The nervous system is a very sophisticated part of an organism responsible for the coordination of the actions and sensory input via the transmission of signals across various parts of the body. Studies have shown that the nervous system’s first tissues were developed for the first time in wormlike creatures at around 550 to 600 million years ago.
The evolution of nervous systems continued from what was relatively simple then to the most complicated structure in the universe – the human brain. The sections below discuss the fascination evolution of various nervous systems.
Early Precursors of the Neurons
The evolution of action potentials started in eukaryotes with single cells. Action potentials are the fundamental activities for any nervous system. They utilized calcium ions instead of sodium but later morphed into larger animals’ transmission of electric signals. These neural precursors are believed to be the earliest forms of nervous systems in organisms.
Evolution of Rudimentary Nervous System in Sponges
Sponges are multicellular organisms, and they developed a crude ‘nervous system’ that is a stage higher than the one of single-celled eukaryotes. Sponges do not have nervous systems because they do not possess cells that can be networked together using synaptic junctions.
There can be no nervous system without neurons. Sponges transmit impulses with the help of several genes that perform the role of synapses. Some proteins are also involved in this entire process, but studies are still going on in physiology. Sponge cells ensure communication by making use of calcium ion waves.
Evolution of Nerve Nets and Nerve Cords
Comb jellies and jellyfish have evolved to use loose nerve nets instead of a centralized nervous system. This nerve net is spread out all over the body in a typical jellyfish, but the distribution is different in comb jelly.
In the latter, the nerve net is clustered around the oral cavity. These nets are made up of sensory neurons sensitive to visual, tactile, and chemical signals alongside efferent neurons that can trigger contractions in the body wall.
There are also cells referred to as intermediate neurons, and they are responsible for the detection of activity in the neurons. These intermediate neurons also transmit signals to clusters of motor neurons and can form ganglia in some instances.
The discussion of nerve cords involves highlighting the fact that most animals have bilateral symmetry. All these organisms are called bilaterians and evolved from a common wormlike ancestor about 600 million years ago. Structures called the nerve cords developed running through the right and left sides of the body. Nerve cords form the rudiments of what is later tagged as the spinal cord.
Dual nerve cords evolved in annelids like the earthworms. These nerve cords span the whole length of the body from the tail to the mouth. They are linked via transverse nerves and assist in coordinating activities on the left and right sides of the organism. The pair of ganglia at the head section works like a basic brain. The photoreceptors let the worms know the degree of illumination during daytime or in darkness.
Evolution of Nervous System in Arthropods
There is a higher level of complexity with the nervous systems of crustaceans and insects. They have evolved a nervous system with a collection of ganglia linked by a nerve cord in their bodies’ central part. There is one ganglion for one body segment, but it is not unusual to see a few ganglia join to form bigger ganglia or even a brain.
Evolution of the Human Brain
The human brain is at the apex of the evolution of all nervous systems. Scientists observed a steady and gradual increase in the volume of brain matter right from the hominids. There is also a consensus that intelligence is directly proportional to brain volume.
Women’s brain volume is slightly lower than the one of men, but the mental capacities are equally impressive. The human brain is the central organ of the human nervous system, and with the spinal cord, it makes up the central nervous system. The brain itself is significantly developed with its three main parts: the brainstem, cerebrum, and the cerebellum.
The peripheral system of afferent and efferent nerves works in concert with the central nervous system. All these structures that form the human nervous system evolved over hundreds of millions of years. Scientists believe that the evolution of the human brain will continue.