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CHAPTER 5: SIMPLE NERVOUS SYSTEMS AND BEHAVIOR What are the properties of the CNS of the simplest animals? Choanoflagellates Probable animal ancestors, unicellular, aggregate in groups, feed on bacteria, similar to some cells in sponges. Bilateral symmetry Radial symmetry Vertebrates Invertebrates with no nervous system Invertebrates with nervous system Simple nervous systems: Invertebrates Gangliar organization of the CNS of invertebrates with bilateral symmetry. (Notice the ventral position.) Octopus intelligence http://www.youtube.com/watch?v=T8cf7tPoN5o Video The neuron Axon terminal (with vescicles) Hippocampal neuron stained for spectrin (red) and tubulin (green). Synapse Myelin: evolved independently in vertebrates and other phyla, apparently several times (present in earthworms and some shrimp species). Most invertebrates lack myelin. Post-synaptic dendrite (with receptors) Neuron # 1 Vescicle with neurotransmitter Extracellular compartment (ions, enzymes, etc.) Receptor Synapse Neuron # 2 Neuron # 1 Na+ Neuron # 2 Neurons: Action potentials http://www.youtube.com/watch?v=ifD1YG07fB8&feature=related Video Neurons: Synaptic transmission http://www.youtube.com/watch?v=9vZI_XKca88 Video Animal evolution: a simplified view Sponges Cnidarians Planarians Arthropods Mollusks Vertebrates Central nervous systems (CNS) Neurons, diffuse nervous systems Multicellular animals, no neurons Diffuse nervous systems in cnidarians Hydra *Neural nets. *No differentiation between CNS-PNS. *Neurons have familiar properties. Jellyfish http://www.youtube.com/watch?v=kZYN-a7BXE0&feature=related Video Functional properties of cnidarian neurons Graded potentials Action potential Presynaptic Postsynaptic Echo Jellyfish Basic behaviors •Simple-system approach •Reflexes •Modal action patterns •Behavioral plasticity (learning) Animal evolution: a simplified view Sponges Cnidarians Planarians Arthropods Mollusks Vertebrates Central nervous systems (CNS) Neurons, diffuse nervous systems Multicellular animals, no neurons Simple-systems approach To study the neural basis of behavior, one approach is to select a simple behavior and a simple nervous system. Simple behavior: •Reflexes •Modal action patterns •Habituation •Sensitization Pupillary reflex Patellar reflex Aplysia californica http://www.youtube.com/watch?v=Q1KI30JmemU Video Simple nervous systems: Mollusks •Few neurons •Large neurons •Stable locations across animals •Identifiable Aplysia californica (sea hare) Basic behaviors •Simple-system approach •Reflexes •Modal action patterns •Behavioral plasticity (learning) Reflex: a simple behavior and a simple neural network A unit of behavior that includes: •An input (stimulus), •Some degree of processing in the CNS (monosynaptic, polysynaptic), and •An output (simple response or secretion). Patellar reflex Gill-withdrawal reflex of Aplysia Gill-withdrawal reflex of Aplysia Stimulating and recording electrodes Gill Abdominal ganglion Siphon nerve Genital nerve Pericardial nerve Water pik Branchial nerve Siphon Basic behaviors •Simple-system approach •Reflexes •Modal action patterns •Behavioral plasticity (learning) Modal action patterns Sequentially organized, species-typical behaviors that once activated develop in a ballistic manner. Dorso-ventral contractions (escape response) Stimulus: jet of salty water simulating a predator (starfish) Animal lands at a distance from previous location MAP in Tritonia Escape MAP in Tritonia https://www.youtube.com/watch?v=JCr1b1mJWoU Video Basic behaviors •Simple-system approach •Reflexes •Modal action patterns •Behavioral plasticity (learning) A conversation with Eric Kandel Up to 16:30 min http://www.youtube.com/watch?v=rHx32Erpyfo Video A conversation with Eric Kandel: Summary • In the 1950s there was a family of competing ideas about how memories could be stored: diffused storage, glial cells, synapses critical. • Explicit or declarative memory: the recall of information about people, places, and objects, and it requires the medial temporal lobe and the hippocampus. • Implicit or procedural memory: perceptual/motor skills, habits, including classical and operant conditioning, habituation, and sensitization. • Aplysia: a simple animal, simple nervous system, and simple behavior, a reduced form of a human brain. • Short-term vs. long-term memory: preexisting connections and proteins vs. gene expression, new protein synthesis, and new connections. • Only those synapses that are active are strengthened. • Experience can alter whether a gene is turned on or off in a neuron. • Brain representations depend on experience. • Survival requires the ability to modify responses through learning. A tentative classification of learning phenomena Learning Phenomena Specific General Nonassociative Associative/Cognitive •Habituation •Short term •Long term? •Classical conditioning •Human language •Instrumental conditioning •Song learning •Sensitization •Short term •Long term? •Rule learning •Imprinting •Social learning Properties of habituation Response Strength 12 10 (3) 8 (1) 6 (2) 4 (2) 2 0 0 6 Resting period 9 Resting 12 period Strong12 10 ISI = 60 s 12 ISI = 10 s 10 8 8 8 6 6 6 12 Response Strength 3 4 4 (5) 2 2 2 0 0 0 0 1 2 3 4 (6) Weak10 4 (4) 15 5 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 Resting 9 10 period 12 Response Strength 12 10 200 Hz 8 (9) 8 (7) 600 Hz 10 6 400 Hz 4 (8) 6 4 600 Hz 2 0 2 DS DS 0 0 1 2 3 4 5 6 7 8 0 Habituation Trials 1 2 3 4 5 6 7 8 9 10 11 12 Habituation of the Galvanic skin response in humans Aplysia’s siphon retraction reflex and learning https://www.youtube.com/watch?v=yLa-cXg8BwM Video Habituation in Aplysia Habituation in Aplysia: Mechanisms ↓Ca++ influx: habituation Habituation of the gill-withdrawal reflex in Aplysia is caused by a decrease in calcium influx into sensory neuron, which causes a reduction in neurotransmitter release onto motor neuron, thus decreasing the motor response (gill contraction). Dishabituation and sensitization in Aplysia Long-term sensitization Short-term sensitization Short-term sensitization and dishabituation in Aplysia: Mechanisms ↓K+ outflux: shortterm sensitization (spike broadening) ↑Ca++ influx: dishabituation (increased excitability) Short-term habituation and dishabituation in Aplysia: A cellular model Morphological changes in long-term habituation and sensitization Long-term habituation Long-term sensitization Normal Evolution of neural plasticity Plasticity: peripheral Lower invertebrates Body surface Effector Plasticity: peripheral & central Higher invertebrates Body surface Effector Plasticity: only in the CNS Vertebrates Body surface Effector Excitatory Plastic