Neural System: CNS vs PNS Structure — NEET Biology

Correct answer: B — S2, S5 and S6

The core concept tested is the accurate definition and components of the Central Nervous System (CNS) and Peripheral Nervous System (PNS), including their subdivisions and nerve fibre characteristics. S1. The Central Neural System (CNS) includes the brain and the spinal cord, serving as the site for information processing. This statement is correct. This is a direct definition from NCERT. S2. The Peripheral Neural System (PNS) is composed of the brain and all cranial nerves extending to the periphery. This statement is NOT correct. The PNS comprises all the *nerves* associated with the CNS (brain and spinal cord), but it does not include the brain itself (which is part of CNS). S3. All nerve fibres of the PNS are classified as either afferent or efferent. This statement is correct. NCERT states: 'The nerve fibres of the PNS are of two types: (a) afferent fibres (b) efferent fibres'. S4. Myelinated nerve fibres are primarily found within the spinal and cranial nerves, ensuring rapid impulse conduction. This statement is correct. NCERT states: 'Myelinated nerve fibres are found in spinal and cranial nerves.' Rapid conduction is an implied benefit of myelination. S5. Unipolar neurons, characterized by a cell body with one axon only, are commonly found in the cerebral cortex of the brain. This statement is NOT correct. Unipolar neurons are found usually in the embryonic stage. Multipolar neurons (one axon and two or more dendrites) are found in the cerebral cortex. S6. The autonomic neural system is a subdivision of the CNS that regulates involuntary organs. This statement is NOT correct. The autonomic neural system is a subdivision of the *Peripheral Nervous System* (PNS), not the CNS. Therefore, statements S2, S5 and S6 are NOT correct. The correct option is B because it accurately identifies the statements that are not correct. Options A, C, and D contain correct statements in their list of 'NOT correct' ones or miss some incorrect ones. Recap: The CNS is brain and spinal cord. The PNS consists of nerves, not the brain. PNS nerves are afferent or efferent. Myelinated fibres are in spinal/cranial nerves. Unipolar neurons are embryonic, multipolar are in the cerebral cortex. The autonomic system is part of the PNS.