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HMB200H1 (44)
Final

# HMB200H1 Final: Lecture 4 Revision Guide Premium

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Department
Human Biology
Course
HMB200H1
Professor
Franco Taverna
Semester
Winter

Description
Lecture 4 Revision Guide Nernst Equation: for 1 ion Equilibrium Nernst-Goldman Equation: for 2+ ions Permeability - Upon receiving signal from other neurons, voltage changes passively Action Potential diffuse  integration zone o Where large # of voltage-dependent ion channels exist - Voltage accumulates—the more channels open, the more channels then open o More depolarized  more channels open - All of nothing response—doesn’t vary in degree Voltage-sensitive ion channels: - Both Na & K (not the K leak channels)—tuned to -50 mV [to open] o Triggers action potential 1. Na channels open a. Na influx  depolarization b. Occurs very quickly 2. K channels open a. K efflux  repolarization b. K channels open more slowly—thus allowing the Na + depolarization 3. K channels close a. K channels close slowly  undershoot (hyperpolarization) + + Refractory Periods 4. Na /K pump a. Repolarizes from undershoot, to resting membrane potential - Passive diffusion of ions allows Action Potentials to diffuse down the axon o Opens adjacent ion channels  Limit the direction of action potentials  Limit the frequency of action potentials Absolute Refractory period: - Sodium channels are inactivated - In the repolarizing period Summation of Inputs - AP’s cannot be generated Relative Refractory period: - Na channels are activatable - K channels are still open - Increased electrical current— required to generate Action - Allows saltatory conduction Potential o Propagation of action potentials at successive nodes of Ranvier Myelination How are messages of different intensities transmitted, if all action potentials are the same? Intensity - Rate Law: intensity is represented by the rate at which the axon fires o Higher intensity—more frequent firing of AP’s o Consistent stimulus—same frequency of Aps  Same amount of neurotransmitter released  Same response of postsynaptic cell Plasticity in signalling - Plasticity is a fundamental feature of the nervous system 1. Dynamic channel functions 2. Changes in channel function 3. Different types of channel subunits 4. Different types of channels 5. Evolutionary processes Hyperpolarizing small changes of postsynaptic voltage, alone not strong enough to afterpotentials generate an action potential - Some channels EPSPs: Excitatory signal—depolarization vary their - Increases AP likelihood function over activity/time IPSPs: Inhibitory signal—hyperpolarize o Certain - Decreases likelihood of AP channel become Summation of multiple inputs: more 1. Temporal efficient a. Inputs from far away sites arriving at the same time (generat e larger 2. Spatial respons a. Inputs from sites close together happen at the same time es) after repeated stimulat ion Neurotransmission - Some neurons use different types of channels to vary their signals Neurotransmitters: o Frog spinal motorne urons— use both slow & + fast K channel
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