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Fenton-Brain & Behavior Week 2 Lecture Notes

by: Willow Frederick

Fenton-Brain & Behavior Week 2 Lecture Notes Natural Science 2

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Willow Frederick

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Notes from week of September 12th-16th.
Brain and Behavior
Andre Fenton
Class Notes
Actionpotential, potassium, na, Charge, voltage, neurons, neurondoctrine
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This 11 page Class Notes was uploaded by Willow Frederick on Friday September 16, 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 72 views. For similar materials see Brain and Behavior in CORE at New York University.

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Date Created: 09/16/16
Brian & Behavior Lecture Notes Week 2 09/13/2016 NEURON DOCTRINE: Cajal considered that neurons were not connected 1. The brain is made up of individual units that contain specialized features such as  dendrites, a cell body, and an axon. 2. Neurons are cells 3. Neurons are specialized  4. Nerve fibers are outgrowths of nerve cells. 5. Neurons contact each other through specialized junctions 6. Law of dynamic polarization: There is a preferred direction for transmission from cell to  cell (dendrite ­> cell body ­> axon) 7. Unity of transmission: The contact between 2 cells can be either excitatory or inhibitory,  but will always be of the same type. 8. Dales’ law: The axon terminal releases a single type of transmitter substance Neuronal Visualization   Golgi (1843­1926) o neuronal staining, impregnated cells with silver nitrate and then reacted to turn  black   Ramon & Cajal (around same time): fine structure of cells in the nervous system Neural Net Theory: Golgi interpreted it as not individual neurons, but that neurons were  physically connected  Implications for localization & communication (electrical or chemical?)  Cajal & Golgi shared the Nobel Prize in 1909  Golgi was not totally wrong, but the dominant way in mammals to study neurons is with  the neuron doctrine Major Parts of the Neuron  Dendritic region=input region  ­myelin sheath: covers axon Neurons come in different shapes but have the same basic structure/function. Variety of Neurons (but functional  organization is preserved) All cells, including neurons, are mostly made up of water! “cells are bags of water, floating in  water” THE TYPICAL EUKARYOTIC CELL: is mostly filled with water! 70 kg person is ~42L water 28 L intracellular fluid (cytoplasm & cytosol) 11 L extracellular fluid 3 L blood plasma  Molecules do not exist in isolation. When we talk about molecules we’re talking about a lot of  them Water is polar aka is charged­ the charge distribuition on the molecule is not balanced, bc  physically where the charges exist on a water molecule that on the O there are more e­ than on  the H side. O is greedy for electrons, so pulls them away from H atoms. O ends up a little more  negative and H a little more positivethat’s how water is polar. (O2 is not polar) The plasma membrane is a fluid phospholipid bilayer with important transmembrane protein  components. Lipids are non­polardo not associate well in water Charged things like to hangout with charged things. Noncharged molecules are uncomfortable in  charged solutions (like water). Lipids together form the cell bag 1. SEPARATION: defines inside vs.  outside of cell 2. REGULATION: of matter flowing in &  out 3. DETECTION: of chemicals at the cell  surface 4. ANCHORING: to a scaffold  (extracellular matrix) 5. JUNCTIONAL/LINKING: of adjacent  cells by specialized membrane junctions  (desmosomes, tight junctions, gap  junctions) Measuring the Resting (Transmembrane) Potential   Energy has the capability to do work—to apply a force across a distance   Energy is stored across the membrane that has the ability to do work   The potential comes from charge separation   The amount of potential energy is the same inside & outside of the cell   What is the force that’s driving all of this? DIFFUSION  o Things go from where they are concentrated, to where they are not  concentrated  o Diffusion is the net result of the random thermal motion of molecules  o Due to diffusion over time, the solute moves from an area of high  concentration to low concentration The phospholipid bilayer acts as a selective barrier to charged & large molecules The concentration of water is always well­balanced on both sides. Charged molecules cannot get thru that fatty layer (above). 