Evolution of nervous systems

Bio334 – Neurobiology 1 – Lecture 2

August 5th 2013 1BIO 334 - Lecture 2 - Evolution of

nervous systems

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

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Why study the evolution of nervous systems

• Curiousity•May provide fundamental insights into nervous system function and development

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http://freethinkerperspective.blogspot.in/2013/05/mind-body-monismdualism.html

How to study evolution of nervous systems?

•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

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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)

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Metazoan (multicellular) phylogenetic tree

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http://genomebiology.com/2006/7/7/R64/figure/F1?highres=y

Metazoan (multicellular) phylogenetic tree

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http://genomebiology.com/2006/7/7/R64/figure/F1?highres=y

Sponges – no nervous system – just muscle-like organs

•Non-motile• Just muscle-like effectors that can control the flow of water•These muscle-like cells also sense environmental cues

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http://www.thebioblog.com/

Metazoan (multicellular) phylogenetic tree

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http://genomebiology.com/2006/7/7/R64/figure/F1?highres=y

Diversity of nervous systems among other members of metazoa

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http://www.pcsd.k12.ny.us/bwoods/Regents%20Biology/Chapter%2014%20Nervous%20Regulation/48-NervousSystems/48-15-NervSystemDiversit-L.gif

Nerve nets – diffuse nervous systems without a brain

•Connect sensory neurons to muscles

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http://www2.estrellamountain.edu/faculty/farabee/biobk/biobooknerv.html

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

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http://www.prokop.co.uk/Research/Drosi-Info/nerve-cords.html

Did these all evolve from a common ancestor?

•Examine the mechanisms and see if subsequent nervous systems could be viewed as modifications

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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

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Post-synaptic density proteins expressed in sponges

•Co-regulation maybe important for forming a functional synapse

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Sakarya et al. PLOS One (2007)Conaco et al. PNAS (2012)

Ventral nerve cord in invertebrates vs. dorsal nerve cord in vertebrates

•Did they evolve independently?

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http://www.prokop.co.uk/Research/Drosi-Info/nerve-cords.html

Vertebrate dorsal nerve cord may be a result of inversion of ventral nerve

cord•Geoffroy Saint-Hilaire, Anton Dohrn

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http://cambrianmammal.wordpress.com/tag/arthropods/l

Conserved expression of genes in the anterio-posterior direction in the CNS

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

Vertebrate dorsal nerve cord may be a result of inversion of ventral nerve cord – more

evidence

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http://cambrianmammal.wordpress.com/tag/arthropods/l

Platynereis – Arendt labhttp://www.embl.de/research/units/dev_biology/arendt/

Tripartite brain might have been present in an ancestor to Bilateria

• Similar divisions in Drosophila and mouse and ascidians• Gene expression similar

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Basic Nervous System Types: One or Many? from the bookEvolution of Nervous systems: Vol 1 edited by Jon Kaas

Ventral and dorsal nerve cords could also have arisen independently from

nerve nets

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Evolution of first nervous systems

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

Evolution of first nervous systems

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nervous systems23

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

Evolution of first nervous systems

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nervous systems24

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

Brain complexity – expansion of cortex

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https://sphotos-b.xx.fbcdn.net/hphotos-prn1/p480x480/309155_515369375148492_2145532623_n.jpg

Brain size vs. brain weight correlation

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https://pantherfile.uwm.edu/rswain/www/class/SUM05/slect1.html

Encephalization quotent

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https://pantherfile.uwm.edu/rswain/www/class/SUM05/slect1.html