATP consumption of a de-myelinated neurone is greater than a myelinated neurone. why?
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Depolarisation occurs across length of membrane so greater entry of sodium ions;
greater active transport to pump back more ions |
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In what two ways can a different intensity stimulus be differentiated?
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Frequency of impulses
Threshold value |
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How is synaptic transmission made to be unidirectional?
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Neurotransmitter is only produced in the presynapticneurone
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What is the importance of synapses?
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Allow a single impulse to be transmitted t omany neurones
Allow a number of impulses to be combined at one neurone |
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What is temporal summation?
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A number of impulses arrive in quick succession down the same neurone, release enough neruotransmitter to exceed the threshold (EPSP) value of the postsynaptic neurone
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What is spatial summation?
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A number of impulses arrive from different neurones at the same time, releasing more neurotransmitter to exceed the threshold EPSP
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What is a cholinergic synapse and what is an adrenergic synapse? Descirbe the acitons of serotonin
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Cholinergic = synapse that releases acetylcholine - most voluntary nerves and neuromuscular junctions
Serotonin regulates sleep/controls mood Dopamine Adrenergic = release noradrenaline (SNS) |
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What are the two different kinds of synapses? How do they function?
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Excitatory and inhibitory. Excitatory release a neurotransmitter that binds to receptors on post-synaptic membrane and produce an EPSP by changing permeability of sodium ion channels
Inhibitory cause hyperpolarisaiton by changing permeability of chloride ion channels (or potassium ion) |
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Describe the transmission of an action potential at a cholinergic synapse
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Action potential arrives at the synaptic knob;
calcium ion channels open/Ca2+ ions diffuse in; vesicles of acetylcholine fuse with presynaptic membrane; acetylcholine diffuses across cleft; binds to specific complementary receptor; sodium ion channels open and sodium ions diffuse in causing depolarisation/EPSP; if threshold exceeded - action potential; acetylcholinesterase hydrolyses into ethanoic acid and choline which diffuse back; ATP recombines |
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Why is it necessary for acetylcholine to be hydrolysed by acetylcholinesterase?
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To recycle choline and ethanoic acid;
to prevent continous generation of an action potential (due ot open Na+ channels) |
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How can the diffusion of chloride ions into the post-synaptic membrane inhibit impulse transmission?
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Hyperpolarisation;
Action potential not produced/stimulation does not reach threshold; Depolarisation does not occur |
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Explain why the demyelination of an axon results in slower conduction than myelinated?
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Depolarisation has to occur across the whole length of an axon;
Depolarisaion occurs only at nodes; impulse unable to jump from node to node/no saltatory conduction |
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Explain the change in resting potential with a metabolic poison
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No respiration/no ATP
no active transport Sodium ions not pumped out sodium ions still diffuse in sodium ions accumulate/more positive inside potassium ions reach equilibrium |
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Explain how spatial summation resulst in an action potential
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Cause sufficient depolarisation;
for threshold |
