Squid. Announcements. L03. ROOTS of NEUROETHOLOGY IN CELLULAR NEUROBIOLOGY. Outline. The Discovery of the Giant Squid Axon KROGH S PRINCIPLE

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1 L03. ROOTS of NEUROETHOLOGY IN CELLULAR NEUROBIOLOGY Announcements 1) Course website: Google Chrome? 2) Writing Assignments W1 3) Discussion section Wednesday 9:05 AM, this room. Carl D. Hopkins Aug. 28, Outline L03. Roots in Cellular Neurobiology 1. Krogh's Principle 2. Neuron doctrine 3. Neuron as connector, integrator, rectifier, transducer, logical device, memory storage, circuit. KROGH S PRINCIPLE For a large number of problems [in biology] there will be some animal of choice, or a few, on which it can be most conveniently studied. August Krogh, The Progress of Physiology, The American Journal of Physiology, (2) pp August Krogh Denmark. Nobel Prize Discovery of capillary motor regulating mechanism 4 Squid The Discovery of the Giant Squid Axon 1936: Young, J. Z. Proc. Roy. Soc. London B. 121:319 (Description of the giant axon of squid, Loligo) Young thought the these curious structures were blood vessels, but he was able to show that upon stimulation with electrical currents they caused the mantle to contract, so he realized they were nerve fibers. John Z. Young F.R.S Zoologist, Oxford University 1

2 Giant nerve fibers in squid Bullock and Horridge (1965) Must See Videos: A. L. Hodgkin and A. F. Huxley, RESTING AND ACTION POTENTIALS IN SINGLE NERVE FIBRES. Physiol. (London), 104(1945)176. After the Discovery of Squid Axon ability to record intracellular voltage first voltage clamp (2 electrodes inside: I, V) ability to perfuse (replace) intracellular ions, d development l t off quantitative tit ti description d i ti off action ti potentials ability to record from both pre- and post-synaptic neurons at giant synapse 2 ms The squid axon did more for axonology than any other single advance in technique during the previous 40 years. Alan Hodgkin (1973) see quote by R. Keynes (2005) Nerve nets in hydra and jellyfish (Cnidaria) Nerve net in hydra NEURON DOCTRINE Neurons in jellyfish 2

3 Santiago Ramon y Cajal Golgi Method used Golgi method provided evidence for Neuron doctrine first evidence of multitude of cell types, neural circuts Kitten cerebellum Basket endings convincing proof of separate cells. - basket cell surrounds cell body but does not connect to purkinje cell. Axons may cross, but not connect. Each element autonomous (a cell) Calaj s Neuron Doctrine The nervous system is composed of cells: glial cells and neurons. Neurons are morphological units. Neurons make intimate contacts (contiguous but not continuous) continuous). Cell bodies and dendrites are conductors, just like axons. Dynamic polarization When there are axon collaterals, they act together. Axons arise in development by neurite outgrowth Summarized in Nobel speech (1906) - shared with Golgi. Electron Microscopy Clinches The Neuron Doctrine 16 ANALYSIS LEVEL First EM: Germany,1930 s. Fixation of tissues (Palade and Porter, 1950 s) molecular Palay, Palade, DeRobertis: Neurons with distinct membranes at synapses (extracellular space in synaptic cleft) (1954-9). whole animal cellular subcellular 17 circuits 18 3

4 Neuron as a wire. The Neuron By Analogy wiring Neuron as a rectifier. Neuron as transducer. components layout Neuron as a connector. Neuron as an summing circuit. Neuron logic. inside components software whole machine Neuron as a memory storage device. Neuron in a circuit Neuron as a Wire Neuron Shape: long axon makes long distance, highly specific contact possible. Neuron electrical properties: signals travel within a neuron travel at high speed use electric signals (insulation) (propagation) (=action potentials) Axon serves as information conduit. -- long distances -- efficiently packaged Consider a scale model of motor neuron (soma = 100 microns; axon = 1 m) (ratio = 1:10,000) Neuron Shape Dye filled axons Branching: permit elaborate connections divergence convergence 21 Axons, longitudinal view Axons, cross section 22 white matter Axon bundles make up nerves gray matter Dorsal Roots (sensory) sensory ganglion (cell bodies) Nerve Cells Communicate with Targets Using Electric Signals 1) Resting neurons are electrically polarized. - resting potential 2) Action potentials: transient events caused by opening of ion channels in membrane. Propagates down axon. 3) Slow potentials: originate in sensory receptors, and at synapses. Local, do not propagate. Ventral roots (motor) spinal cord

