Biology 325 Fall 2004 Synapses and synaptic integration I Introduction operation of NS depends on flow of information through network of neurons functionally connected by synapses II Types of synapses A Structure arrangement 1 axodendritic 2 axoaxonal 3 axosomatic B Functional classification 1 electrical synapses gap junctions 2 chemical synapses release of neurotransmitter NT direct opening of ion channels activation of second messenger systems C Complexity of neuronal network III Mechanism of synaptic transmission A Structure of chemical synapses pre postsynaptic cell NT vesicles synaptic cleft receptor channels B Events of synaptic transmission 1 NT binds receptors a opens channels fast synaptic potentials b 2nd messenger system activated slow synaptic potentials 2 Termination of NT effects a degradation NT b removal NT c diffusion NT 3 NT vesicle dynamics a V snare t snare proteins b Cycling of presynaptic vesicles IV Postsynaptic potentials synaptic integration A EPSP graded depolarizing response opens Na Ca or Na K channels excitation vs facilitation B IPSP graded hyperpolarizing response opens Cl or K channels C Synaptic integration single neuron forms synapses with thousands of other neurons receives input from thousands of other neurons response of postsynaptic neuron depends on additive effect or summation of all EPSPs and IPSPs and their integration at axon hillock the grand postsynaptic potential 1 temporal summation addition of PSPs occurring very close together in time because of rapid firing of a single presynaptic neuron one or more presynaptic fibers transmit impulses in rapid succession 2 spatial summation addition of PSPs originating simultaneously from several different presynaptic neurons when postsynaptic neuron is stimulated by large number of terminals at same time D Modification of synaptic events 1 postsynaptic inhibition a IPSP b inhibitory interneurons example of reciprocal innervation 2 presynaptic inhibition involves axoaxonal synapse mechanism 3 presynaptic facilitation mechanism 4 negative feedback inhibition involves axon collateral to inhibitory interneuron 5 synaptic potentiation increased basal levels intracellular calcium 6 neuromodulation V Organization of neurons in neuronal pools types of circuits determine integration and transmission of information A Diverging circuits B Converging circuits C Reverberating circuits D Parallel after discharge F Functional zones within neuronal pools 1 discharge zones 2 facilitation zones VI Neurotransmitter systems A Acetylcholine excitatory at neuromuscular junction NMJ ANS inhibitory excitatory to visceral effector excitatory at ANS ganglia receptors muscarinic nicotinic receptor structure receptor mode of action muscarinic nicotinic B Biogenic amines 1 catecholamines a norepinephrine and epinephrine types of receptors alpha beta receptor mode of action b dopamine location receptors and mode of action 2 indolamines a serotonin location receptors and mode of action b histamine location receptors and mode of action C Excitatory amino acids 1 glutamate 2 aspartate D Inhibitory amino acids 1 glycine 2 GABA E Polypeptides endorphins enkephalins F Purines G Gases