Neuronal Resting State & Action Potential: Ion Concentrations & Channels, Study notes of Psychology

Download Neuronal Resting State & Action Potential: Ion Concentrations & Channels and more Study notes Psychology in PDF only on Docsity! 1 1 Membrane Neurophysiology Overview of the Neuronal Membrane, Associated Ions, and Ion Channels 2 Structure of a Neuron at Rest + + + + + + + + + + + + + Na+ Cl- _ _ _ _ _ _ _ _ _ _ _ _ _ _ K+ Anions - 3 Measuring the Difference Between the Inside and Outside of a Neuron A axon from a giant squid is placed in seawater in a recording chamber. Glass microelectrode is inserted into axon. Voltage measures inside with respect to outside -70 mV Chamber Axon Voltmeter Microelectrode 4 Resting Membrane Potential Is the difference in voltage between the inside and outside of the axon membrane. 5 Concept Influx Material (Ions) moving to the inside of a membrane. Efflux Material (Ions) moving from the inside to the outside of a membrane. Equilibrium – Where material (ions, concentrations, etc.) are equal on both sides of a membrane. 6 Why do Ion’s Move? Concentration Differences – Compounds move from high concentrations to lower concentrations. Electrostatic Pressure – Like charges repel each other – Opposite charges attract each other. 2 7 Why is There a Resting State? Can be explained by the Nernst Equation in non-living organisms and Goldman-Hodgkin- Katz equation in living organisms The neuron membrane is selectively permeable to certain ions. Sodium Na+ Potassium K + Chloride Cl – Calcium Ca++ 8 Resting State At rest, K+ ions can leave the axon while few Na ions can enter the axon Causes the exterior of the nerve cell membrane to be more positive than the inside of the axon 9 Result Have high concentrations of Na and Cl on the outside of the axon High concentrations of K and Anions on the inside of the axon. 10 Ion Concentrations at Rest High Na+ High Cl- Low K High K+ Anions - Low Na 11 Relative Ion Concentrations Across the Axon Membrane 12 Concept Depolarizaton = Becomes more positive Hyperpolarization = Becomes more negative 5 25 Decremental Changes Point of Stimulation -70 -50 40 -60 -60 -50 -40 26 Charges Decrease in Both Directions from the Point of Stimulation Begin to stimulate, get depolarization (becomes more positive) K begins to move against the membrane and tries to leave by passive diffusion. – If the membrane is thick, the length of dissipation also increases. 27 Length Constant Distance along the membrane from the point of stimulation where the change in the resting potential has dissipated to 37% of the original 28 Point of Stimulation 100 mV 37% Dissipation 37mV Length Constant 29 100% 37% Point of Stimulation Length Constant 30 Temporal Summation Present a stimulus every ___ milliseconds. Observe depolarization Time Vm - 60 - 45 6 31 Resistance If membrane is resistant to K leaving, it becomes more difficult for K to leave Speed is the same All is done by passive channels. Decrease resistance by increasing the diameter of the axon. Thus, length constant will also dictate temporal summation 32 How do you get an Action Potential? 33 Answer Add and Subtract Charges Generally, must depolarize the membrane 15mV to get voltage gated channels to open and get an action potential. 34 A B C D Action Potential 35 A B C D Stimulate A Here, Depolarize 20mV Measure Here, Get 5mV Depolarization Action Potential 36 A B C D Stimulate D Here, Depolarize 20mV Measure Here, Get 3mV Depolarization Action Potential 7 37 A B C D Stimulate B Here, Depolarize 20mV Measure Here, Get 8mV Depolarization Action Potential 38 A B C D Stimulate C Here, Depolarize 20mV Measure Here, Get 15mV Depolarization Action Potential 39 Action Potential A alone Get Nothing B alone Get Nothing D alone Get Nothing C alone Voltage channels open - get AP A + B + D Voltage channels open – get AP 40 Influences Distance away - Length constant Temporal summation Inhibitory neurons – Cause hyperpolarization at the hillock (becomes more negative) Combination of depolarization and hyperpolarization determines if Voltage-Gated channels open. 41 Alcohol Alters the lipid bilayer Causes less Na to enter Less depolarization, fewer action potentials to begin 42 Action Potential General Overview Occurs because voltage gated channels open Results in rapid and large Na influx Get rapid depolarization and hyperpolarizaton 10 55 Receptors Two Major Types – Ionotropic – Metabotropic 56 Ionotropic Receptors Receptor and Ion Channel are one Unit Ach binds to alpha subunit Beta and Delta subunits are concerned with regulatory functioning e.g., Nicotinic Na Pore ɤ ɤ ɤ β Δ 57 Characteristics Are very rapid to respond – put on some NT and the channel opens – Take of the NT and the channel closes Is a simple system Ion channel is part of the receptor. Most are not 58 Metabotropic Receptors (Metabolism) Ion Channel and receptor sites are in different locations. Uses Intracellular Messengers from the binding site to the ion channel - Called second messengers Cyclic AMP (CAMP) Calcium Calmodulin Ion Channel Binding Site Messenger NT 59 Characteristics The channel is not part of the receptor There are intermediate steps that occur – Must put a phosphate group on the ion channel Called Phosphorlation Are slow to respond compared to ionotropic receptors Are slow to shut down – Remove NT but have a delay to remove the phosphate groups – thus, the system still works for awhile Provides more regulation of the system. 60 Metabotropic Receptors 11 61 How to Shut Down the System Remove the phosphate group on the channel – closes the ion channel Remove the second messenger – Pump out the Ca Remove the NT 62 How? Degrade – Simplest method – E.g., Acetylcholinesterase (AChE) Is on the surface of the Postsynaptic Membrane Degrades ACh. Is also in the synaptic Cleft 63 Sequence 64 Second Way Reuptake – Reabsorb NT into the Presynaptic Element Lashachle Theorm At equilibrium, NT bound on the receptor is the same concentration as the NT that is not bound. Remove NT from the cleft and the NT on the receptors comes off Based on concentration gradients 65 How Do You Degrade and Bind on Receptors Simultaneously? Receptors have more affinity Binds tighter 66 Several Types of Voltage Gated K Channels Delayed (classic type) A (Shaker-related or Kv) Anomalous Rectifiers (Inward Rectifiers) – Have 5 subtypes (Kir 1-Kir 5) K(ATP) channels Each have different roles – Some important for cardiac functioning – Some have a role in diabetes