QUIZ YOURSELF What are the factors that produce the resting potential? How is an action potential initiated and what is the subsequent flow of ions during the action potential? 1 COLOSSAL NEURON ACTIVITY Spinal Cord 2 1
Afferent Neuron Efferent Neuron Activating Stimulus (Dendrites) Action Potential D Soma A X Na+ O N Synaptic Knob Synapse NT Receptor Deactivating Enzyme A X O Na+ N 3 4 SYNAPTIC ACTION, NEUROCHEMISTRY, AND NEUROPHARMACOLOGY Dr. Steinmetz 2
OUTLINE What is a synapse? How does the neuron communicate via chemicals? What are the properties of a synapse? Graded potentials (EPSPs/IPSPs) Summation 5 SYNAPSE 6 3
SYNAPTIC TERMINALS 7 OUTLINE What is a synapse? How does the neuron communicate via chemicals? What are the properties of a synapse? Graded potentials (EPSPs/IPSPs) Summation 8 4
NEURAL SIGNALING All neurons perform the following tasks: Input from sensory receptors or other neurons Processing input signal is processed in the soma and the decision of whether or not to send an output is made Signal Conduction action potential Output release of neurotransmitters 9 SOME NEUROTRANSMITTERS Acetylcholine Glutamate Serotonin Dopamine Norepinephrine Epinephrine GABA Nitric Oxide (Gas) 10 5
4. Action potential causes calcium to enter, releasing neurotransmitter 11 8. Empty vessicles travel back to cell body. 12 6
NEURAL SYNAPSE VIDEO 13 http://www.youtube.com/watch?v=hxx9qljetsu SYNAPTIC TRANSMISSION Neurotransmitter release Calcium ion channels open when action potential reaches presynaptic terminal Ca++ ions cause vesicles to move to release sites Number of vesicles released vary 14 7
Calcium is Required for Neurotransmitter Release...zzzzzzz 15 EXOCYTOSIS Release of neurotransmitters Vesicle trafficking Vesicle tethering Vesicle docking Vesicle fusion SNARE Proteins 16 8
9/17/12 EXOCYTOSIS SNAPS AND SNARES (SNAP RECEPTORS) 17 SYNAPTIC TRANSMISSION Neurotransmitter release Transmitter substance diffuses across synaptic cleft Attach to receptor sites on postsynaptic membrane 18 9
NEURAL SIGNALING All neurons perform the following tasks: Input from sensory receptors or other neurons Processing input signal is processed in the soma and the decision of whether or not to send an output is made Signal Conduction action potential Output release of neurotransmitters 19 RECEPTORS Key in lock model Ion-channels on postsynaptic membrane are chemically gated Not all or none Ionotropic: Direct actions on ion channels Metabotropic: Indirect action on ion channels 20 10
IONOTROPIC RECEPTORS 21 METABOTROPIC RECEPTORS 22 11
Mechanisms of Metabotropic Receptors Figure 3.13 Sequence of events at a metabolic synapse, using a second messenger within the postsynaptic neuron 23 SECOND MESSENGERS Neurotransmitters can produce chemical changes within the cell These second messengers produce ion channel changes Acting on ionotrophic receptor directly open or close channels Acting on metabotrophic receptor indirectly open or close channels Neurotransmitters can act in both ways 24 12
THOUGHT QUESTION Transmission of visual and auditory information relies largely on ionotropic synapses. Why is ionotropic better than metabotropic for these purposes? For what purposes might metabotropic synapses be better? 25 PRESYNAPTIC NT RECEPTORS Heteroreceptor - neurotransmitter from another axon binds the an axon terminal to increase (facilitation) or decrease (inhibition) neurotransmitter output 26 13
PRESYNAPTIC NT RECEPTORS Autoreceptor - neurotransmitter comes back to the same axon terminal to regulate neurotransmitter release providing feedback Autoreceptor 27 STOPPING NEUROTRANSMITTER EFFECTS Enzymes break down at receptor site Neurotransmitter reuptake returned to presynaptic membrane Allows for transmission of many messages 28 14
