Nervous system

Nervous system

Fun facts about neurons• Most specialized cell in

animals• Longest cell– blue whale neuron• 10-30 meters

– giraffe axon• 5 meters

– human neuron• 1-2 meters

Nervous system allows for 1 millisecond response time

Evolution of:• The simplest animals with nervous systems, the

cnidarians, have neurons arranged in nerve nets~

• A nerve net is a series of interconnected nerve cells, these are not specialized at all

Nerve net

Evolution of:• All these do is contract and relax the

gastrovascular cavity… THAT’S IT!!!~

• A nerve net is a series of interconnected nerve cells, these are not specialized at all

Nerve net

So, you mean to tell me… they don’t THINK??!!??!!

Ohhhh, but this net brings purposeful movements

Evolution of:• More complex animals actually have multiple

nerve cells bound together

• Information flows along a specific route

Nerve net

Eyespot

Brain

Nervecords

Transversenerve

Brain

Ventralnerve cord

Segmentalganglia

(c) Planarian (flatworm) (d) Leech (annelid)

Simplest CNS

Evolution of:• Elongated, bilaterally symmetrical organism are

CEPHALIZED

• Clustering of neurons at at the front end of the body…

ex. Cephalization: ANNELID

ex. Cephalization: ARTHROPOD

ex. Cephalization: VERTEBRATE

Evolution of:• In vertebrates

– The CNS is composed of the brain and spinal cord– The peripheral nervous system (PNS) is composed of

nerves and

ganglia.Nerve net

Organization of Vertebrate Nervous System

The spinal cord conveys information from and to the brain