1. Nervous Systems
From Simple to Complex

2. Primitive or Advanced?
The hydra’s nervous system consists of a nerve net: a loose mesh of nerve cells that can interact to perform reflexes
The chimp, like other vertebrates, has a well developed brain, spinal cord, and nerve pathways.

3. The most primitive Is the sponge: no nervous system
Each cell functions on its own.
1 step up is the nerve net, seen in cnidarians such as sea anemone with radial symmetry

4. Moving Up… Bilateral symmetry paves the way for cephalization
Mirror images on right and left sides, with the same array of nerves and muscles
Cephalization is the clustering of nerve cells in the head
Ganglia is a cluster of nerve cells, almost a primitive brain

5. Moving Up…
Brain is present in arthropods, such as crayfish and insects.
May see a ventral nerve cord
Paired nerves and sensory organs (bilateral symmetry)

6. Moving up… Vertebrates saw the brain increasing in complexity
Forebrain: highest integrating centers
Midbrain: coordinates reflex responses to sight, sounds
Hindbrain: basic tasks such as breathing, heart rate, coordinates some sensory input

7. Moving up The forebrain increases in size and complexity
The hindbrain becomes the cerebellum
See page 590 in your textbook

8. Relationship of structure to function
More complex the structure, the more advanced the function
Size of the overall brain
Size of the cerebrum in relation to the overall brain size
Convolutions increase surface area