left-right reversal of CNS: Why?

J. A. Kiernan jkiernan at julian.uwo.ca
Wed Sep 4 13:20:39 EST 1996

In article <50hd6j$4op at decius.ultra.net> wiemanh at ma.ultranet.com (Henry M. Wieman) writes:
>From: wiemanh at ma.ultranet.com (Henry M. Wieman)
>Subject: left-right reversal of CNS: Why?
>Date: Tue, 03 Sep 96 12:41:55 GMT

>Why does the CNS have right and left reversed in relation to rest of the body?

  Cajal put forward a very plausible explanation based on the
  fact that images on the retina are left/right inverted. 
  Without the visual and motor decussations it would need peculiar 
  and complicated circuitry to make a movement of one side of the
  body that related to something in the ipsilateral visual field.
  See his "Recollections of my Life" for a concise explanation
  with diagrams.

>Specifically, do any invertebrates show the reversal?

  Yes. This is cited in support of the withdrawal-from-harmful-contacy
  theory. See Sarnat & Netsky: Evolution of the Nervous system.

                                     John A. Kiernan
                                     Department of Anatomy
                                     Univ. of Western Ontario
                                     LONDON, Canada  N6A 5C1
                                     e-mail: kiernan at uwo.ca

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