1. Arthropod neurons and nervous system
Carmen Ramona Smarandache-Wellmann 
Current Biology 
Volume 26, Issue 20, Pages R960-R965 (October 2016)
DOI: /j.cub
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2. Figure 1 Morphology of the arthropod CNS.
Schematic of arthropod CNS: (A) Myriapoda; (B) Insecta; (C) Crustacea; (D) Chelicerata. The brain (b) is located anteriorly in the head. The ventral nerve cord is a chain of segmental ganglia, some compressed. (A) In a centipede, ganglia are metameric and connected via the paired connectives. The ventral nerve cord of some insects, such as dragonflies (Bi), and crustaceans, such as crayfish (Ci), are spatially distributed; only the subesophageal ganglion (SOG) and the terminal ganglion are compressed. The CNS of evolutionarily younger insects, such as fruit flies (Bii), and of brachyurian crabs (Cii) is compressed. In insects the brain is fused to the SOG; and the thoracic ganglia form with the abdominal ganglia a thoracic mass. In crabs the subesophageal, the thoracic and the abdominal ganglia are compressed into a subesophageal mass, the thoracic ganglion. (D) Chelicerate CNS is strongly compressed. The first three neuromers form the brain, or syncerebrum. It lies dorsal to the fused subesophageal and thoracic segments and form together the synganglion. (Di) The abdominal ganglia of a scorpion are spatially distributed. (Dii) In arachnids, the abdominal segments are compressed into the synganglion. Abbreviations: b, brain, when fused with the following segments and positioned above of others shown in grey; SOG, subesophageal ganglion; TG, thoracic ganglion; AG, abdominal ganglion; ch, cheliceral; pp, pedipalp; wl 1–4, walking leg nerves 1–4. Figures adapted from: (Bi) Wendler (1999) with permission of Springer, (Ci) Storch and Welsch (2009), with permission of Springer; (Cii) Thomson (1916); (Di) Preprinted by permission from Macmillan Publishers Ltd: Nature Tanaka et al. (2013); (Dii) Adapted from Lehmann et al. (2016) by permission of Oxford University Press.
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3. Figure 2 Ganglia in insects and crustaceans.
Schematics of three pairs of orthogonal sections through: (i) a thoracic ganglion of an insect; and (ii) an abdominal ganglion of a crustacean. The basic structure is strongly preserved across species and across homologous segments. Tracts of axons run rostro-caudally through the ganglia, while commissures connect the bilateral ganglia. Neuropils are the center for synaptic interaction. The color coding is preserved across the figure. (A) Transversal section at the height of the first nerve root. The tracts are layered and separated by commissures. (B) Sagittal section through the ganglia at the height of the medial dorsal tract. The numbering of the dorsal commissures is different in the two species, but they are layered in a similar fashion. (C) Frontal section in the dorsal part of the ganglia showing the tracts, and commissures in the two species. Abbreviations: MDT, medial dorsal tract; LDT, lateral dorsal tract; DMT, dorsal medial tract; DIT, dorsal intermediate tract; DLT, dorsal lateral tract; VIT, ventral intermediate tract; VMT, ventral medial tract; VLT, ventral lateral tract; MVT, medial ventral tract; LVT, lateral ventral tract. Commissures: DC 1–7, dorsal commissure 1–7; AVC, anterior ventral commissure; PVC, posterior ventral commissure. Neuropils: hN/HN, horseshoe neuropil; lVAC, lateral part of ventral association center; mcN, medial coarse neuropil; vcN, ventral coarse neuropil; LN, lateral neuropil. Giant axons: MG, medial giant; LG, lateral giant. Figures adapted from: (Ai) Goldammer et al. (2012); (Bi) after Kittman et al. (1991); (Ci) after Gregory (1974); (Aii,Bii,Cii) Elson (1996) and Skinner (1985).
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4. Figure 3
Morphology of neuron types in invertebrate and vertebrate CNSs.
Schematics of invertebrate (A) and vertebrate (B) neurons. The color code is preserved across the figure: red, dendrites; yellow, soma; cyan, axon; blue, primary neurite; orange, spike initiation zone/axon hillock; green synaptic boutons. (Ai) Bipolar sensory neuron of invertebrate. (Aii) Monopolar invertebrate interneurons. The dendritic tree is the point of integration and transfer of information. (Aiii) Monopolar invertebrate motor neurons. (Bi) Unipolar or pseudounipolar sensory neurons of vertebrates. (Bii) Two types of multipolar vertebrate interneurons. (Biii) Multipolar motor neuron of vertebrates. (C) Example of an identified interneuron in (i) stick insects, E4, and (ii) crayfish, Commissural Interneuron 1. Both project through a homolog commissure to the contralateral side. (D) Invertebrate motor neuron pools in (i) stick insects and in (ii) crayfish. Figures adapted from: (Ci) Büschges and Wolf (1995); (Di) Goldammer et al. (2012); (Dii) Mulloney and Smarandache-Wellmann (2013).
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