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Q5(e):
Write short notes on the following: (e) Synapse
Solution :
1. Theoretical Definition and Structural Basis
A synapse is a highly specialized functional junction through which a neuron transmits a signal—either electrical or chemical—to another neuron or to a non-neuronal effector cell, such as a muscle or gland cell. [Per the Neuron Doctrine, neurons are discrete units, and the synapse serves as the critical site of intercellular communication].
2. Schematic Representation of a Chemical Synapse
3. Components of a Chemical Synapse
A chemical synapse consists of three primary structural components:
- Presynaptic Membrane: The membrane of the terminal button of the axon carrying the impulse. It contains voltage-gated $Ca^{2+}$ channels and synaptic vesicles filled with neurotransmitters.
- Synaptic Cleft: A fluid-filled space ($20–40 \text{ nm}$ wide) separating the presynaptic and postsynaptic neurons. This physical gap necessitates chemical signaling to bridge the discontinuity.
- Postsynaptic Membrane: The membrane of the dendrite or cell body of the receiving neuron. It is embedded with specific ligand-gated ion channels and neurotransmitter receptors.
4. Mechanism of Signal Transmission
The transmission process follows a rigorous sequence of physiological events:
- Depolarization: The action potential reaches the presynaptic terminal, triggering the opening of voltage-gated $Ca^{2+}$ channels.
- Exocytosis: Influx of $Ca^{2+}$ ions into the terminal induces synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft via exocytosis.
- Diffusion & Binding: Neurotransmitter molecules diffuse across the synaptic cleft and bind to specific receptors located on the postsynaptic membrane.
- Ion Channel Activation: Binding triggers the opening of ion channels, allowing ions (e.g., $Na^+$, $K^+$, $Cl^-$) to flow across the membrane. This creates either an Excitatory Postsynaptic Potential (EPSP) or an Inhibitory Postsynaptic Potential (IPSP).
5. Comparative Analysis of Synaptic Types
| Feature | Electrical Synapse | Chemical Synapse |
|---|---|---|
| Mechanism | Direct ionic current (Gap junctions) | Neurotransmitter mediation |
| Speed | Extremely fast (near-instantaneous) | Slight synaptic delay |
| Directionality | Bi-directional | Uni-directional |
Final Solution: A synapse is the structural and functional gap between neurons where impulses are transmitted via chemical messengers (neurotransmitters) or direct electrical current, ensuring the precise regulation and integration of neurological signals throughout the nervous 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
- 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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