AIIMS 2012
- Exam
- AIIMS
- Year
- 2012
- Subject
- Zoology
- Chapter
- Neural Control and Coordination
AIIMS 2012 · Zoology · Neural Control and Coordination
Assertion : Mylein sheath insulates the nerve fibre and prevents...
Assertion : Mylein sheath insulates the nerve fibre and prevents its depolarisation.Reason : Nerve impulses are conducted more rapidly in non - myelinated nerve fibres than in myelinated ones.
Options
- AIf both assertion and reason are true and reason is the correct explanation of assertion
- BIf both assertion and reason are true but reason is not the correct explanation of assertion
- CIf assertion is true but reason is false
- DIf both assertion and reason are false
Correct answer
C. If assertion is true but reason is false
Step-by-step solution
In non-myelinated nerve fibres, the ionic changes are repeated over the membrane all along the length of the fibre. So, the action potential flows all along the membrane over the entire length of the fibre. But in myelinated fibres, the ionic changes and the consequent depolarisation can take place only at the nodes of Ranvier free from myelin sheath, because the myelin sheath between the nodes insulates the fibre and prevents its depolarisation. So, the action potential in effect jumps from one node to the next.This is called saltatory conduction of nerve impulses. Because of this, nerve impulses do not have to run all along the myelinated nerve fibre. This is why nerve impulses are conducted far more rapidly in myelinated fibres than in the non - myelinated ones.