The Brain Origins and Diversity The Generalised Vertebrate

The Brain Origins and Diversity

The Generalised Vertebrate Brain

The Generalised Vertebrate Brain � All chordates: Front end of notochord thickened – Brain � All vertebrates: Tripartite brain structure • Forebrain • Midbrain • Hindbrain � Most primitive condition: • F – Smell; M – Vision; H – Balance, vibration detection

The Generalised Vertebrate Brain

The Generalised Vertebrate Brain

Brain Development

Brain Development

Petromyzontida - Lampreys

Petromyzontida - Lampreys � Small cerebellum • simple mode of locomotion � Rest of hind-brain highly developed • To control powerful sucking structures – med. obl. � Pineal eye • Affect expansion of melanophores – skin colour

Chondrichthyes – e. g. Catsharks

Chondrichthyes – e. g. Catsharks � Pineal organ • Non-secretory, no visual function � Hypothalamus developed well- • Regulation of unconditioned reflexes • ‘Higher’ vertebrates � Large mid-brain • Vision

Amphibia – e. g. Frogs � Large optic lobes � Hippocampal commissure • Link to reptiles, mammals � Pineal body • Vestigial in adults � Cerebellum v. small • Inactive animal, moves principally in 1 plane

Reptilia – e. g. Lizards �Small brain • 0. 5% of body weight in lizards, several inches in dinosaurs weighing 20 tons �Cerebral hemispheres • Bigger than amphibians’ • Olfactory bulbs – linked to Jacobson’s organs

Aves – e. g. Pigeons �Second in brain size to Mammalia �Med. obl. ventral flexure • Similar to Reptilia �Cerebellum large • Flight, equilibrium control

Aves – e. g. Pigeons �Cerebral hemispheres large • Massive corpora striata • For control of reflex behaviours governing lives of birds • Diencephalon hidden

Mammalia – e. g. Rabbits � Hemispheres united via corpus callosum • Commissural fibres � Cerebral hemispheres more extensively developed � Cerebellum complex large,