SYNAPSE,NERVE IMPULSE

                                       

Q  : What is synapse? How nerve impulse is transmitted from one neuron to another?

Ans:- SYNAPSE

             Consective neurons are so arranged that the axon endings of one neuron are "connected" to the dendrites of the next, But there is no cytoplasmic connection between them and microscopic gaps are left between them. Each of these contact points is called synapse. A single cell body may form synapse with many axon endings.

             A nerve impulse is passed from one neuron to the other through the synapse. An impulse arriving at the terminations of an axon liberates one or more chemicals at the axon endings. These chemicals are known as transmitters e.g., ester acetylcholine is a common transmitter. The transmitters diffuse across the minute gaps at the synapses to the membrane of the next neuron causing changes in its permeability to certain ions.

Q  : What is the nerve impulse. How nerve impulse moves from one end of the neuron to the other end?

 

A nerve fiber showing resting potential and active potential

Ans:-NERVE IMPULSE

 

Definition

           A nerve impulse is a wave of electro-chemical changes which travels along the length of the neuron involving chemical reactions and movements of ions across the cell membrane.

Movement of nerve impulse

            When axon Is not excited, its outer surface 1S electrically ore ad outer surface is electrically more positive than the inside. This net difference in change between the inner and other surface of a nonconducting neuron is called the resting membrane potential. Normally a nerve impulse is initiated by a proper stimulus applied at one of the neuron and it causes a localized change in the resting membrane potential. The resting membrane potential is replaced by a new potential called the active membrane potential. Now inner surface of the membrane becomes more positive than the outside. This change is so brief that only a part of the neuron is in the active membrane potential. When the impulse has passed the cell membrane quickly returns to the original resting potential state.

             It has been observed that nerve potential arises because of the differences between the concentration of certain ions (Na+, K+ etc.) on the two sides of the membrane. Sodium and potassium the most important ions. Sodium ions are ten fold high in concentration outside than inside the membrane surface while potassium ions are twenty times more than inside the concentrated inside than outside. Similarly large negative organic ions are much more inside the neuron than outside. Under normal conditions nerve cell membrane is permitted only a small number of potassium ions to move outward, thus generating a resting membrane potential of 0.07 volts. When a nerve impulse passes along the nerve cell membrane, its permeability to sodium ions than potassium ions is increased. Sodium ions move inward thus making inside more positive than outside and giving an active membrane potential of 0.05 volts. Soon after passage of the nerve impulse the resting membrane potential is restored. Normal rate of nerve impulse is about 100 m/sec but its speed varies in different parts of the body it has been found that stronger the stimulus more fibers will be affected but the speed of the stimulus remains the same.