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The '''brain''' is the center of the [[nervous system]] in all vertebrate, and the majority of invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the [[skull]] and close to the primary sensory apparatus of [[vision]], [[hearing]], balance, [[taste]], and [[smell]].  

The '''brain''' is the center of the [[nervous system]] in all vertebrate, and the majority of invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the [[skull]] and close to the primary sensory apparatus of [[vision]], [[hearing]], balance, [[taste]], and [[smell]].  

<center>For lessons on the [[topic]] of the '''''Brain''''', follow [http://nordan.daynal.org/wiki/index.php?title=Category:Brain '''''this link'''''].</center>

<center>For lessons on the [[topic]] of the '''''Brain''''', follow [https://nordan.daynal.org/wiki/index.php?title=Category:Brain '''''this link'''''].</center>

Brains can be extremely complex. The human brain contains roughly 100 billion [[neuron]]s, linked with up to 10,000 synaptic connections each.  These neurons communicate with one another by means of long protoplasmic fibers called [[axon]]s, which carry trains of signal pulses called action potentials to distant parts of the brain or body and target them to specific recipient cells.

Brains can be extremely complex. The human brain contains roughly 100 billion [[neuron]]s, linked with up to 10,000 synaptic connections each.  These neurons communicate with one another by means of long protoplasmic fibers called [[axon]]s, which carry trains of signal pulses called action potentials to distant parts of the brain or body and target them to specific recipient cells.