AIM SWBAT describe synaptic transmission and impulse processing.

Criteria for Success [ ] I can list and describe the components of a synapse. [ ] I can describe process of synaptic transmission. [ ] I can differentiate between action potential and resting potential. [ ] I can compare and contrast neuronal pools, convergence and divergence.

3 The Synapse Nerve impulses pass from neuron to neuron at synapses, moving from a pre-synaptic neuron to a post-synaptic neuron. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites Impulse Synaptic cleft Axon of presynaptic neuron Cell body of postsynaptic neuron Axon hillock of Postsynaptic neuron Axon of presynaptic neuron

4 Synaptic Transmission Neurotransmitters are released when impulse reaches synaptic knob Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondrion Synaptic knob (a) Synaptic cleft Neurotransmitter Axon Ca +2 Presynaptic neuron Direction of nerve impulse Synaptic vesicles Cell body or dendrite of postsynaptic neuron Synaptic vesicle Vesicle releasing neurotransmitter Axon membrane Polarized membrane Depolarized membrane Ca +2

5 Animation: Chemical Synapse Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

6 Cell Membrane Potential A cell membrane is usually electrically charged, or polarized, so that the inside of the membrane is negatively charged with respect to the outside of the membrane (which is then positively charged). This is as a result of unequal distribution of ions on the inside and the outside of the membrane.

7 Distribution of Ions Potassium (K + ) ions are the major intracellular positive ions (cations). Sodium (Na + ) ions are the major extracellular positive ions (cations). This distribution is largely created by the Sodium/Potassium Pump (Na + /K + pump). This pump actively transports 3 sodium ions out of the cell and 2 potassium ions into the cell.

8 Action Potentials At rest, the membrane is polarized (RMP = -70) Sodium channels open and membrane depolarizes (toward 0) Potassium leaves cytoplasm and membrane repolarizes (+30) Threshold stimulus reached (-55) Brief period of hyperpolarization (-90) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Region of depolarization (b) Region of repolarization (c) –70 –0 –70 –0 –70 –0 K+K+ Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Threshold stimulus Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Na + channels open K + channels closed K + channels open Na + channels closed

9 Action Potentials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Milliseconds Membrane potential (millivolts) Action potential Hyperpolarization –40 –20 –60 –80 Resting potential Resting potential reestablished

10 Action Potentials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Direction of nerve impulse ––––––––– ––––––––– ––––––––– ––––––––– ––––––––– ––––––––– (b) (c) Region of action potential

11 Animation: Action Potential Propagation in Myelinated Neurons Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

12 Animation: Action Potential Propagation in Unmyelinated Neurons Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

13 All-or-None Response If a neuron axon responds at all, it responds completely – with an action potential (nerve impulse) A nerve impulse is conducted whenever a stimulus of threshold intensity or above is applied to an axon All impulses carried on an axon are the same strength

14 Animation: The Nerve Impulse Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

15 Impulse Processing Way the nervous system processes nerve impulses and acts upon them Neuronal Pools Interneurons Work together to perform a common function May excite or inhibit Convergence Various sensory receptors Can allow for summation of impulses Divergence Branching axon Stimulation of many neurons ultimately

16 Neuronal Pools Groups of interneurons that make synaptic connections with each other Interneurons work together to perform a common function Each pool receives input from other neurons Each pool generates output to other neurons

17 Convergence Neuron receives input from several neurons Incoming impulses represent information from different types of sensory receptors Allows nervous system to collect, process, and respond to information Makes it possible for a neuron to sum impulses from different sources (a) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18 Divergence One neuron sends impulses to several neurons Can amplify an impulse Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (b) 4 5 6