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Lecture 3

BGYB30H3 Lecture 3 Notes The Action Potential 1 Sep 17

Biological Sciences
Course Code
Ingrid L.Stefanovic

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BGYB30H3 Lecture 3 Notes
-all cells try to maintain resting potential (nerve and muscle cells)
-these cells respond to changes in membrane permeability by opening and closing ion channels
-electrodes are used to give voltage readings through a voltmeter (able to measure differences in
membrane potential between IC and EC compartments
-membrane potential difference is relative to 0
-depolarization is that membrane potential is moving towards 0
-hyperpolarization is that membrane potential is moving more negative than resting membrane
-repolarization is that membrane potential moves away from 0 to resting membrane potential
-sodium channel has inactive and active gate
-at rest, sodium active gate is closed and inactive gate is open
-depolarization involves opening active gate
-at 30mV, inactivation gate closes, in repolarization, activation gate closes
-sodium flux happens when both gates are open
-the two types of potassium channels are leak and non leak channels
-at RMP, leak channels are open and non leak are closed
-depolarization involves leak channels closed and non leak channels are opened
-hyperpolarization involves leak channels open and non-leak channels are closed
-potassium channels are slow to activate and inactivate
-sodium channels are quick to activate and inactivate
-changes in membrane potential are localized in the cell membrane while the rest of the cell is
negatively charged
-IC and EC are relatively stable
-axon hillock of the neuron is the trigger zone where action potentials occur and travel
-chemicals move up and down axon while electricity moves down axon
-myelin sheath insulates the neuron and is comprised of glial cells
-cell body collects and integrates info
-there is either fast or slow chemical signaling
-chemical signals such as peptides are packaged by the Golgi apparatus and sent down the axon
transport quickly
-microtubules direct flow of chemical messengers in the axon
-retrograde transport moves chemical signals back up axon to be broken down by lysosomes
-anterograde transport moves chemical signals down the axon to release vesicles
-at the synaptic junction, vesicles are released by exocytosis
-amplitude of graded potentials is directly proportional to the strength of the triggering signal
-graded potentials decrease in amplitude as it moves through the cell body by local current flow
-Ál]uµ]v]Ìu}À]vP}ÁvZoo}Çv}v[}µvction potential
- (-55mV) is the threshold to generate action potentials
-strong stimulus decreases in size but will be above threshold to generate action potential
-amplitude of action potential is not directly proportional to stimulus (once at threshold is reached,
same action potential no matter strength of stimulus)
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