QUIZ YOURSELF. How are vesicles released into the synaptic cleft? How are neurotransmitter effects terminated? What are the two types of neurotransmitter receptors and how do they work? 29 30 15
9/17/12 EXOCYTOSIS SNAPS AND SNARES (SNAP RECEPTORS) 31 YOUR QUESTIONS.. Can g-protein signaling be lost? Yes. G-protiens cause an increase of the second messenger (like camp) Does déjà vu use ionotropic channels? We Why don t know, but. is reflex arc slower than conduction along a single axon? 32 16
OUTLINE What is a synapse and how was it discovered? How does the neuron communicate via chemicals? What are the properties of a synapse? Graded potentials (EPSPs/IPSPs) Summation 33 NEURAL SIGNALING All neurons perform the following tasks: Input from sensory receptors or other neurons Processing input signal is processed in the soma and the decision of whether or not to send an output is made Signal Conduction action potential Output release of neurotransmitters 34 17
POST-SYNAPTIC MEMBRANE EFFECTS Presynaptic Neuron Postsynaptic Neuron 35 EPSP VS IPSP 36 http://www.youtube.com/watch?v=lt3vkar4roo 18
POST-SYNAPTIC MEMBRANE EFFECTS Transmitter-gated ion channels Channels on post synaptic membrane Sensitive to specific neurotransmitter substances 37 TWO TYPES OF SYNAPSES Excitatory Inhibitory 38 19
EXCITATORY SYNAPSES Causes Na+ to enter cell Does this lead to depolarization or hyperpolarization? Depolarization (more pos) Excitatory Post-Synaptic Potential = EPSP 39 INHIBITORY SYNAPSES Causes K+ to leave the cell and Cl- to enter Does this lead to depolarization or hyperpolarization? Hyperpolarization (more neg) Inhibitory Post-Synaptic Potential = IPSP 40 20
Does an EPSP mean that there will be an action potential? 41 OUTLINE What is a synapse? How does the neuron communicate via chemicals? What are the properties of a synapse? Graded potentials (EPSPs/IPSPs) Summation 42 21
SPATIAL AND TEMPORAL SUMMATION 43...SUMMATION EFFECTS Temporal Summation - Rapid events at the same location 44 22
SUMMATION EFFECTS EPSP & IPSP's are graded not all-or-none Only if combined effects reach threshold at axon hillock will action potential occur 45 TEMPORAL SUMMATION: ELECTROPHYSIOLOGY 46 23
RELATION EPSPS, IPSPS, ACTION POTENTIALS Spontaneous firing rates EPSP increase firing rate IPSP decrease it 47 THOUGHT QUESTION Stimulating neuron A causes an action potential in neuron C after a short delay Synapse A-B is inhibitory How is this possible? 48 24
NEURAL SIGNALING All neurons perform the following tasks: Input from sensory receptors or other neurons Processing input signal is processed in the soma and the decision of whether or not to send an output is made Signal Conduction action potential Output release of neurotransmitters 49 INPUT and PROCESSING Transmitter-gated receptor channels EPSP / IPSP Summation TRANSMISSION and NT RELEASE Voltage-gated channels Action Potentials = all or nothing principle Synaptic events to release neurotransmitters exocytosis 50 25
FOR NEXT TIME Read the rest of Chapter 4 Work on Week 3 Neuroanatomy Lab (Internal Structures) for lab practical tomorrow Be prepared to write the story of nerve conduction from stimulation at the dendrites to the stimulation of the next neuron 51 Afferent Neuron Efferent Neuron D Activating Stimulus D D (Dendrites) Action Potential Soma A X O N Na+ Synaptic Knob Synapse NT Receptor Deactivating Enzyme A X O N Na+ 52 26
YOUR QUESTIONS. Is the sodium potassium pump working during the action potential? Yes, but it can t keep up! If there isn t a strong enough impulse to reach threshold, do any sodium gates open? Sodium gates do not open until threshold is reached Do dendrites have action potentials? They can, but usually don t. We will talk about second messenger systems, EPSP/IPSPs, etc. 53 27