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USC - BIOL 243 - Class Notes - Week 10

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USC - BIOL 243 - Class Notes - Week 10

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background image Notes from 3/29 and 3/31  I.  Resting Membrane Potential    a.  How?      K+ (potassium) leakage channels are more leaky than Na+ (sodium) leakage channels      SLIDE 15    II.  Signals      Depolarization- reduction in membrane potential--> toward 0 mV, less polarized, inside 
becomes less negative (more positive)  
    Hyperpolarization- increase in membrane potential, moving away from 0 mV, inside becoming 
more negative 
  c.  Types of Signals    1.  Graded potentials- short lived, local changes in membrane potential, act over a short 
distance (not foot to brain, only a few millimeters, very important) SLIDES 18-19 
  2.  Action potentials- act over a long distance, require voltage gated ion channels, neuron or 
muscle cells are the only cells that can support action potentials (epithelial cells, etc. cannot, 
transport signal from big toe to brain quite rapidly) SLIDE 21 
  1.  Depolarization- membrane is depolarized to -50  to -55 mV (threshold)    At -50 to -55 threshold, the Na+ voltage gated ion channels open (Na+ rushes in)--> 
membrane is depolarized more--> more voltage gated ion channels open (more Na+ 
rushes in)--> more depolarization (positive feedback loop) 
  All the way to +30 mV (now positive on the inside)    2.  Repolarization- whole polarity of membrane is reversed (negative on outside, positive 
on inside, +30 mV on inside)  
  electrical gradient for Na+ into cell becomes unfavorable b/c now the inside is 
positively charged an Na+ is positively charged 
  Voltage gated Na+ ion channels close NO MATTER WHAT     2 points above stop Na+ flow into cell    Voltage K+ gated ion channels open     Concentration gradient of K+ from inside to outside is favorable, and electrical 
gradient from + to - is now favorable so flow of K+ out of cell which will restore 
resting membrane potential  
  c.  How is the Action Potential Moved?    a.  Propagation of Action Potential      Lateral movement of Na+ ions--> depolarizes next patch of membrane to -50 to 
-55 mV (all it takes to get an action potential to pass onto next patch of 
membrane, threshold must be reached) 
    Action potentials only go in 1 direction      Why not both ways?      Na+ ion channels are closed and cannot open (referred to as refractory 
period)  
    The membrane potential goes a little below -70 mV (hyperpolarized), so 
it takes a stronger signal  
    Threshold: -50 to -55 mV      Action potential is all or none      Intensity: the action potentials of lightly clunking foot vs dropping something 
very heavy on it are the SAME, but the frequencies differ and determine the 
intensity (intensity is coded by frequency) SLIDE 28 
 
background image   Refractory Periods: the nerve can't be stimulated      Absolute- when the Na+ voltage channels are just closed or are already 
open  
    Relative- Na+ voltage gates could open but need a stronger signal b/c the K+ 
ion channels are either open or have already overshot and have 
hyperpolarized 
    Conduction Velocity:    1.  Larger diameter of axon- transmit action potentials faster than skinnier 
ones 
  2.  Presence of myelin sheath- transmit action potentials faster       Satatory conduction- jumping from one Node of Ranvier to the next      Nerve Fibers     .  Fast- large diameter, myelinated (would supply skeletal muscle)    A.  Intermediate- medium diameter, lightly myelinated (autonomic nervous 
system or visceral sensory neurons) 
  B.  Slow- small diameter, not myelinated at all (autonomic nervous system)    3-31-2016    I.   Synapse- space in between presynaptic and postsynaptic neuron    1.  Electrical synapse      Bridged junction      No synaptic cleft (space between neurons)      Found in smooth muscle and brain    2.  Chemical synapse     1.  Action potential travels down to axon terminal     2.  Action potential depolarization opens voltage gated Ca+ ion channel     3.  Net Ca+ flow into presynaptic neuron promotes fusion of synaptic vesicles with the  membrane, causing neurotransmitter release    4.  Neurotransmitter diffuses across synaptic cleft, and bind to a receptor (chemically gated  ion channel) on the postsynaptic neuron     5.  Causes the opening or closing of the ion channel    6.  Entire cycle is reset- Ca+ pumped out of cell, neurotransmitter is destroyed  (acetylcholine esterase is degraded by enzyme activity, diffused away, or taken up by 
endocytosis) 
  Presnyaptic neuron- left of/before synapse in reference    Postsynaptic neuron- right of/after synapse in reference    Synaptic delay                    Signal travels from dendrites, down the axon    i.  Axodendritic- presynaptic neuron synapses with dendrite of postsynaptic neuron    ii.  Axosomatic- presynaptic neuron synapses with cell body of postsynaptic neuron    iii.  Axoaxonic- presynaptic neuron synapses with axon of postsynaptic neuron     II.  Post Synaptic Potentials     a.  Excitatory Postsynaptic Potential (EPSP)- depolarize    Neurotransmitter opens K+ and Na+ ion channels   

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School: University of South Carolina
Department: Biology
Course: Human Anatomy and Physiology I
Professor: Lewis Bowman
Term: Spring 2016
Tags:
Name: Notes from 3/29 and 3/31
Description: Detailed notes from class on the 29th and 31st!
Uploaded: 03/31/2016
3 Pages 35 Views 28 Unlocks
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