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The Architecture of Nervous Systems General principles from an evolutionary perspective. Development of the vertebrate nervous system Identity and organization of functional systems Some basic structural features of the nervous system.

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The Architecture of Nervous Systems General principles from an evolutionary perspective. Development of the vertebrate nervous system Identity and organization of functional systems Some basic structural features of the nervous system. Non-mammalian neurobiology.

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Cnidaria: hydra (also jellyfish, corals, and anemones) Nerve net: diffusely distributed network of neurons Two layers of body wall Hydra

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sponges Hydra Sensory cells are bipolar Effector cells are muscles or glands Motorneurons signal to effector cells and to each other as well. Some general features of the nervous system are present in primitive animals.

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Fundamental features of nervous systems: Polarity of signaling: information flows from dendrites and soma to axon (exception: amacrine processes) Divergence of signaling: information travels widely Convergence of signaling: any one neuron receives input from multiple sources. Cephalization: neurons and sensory receptors become concentrated rostrally Centralization: neurons concentrate in body areas with specialized function

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Flatworms: planaria Flatworms are bilaterally symmetric and have three tissue layers (endoderm, mesoderm and endoderm) The nervous system has collections of neurons called ganglia. Axons run through nerve cords.

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Interneurons: local interneurons projection interneurons Increase possibilities for information processing. Also can act as switches, pacemakers. Flatworms: planaria

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Annelids and arthropods (and molluscs): are segmented: body segments are repeated along the rostrocaudal axis have a ventral nerve cord bilateral ganglia or fused ganglia are present in each segment and are connected by longitudinal bundles of axons

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Examples:

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Molluscs:

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The Nobel Prize in Physiology or Medicine for 2000 Arvid Carlsson, Paul Greengard and Eric Kandel for their discoveries concerning "signal transduction in the nervous system"

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-are individually identifiable, have the same morphology in each individual -can be repeatedly located in the same position -are often very large in size Invertebrate neurons: the Retzius cells of the leech as an example In a ganglion in a test tube

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Amphioxus: a primitive chordate The amphioxus has a dorsal nerve cord and a notochord.

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Amphioxus: a primitive chordate The amphioxus has a dorsal nerve cord and a notochord.

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Vertebrates: the nervous system forms from the neural plate.

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Descriptors for relationships: rostral (toward nose) caudal (toward tail) dorsal (toward back) ventral (toward belly) superior (above) inferior (below) anterior (in front) posterior (behind) Note: in the spinal cord dorsal/ventral and anterior/posterior are used interchangeably. Vocabulary

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Central nervous system: spinal cord and brain, including retina. areas containing nerve cell bodies = gray matter areas containing axons = white matter areas in which axons and dendrites synapse = neuropil collections of nerve cell bodies= nuclei (nucleus) axon fiber tracts: fasciculi (fasciculus), peduncle, commissure, lemnisci (lemniscus), tracts Peripheral nervous system: sensory and autonomic ganglia, peripheral nerves. collections of nerve cell bodies = ganglia collections of axons = nerves Vocabulary

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Afferents: axons (nerve fibers) projecting into CNS , inputs to brain, ascending fibers (example: sensory fibers from periphery) Efferents: fibers projecting out of CNS, outputs from brain; descending fibers (example: motor fibers projecting to muscles.) Interneurons: Intrinsic neurons with axonal connections that remain within the local circuit Vocabulary

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The spinal cord. Cervical and lumbar enlargements: arise due to masses of motoneurons for upper and lower limbs.

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Dorsal roots: carry sensory information from dorsal root ganglion into the dorsal horn. Ventral roots: carry motor information out of the ventral horn. The spinal cord.

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Dorsal roots: carry sensory information from dorsal root ganglion into the dorsal horn. Ventral roots: carry motor information out of the ventral horn. The spinal cord. Afferent Efferent

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Local circuits within the cortex also have afferents (inputs) and efferents (outputs). Afferent Efferent

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The Organization of the Nervous System

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The basic wiring diagram of the nervous system. (everything is connected to everything) Behavior is determined by the motor system, which is influence by sensory input, intrinsic behavioral state and cognition. Reflexes result from sensory input, some inputs are voluntary.

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History of neuroanatomical techniques: 1873: Golgi impregnation 1885: Selective stains for degenerating myelinated fibers (Marchi and Algeri) Mid 1950s: selective silver staining for all fibers (Nauta) 1970s: antibody staining, fluorescent markers, radiolabelled amino acids, retrograde tracers, in situ hybridization of nucleic acids

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The Nobel Prize in Physiology or Medicine 1906 "in recognition of their work on the structure of the nervous system"

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Golgi staining: potassium chromate and silver nitrate (1873) Golgi's drawing of the hippocampus impregnated by his stain (from Golgi's Opera Omnia). Nobel e-museum

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Camillo Golgi Nobel Lecture December 11, 1906 The Neuron Doctrine- theory and facts. “..Far from being able to accept the idea of the individuality and independence of each nerve element, I have never had reason, up to now, to give up the concept which I have always stressed, that nerve cells, instead of working individually, act together, so that we must think that several groups of elements exercise a cumulative effect on the peripheral organs through whole bundles of fibers.” The nervous system as a diffuse reticular syncytium? (i.e. a mass of cytoplasm with many nuclei but no internal cell boundries)

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The Neuron Doctrine: (Santiago Ramon y Cajal) Neurons are cells. Each is an individual entity anatomically, embyologically, and functionally. Also: Neurons have a functional polarity. l

