The synapse Synapses and Simple Neural neurotransmitter + Na Circuits + ! K Synaptic vesicles containing Presynaptic Today’s topics: membrane neurotransmitter • Review action potentials Voltage-gated • The Synapse Ca2+ channel – Summation Ca2+ – Neurotransmitters Postsynaptic – Various drugs membrane http://images.lifescript.com/images/ebsco/images/synapse_neurotransmitter.JPG • Memory Ligand-gated ion channels 2 April 2012 How is the signal sent? How is the signal turned off? Signals can be excitatory or inhibitory Summation of Signals! The effects are SUMMED EPSP - excitatory post-synaptic potential IPSP - inhibitory post-synaptic potential Example: Neuron D receives inputs from A, B, and C. How would you Some Neurotransmitters! make it fire under the situation: (see Table 48.1) • Acetylcholine! • Only when A and B are • Norepinephrine! both signaling? A • Dopamine! • Serotonin! • Either A or B? • Glutamate! • A and B but not C? B D • GABA! C • And lots more! 1 Table 48-1 Acts as Precursor L-Dopa-> Dopamine Stimulates Release of NT Black Widow venom-> Ach Blocks Relase of NT Botulinum -> Ach Blocks Reuptake Stimulates Receptors Cocaine -> Dopamine Nocotine -> Ach Blocks Receptors Curare, Atropine -> Ach Actions of Various Drugs Fig. 49-22 Nicotine stimulates Dopamine- releasing neuron. Opium and heroin decrease activity of inhibitory neuron. Cocaine and amphetamines block removal of dopamine. Reward system response Mescaline (from peyote) mimics norepinephrine. Psilocybe cubensis (Magic mushrooms) 2 Cell body of Gray A very simple sensory neuron in matter dorsal root neural circuit ganglion Memory! White matter NY Times! Spinal cord (cross section) Sensory neuron Motor neuron Fig. 49-3 Interneuron Fig. 49-19 Figure 49.20a N1 N1 Ca2+ Na+ N2 N2 (a) Synapses are strengthened or weakened in response to activity. Mg2+ Glutamate NMDA receptor (open) NMDA Stored AMPA receptor receptor (closed) (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses. Figure 49.20c AMPA NMDA receptor receptor Action potential Synapse exhibiting LTP 3 .