I. Nervous System Organization

A. Radial Systems B. Bilateria- lots of variation C. Nervous System and Lifestyle

Radial Systems

• Cnidarians 

• Simplest animals with nervous systems

• Nerve net: interconnected neurons 

• No central control organ

• Impulses in both directions, spread through net 

• (decentralized)

Echinoderms

• Technically bilateral but superficially radial as adults!

• Nerve ring: central control structure

• Signals radial nerves

• -> signals muscles  

• decentralized

Bilateria- lots of variation

• Platyhelminthes - planarians

• Simplest clearly defined CNS

• Brain, eyespots at anterior

• Ladder type nervous system

• 2 longitudinal nerve cords

• Transverse nerves “rungs”

Annelids and Arthropods

• More complex brain (segmented)

• Ganglia: segmentally arranged clusters of neurons 

Vertebrates

• CPS- brain and spinal cord

• PNS- Nerves and ganglia

Nervous System and Lifestyle

• Cition- slow moving -> simple

• Squid- fast moving -> complex

• Same phylum, different nervous systems