5 Nerve cell at rest has a voltage across its membrane = resting potential Action Potentials The Action Potential (spike): Transient (1 millisecond duration) de-polarization peak voltage = +55 mv inside (mainly due to influx of Na + ions) All or None (threshold) propagates along axon Some Ion Channels in Nerve Membranes are Voltage-Dependent Ion selective AND Voltage dependent (opening controlled by voltage) outside cell cell at rest (-70 mv) cell partly depolarized (-30 mv) cell depolarized (+55 mv) The Sodium Channel Potassium Channels 29 Structure worked out in 1998 (Doyle et al. Roderick MaKinnon lab) 30 5

6 How the action potential propagates Propagation Velocity t Measuring velocity with two electrodes velocity = distance / time myelinated nerve: 10 to 100 m/sec Neuron as Rectifiers Excitatory Influx of cations (+ charge) cause membrane depolarization SYNAPSES Neuron as a Transducer How do signals get started in neurons? sensory receptor neuron Crayfish Stretch Receptor Neural code for stretch intensity is the frequency of nerve impulses

7 Adaptation Pharmachological blockers can sort out the various ion channels responsible for the receptor potential, adaptation, and spikes. SA RA Membrane channels MSC mechanosensitive Na sodium K potassium Cl - chloride Bo Rydqvist, Jia-Hui Lin, Peter Sand, Christer Swerup (2007) Mechanotransduction and the crayfish stretch 37 receptor. Physiol. & Behavior. 92: Bo Rydqvist, Jia-Hui Lin, Peter Sand, Christer Swerup (2007) Mechanotransduction and the crayfish stretch 38 receptor. Physiol. & Behavior. 92: Summation Synapses: synaptic potentials sum on the post-synaptic cell, providing for: -- spatial summation: -- temporal summation: -- subtraction: Wine, J. (1984). J. Experimental Biology. 112: Fine Tuning the Neuron as Integrator (summing network) Excitatory synapse generates a depolarizing potential. Membrane voltage decreases exponentially with distance. Neuron as Connector Some neurons serve to relay signals from one cell to another. Signal is relayed from input to the output Rise time increases with distance. Consider a synapse on a dendrite

8 2 Neuron Logic AND logic Output spike only if are active at same time. OR logic Output spike if either 1 or 2 are active Neuron Memory Synapses retain a memory of recent events. Depression: recent activity leads to decrease in response. 1 3 NOT logic Output spike if 1 OR 2, but NOT 3 Facilitation: recent activity leads to increase. Pre-synaptic inhibition. Pre-synaptic facilitation Changing the Strength of a Synapse Fatigue depletion of synaptic transmitter Habituation decrease in amount of transmitter released, but not due to fatigue Sensitization increase in amount of transmitter released Changing the Strength of Synapses Pre-synaptic excitation a synapse on a synapse (primes synapse to be stronger). Hebbian Learning NMDA receptor for glutamate: synapse is made stronger if activated when cell already depolarized Neural Circuits and Behavior Tracing circuitry of neural connections leads to understanding of how behavior is influenced by neuronal action. 3. synapse Neural Circuits and Behavior cell body 4. motor neuron 2. sensory dendrite 1. sensory transduction stimulus muscle Perception correlates with characteristics of neural circuit

