RML MAINS 2025
Applied Anatomy
Easy
What is the main function of the Myelin Sheath?
Appeared in: RML MAINS 2025
Explanation
- The myelin sheath is a fatty, insulating layer that wraps around the axons of many neurons.
- This insulation allows for a process called saltatory conduction, where the nerve impulse 'jumps' between the unmyelinated gaps known as the Nodes of Ranvier.
- This jumping mechanism dramatically increases the speed of nerve impulse transmission, making it up to 50 times faster than in unmyelinated fibers.
- The sheath also serves to insulate the nerve fiber, preventing signal leakage to adjacent neurons and conserving metabolic energy.
Why Other Options Were Wrong
- Option A: While the myelin sheath offers physical protection, its primary function is not immunological defense against infection. That role is primarily carried out by microglial cells in the central nervous system.
- Option B: Neurotransmitters are chemical messengers synthesized in the neuron's cell body (soma) and stored in vesicles at the axon terminal, not produced by the myelin sheath.
- Option D: The myelin sheath is a structure within the nervous system and has no physiological role in the growth or repair of bone tissue, which is the function of osteoblasts and osteoclasts.
Related Visual
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Function of the Myelin Sheath in Nerve Impulse Conduction as background academic context rather than a clinical decision trigger.
- Damage to the myelin sheath (demyelination) is the underlying cause of several debilitating neurological disorders, most notably Multiple Sclerosis (MS) and Guillain-Barré syndrome.
- In these conditions, the loss of myelin slows or blocks nerve conduction, leading to symptoms such as muscle weakness, paralysis, numbness, pain, and vision problems.
- What if? If a patient is diagnosed with a demyelinating disease like MS, nursing priorities shift to managing symptoms, preventing complications from immobility (like pressure ulcers and contractures), administering immunomodulatory therapies, and providing psychosocial support for a chronic illness.
How to Approach the Question
- This is a factual recall question from anatomy and physiology.
- First, identify the key term in the question stem: 'Myelin Sheath'.
- Access your knowledge about the structure and function of a neuron. Recall that the myelin sheath is a fatty covering.
- Think about the function of insulation in electrical wires, which is a good analogy. Insulation speeds up signal transmission and prevents short-circuiting.
- Evaluate the options in this context. 'Increases the speed of nerve impulse transmission' directly aligns with the insulating function of myelin.
- Eliminate the other options as they relate to different physiological systems or parts of the neuron: infection (immune system), neurotransmitters (neuron cell body/terminal), and bone tissue (skeletal system).
Concept Tested & Keywords
- Concept Tested: Function of the Myelin Sheath in Nerve Impulse Conduction
- Stem keywords: Myelin Sheath, main function
- Lead-in keywords: What is
Question ID
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Reference Book
E6 Physiology Essentials Sembulingam 10e Part 3 p. 36-38
E6 Medicine Harrison 22e Part 2 p. 1301-1303
E6 Physiology Review Sembulingam 5e p. 154-156
Practise the full RML MAINS 2025
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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