Chapter 3: The Neuronal Membrane at Rest
Chapter 3: The Neuronal Membrane at Rest NEUROSC 3000 - 020
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NEUROSC 3000 - 020
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This 9 page Class Notes was uploaded by Victoria Gonzalez on Wednesday September 30, 2015. The Class Notes belongs to NEUROSC 3000 - 020 at Ohio State University taught by Robert Boyd in Summer 2015. Since its upload, it has received 34 views. For similar materials see Introduction to Neuroscience in Neuroscience at Ohio State University.
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Date Created: 09/30/15
Chapter 3 The Neuronal Membrane at Rest Victoria Gonzalez Learning Objectives 0 Understand basic structure of cell membrane and proteins 0 Understand basic electrical concepts resistance conductance voltage current and how ion movement is controlled 0 Understand concept of equilibrium potential and be able to apply it 0 Understand the Nernst and Goldman equations be able to apply them 0 Understand basic structure and function of potassium channels 1 Neuronal membrane at rest a Passive conduction of signal only works for short distances b Action potential conducts a signal without the loss of strength i They do not diminish over distance they are signals of xed size and duration c Need resting potential to generate action potential spike impulse d Resting potential varies between different types of neurons 2 Signaling depends on excitable membranes a Excitable cells excitable membrane can generate action potentials nerve impulses b Excitable cells at rest have a resting membrane potential when the inside of the cell is negative compared to the outside c Action potential is a brief reversal of this condition when the outside of the cell is more negative than the inside d How do cells generate a charge difference across the membrane i Ions on both sides of the membrane ii The membrane iii Protein channels that span the membrane 3 Nervous system a Central nervous system brain and spine b Peripheral nervous system i Somatic pathways voluntary movement of skeletal muscles ii Autonomic pathways involuntary controls muscles glands 1 Sympathetic nervous system a Controls the body s responses b Fight or ightquot 2 Parasympathetic nervous system a Controls homeostasis b Rest and digestquot 4 What do you need to generate a resting potential a Cytosol i Made up of mainly water polar ii Polar molecules dissolve in water iii Ions carry positive and negative charges 1 Ions are responsible for resting and action potentials iv Ions are surrounded by clouds of water called spheres of hydration they insulate ions from one another iii 1 Iquot J liarn v Ions can be monovalent 1 divalent 2 etc vi Cations are positive anions are negative vii Important for neurophysiology Ca2 K Na Cl39 b Plasma membrane phospholipid bilayer i Ions and polar molecules are hydrophilic ii Molecules with nonpolar covalent bonds are hydrophobic oils lipids iii Phospholipid membrane forms a barrier to water and ions allowing membrane potentials to form iv Hydrophilic head made of phosphate points toward water v Hydrophobic tail made of hydrocarbons points toward the inside of the membrane c Membrane proteins i A cell s properties are determined by the types of proteins expressed ii 20 amino acids properties are determined by R groups iii Chains of amino acid polypeptide are held together by peptide bonds iv Proteins can be made of one or more polypeptides v Proteins include enzymes the cytoskeleton and neurotransmitter receptors vi Ion channels 1 Have both hydrophobic and hydrophilic regions 2 Selective 3 Gated opening and closing is controlled vii Pumps 1 Ions are transported across membranes against their concentration gradients with the use of ATP 5 Movement of ions a In uenced by diffusion and electricity i Diffusion random movement from a region of high concentration to a low concentration down concentration gradient 1 Temperature dependent 2 The membrane has channels permeable to ions 3 There is a concentration gradient across the membrane ii Electricity 1 Electrical current I movement of electrical charge positive in the direction of positive charge movement a Measured in amps 2 How much current ows depends on a Electric potential voltage V the force exerted on a charged particle the difference in charge between the anode and the cathode b Electrical conductance relative ability of an electrical charge to migrate from one point to another 3 Voltage is a measure of the difference in charge between an anode and cathode a The bigger the difference the more current there will be 4 Conductance g siemens the relative ability for a charge to move from one place to another a Depends on the number of particles available to carry the charge and how easily they can travel 5 Electrical resistance R ohms the relative inability of an electric charge to migrate a Opposite of electrical conductance b R 19 c Ohm s law gV current is the product of the conductance and the potential difference 6 lons at resting potential a Membrane potential Vm is the voltage across the membrane i Measured by inserting a microelectrode in the cytosol ii Typical resting potential 65 mV b Inside of the cell is more negative relative to the outside c Without the negative potential inside the neuron there is no transmission 7 Equilibrium potential a Equilibrium occurs when diffusional chemical and electrical forces are equal and opposite at 80 Vm b Ionic equilibrium potential equilibrium potential the potential difference that balances the ionic concentration gradient 8 To generate an electrical potential difference a Large changes in the membrane potential are produced by tiny changes in ionic concentrations 000001 mM b The net difference in charge occurs at the inside and outside surfaces of the membrane i The membrane acts as a capacitor by storing charge c lons move across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potential i Vm Eion for each different ion is the ionic driving force ii Move in direction that moves the cell toward Eion d Each ion has an equilibrium potential calculated from the concentration difference across the membrane 9 Nernst equation a Exact equilibrium potential Eon can be calculated using Nernst equation b lons have their own equilibrium potential c Takes into consideration the charge of the ion the temperature and the ratio of the external and internal ion concentrations i Determines if the cell is positive or negative at equilibrium for each ion 10 Goldman equation relative permeability to multiple ions can be factored in 11 Distribution of ions across the membrane a K and negatively charged proteins A39 are more concentrated inside the cell b Na and Ca2 are more concentrated outside the cell 12 How are the concentration differences across the membrane established a lon pumps work against the concentration gradient i Sodiumpotassium pumps NaK uses ATP 1 Exchanges internal sodium for external potassium a 3 Na out for every 2 K in 2 Uses 70 of the brain s ATP ii Calcium pumps Ca2 transport calcium ions out of the cell 1 Other proteins and channels help too b Potassium channels i Key to determining a neuron s resting membrane potential Vm ii First cloned in a fruit y 1 Led to isolation of many potassium channels 2 Led to understanding of potassium and other channel structures iii Mutations in potassium channels lead to severe neurological problems or death iv External potassium must be regulated carefully 1 Membrane potential close to Ek due to high permeability to cell potassium a Ek membrane potential of K 2 Changing K outside can change membrane potential a Increasing extracellular potassium can cause the cell to depolarize Goldman 3 Bloodbrain barrier protects from excess potassium 4 Muscles have no protection from excess potassium a Can have serious consequences on body philology 5 Intravenous potassium is a lethal injection a Too much extracellular K inhibits resting potentials b Since muscles do not have protection the cardiac muscle cannot generate impulses needed to contract heart stops beaUng 6 Hodgkin and Katz used manipulation of the external K concentration to show that resting potential is mostly set by K permeability of neurons v Potassium spatial buffering astrocytes dissipate excess K outside of neurons through their extensive network
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