NEET PG DENTAL EXAM

Detailed explanation-1: -All animals have a true nervous system except sea sponges. Cnidarians, such as jellyfish, lack a true brain but have a system of separate but connected neurons called a nerve net.

Detailed explanation-2: -Sponges are the only multicellular animals without a nervous system. They do not have any nerve cells or sensory cells. However, touch or pressure to the outside of a sponge will cause a local contraction of its body.

Detailed explanation-3: -Under the entry for “nervous system”, Encyclopædia Britannica states that [i]n animals, in addition to chemical regulation via the endocrine system (which plants have), there is another integrative system called the nervous system. Most dictionaries and textbooks maintain that only animals have nervous systems.

Detailed explanation-4: -Compared to invertebrates, vertebrate nervous systems are more complex, centralized, and specialized. While there is great diversity among different vertebrate nervous systems, they all share a basic structure: a CNS that contains a brain and spinal cord and a PNS made up of peripheral sensory and motor nerves.