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Control and Co-ordination — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYControl and Co-ordination5 Marks
Question
Explain transmission of nerve impulse across a synapse.$\#\#\#$ Explain how is impulse transmitted through a synapse?
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Answer

  1. The nerve impulse travels along the axon of the pre$-$synaptic neuron to the axon terminal.
  2. Pre$-$synaptic neurons or axons have several synaptic knobs at their ends or terminals.
  3. These knobs have membranous sacs, called synaptic vesicles having neurotransmitter molecules.
  4. When an impulse reaches a synaptic knob, voltage sensitive $Ca^{++}$ channels open and calcium ions $(Ca^{++})$ diffuse inward from the extracellular fluid.
  5. The increased calcium concentration inside the cells, initiates a series of events that help to fuse the synaptic vesicles with the cell membrane of pre$-$synaptic neuron, where they release their neurotransmitters by exocytosis.
  6. The neurotransmitters bind to the receptors of the post$-$synaptic cell,
  7. This action is either excitatory $($stimulating$)$ or inhibitory $($slowing down/stopping$).$
  8. Once the impulse has been transferred across the synapse, the enzyme like acetyl cholinesterase destroys the
  9. neurotransmitter and the synapse is ready to receive a new impulse.

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