Anatomy and Cell Biology 4451F/G Lecture Notes - Lecture 2: Sea Anemone, Human Brain, Myelencephalon
17 May 2018
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Lecture 2 – Brain Evolution
C. elegans: 302 neurons, 5000 chemical synapses, 200 gap junctions
Since the worm is transparent, you can see the nervous system network. The genome has also been
completely sequenced, so you can add fluorescent tags to any of the pumps or neurotransmitters.
Codesatio of rai evolutio
• Sea anemone: the primitive neuronal system is very diffuse, and only served to help an
organism move its tentacles.
• Leech: the next stage of evolution, which has a bilateral nervous system. Instead of having a
diffuse, evenly distributed neuronal map, you see something similar to nerves (clumps of axons
and synapses)
• Snail: you can observe the formation of ganglions, where even the cell bodies start to clump
together at the head end of the organism, whereas nerves only have the axons and synapses
clumping
• Vertebrates: this is where we first start to see the brain, as an extension of the spinal cord.
In all the primitive vertebrate animals, we see that a huge are of the brain is dedicated to processing
olfaction. Once you move to the rodents, you still see a huge portion for olfaction at the rostral end of
the brain. Overall, you see a sequential condensation in the evolution of the brain – the primitive forms
had distributed and diffuse neural networks, which over time condensed to form nerves, ganglions, and
eventually an organ structure (i.e. the brain)
Within the vertebrates, brain evolution is
noted by an immense increase in size,
specifically relative to the body size – fish and
birds have small brains, while rodents and
felines have slightly larger brains. This pattern
continues, and in apes and humans, the
brain-to-body ratio is the largest. This
primary contribution to the increase in size, is
due to the cerebrum which becomes highly
folded and expands over to cover the
cerebellum. The cerebellum also increases in
size and becomes highly folded, but not as
much as the cerebrum
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Document Summary
Lecture 2 brain evolution: elegans: 302 neurons, 5000 chemical synapses, 200 gap junctions. Since the worm is transparent, you can see the nervous system network. Leech: the next stage of evolution, which has a bilateral nervous system. In all the primitive vertebrate animals, we see that a huge are of the brain is dedicated to processing olfaction. Once you move to the rodents, you still see a huge portion for olfaction at the rostral end of the brain. Overall, you see a sequential condensation in the evolution of the brain the primitive forms had distributed and diffuse neural networks, which over time condensed to form nerves, ganglions, and eventually an organ structure (i. e. the brain) Within the vertebrates, brain evolution is noted by an immense increase in size, specifically relative to the body size fish and birds have small brains, while rodents and felines have slightly larger brains.
