Lecture 8a

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Lecture 8a Powered By Docstoc
					Evolution of the Brain

 Ontogeny recapitulates phylogeny?
 Ontogeny of brain is rapid.
    – Mirrors what we see in the evolutionary
      history of the vertebrates.
    – Begins as an expanded neural tube
    – Has Olfactory, Optic, and Otic lobes.
Mesencephalon, and
correspond to the
Olfactory, Optic, and
Otic portions of the
Evolution of the Brain
 Notice, there are several flexures in the
 The basic nerve tube (primordial brain)
  has the basic afferent and efferent
 Components above the ‘tube’ generally
  are association centers.
 Association neurons can be complex
  and operate on several levels.
Brain Architecture

 Some re-organization in the brain
 Reticular system
    – Basic motor control of locomotion in lower
    – Still present in mammals, but mediated by
      higher control centers.
   Brain is bilaterally symmetric, with
    ‘wiring’ between halves.
Medulla oblongata
 Lower vertebrates: essentially comparable to
  anterior section of spinal cord.
 Contains cranial nerves III, IV, V, VI, VII, IX,
  and X.
 In Higher vertebrates, the efferent and
  afferent columns are broken down into
  discrete nuclei.
 Contains reflex circuits for sensory reception
  and responding effector organs of the head
  and gill region.

 Coordination and regulation of activities
  and the maintenance of posture.
 Equilibrium and body orientation.
 In mammals, plays an important role in
    – Primary inputs are 1) acoustico-lateralis
      and 2) proprioceptors.
    – Skink, optic, and olfactory inputs.
Midbrain and Diencephalon
   All vertebrates – center of nervous correlation
    and coordination.
   Higher vertebrates – way station between
    lower brain areas and cerebral hemispheres.
   Includes the tectum and tegmentum.
   Floor of Diencephalon contains optic chiasma
    and pituitary gland (hypophysis cerebri)
   Fish and amphibians – tectum is major brain
   Reptiles and birds – also important.
   Mammals – significantly reduced.
Cerebral Hemispheres

 Initially, they were just loci of olfactory
 In early tetrapods, they were centers of
  sensory correlation.
 In mammals, they are association
Cerebral Hemispheres

   Why begin as olfactory?
    – Olfaction was perhaps the most important
      sense in early vertebrates.
    – Olfaction is still crucial even to most
      mammals (think of dogs).
    – Olfaction is less important in primates, but
Cerebral Hemispheres

   In fish and amphibians, the cerebral
    hemispheres can be divided into
    – Paleopallium (olfactory lobe)
    – Archipallium (hippocampus)
    – Neopallium
    – Basal nuclei
Cerebral Hemispheres

   Primitively, the cerebral hemisphere is
    merely an olfactory lobe.
    – Fibers go either to the tectum, or to the
   Amphibians
    – Fibers to the basal nuclei (corpus striatum
      in mammals), the thalamus, and the
Cerebral Hemispheres
   Gray matter moves to the surface to
    become the pallium (cloak).
    – The paleopallium is still primarily olfactory.
    – The archipallium is antecedent to the
      hippocampus of mammals. It is a
      correlation center in all tetrapods, and is
      related to emotional behaviors.
   Note – modern teleosts do not use
    extensive olfaction, and not surprisingly,
    the basal nuclei and paleopallium in
    teleosts is displaced.
Cerebral Hemispheres

 Reptiles
 Birds
    – Also have reduced sense of smell
    – Minimal development of neopallium, but
      extensive basal nuclei (hence, bird brain).
   Mammals
    – Monotremes and Marsupials
    – Eutherians

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