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Q3(a):
Explain the following processes: (a) Polarisation of the membrane of a nerve fibre
Solution :
Theoretical Foundation: The Resting Membrane Potential
The polarization of a nerve fiber membrane, commonly referred to as the Resting Membrane Potential (RMP), is the electrical state of a neuron when it is not conducting an impulse. In this state, the axonal membrane is more permeable to potassium ions ($K^+$) and nearly impermeable to sodium ions ($Na^+$). [Per the Goldman-Hodgkin-Katz equation principles].
Step 1: Distribution of Ions and Selective Permeability
The axoplasm inside the axon contains high concentrations of $K^+$ and negatively charged proteins, while the extracellular fluid (ECF) contains high concentrations of $Na^+$. This chemical gradient is maintained by the following mechanisms:
- Selective Permeability: The membrane possesses leak channels that allow $K^+$ to diffuse out of the cell more readily than $Na^+$ can diffuse in.
- Protein Anions: Negatively charged proteins trapped inside the axon contribute to the net negative charge of the interior.
Step 2: The Sodium-Potassium Pump ($Na^+/K^+$-ATPase)
To maintain the concentration gradient against passive diffusion, the neuron utilizes active transport. [By the principle of primary active transport].
The $Na^+/K^+$-ATPase pump performs the following stoichiometry for every cycle:
| Action | Ions Moved | Energy Source |
|---|---|---|
| Efflux | $3\ Na^+$ ions out of the cell | Hydrolysis of $1\ ATP$ |
| Influx | $2\ K^+$ ions into the cell | Hydrolysis of $1\ ATP$ |
Step 3: Establishment of Potential Difference
As the pump removes more positive charge ($3\ Na^+$) than it brings in ($2\ K^+$), and considering the net loss of $K^+$ via leak channels, the intracellular environment becomes electronegative relative to the exterior. This establishes a resting potential typically measured at approximately $-70\ mV$.
Summary of Variables
- Intracellular environment: High $[K^+]$, High $[Proteins^-]$
- Extracellular environment: High $[Na^+]$, High $[Cl^-]$
- Membrane state: Electrically negative inside relative to outside.
Final Solution: Polarisation refers to the resting state of the axonal membrane where the exterior is positively charged relative to the interior, maintained by the unequal distribution of ions via the selective permeability of leak channels and the active operation of the $Na^+/K^+$-ATPase pump, resulting in a resting membrane potential of approximately $-70\ mV$.
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(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(b): Distinguish between: (b) impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre
- 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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