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UIUC PSYC 210 - How Neurons Work 1-27

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Slide 1Slide 2Slide 3Slide 4Slide 5Signaling - Electrical PotentialsConduction of the Action PotentialRegeneration of Action PotentialRegeneration of Action PotentialRefractory PeriodsConduction VelocitySaltatory Conduction in Myelinated AxonsCells in the Nervous SystemSlide 14Two Types of SynapsesEvents at a Chemical SynapseEvents at a Chemical SynapseEvents at a Chemical SynapseTwo Type of ReceptorsIonotropic ReceptorsMetabotropic ReceptorsSynaptic TransmissionMore DefinitionsNotesTwo Major Dopamine SystemsFunctions of DopamineMore on How Neurons WorkJanuary 27, 2016More on How Neurons Work – the Basicsa x o nc e l lb o d ya x o nt e r m i n a l sI n p u t Z o n eL i g a n d - g a t e d c h a n n e l sC o n d u c t i n g Z o n e V o l t a g e - g a t e d c h a n n e l sO u t p u t Z o n eK+N a+a x o n h i l l o c k•Neuron with semi-permeable membrane (selective)•Two batteries: sodium (Na+) – enters inside positive potassium (K+) – exits inside negativeMore on How Neurons Work – the Basicsa x o nc e l lb o d ya x o nt e r m i n a l sI n p u t Z o n eL i g a n d - g a t e d c h a n n e l sC o n d u c t i n g Z o n e V o l t a g e - g a t e d c h a n n e l sO u t p u t Z o n eK+N a+a x o n h i l l o c k•Resting potential of neuron = -60 mV to -70 mV•Neuron is polarized (not zero potential)More on How Neurons Work – the Basicsa x o nc e l lb o d ya x o nt e r m i n a l sI n p u t Z o n eL i g a n d - g a t e d c h a n n e l sC o n d u c t i n g Z o n e V o l t a g e - g a t e d c h a n n e l sO u t p u t Z o n eK+N a+a x o n h i l l o c k•Input Channels:•ligand-gated (on dendrites and cell body)•depolarize or hyperpolarize the neuronMore on How Neurons Work – the Basicsa x o nc e l lb o d ya x o nt e r m i n a l sI n p u t Z o n eL i g a n d - g a t e d c h a n n e l sC o n d u c t i n g Z o n e V o l t a g e - g a t e d c h a n n e l sO u t p u t Z o n eK+N a+a x o n h i l l o c k•Conducting Channels:•voltage-gated Na+ (open fast) then close•voltage-gated K+ (open slow)Signaling - Electrical Potentialsa x o nc e l lb o d ya x o nt e r m i n a l sI n p u t Z o n eL i g a n d - g a t e d c h a n n e l sC o n d u c t i n g Z o n e V o l t a g e - g a t e d c h a n n e l sO u t p u t Z o n eK+N a+a x o n h i l l o c k•Equilibrium Potentials•Resting Potential•Graded Potentials:–Excitatory Postsynaptic Potential (EPSP)–Inhibitory Postsynaptic Potential (IPSP)•Action Potential•Sodium/Potassium pumps – recharge Resting potential (-60 to -70 mV)EPSPAction potentialThresholdNa/K pumps activeConduction of the Action Potential•As the action potential is conducted along the axon, the potential does not change size or shape. •This is because the potential is regenerated at each point along the axon.•No regeneration, potential decreases = graded conductionRegeneration of Action Potential•After reaching threshold, Na+ enters through the voltage-gated channels.•The entry of Na+ causes the membrane potential to reach +30 mV.•The positive charge opposes Na+ entry (equilibrium)•Positive charge spreads along the membrane, depolarizes adjacent parts and the process repeats. +++Na+12Spread of charge+++Na+3+++Na+54Regeneration of Action Potential+++Na+122Spread of charge+++Na+3+++Na+54• Membrane depolarization opens voltage-gated Na+ channels and Na+ enters the neuron (1).• The spread of charge (2) depolarizes adjacent points along the membrane, opens voltage-gated channels, Na+ enters (3), etc. (4,5)4• Backward spread (2,4) of charge does not open voltage-gated Na+ channels because these channels not only close they inactivate!Refractory Periods•Absolute refractory period:–Lasts about 1 msec (1/1000 sec)–Sodium channels closed and inactivated, so the neuron will not generate another action potential–Limits neuron to a maximum of 1000 action potentials per second•Relative refractory period:–Lasts 3 to 4 msec–Hard to generate action potential, but possible.Conduction VelocitySpeed of conduction in uninsulated axon varies from .1 meter/sec to 35 meters/sec - depends on axonal thickness –Thick axon = fast conduction, more charge carriers (ions)–Thin axon = slow conduction, fewer charge carriersSaltatory Conduction in Myelinated Axons• Many axons are insulated by myelin, which is made by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system.• Current flows to the next Node of Ranvier so the action potential “jumps” from node to node (saltatory conduction).• Action potential can fail at two nodes and still be regenerated.• Speed of saltatory conduction is up to 120 meters/sec (4 times faster than unmyelinated axons)Cells in the Nervous System•Neurons–100 to 150 billion•Glia–Supporting cells–Form a barrier between the blood and the brain (blood/brain barrier)More on How Neurons Worka x o nc e l lb o d ya x o nt e r m i n a l sI n p u t Z o n eL i g a n d - g a t e d c h a n n e l sC o n d u c t i n g Z o n e V o l t a g e - g a t e d c h a n n e l sO u t p u t Z o n eK+N a+a x o n h i l l o c kTwo Types of Synapses•Chemical synapse–Most common–Terminal filled with vesicles that release neurotransmitter–Synaptic delay (~1 ms)–Can be modulated•Electrical synapse–Tight junction–Fast / No cleft–Electrical potential travels directly to next neuron.Neurotransmitter manufactured in cell body by ribosomes along with rough endoplasmic reticulum (ER)Moved by smooth ER to Golgi apparatus and packaged into synaptic vesiclesEvents at a Chemical SynapseMicrotubules transport synaptic vesicles (and other material including enzymes that can synthesize neurotransmitters) down the axon to the synaptic terminalEvents at a Chemical SynapseEvents at a Chemical Synapse1. Action potential invades synaptic terminal.2. Open voltage-gated calcium channels, Ca2+ enters the terminal.3. Ca2+ causes synaptic vesicles to bind to presynaptic membrane.4. Vesicles burst open and release contents.5. Neurotransmitter diffuses across cleft and binds to receptors.6. Neurotransmitter becomes …


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