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Q3(c):
Explain the following processes: (c) Transmission of a nerve impulse across a chemical synapse
Solution :
Step 1: Structural Setup of the Chemical Synapse
A chemical synapse is a specialized junction where the terminal of a presynaptic neuron communicates with the membrane of a postsynaptic neuron. The components include:
- Presynaptic Membrane: The membrane of the synaptic knob containing voltage-gated $Ca^{2+}$ channels.
- Synaptic Cleft: A fluid-filled space (approximately $20\text{--}40\text{ nm}$ wide) separating the two neurons.
- Synaptic Vesicles: Intracellular sacs containing chemical neurotransmitters (e.g., Acetylcholine).
- Postsynaptic Membrane: The membrane of the dendrite or cell body containing specific receptor proteins.
Step 2: Depolarization and Ion Influx
When an action potential (nerve impulse) reaches the presynaptic terminal, it triggers the depolarization of the presynaptic membrane [By the Opening of Voltage-Gated Channels]. This change in membrane potential causes the voltage-gated $Ca^{2+}$ channels to open. Consequently, calcium ions ($Ca^{2+}$) flow from the extracellular fluid into the synaptic knob along their electrochemical gradient.
Step 3: Exocytosis of Neurotransmitters
The influx of $Ca^{2+}$ ions stimulates the synaptic vesicles to migrate toward and fuse with the presynaptic membrane [Mechanism: SNARE-protein mediated exocytosis]. Upon fusion, the vesicles release their neurotransmitter content into the synaptic cleft via exocytosis.
Step 4: Binding and Postsynaptic Response
The neurotransmitters diffuse across the synaptic cleft and bind to specific receptor sites present on the postsynaptic membrane. This binding opens ion channels, allowing the influx of ions that generate a new potential in the postsynaptic neuron.
Step 5: Nature of the Generated Potential
The resulting potential in the postsynaptic neuron may be:
| Type | Effect | Mechanism |
|---|---|---|
| Excitatory Postsynaptic Potential (EPSP) | Depolarization | Opening of $Na^+$ channels. |
| Inhibitory Postsynaptic Potential (IPSP) | Hyperpolarization | Opening of $K^+$ or $Cl^-$ channels. |
Final Solution: The transmission of a nerve impulse across a chemical synapse involves the conversion of an electrical signal (action potential) into a chemical signal (neurotransmitter release), which then triggers an electrical response in the postsynaptic cell through the activation of ligand-gated ion channels.
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
- 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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