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Neurons have a functional polarity. Incoming information arrives Information is assimilated Information is sent to next neuron synapses

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The irresistible conception of the reticular suggestion of which I have spoken to you (which changes every 5 or 6 years) has led several physiologists and zoologists to object to the doctrine of propagation of nerve currents by contact or at a distance. All their allegations are based on the findings of incomplete methods... In spite of the pains I have taken to perceive the supposed intercellular anastomoses in preparations made with diverse coloration processes I have never succeeded in finding any definite ones, that is to say, showing themselves as clearly and sharply as the free endings. If the said intercellular unions are not the result of an illusion, they represent accidental dispositions, perhaps deformities whose value would be almost nil in the face of the nearly infinite quantity of the perfectly observed facts of free ending. Santiago Ramon y Cajal Nobel lecture, Dec 12, 1906 The structure and connexions of neurons.

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Synapses visualized by electron microscopy. (20m nm cleft with synaptic vesicles on one side and postsynaptic density on the other)

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REVISIONS of the NEURON DOCTRINE   1. The presence of electrical synapses – gap junctions (Furshpan and Potter, 1959)   2. Axo-axonic synapses   3. Dendro-dendritic synapses (e.g. amacrine cells of the retina; granule cells of the olfactory bulb (Shepherd) 4. Transynaptic regulation of transmitters, enzymes; transynaptic transport of amino acids, viruses   5. Metabolic subunits within the neuron (e.g. spines as microcompartments)   6. Backpropogation of action potentials from the soma to the dendrites Laslo Zaborsky, Ph.D. MD. Rutgers U.

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Multipolar Unipolar

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J. Comp. Neurol. 462(2): 168-179 Example of morphology of an invertebrate neuron: the parasol cell of the crayfish brain. (Mike Mellon, UVA Dept of Biology) Olfactory,photic, tactile

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Examples of morphology of vertebrate neurons.

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Motor neurons and interneurons typically unipolar Neuronal somata in rind or ganglia Dendritic processes arise directly from axons in most cases Synapses in neuropil Few types glia Lack myelin Large cells in many instances Individually identifiable in many instances Neural circuits have relatively few neurons Motor neurons and interneuons typically multipolar Neuronal somata typically grouped in nuclei, cortical lamina or throughout ganglia Dendritic processes arise from soma Several distinct types of glia Have myelin and thus saltatory conduction Few cells that are very large Few individually identified neurons Neural circuits have many components Similarities and differences between the nervous systems of invertebrates and vertebrates Inverebrate nervous systems Vertebrate nervous systems

Nature 417, 359 - 363 (16 May 2002)Robots in invertebrate neuroscience BARBARA WEBB : 

Nature 417, 359 - 363 (16 May 2002) Robots in invertebrate neuroscience BARBARA WEBB Can we now build artificial animals? A combination of robot technology and neuroethological knowledge is enabling the development of realistic physical models of biological systems. And such systems are not only of interest to engineers. By exploring identified neural control circuits in the appropriate functional and environmental context, new insights are also provided to biologists. Robot modeling of a cricket’s escape response.

Nature 417, 359 - 363 (16 May 2002)Robots in invertebrate neuroscience BARBARA WEBB : 

Nature 417, 359 - 363 (16 May 2002) Robots in invertebrate neuroscience BARBARA WEBB …invertebrate systems have been a particularly successful area for the approach. Invertebrate behaviours tend to be more stereotyped and thus easier to analyse comprehensively. The number of neural connections between sensing and action is orders of magnitude less than for vertebrates, making the possibility of complete pathway mapping plausible. We should have comparable processing power available in modern computers to that in insect brains, so failure to replicate their behavioural capabilities will indicate areas in which we lack knowledge of how the systems work.

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Understanding the physiological factors underlying the sign of the synaptic potential Or

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Understanding the physiological factors underlying the sign of the synaptic potential Or A day at the beach.

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Lobster Dactyl Opener Muscle 2.7º 0.5 mV 0.5 mV 250 ms Excitatory Junction Potential (EJP) Inhibitory Junction Potential (IJP)

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twitch contractions, relaxations & muscle tone Intracellular recording Muscle tension Lobster Dactyl Opener Muscle

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insight overview 318 NATURE | VOL 417 | 16 MAY 2002 | www.nature.com Non-mammalian models for studying neural development and function Eve Marder Early neuroscientists scoured the animal kingdom for the ideal preparation with which to study specific problems of interest. Today, non-mammalian nervous systems continue to provide ideal platforms for the study of fundamental problems in neuroscience. Indeed, the peculiarities of body plan and nervous systems that have evolved to carry out precise tasks in unique ecological niches enable investigators not only to pose specific scientific questions, but also to uncover principles that are general to all nervous systems. Nature 417, 364 - 365 (16 May 2002) All Creatures Great and Small: National Institutes of Health NINDS, NICHD, NIDA, NIDCD, NIGMS, NIMH : statements detailing the non-mammalian systems they fund and why.

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Antibody staining for GABAA and GABAB receptors in the retina.

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Neuroanatomical techniques 1873: Golgi impregnation 1885: Selective stains for degenerating myelinated fibers (Marchi and Algeri) Mid 1950s: selective silver staining for all fibers 1970s: antibody staining, fluorescent markers, radiolabelled amino acids, retrograde tracers, in situ hybridization of nucleic acids