Nervous Systems From Simple to Complex

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.

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

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

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)

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

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

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