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Brain & Behavior Week 3 Notes

by: Willow Frederick

Brain & Behavior Week 3 Notes Natural Science 2

Marketplace > New York University > CORE > Natural Science 2 > Brain Behavior Week 3 Notes
Willow Frederick

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About this Document

These notes cover last week's notes (9/20-9/22). All about action potentials, etc. Includes notes from lecture, lab, and the review session led by our TAs.
Brain and Behavior
Andre Fenton
Class Notes
Actionpotential, neurons, voltage, lab, Myelin, resistance, axon, dendrite, signal
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This 4 page Class Notes was uploaded by Willow Frederick on Monday September 26, 2016. The Class Notes belongs to Natural Science 2 at New York University taught by Andre Fenton in Fall 2016. Since its upload, it has received 58 views. For similar materials see Brain and Behavior in CORE at New York University.


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Date Created: 09/26/16
Brain & Behavior Week 3: 9/20­ 9/22 Lecture 5: Neural Communication 2: Synapses­ Connections & Influence How do we get another AP to occur one after another?   Wait 2 milliseconds or so (not long!)  Conduction speed: 1 to 100m/sec  Signal speed determined by how wide the axon is (wider=easier flow) and if there is  myelin on the axon   How quickly we go thru the cycle determines how quickly the AP’s propagate down the  axon   Initiation­ at the axon hillock Density of the current is greater near the entrance In axons in different parts of the brain, it’s really important to send signals really fast, but in  other parts it’s not that important   The axons that detect pain are slower at this (i.e. hitting your hand w/a hammer)   Insulator= myelin (basically fat)  o Prevents the sodium from leaving  sodium leaves thru channels at the ‘nodes of  ranvier’ o The impulse jumps from node to nodecalled salutatory (jumping) conduction o Multiple Sclerosis (MS) Synaptic potentials are local (graded) potentials: a chemical process (look @ this slide on Ppt)  Postsynaptic potential (PSP):   (EPSP)  neurons release neurotransmitters across the junction bw the cells, called the synapse  o the yellow cell interprets that chemicalmakes proteins that are designed to  receive those proteins  Comparing Axons & Dendrites Size # per neuron Info Flow Voltage Changes AXON Thin, uniform One (but can  Away from cell  All­or­none have branches) body DENDRITE Thick, variable many Into cell body Graded variable Difference bw Graded Potentials & Action Potentials  The bigger the amplitude, the bigger the muscle stretch o The louder the sound, the larger the signal to the ears from those neurons o Neurons report intensity via size/magnitude of signal o AP’s report intensity via frequency/rate  Synapse: site where electrical signals are transmitted from one excitable cell to another   Unidirectional: presynaptic postsynaptic   Can have a + excitatory response increases the postsynaptic probability of an AP  Or can have an inhibitory response, moving membrane potential further away from AP  (decreases the postsynaptic probability of an AP)  Synaptic pathways can be divergent or convergent   Synapse is 20­40 nm wide (REALLY small) Functional Anatomy of a Chemical Synapse (STUDY THIS SLIDE ON PPT) QUIZ REVIEW   2 ways that sodium ions move across the cell membrane? Active transport or diffusion o Which direction does sodium move in each case? o Which way requires metabolic energy?  2 ways that potassium ions move across the cell membrane? o Which direction does potassium move in each case? o Which way requires metabolic energy?  Nernst equation is the first to look at the membrane potential, but only addresses  equilibrium for one ion at a time  o Individually cannot explain each voltage   Intracellular (inside cell) is negative (polarized)  Extracellular (outside cell) is positive  o Membrane of the cell is made of phospholipids (phospholipid bilayer­fat)  Size: Big things (such as a protein) can’t cross the membrane—only small stuff can cross  the membrane –­lipid bilayer is impermeable to charged ions & to big ions o Based on their electrical properties  When it’s unchargedcan cross easily –diffusion  Other way to cross membrane—lipids open channels – facilitated  transport  It ions are lipophobiccannot cross   If ions are hydrophilic   ACTIVE TRANSPORT: go against the concentration gradient (low to high) —requires ATP (energy)  Active transport is the role of the sodium potassium pump   Diffusion force: high to low concentration—no energy required!  Resting membrane potential: ­60 mV o A lot of sodium outside the cell, lots of K+ inside the cell o Permeability= conductance  o Inside  K+ (150)  Na+ (15)  Cl­ (10) o Outside   K+ (5)  Na+ (150)  Cl­ (110) o K+ can use facilitated transport to go from high to low concentration –goes out of  the cell   then the interior is more negative   K+ goes in & out­ can’t decide where to be (attracted to negative charge) —@some point, there is equilibrium outside vs. inside of cell   With the electrical gradient, K+ goes from positive (outside) to negative  back to inside  o Na+ goes from outside to inside  o Cl­ goes from outside to inside   NERNST EQUATION  o E of K+  The membrane will be at ­88mV o E of Na+    GOLDMAN EQUATION –tried to explain ­60mV, the resting membrane potential  o What Nernst didn’t take into account was the distribution of each ion channel  o Used the permeability of the membrane for each ion to explain the resting  membrane potential  o Cell has a lot of K+ channels, few for Na+ & Cl­ LAB 3 NOTES Neurons receive 2 types of local graded potentials (messages)  Excitatory (EPSPs): resting membrane potential becomes more positive   Inhibitory (IPSPs): resting membrane potential becomes more negative  Action potentials transmit messages by moving down the axon  (electrical) create neurotransmitters to translate message to next neuron in synaptic space  (chemical)  Local graded potentials always hit resistence as they move along the axon & lose  energy/get weaker message goes slower and/or for shorter distance    Spatial Summation: different voltage amounts from different messages at the dendrite  add together   Temporal Summation: ifLGPs arrive at the same time & they cancel each other out   Switch from 100K (Ri) to 30K (Ri)= less resistance  o 100K has higher internal resistance (Ri) o How can we get lower Ri? fatter dendrite   The lower the Rm is, the shorter the length constant  o If Rm is very high, nothing can leak out/ions stay inside longer length constant  (traveling distance) o How do we get a higher Rm?  myeline sheath   The lower Ri (internal resistence), the longer the length constant (traveling distance)  inside  


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