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1. Emergence of Nervous Systems (~600 million years ago)
Nervous systems (NS) made their first biological appearance approximately 600 million years ago in the animal kingdom. Jellyfish that roamed the oceans of the pre-Cambrian era are the earliest known species with a primitive nervous system, called the nerve net. This biologically unique arrangement allowed them to respond to their surroundings, marking the birth of simple nervous systems.
2. Development of the Central Nervous System (CNS) (~500 million years ago)
Approximately 500 million years ago, more advanced animals like flatworms emerged, marking the origin of bilateral symmetry, cephalization and the central nervous system (CNS). Higher coordination between sensory and motor functions was necessary for more complex survival strategies, resulting in the evolution of the centralized system.
3. Differentiation within the CNS (500-400 million years ago)
Within this centralized system, further specializations led to more complex divisions, notably separating the brain and spinal cord. The earliest ancestors of vertebrates, the lancelets, show the beginnings of an ascendant nerve cord and a primitive brain, indicating the evolution was in full swing by this phase.
4. Development of the Triune brain (320 million years ago)
Attributed to the early reptilian ancestors, the central nervous system developed considerably, featuring three discrete layers: the hindbrain, midbrain, and forebrain – known as the Triune brain. This marked a milestone in the nervous system’s ability to regulate more complex body systems and behaviors.
5. Emergence of the Neocortex (~200 million years ago)
With the appearance of early mammals, there was an expansion in the outer layer of the brain – the neocortex. This region allowed animals enhanced learning, perception and problem-solving abilities, giving mammals more complex and adaptable behaviors than their predecessors.
6. Growth and Complexification of the Human Brain (~6 million years ago)
The human lineage saw a dramatic expansion of the neocortex. In comparison with closely-related primates, this growth allowed for the development of advanced cognitive functions, including language, abstract thought, and consciousness.
7. Advent of Modern Neuroscience (mid-20th century)
The discovery of the structure and function of the neuron by Santiago Ramón y Cajal, Charles Sherrington, and John Eccles marked the beginning of the modern era of neuroscience. Further developments, including understanding neural networks, neuroplasticity, and mapping the human brain, have built on these foundations.
8. Neuroinformatics & Computational Neuroscience (Late 20th, early 21st century)
Today, the growing fields of neuroinformatics and computational neuroscience are opening up new frontiers. These disciplines focus on creating computational models of neural systems and developing tools for managing, sharing, and analyzing the data we collect about the nervous system – a vital step in the continuing evolution of our understanding of the nervous system.