Nervous System Part TwoS Y N A P S E S A N D N E U R A L I N T E G R A T I O N The Nervous System Junction between Adjacent neurons Mediates information transfer Postsynaptic neuron Copyright © 2010 Pearson Education, Inc. Dendrites Axosomatic synapses Axon of presynaptic Neurons are electrically coupled (joined by gap junctions) Communication is very rapid Important in Embryonic tissue Unidirectional Copyright 2009 John Wiley & Sons, Inc. 8 Signal transmission at the chemical synapse The Synapse Excitatory Postsynaptic Potentials (EPSP) Inhibitory Postsynaptic Potentials (IPSP) Excitatory Postsynaptic Potentials (EPSP) Depolarizes postsynaptic cell membrane Copyright © 2010 Pearson Education, Inc. Figure 11.18a An EPSP is a local depolarization of the postsynaptic membrane that brings the neuron closer to AP threshold. Neurotransmitter binding opens chemically gated ion channels, allowing the simultaneous pas- sage of Na+ and K+. Time (ms) Threshold Stimulus Inhibitory Postsynaptic Potentials (IPSP) Hyperpolarizes postsynaptic cell membrane An IPSP is a local hyperpolarization of the Time (ms) Threshold Stimulus Thought Question Strychnine is a pesticide that is used against small vertebrates. This chemical is an antagonist to glycine, what symptoms might an animal or human experience if they ingest this substance? The Synapse Action potential Ca2+ entry causes neurotransmitter- containing synaptic vesicles to release their contents by exocytosis. Chemical synapses Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. Binding of neurotransmitter opens ion channels, resulting in graded potentials. Neurotransmitter effects are terminated by reuptake through transport proteins, enzymatic degradation, or diffusion away from the synapse. Ion movement Graded potential Neuroplasticity Idea that the brain is not hardwired. Following injury or changes in use, the brain is able to changes its neural circuits. Neurons can adapt and change their functions dependent on need. Synaptic plasticity Changes in the use of a neuronal connection can lead to changes at the synapse. Increased/decreased amount of calcium released at the axon terminal (this changes the amount of NT released) Altering the number of receptors on the postsynaptic cell membrane (happens by triggering a second messenger system which affects gene transcription for the receptors) Neural Integration EPSP’s can summate to reach threshold IPSP’s can also summate with EPSP’s Cancel each other out Excitatory synapse 1 (E1) Excitatory synapse 2 (E2) add together. One or more presynaptic neurons transmit impulses in rapid-fire order Spatial summation Postsynaptic neuron is stimulated by a large number of terminals at the same time Neuronal Circuits May consist of thousands of neurons Often include excitatory and inhibitory neurons Copyright © 2010 Pearson Education, Inc. Figure 11.21 Presynaptic Neuronal Circuits Diverging circuit May affect a single pathway or several Common in both sensory and motor systems Figure 11.22a Figure 11.22b Neuronal Circuits Converging circuit Figure 11.22c, d We’ll come back to this when we cover reflexes Questions? Don’t forget homework for lab, due at the beginning… Lab Exercise 17 pg.’s 265 (all) and 265 #9 & 10 only (top) PreLab 1