Bio334 Neurobiology 1 Lecture 2

Transcription

1 Evolution of Bio334 Neurobiology 1 Lecture 2 1

2 Questions from the last lecture Patients with Broca s area lesions do have trouble writing Golgi Cajal debate reticular theory of the brain vs. individual cells 2

3 Why study the evolution of Curiousity May provide fundamental insights into nervous system function and development 3

4 How to study evolution of? Soft tissue not preserved properly so fossil record is not useful Instead study and compare the nervous systems of living animals from different phyla Caveat these animals have also gone through evolution 4

5 What is a nervous system? A nervous system is an organized constellation of cells (neurons) specialized for the repeated conduction of an excited state from receptor sites or from neurons to effectors or to other neurons Bullock and Horridge (1965) Additionally should be capable of endogenously generating activity Passano (1963) 5

6 Metazoan (multicellular) phylogenetic tree 6

7 Metazoan (multicellular) phylogenetic tree 7

8 Sponges no nervous system just musclelike organs Non-motile Just muscle-like effectors that can control the flow of water These muscle-like cells also sense environmental cues 8

9 Metazoan (multicellular) phylogenetic tree 9

10 Diversity of among other members of metazoa %20Regulation/48-NervousSystems/48-15-NervSystemDiversit-L.gif 10

11 Nerve nets diffuse without a brain Connect sensory neurons to muscles 11

12 Bilateralia animals with bilateral symmetry have a organised nervous system Brain and nerve cord Cephalization brain and sense organs close to one end of the body 12

13 Did these all evolve from a common ancestor? Examine the mechanisms and see if subsequent could be viewed as modifications 13

14 Action potential present in unicellular organisms Calcium based Could have been adapted to use sodium and potassium based currents Electrical signaling is fast and can travel quickly over long distances High fidelity Is also specific can activate target neurons without activating neurons on the way 14

15 Post-synaptic density proteins expressed in sponges Co-regulation maybe important for forming a functional synapse Sakarya et al. PLOS One (2007) Conaco et al. PNAS (2012) 15

16 Ventral nerve cord in invertebrates vs. dorsal nerve cord in vertebrates Did they evolve independently? 16

17 Vertebrate dorsal nerve cord may be a result of inversion of ventral nerve cord Geoffroy Saint-Hilaire, Anton Dohrn 17

18 Conserved expression of genes in the anterio-posterior direction in the CNS Origin and evolution of the first nervous system from the book Evolution of Nervous systems: Vol 1 edited by Jon Kaas 18

19 Vertebrate dorsal nerve cord may be a result of inversion of ventral nerve cord more evidence Platynereis Arendt lab its/dev_biology/arendt/ 19

20 Tripartite brain might have been present in an ancestor to Bilateria Similar divisions in Drosophila and mouse and ascidians Gene expression similar Basic Nervous System Types: One or Many? from the book Evolution of Nervous systems: Vol 1 edited by Jon Kaas 20

21 Ventral and dorsal nerve cords could also have arisen independently from nerve nets 21

22 Evolution of first Origin and evolution of the first nervous system from the book Evolution of Nervous systems: Vol 1 edited by Jon Kaas 22

23 Evolution of first Origin and evolution of the first nervous system from the book Evolution of Nervous systems: Vol 1 edited by Jon Kaas 23

24 Evolution of first Origin and evolution of the first nervous system from the book Evolution of Nervous systems: Vol 1 edited by Jon Kaas 24

25 Brain complexity expansion of cortex 25

26 Brain size vs. brain weight correlation 26

27 Encephalization quotent 27