The nervous systems of invertebrates differ from the nervous systems of
vertebrates in the following way:
Invertebrate neurons lack a myelin sheath around their axons.
Invertebrate neurons do not generate action potentials
Invertebrate neurons lack electrical synapses
All of the above

Invertebrate neurons fundamentally differ from vertebrate neurons, primarily because invertebrate neurons lack a myelin sheath around their axons, which is a hallmark vertebrate adaptation for faster nerve conduction. This multiple-choice question tests core concepts in comparative neurobiology for exams like CSIR NET Life Sciences. The correct answer is the first option, as it accurately captures the most definitive structural distinction.​

Option Analysis

• Invertebrate neurons lack a myelin sheath around their axons: Correct. Myelin, formed by glial cells like Schwann cells or oligodendrocytes, insulates axons in vertebrates to enable saltatory conduction, boosting impulse speed. Invertebrates lack true compact myelin; their axons may have glial wrappings but no myelin-specific proteins like MBP or PLP.​

• Invertebrate neurons do not generate action potentials: Incorrect. Invertebrates, from annelids to arthropods, generate action potentials via voltage-gated ion channels, though conduction is slower without myelin.​

• Invertebrate neurons lack electrical synapses: Incorrect. Electrical (gap junction) synapses are common in invertebrates like Drosophila for rapid signaling, unlike vertebrates that favor chemical synapses.​

• All of the above: Incorrect, as only the first option holds true.

Evolutionary Context

Myelin evolved in vertebrates to support complex, rapid neural processing in larger bodies. Invertebrates rely on unmyelinated axons or pseudo-myelin in some cases (e.g., annelids), prioritizing decentralized ganglia over centralized brains. For CSIR NET aspirants, focus on myelin’s absence as the key differentiator in neuron structure questions.