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Notes from 3/29 and 3/31

by: Haley Johnson

Notes from 3/29 and 3/31 BIOL 243 001

Haley Johnson
GPA 3.6

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Detailed notes from class on the 29th and 31st!
Human Anatomy and Physiology I
Lewis Bowman
Class Notes
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This 3 page Class Notes was uploaded by Haley Johnson on Thursday March 31, 2016. The Class Notes belongs to BIOL 243 001 at University of South Carolina taught by Lewis Bowman in Spring 2016. Since its upload, it has received 34 views. For similar materials see Human Anatomy and Physiology I in Biology at University of South Carolina.

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Date Created: 03/31/16
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) o 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) o 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) o electrical gradient for Na+ into cell becomes unfavorable b/c now the inside is positively charged an Na+ is positively charged o Voltage gated Na+ ion channels close NO MATTER WHAT o 2 points above stop Na+ flow into cell o Voltage K+ gated ion channels open o 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  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) o Presnyaptic neuron- left of/before synapse in reference o Postsynaptic neuron- right of/after synapse in reference o Synaptic delay o 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 o Neurotransmitter opens K+ and Na+ ion channels o Some depolarization due to net flow of Na+ into cell b. Inhibitory Postsynaptic Potential (IPSP)- hyperpolarize o Neurotransmitter opens K+ or Cl- ion channel o Hyperpolarization c. Graded potentials- short graded changes in membrane potential i. Axodendritic synapse: no voltage gated ion channels in dendrite of postsynaptic neuron so there is graded potential but no action potential around the cell body and dendrites, however there are chemical gated ion channels here; there are only voltage gated ion channels in the axon of the postsynaptic neuron o Axon hillock- point of attachment of axon to cell body o Factors determine initiation of action potential on postsynaptic neuron:  Temporal summation- resting membrane potential is -70 mV, but when stimulus is a little far apart, the voltage never reaches the threshold of -55 mV as the signal travels across neuron, which doesn’t create an action potential down axon; however with temporal summation, the stimuli are closer together (fires once and fires again very quick), so the second one pushes the voltage higher, past the -55 mV threshold, creating an action potential; A SINGLE EPSP CANNOT INDUCE AN ACTION POTENTIAL, THEY MUST SUMMAE TO REACH THRESHOLD, ONE ORE MORE PRESYNPATIC NEURONS TRANSMIT IMPUSLES IN RAPID FIRE ORDER  Spatial summation- 2 presynaptic neurons attach to the same postsynpatic neuron (maybe one is axodendritic and the other is axosomatic); POSTSYNAPTIC NEURON IS STIMULATED BY A LARGE # OF TERMINALS AT THE SAME TIME o Adaptation- uncoupling of stimulus strength--> generation of action potential (no longer firing, despite having the same stimulus; i.e. put shirt on in morning, feel it at first, but not reminded by nerves all day that you have it on) o Synaptic potentiation- repeat stimulated increases pre and post synaptic neurons ability (i.e. first time you throw baseball is bad but the more and more you do it, the better you will get)  Presynaptic neuron has these effects- higher Ca+, more neurotransmitters  Postsynaptic neuron has these effects- more acceptors, partially depolarized d. Neuronal Pools- function groups of neurons that process info; circuits . Diverging pool- original signal from localized part is spread out to multiple parts of the brain (know where we are bit by spider on body) i. Converging pool- information that is initially carried by numerous neurons converges on one (one pleasure area of brain) ii. Reverberating/Oscillating- co-lateral synapse, continuous output i.e. short term memory, arm swinging in loop, respiratory cycle iii. Parallel After Discharge- 1 synapse, vs 2 synapses, vs 3 synapses i.e. higher mathematics


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