Everything about Cephalization totally explained
Cephalization is an
evolutionary trend, whereby
nervous tissue, over many generations, becomes concentrated toward one end of an organism. This process eventually produces a
head region with
sensory organs.
Cephalization is intrinsically connected with a change in
symmetry. It accompanied the move to bilateral symmetry made in
flatworms, with
ocelli and
pinnae placed in the head region. The cephalization/bilateral symmetry combination allowed animals to have sensory organs facing the direction of movement, allowing a more focused assessment of the environment into which they're moving. In addition to a concentration of sense organs, all animals from
annelids on also place the mouth in the head region. This process is also tied to the development of an anterior
brain in the
chordates from the
notochord. A notable exception to the trend of cephalization throughout evolutionary advancement is
phylum Echinodermata, which, although having a bilateral ancestor, as evidenced by their
embryology, develop into a pentaradial animal with no concentrated neural ganglia or sensory head region. However, some echinoderms have developed bilateral symmetry secondarily.
In
neuroembryology, neural induction of the
ectoderm forms a
neural tube which undergoes cephalization to form initially 3, then 5
vesicles as a developing embryo. It is the internalized ectoderm which goes on to become the
central nervous system,
peripheral nervous system and
epidermis.
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