Life – Biological study – 1 – neuron

What is Life?
Properties of Life:

Be Positive !
Cellular Structure: the unit of life, one or many`Metabolism: photosynthesis, respiration, fermentation, digestion, gas exchange, secretion, excretion, circulation–processing materials and energy
Growth: cell enlargement, cell number
Movement: intracellular, movement, locomotion
Reproduction: avoid extinction at death
Behavior: short term response to stimuli
Evolution: long term adaptation

beyond words

Structure and Function

The neural network in a Hydra
This system is not centralized and thus local stimulation gives mostly local response
A slightly more centralized nerve system in jellyfish:Neural ring around opening of medusa is the “central” system for coordinating swimming motions
Peripheral nerves connect to cnidoblast, so when a nematocyst is fired, a signal goes back to the nerves in the mouth to direct it to potential prey.

in flatworms there is an evolutionary progression from:…a nerve net as in the hydra.
…to a cephalized system with two major longitudinal nerves.

The nerve system in round worms has less than 300 nerves,
but a complex map with a centralized area and a large ventral nerve