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Q9(b):
Answer the following: (b) Which part of our central neural system acts as a master clock?
Solution :
Identification of the Master Clock
The part of the human central neural system (CNS) that functions as the master biological clock is the Suprachiasmatic Nucleus (SCN). [Per neurobiological consensus, the SCN acts as the primary pacemaker for circadian rhythms].
Anatomical Localization
The Suprachiasmatic Nucleus is a tiny region located within the hypothalamus, situated directly above the optic chiasm. [By anatomical positioning, it receives direct input from the retina via the retinohypothalamic tract].
Functional Mechanism
The SCN regulates physiological and behavioral processes—such as the sleep-wake cycle, hormonal secretions, and core body temperature—through the following mechanisms:
- Photoreception: Specialized photosensitive ganglion cells in the retina detect light intensity and transmit this information to the SCN. [By the Principle of Entrainment, this synchronizes internal rhythms with the 24-hour solar cycle].
- Endocrine Modulation: The SCN signals the pineal gland to modulate the secretion of melatonin. High levels of light suppress melatonin, promoting wakefulness, while darkness promotes its release, inducing sleep. [Per the Feedback Loop Model of Circadian Regulation].
- Transcriptional Oscillations: At the cellular level, the SCN functions through a molecular loop involving the expression of 'clock genes' (such as CLOCK and BMAL1) that oscillate in a rhythmic manner.
Comparative Overview of Circadian Control
| Feature | Description |
|---|---|
| Biological Entity | Suprachiasmatic Nucleus (SCN) |
| Anatomical Site | Anterior Hypothalamus |
| Primary Input | Retinal Ganglion Cells (Light/Dark stimuli) |
| Primary Output | Pineal Gland (Melatonin secretion) |
Final Solution: The Suprachiasmatic Nucleus (SCN), located in the hypothalamus, acts as the master clock of the central neural system.
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?
- 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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