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35 Cards in this Set
- Front
- Back
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Where do neurones meet? Do they touch? |
Meet at a synapse They don’t touch > communicate across a small gap called a synaptic cleft |
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Why does the sodium potassium pump mean the neurone is more positively charged on the outside? |
Both sodium and potassium are positively charged Ratio created means more positive charge on outside as 3 Na+ are pumped out when only 2 K+ are pumped in! Each has +1 charge therefore this adds a net +1 charge to the outside (3-2 = 1) |
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Sodium potassium pump |
• pumps > active transport (using ATP) • 3 Na+ out for every 2 K+ in • membrane impermeable to sodium ions > x move back in > Na+ electrochemical grad created • membrane permeable to potassium ions > move back in by facilitated diffusion through k+ ion channels • brings back to resting potential (-70mV) >> outside ^ +vely charged than inside of the cell |
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What does neurotransmitters binding to receptors lead to? (CNS & endocrine system) |
• triggers an action potential in neurone • triggers release of hormones secreted from glands |
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Oscilloscope function |
Measures the potential difference |
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Synaptic cleft |
Gap between the neurones |
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What is meant by a volted gated channel ? |
A channel that only opens at a certain voltage e.g. K+ & Na+ channels |
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Stimulus (1st step of impulse transmission) |
Excites neuron cell membrane causing depolarisation |
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Depolarisation (process) |
• stimulated by impulse > action potential arrives • +40 mV • Na+ open > (INFLUX) move into neurone > +ve feedback • down electrochemical gradient (originally ^ +ve on outside so moves inside) |
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Repolarisation (process) |
• No stimulation > action potential leaves • -70 mV • Na+ closed • K+ open > (EFFLUX) K+ diffuse out of neuron 1) down electrochemical grad (originally ^ +ve charges inside neurone) 2) down conc. grad (^ inside neurone so moves outside) |
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Hyper polarisation |
• -80mV (refractory period) • Na+ close • K+ open > slow to close > K+ EFFLUX leaves neurone (causes ‘overshoot’) >>down electrochemical gradient as ^ +ve on outside |
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Resting potential (process) |
• -70 mV • polarised • voltage gates (Na+ & K+) closed • sodium potassium pump returns membrane to rest until excited |
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What type of cells have a potential difference across the cell membrane? |
All cells |
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Where are the sodium potassium pumps & potassium ions channels found? |
On the cell membrane |
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How is the negative charge in a neurone created |
Movement of K+ outside of the neurone (efflux) as membrane permeable to K+ |
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Potassium ions channel |
• facilitated diffusion (passive, down conc grad) • membrane is permeable to K+ > able to diffuse in & out of neurone through these channels |
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What is potential difference? |
A difference in voltage across a membrane |
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What is saltatory conduction |
Jumping of the electrical impulse from one node of ranvier to another (> to speed up impulse transmission) (only places where depolarisation can occur) |
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Propagation of impulse |
Sending the impulse |
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Why can’t a new action potential be immediately generated? |
• ion channels closed as recovering • time delay between action potentials > ensures action potentials x overlap (are discrete/separate impulses) • ensures action potentials are unidirectional (travel in one direction) |
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What is the role of the myelin sheath? |
• myelin sheath made up of schwann cells • saltatory conduction > impulse jumps from node to node • insulates > prevents other impulses travelling down neurone (x interfere w/ impulse) • ^ speed of impulse transmission • depolarisation ONLY occurs at nodes of Ranvier • local currents over long distances |
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How does the action potential move along the neurone? |
1) sodium ions diffuse sideways 2) causes sodium ions channels in next region to open > Na+ diffuse into that part 3) causes wave of depolarisation to travel along neurone +wave moves away from parts of the membrane in the refractory period as these x fire action potential |
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What causes a greater reaction to a stimulus |
• ^ frequency of impulse transmission (STRENGTH IS UNIFORM/ doesn’t change) |
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Why are messages changed |
Electrical> chemical so it can be transferred to the next neurone along |
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Synapse |
Junction between a pre synaptic neurone and post synaptic neurone (Where they join, the WHOLE thing) |
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Synaptic knob |
On both pre and post synaptic neurones Contains synaptic vesicles with chemicals called neurotransmitters |
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What is acetylcholine involved in |
controlling muscle contraction and heart rate |
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Impulse arrives (chemical process) |
1) action potential arrives at synaptic knob 2) (stimulation) causes voltage gated calcium channels to open 3) calcium ions diffuse into the synaptic knob 4) calcium ions actively pumped out afterwards (active transport) |
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Neurotransmitter release |
1) Influx of Ca+ into synaptic knob (& ATP from mitochondria) causes synaptic vesicles to move to presynaptic membrane 2) vesicles fuse with pre synaptic membrane 3) release neurotransmitter into synaptic cleft by exocytosis |
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Stimulation of the postsynaptic membrane |
1) neurotransmitter diffuses across synaptic cleft & bind to specific receptors on proteins of post synaptic membrane 2) causes sodium ion channels in post synaptic neurone to open 3) influx sodium ions causes depolarisation if this reaches the voltage threshold leading to an action potential |
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Inactivation of neurotransmitter |
1) enzymes break down the neurotransmitter > diffuses away from the synaptic cleft 2) actively pumped into presynaptic neurone (reputake channels) 3) taken up by cells of the nervous system |
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Acetylcholinesterase |
• enzyme (at post SM) that breaks down acetylcholine so that it can x bind to receptors > reabsorbed by presynaptic neurone • acetylcholine > acetate + choline |
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What does the opening of potassium channels cause? |
Repolarisation |
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What does sodium channels opening lead to? |
Depolarisation |
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How is potential difference created? |
Generated through ion pumps & channels |
