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Mysterious nervous system of comb jellies

Why in News?

5. Comb jellies, or ctenophores, are ancient marine animals with unique features that have sparked scientific curiosity. Recent research has discovered a surprising aspect of the comb jelly's nervous system.

What are Comb Jellies?

5. Comb jellies are marine animals that have fascinated scientists for decades due to their unique features and evolutionary history.
5. They are among the earliest branching extant lineages of the animal kingdom and have a complex nervous system that differs from other animals.
5. They are transparent, gelatinous animals that use long ciliary comb plates to propel their body through the water column.
5. They range in size from a few millimetres to over a metre in length and have diverse shapes and colours. Some of them can produce bioluminescence, a phenomenon where living organisms emit light.
5. They belong to the phylum Ctenophora, which contains about 200 species. They are found in all oceans and habitats, from polar to tropical regions, from shallow coastal waters to deep-sea trenches.
5. They feed on plankton, small fish and other invertebrates, using sticky tentacles or oral lobes to capture their prey.
5. Invertebrates are animals that do not possess a backbone or vertebral column.

How does the Comb Jelly Nervous System Work?

5. Unlike most animals, comb jellies do not have a brain. Instead, they have a nerve net that consists of interconnected neurons distributed throughout their body.
5. The nerve net controls various functions such as locomotion, feeding, sensory perception and bioluminescence.
5. The neurons in the nerve net are not connected by synaptic junctions, as would be expected in the nervous system of any other animal.
5. Instead, they are fused and share a continuous membrane, forming what scientists call a syncytium. This means that there are no gaps between nerve cells and that electrical signals can flow freely along the network.
5. However, not all neurons in the comb jelly nervous system are fused. Some of them still connect with other nerve cells through synapses.
5. This suggests that comb jellies use two different modes of communication between their nerve cells: a synaptic mode and a syncytial mode (i.e., without any synapses).
5. The discovery of syncytia in comb jellies has profound implications for understanding the evolution of nervous systems and neurons.
5. It challenges the traditional view that synapses are essential for neural communication and that they evolved only once in the common ancestor of all animals.

Synapses

Synapses are the places where neurons connect and communicate with each other. Each neuron has anywhere between a few to hundreds of thousands of synaptic connections, and these connections can be with itself, neighbouring neurons, or neurons in other regions of the brain