9 Neuronal Activity is both Necessary and Sufficient A) Correlation between behavior and activity of a particular neuron (LGI) B) Sufficient: artificial stimulation of the neuron causes both a spike, and the behavior. C) Necessary: if the neuron spike is blocked, the natural behavior is blocked, even though stimulus is OK. Complex Behavior, Complex Circuits The PYLORIC muscles and patterns of contraction. Stomatogastric Ganglion of Lobster. A restricted neural network (30 cells). Controls muscles of gastric mill and the pylorus (movements involved in griding of food and of digestion) The End 51 References Bullock, T. H. (1948). Properties of a single synapse in the stellate ganglion of squid. J. Neurophysiol. 11, Bullock, T. H. (1959). The neuron doctrine in electrophysiology.. Science 129, Bullock, T. H., Bennett, M. V. L., Johnston, D., Josephson, R., Marder, E. and Fields, R. D. (2005). The Neuron Doctrine, Redux. Science 310, Bullock, T. H. and Horridge, G. A. (1965). Structure and function in the nervous systems of invertebrates. San Francisco: W. H. Freeman & Co. Debanne, D. (2004). Information processing in the axon. Nat Rev Neurosci 5, Doyle, D. A., Morais Cabral, J., Pfuetzner, R. A., Kuo, A., Gulbis, J. M., Cohen, S. L., Chait, B. T. and MacKinnon, R. (1998). The structure of the potassium channel: molecular basis of K+ conduction and selectivity. Science 280, Hodgkin, A. L. (1973). Address of the President Sir Alan Hodgkin at the Anniversary Meeting, 30 November Proc. R. Soc. Lond. B 183, Hodgkin, A. L. (1992). Chance and Design: Reminisces of Science in Peace and War. Cambridge: Cambridge University Press. Hodgkin, A. L. and Huxley, A. F. (1945). Resting and action potentials in single nerve fibres. J Physiol 104, Hodgkin, A. L. and Huxley, A. F. (1952a). The components of membrane conductance in the giant axon of Loligo. J Physiol 116, Hodgkin, A. L. and Huxley, A. F. (1952b). Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo. J Physiol 116, Hodgkin, A. L. and Huxley, A. F. (1952c). The dual effect of membrane potential on sodium conductance in the giant axon of Loligo. J Physiol 116, Hodgkin, A. L. and Huxley, A. F. (1952d). Movement of sodium and potassium ions during nervous activity. Cold Spring Harb Symp Quant Biol 17, Hodgkin, A. L. and Huxley, A. F. (1952e). A quantitative description of membrane current and its application to conduction and excitation in nerve. J. Physiol. (London) 117, Hodgkin, A. L., Huxley, A. F. and Katz, B. (1952). Measurement of current-voltage relations in the membrane of the giant axon of Loligo. J Physiol 116, Keynes, R. (2005). J. Z. and the discovery of squid giant nerve fibers. Journal of Experimental Biology 208, Krogh, A. (1929). The progress of physiology. American Journal of Physiology American Journal of Physiology 90, MacKinnon, R., Cohen, S. L., Kuo, A., Lee, A. and Chait, B. T. (1998). Structural conservation in prokaryotic and eukaryotic potassium channels. Science 280, Palade, G. and Palay, S. L. (1954). Electron microscope observations of interneuronal and neuromuscular synapses. Anatomical Record 118, Palay, S. L. and Palade, G. E. (1955). The fine structure of neurons. J Biophys Biochem Cytol 1, Ramon y Cajal, S. (1906). The structure and connexions of neurons. Amsterdam: Elsevier Publishing Company Ramón y Cajal, S. ( ). Histologie du système nerveux de l'homme et des vertébrés. Paris: A. Maloine. Ramón y Cajal, S. (1995). Histology of the Nervous System. New York: Oxford University Press. Rydqvist, B., Lin, J. H., Sand, P. and Swerup, C. (2007). Mechanotransduction and the crayfish stretch receptor. Physiol Behav 92, Wine, J. (1984). The structural basis of an innate behavioural pattern. Journal of Experimental Biology 112, Young, J. Z. (1936). The structure of nerve fibers in cephalapods and crustacea. Proceedings of the Royal Society of London (B) Biological Sciences 121, Young, J. Z. (1938). The functioning of the giant nerve fibres of the squid. Journal of Experimental Biology 15,