How do generation,conduction and transmition of an impulse takes place
Generation of Nerve Impulse
Whenever we touch any object the immediate response of the nervous system is to send signals through nerves to the spinal cord. The neurons then transmit the signal from spinal cord to brain. Brain cells transmit the signal along their axons to the neighbouring neurons via synapses. When the information in form of electrical signals reaches the axon’s end the voltage trigger releases the neurotransmitters which are brain’s chemical messengers. The neurotransmitters are travelled across the synapse till they reach potassium ion channels. Potassium ions enter the cells making inside of the cell more positive than outside. When the signal reaches axon terminal calcium ions move inside the cell and vesicles filled with neurotransmitters are expelled out of the cell.
Conduction of Nerve Impulse
- In the resting state, the membrane of the nerve cell is more permeable to the K + ions and impermeable to Na + ions. Also only 2 K + ions move inside for 3 Na + ions to come out of cytoplasm of axon called axoplasm.
- The membrane of nerve cell is also impermeable to negatively charged proteins present inside the axoplasm. Thus, it does not let them go out. As a result, the axoplasm has more concentration of negatively charged proteins than positively charged Na + and K + . This makes the over all charge inside the axoplasm negative and outside the membrane becomes positive due to more number of Na + . Hence, the outer surface of the membrane possesses positive charge and the inner surface possesses negative charge. This potential difference is called Resting Potential.
- When stimulus is applied at a particular site (say site A), of the nerve cell that site of the membrane becomes freely permeable to the influx of Na +. This causes increase in the overall positive charge inside the axoplasm and thus polarity is reversed.
- The membrane is now depolarised, and the potential difference across the site is called Action Potential (nerve impulse).
- At a site (B) that is adjacent to the depolarised site (A), the outer surface of the membrane has positive charge and the inner surface has negative charge.
- Depolarised site (A): Positive (in) and Negative (out)
- Adjacent site (B): Positive (out) and Negative (in)
- Due to the potential difference between two points (point A and point B) inside as well as outside, current starts flowing on both sides.
- Current flow on the inner surface is from site A to B
- Current flow on the outer surface is from site B to A
- This completes the circuit of current flow. Due to this circuit, the impulse travels to point B and polarity of site B is reversed and action potential is generated at site B in the same way as at point A. Hence, the impulse travels to site B, and we say that this impulse is conducted. This sequence is repeated along the length of the axon.
- Stimulus-induced permeability to Na+ is short-lived, and is quickly followed by permeability to K+. When this happens, the resting potential is restored, and once more, the site can be stimulated.
Transmission of Nerve Impulse
Nerve impulse is an electrical signal that travels through the nerve cells. When there is any change in our body state which is detected by the nerve receptors, they send the information or message regarding this change through nerve impulses to the brain. Synapse exists at the end of each neuron to transmit nerve impulses from one neuron to another. It permits a neuron to pass electric impulse to another cell. At the synapse the plasma membrane of signal passing neuron comes in contact to the membrane of the neuron where the signal has to be sent. The signal is then passed through the membranes to the next neuron.Regards