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Which of the following has the largest percentage of its brain devoted to prosencephalon?
A) Fish
B) Cat
C) Frog
D) Bird

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Last updated date: 01st Mar 2024
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IVSAT 2024
Answer
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Hint: During the embryonic development initially, three vesicles of the brain are formed and these are Prosencephalon, mesencephalon and rhombencephalon which gives rise to forebrain, midbrain and hindbrain respectively. Mammals have the largest percentage of the brain devoted to prosencephalon

Complete step by step answer: Brain acts as a ‘command and control system’ which controls almost all the voluntary actions of the body and it is situated in the cranial cavity. As evolution has taken place, cranial capacity has increased. Evolution has happened in the following sequence, i.e. invertebrates, fishes, amphibians, reptiles, birds and mammals. In this sequence, only evolution of the brain has occurred. So in this hierarchy, mammals are the advanced ones and hence, they have got the most evolved brain (larger prosencephalon). In the options given above, a cat comes under mammals and hence it has the most advanced brain. The nervous system is divided into the Central nervous system (CNS), the peripheral nervous system (PNS) and the Autonomous nervous system (ANS). PNS consists of 10 pairs of cranial nerves and 10 pairs of spinal nerves. ANS is divided into sympathetic and parasympathetic nervous systems. They control the involuntary function of visceral organs. CNS consists of the brain and spinal cord. The brain is situated in the cranial cavity and covered by two meninges, Piamater and Dura mater. The brain is divided into forebrain, midbrain and hindbrain. Forebrain (Prosencephalon) is the anterior-most part and it is the largest part consisting of a pair of olfactory lobes and cerebral hemisphere and Diencephalon. The anterior part of the olfactory lobes is narrow and free but is fused at the posterior side. A small cavity is present in the olfactory lobes called olfactory ventricles. The midbrain (Mesencephalon) consists of two large oval-shaped optic lobes. The hindbrain (Rhombencephalon) includes cerebellum and medulla oblongata.
Hence, the correct answer is option B.

Note: Only reflex action is the action in which the brain is not much involved. It is regulated by the spinal cord to get a quick response and protect the body from any injury. Otherwise, brain involvement can delay the process and one may get injured.
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