Nervous System - Continue - PDF

The nervous system - continue X.Liu PSYC2190 Review Diffusion Force = Electrostatic Pressure Force Equilibrium X.Liu PSYC2190 the Nernst equation E=RT/zF ln [Ion]out/[Ion]in E= membrane potential z=valence of ion (charge)...

The nervous system - continue X.Liu PSYC2190 Review Diffusion Force = Electrostatic Pressure Force Equilibrium X.Liu PSYC2190 the Nernst equation E=RT/zF ln [Ion]out/[Ion]in E= membrane potential z=valence of ion (charge) F=Faraday constant for electrical forces T=absolute temperature (in Kelvin) R=universal gas constant [Ion]=concentration of ion, inside or outside the cell X.Liu PSYC2190 Establishing the Membrane Potential Extracellular- Positive Leaking Channel Gated Channel Na/K Pump Intracellular - Negative X.Liu PSYC2190 ENa= 62 mV Resting Potential: –70 mV Extracellular- Positive Leaking Na+ Channel Na+ Na+ Na+ Gated Channel Na+ Na+ Na/K Pump Intracellular - Negative X.Liu PSYC2190 EK= -80 mV Resting Potential: –70 mV Extracellular- Positive Leaking Channel K+ K+ Gated Channel K+ K+ Na/K K+ Pump Intracellular - Negative X.Liu PSYC2190 Membrane Potential: –70 mV Extracellular- Positive Leaking Na+ Channel Cl- K+ Na+ Na+ A- K+ Gated Cl- Channel Cl- K+ Na+ Cl- Na/K K+ Pump Intracellular - Negative X.Liu PSYC2190  Comparison Membrane Inside Neuron Current Response Potential Hyperpolarization Increase More negative Negative Graded Potential Decrease Less negative Positive Graded Potential or Depolarization Action Potential X.Liu PSYC2190 The Action Potential Caused by the brief opening of voltage-gated Na+ Channels and then the brief opening of voltage-gated K+ Channels. X.Liu PSYC2190 The Action Potential X.Liu PSYC2190 The Action Potential X.Liu PSYC2190  The Action Potential Na+ channels open rapidly, Na+ enter cell --- depolarizing the neuron After the opening of Na+ channels, K+ channels open, K+ begins to leave cell At the peak, Na+ channels close, no more Na+ enters neuron X.Liu PSYC2190 The Action Potential K+ continues to leave cell – causing membrane potential to return to the resting level. K+ channels close slowly, so more than “necessary” K+ leaves the cell – causing hyperpolarization (Undershoot) Refractory period – hard to “fire” again X.Liu PSYC2190 The Action Potential K+ channels closed, and Na+ channels reset – causing membrane potential to return to resting level. Re-establishes equilibrium Concentration Gradient = Voltage Gradient X.Liu PSYC2190  Recall that there was a threshold of current necessary to produce an AP If we increase the level of the pulse currents beyond the threshold, what happens? – A. The amplitude of the AP increases w/ increases in current. – B. The amplitude of the AP remains constant. Action Potential is All or None X.Liu PSYC2190 The Rate Law The strength of a stimulus is represented by the rate of firing of an axon. The magnitude (size) of each action potential is always constant. Stronger stimuli = more APs X.Liu PSYC2190 Conduction of the Action Potential When an action potential is triggered, its size remains the same as it travels down the axon. The graphs at the top of the figure represent the size (amplitude) of the action potential as it moves along the axon from left to right. X.Liu PSYC2190 X.Liu PSYC2190 Let’s do our Neural Beats again! X.Liu PSYC2190 Saltatory Conduction Myelin acts as an insulator that aids conduction. Restricts points at which extracellular Na+ may enter X.Liu PSYC2190 Saltatory Conduction X.Liu PSYC2190 Saltatory Conduction AP Leap Frog X.Liu PSYC2190 X.Liu PSYC2190 Communication Between Neurons Neural Computation -- Decision making The Synapse – Pass the information X.Liu PSYC2190 Function of neurons (review) Take in information Make a decision (Maybe) pass that information along X.Liu PSYC2190 Synaptic Connections between Neurons The arrows represent the direction information is traveling. X.Liu PSYC2190 Communication Between Neurons X.Liu PSYC2190 X.Liu PSYC2190 Again, it’s all about ions EPSP and IPSP are graded potentials: the size is proportional to the stimulation Even at high stimulation, AP is not produced No voltage‐sensitive channels on the cell body (there are exceptions) Spread passively over the dendrite/cell body X.Liu PSYC2190 AP vs. Graded Potentials X.Liu PSYC2190 What happens next X.Liu PSYC2190 Temporal Summation X.Liu PSYC2190 Spatial Summation X.Liu PSYC2190 What is Critical X.Liu PSYC2190 Whether to go to a party There’s a party + + Your crush will go Crush’s partner also go X.Liu PSYC2190 Summation Remember, EPSPs & IPSPs spread passively over the cell body – so they decay Point of origin matters! Inputs from farther out on the dendrite contribute less. More like a weighted sum X.Liu PSYC2190 The Computation can be Complex - - - - + + X.Liu PSYC2190 X.Liu PSYC2190 Let’s zoom in X.Liu PSYC2190 Details of a Synapse X.Liu PSYC2190 Presynaptic Events X.Liu PSYC2190 Presynaptic Events X.Liu PSYC2190 Presynaptic Events X.Liu PSYC2190 Presynaptic Events X.Liu PSYC2190 In the Synaptic Cleft X.Liu PSYC2190 Postsynaptic Events Neurotransmitter molecules fit the binding sites of receptors like keys fit into locks. Neurotransmitter binding conveys the neural message to the postsynaptic cell. X.Liu PSYC2190 Ionotropic Receptors The ion channel opens when a molecule of a neurotransmitter attaches to the binding site. For purposes of clarity the drawing is schematic; molecules of neurotransmitters are actually much larger than individual ions. X.Liu PSYC2190 Ionic Movements During Postsynaptic Potentials X.Liu PSYC2190 Metabotropic Receptors When a molecule of neurotransmitter binds with a receptor, a chain of chemical events is initiated. The end result of the chain of events is to indirectly open an ion channel or produce another intracellular change in the cell. X.Liu PSYC2190