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The Brain of the Planarian as the Ancestor of the Human Brain

Published online by Cambridge University Press:  18 September 2015

Harvey B. Sarnat  and
Martin G. Netsky
Harvey B. Sarnat*
Affiliation:
Departments of Paediatrics, Pathology, and Clinical Neurosciences, University of CalgaryFaculty of Medicine, Calgary, Alberta
Martin G. Netsky
Affiliation:
Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee, U.S.A.
*
Alberta Children's Hospital, 1820 Richmond Road S.W., Calgary, Alberta T2T 5C7
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Abstract:

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The planarian is the simplest living animal having a body plan of bilateral symmetry and cephalization. The brain of these free-living flatworms is a biiobed structure with a cortex of nerve cells and a core of nerve fibres including some that decussate to form commissures. Special sensory input from chemoreceptors, photoreceptor cells of primitive eyes, and tactile receptors are integrated to provide motor responses of the entire body, and local reflexes. Many morphological, electrophysiological, and pharmacological features of planarian neurons, as well as synaptic organization, are reminiscent of the vertebrate brain. Multipolar neurons and dendritic spines are rare in higher invertebrates, but are found in the planarian. Several neurotransmitter substances identified in the human brain also occur in the planarian nervous system. The planarian evolved before the divergence of the phylogenetic line leading to vertebrates. This simple worm therefore is suggested as a living example of the early evolution of the vertebrate brain. An extraordinary plasticity and regenerative capacity, and sensitivity to neurotoxins, provide unique opportunities for studying the reorganization of the nervous system after injury. Study of this simple organism may also contribute to a better understanding of the evolution of the human nervous system.

Type
Special Features
Information
Canadian Journal of Neurological Sciences , Volume 12 , Issue 4 , November 1985 , pp. 296 - 302
Copyright
Copyright © Canadian Neurological Sciences Federation 1985

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