3 important ways small molecules cross the plasma membrane 1. Diffusion (o2, co2, for example) 2. Facilitated diffusion (glucose, h2O for ex) 3. Active transport (Na+, K+, Ca2+ for ex) A salt: something that when you put it in water, it separates in pieces according to charge (ex.  sodium & chloride separate from each other) **Memorize slide “The Distribution of Ions Inside & Outside of a Neuron” (slide 22) The ion content of the intra­ & extra­cellular fluids differ  Two forces determine ion separation  1. CHEMICAL a. Diffusion: high to low concentration  2. ELECTRICAL a. Charge interactions: opposites attract, like charges repel b. Charge separationvoltage (potential) Ionic Forces Underlying Electrical Signaling in Neurons  1. Diffusion a. Particles move from areas of high concentration to areas of low concentration  (aka they move down their concentration gradient) 2. Diffusion thru semipermeable membranes a. Cell membranes permit some substances to pass thru but not others 3. Electrostatic Forces a. Like charges repel, opposites attract Ion concentration gradients are  actively maintained by the NaL­ ATPase (sodium­potassium pump) Potassium= K+ Sodium= Na+ Membrane lets K+ pass thru The Nernst Equation defines the equilibrium potential i.e. the transmembrane electrical  potential at equilibrium  **Prof said he won’t ask us to calculate all this but we’ll have to understand it! The Goldman Equation defines the equilibrium membrane potential when the membrane is  permeable to more than one ion.  **Prof said be sure to review the Ionic Basis of the Resting Potential  **watch these animations Lecture 4­ 09/15/2016 Neural Communication 1: The exciting electrical Language of Neurons  Theme: The separation of charged molecules (ions) is regulated by channel proteins to generate  bioelectric signals Resting State of a Healthy Cell  Voltage= charge separation  o is regulated by the barrier (cell membrane)  Ions: Na+ & K+  Permeability/ diffusion  Channels  Electrical potential   Know: the ion content of the intra­ and extra­cellular fluids differe—Know the ratios  (more K+ or Na+ on the inside or outside of the cell?)  2 forces decide on separation  Nernst Equation: defines the equilibrium potential i.e. the transmembrane electrical potential at  equilibrium   Gas laws  Goldman Equation: **we’ll never be asked to use this   the relative ease of how ions move across the membrane, will determine the potential of a cell, taking into account all of the ions that permeate thru that membrane   valves to open & close in membrane to regulate voltage= channel proteins ACTION POTENTIAL : a non­linear eventchange the voltage across the membrane o depends on selective gating by ion channels   APs help us explain reflexes   neural circuits  afferents  efferents  spike initiating zone­ where action potential initiates  o usually pretty close to where axon joins cell body o what initiates an AP? –a neuron sends info down an axon, away from cell body  AP is created by a depolarizing currentresting potential (­70mV) goes  towards 0mV  When it reaches ­55mV (threshold), an AP can happen!   now ions cross the neuron membrane. This is where Na+ & K+ come in. o (Inside of the neuron is more Negative than outside) o sodium (Na+) channels open & Na+ rushes into the neuron o neuron becomes more positive aka depolarized  When potassium (K+) channels open, K+ rushes out of the cell, which reverses the  depolarization.  o voltage returns to about ­70mV Here's a short video of how an AP works Oh wait, Hank Green made a CrashCourse video on it. Watch it   How does your body know the difference bw a papercut and getting your hand cut off?  Measure rate instead of amplitudenot the size of the AP, but how many of them  Hodgkin & Huxley­ their model (1952)/ equivalent circuit  o  describes how action potentials are initiated (in the squid giant axon, in their  work) o received nobel prize in physiology/medicine   A super helpful graphic from the textbook: Anesthetics & Poisons o Tetrodotoxin (TTX): blocks the voltage gated Na+ channel outside the nerve o Local Anesthetics­ lidocaine blocks the voltage gated Na+ channel from inside the nerve  o Scorpion Venoms­ block inactivation gates of the voltage gated Na+ channel  How a toilet is like an axon. . .


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