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Q10(b):
Distinguish between: (b) impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
Solution :
Step 1: Theoretical Foundation of Neural Impulse Conduction
The conduction of a nerve impulse (action potential) relies on the selective permeability of the axolemma to ions ($Na^+$ and $K^+$) and the presence of voltage-gated ion channels. The presence of a myelin sheath—a lipid-rich insulating layer formed by Schwann cells—fundamentally alters the mechanism of propagation.
Step 2: Comparative Analysis of Conduction Mechanisms
In unmyelinated fibers, the action potential propagates as a continuous wave of depolarization along the entire length of the axonal membrane. In contrast, myelinated fibers utilize a specialized, energy-efficient process known as saltatory conduction.
| Feature | Unmyelinated Nerve Fibre | Myelinated Nerve Fibre |
|---|---|---|
| Conduction Type | Continuous propagation | Saltatory conduction (jumping) |
| Depolarization Sites | Every point along the axolemma | Restricted to the Nodes of Ranvier |
| Speed of Impulse | Slower ($0.5 - 2.0 \, m/s$) | Faster (up to $120 \, m/s$) |
| Energy Consumption | Higher (due to massive $Na^+/K^+$ pump activity) | Lower (restricted ion flux) |
Step 3: Visual Representation of Saltatory vs. Continuous Conduction
Step 4: Logical Justification of Saltatory Conduction
The myelin sheath acts as an electrical insulator with high resistance and low capacitance [Per the properties of biological membranes]. Because voltage-gated $Na^+$ channels are highly concentrated at the Nodes of Ranvier (gaps in the myelin), the action potential cannot be generated under the myelin internodes.
- The impulse "jumps" from one Node of Ranvier to the next, significantly reducing the surface area of the membrane that must be depolarized.
- This reduction in ion flux decreases the metabolic load required to restore the resting membrane potential via the $Na^+/K^+$ ATPase pump.
Final Solution: Impulse conduction in unmyelinated nerve fibres is a continuous, slower process involving progressive depolarization of the entire membrane, whereas impulse conduction in myelinated nerve fibres is a saltatory, rapid process where depolarization occurs exclusively at the Nodes of Ranvier due to the insulating effect of the myelin sheath.
More Questions from Class 11 Biology Neural Control and Coordination EXERCISES
- Q1: Briefly describe the structure of the Brain
- Q2(a): Compare the following: (a) Central neural system (CNS) and Peripheral neural system (PNS)
- Q2(b): Compare the following: (b) Resting potential and action potential
- Q3(a): Explain the following processes: (a) Polarisation of the membrane of a nerve fibre
- Q3(b): Explain the following processes: (b) Depolarisation of the membrane of a nerve fibre
- Q3(c): Explain the following processes: (c) Transmission of a nerve impulse across a chemical synapse
- Q4(a): Draw labelled diagrams of the following: (a) Neuron
- Q4(b): Draw labelled diagrams of the following: (b) Brain
- Q5(a): Write short notes on the following: (a) Neural coordination
- Q5(b): Write short notes on the following: (b) Forebrain
- Q5(c): Write short notes on the following: (c) Midbrain
- Q5(d): Write short notes on the following: (d) Hindbrain
- Q5(e): Write short notes on the following: (e) Synapse
- Q6: Give a brief account of Mechanism of synaptic transmission.
- Q7: Explain the role of $Na^+$ in the generation of action potential.
- Q8(a): Differentiate between: (a) Myelinated and non-myelinated axons
- Q8(b): Differentiate between: (b) Dendrites and axons
- Q8(c): Differentiate between: (c) Thalamus and Hypothalamus
- Q8(d): Differentiate between: (d) Cerebrum and Cerebellum
- Q9(a): Answer the following: (a) Which part of the human brain is the most developed?
- Q9(b): Answer the following: (b) Which part of our central neural system acts as a master clock?
- Q10(a): Distinguish between: (a) afferent neurons and efferent neurons
- Q10(f): Distinguish between: (f) cranial nerves and spinal nerves.
CBSE Solutions for Class 11 Biology Neural Control and Coordination
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Chemical Coordination and Integration
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