MEDICAL PHYSIOLOGY

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: -Nervous systems are found in almost all multicellular animals, but vary greatly in complexity. The only multicellular animals that have no nervous system at all are sponges and microscopic bloblike organisms called placozoans and mesozoans.

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: -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-5: -Although humans and animals (technically “non-human animals”) may look different, at a physiological and anatomical level they are remarkably similar. Animals, from mice to monkeys, have the same organs (heart, lungs, brain etc.) and organ systems (respiratory, cardiovascular, nervous systems etc.)