| 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. |