GENERATION AND CONDUCTION OF NERVE IMPULSE by Yashendra.pptx

nerve impulse generation is discussed

1. GENERATION AND CONDUCTION OF NERVE IMPULSE BY – YASHENDRA SINGH M.Sc. Final (ZOOLOGY)

2. A typical neuron

3. Generation of Nerve Impulse Polarisation Depolarization Repolarisation

4. Ion Channels A) Leaky channel B) Mechanically gated channel C) Voltage gated channel D) Ligand gated channel

5. Polarisation *At resting stage the axonal membrane is comparatively more permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+). *Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. *Consequently, the axoplasm inside the axon contains high concentration of K+and negatively charged proteins and low concentration of Na+. *In contrast, the fluid outside the axon contains a low concentration of K+, a high concentration of Na+ and thus form a concentration gradient.

6. * These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na+ outwards for 2 K+ into the cell. *As a result the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged & therefore is polarised . ( Polarisation ) *The electrical potential difference across the resting plasma membrane is called as the resting potential & this is about –70 mV.( the negative sign indicates that inside the cell is negative with respect to the outside)

7. Depolarisation *On applying stimulus at a site on the polarized membrane the membrane at the site becomes freely permeable to sodium ion. *This leads to a rapid influx of sodium ion followed by the reversal of the polarity. *The outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. *This phenomenon is known as depolarisation .

8. *After the depolarisation a nerve impulse is initiated. *This is generated by a change in the Na+ ion channels. * A potential is generated & it causes sudden opening of the sodium gates *Opening of gates increases the permeability of the axon membrane to Sodium ions which enter by diffusion. *This increases the number of positive ions inside the axon.

9. *A change of +10 mV in potential difference from RMP through influx is sufficiently significant to trigger a rapid influx of Na+ ions leading to generation of action potential. *This change of + 10 mV is called as threshold stimulus. *Due to rapid & constant entry of Na+ ion the membrane potential shoots up from –70 mv to +30 mV. *This potential is called as action potential.

10. Repolarisation *After a fraction of second the sodium ion gates get closed. *Depolarization of the axon membrane causes potassium ion gets to open. *Potassium therefore diffuses out of the cell. *Diffusion of potassium ions out of the cell makes the inside of cell less positive or more negative. *Now the process of repolarization or returned to the original resting potential (–70mV)begins.

11. *The neurone is now prepared to receive another stimulus and conduct it in the same manner. *The time taken for restoration of resting potential is called refractory period because during this period the membrane is incapable of receiving another impulse. *The whole process of depolarization and repolarization is very fast * It takes only about 1 two 5 millisecond.

12. Conduction of Nerve Impulse:-

13. Saltatory Conduction of Nerve Impulse *This type of conduction occurs in myelinated fibre . * Mylein is fatty material with high electrical resistance and acts as an electrical insulator. *The gaps between two adjacent myelin sheaths are called nodes of ranvier . *The action potential jumps from node to node and passes along the myelinated axon. *This type of conduction is called saltatory conduction.

14. Synapse *It is the junctional region between two neurons where nerve impulse is transferred from one neuron to another. * Telodendria of one neurone form synapse with dendron of next neuron. *It transmits impulse in the form of electrochemical wave. Synapse = Pre synaptic knob + synaptic cleft + post synaptic membrane

15. Neurotransmission

16. Thank You