Nerve impulses propagate along nerve fibers via changes in electrical potential and ion flow. In non-myelinated fibers, the impulse propagates continuously as sodium ions flow into the fiber, reversing the potential and allowing potassium ions to repolarize the fiber back to resting potential. In myelinated fibers, ion channels are only present at the nodes of Ranvier, allowing the impulse to jump between nodes via saltatory conduction. Nerve impulses are transmitted unidirectionally and obey the all-or-none principle of firing only when a threshold is reached.

1. NERVE IMPLUSE
In Non-Myelinated and Myelinated
nerve fibre

2. DEFINITION-
Nerve impulse is the sum total of
chemical and physical events in the
propagation of a wave of physiological
activity along a nerve fibre.

3. The mode of transmission of nerve
impulse is different in myelinated and
non-myelinated nerve fibre.

4. PROPAGATIONOF NERVE IMPULS IN NON-
MYELINATEDNERVE FIBRE-
The five basic step of this process are-
 Resting state.
 Depolarization.
 Repolarization.
 Metabolic pump.
 The Action potential.

5. 1.RESTING STATE-
 When the neuron is not sending an
impulse the charge difference is
maintained inside and outside of the axon
cell. This is called the resting potential
where it is polarized which is about -
.07volt or -70mv.
 Due to high concentration of Na+ ions the
extra cellular fluid become positive.

6. Due to presence of large amount of organic
anions, The axoplasm become negative.

7. 2.DEPOLARIZATION-
 A Nerve cell is stimulated.
 The positively charged Na+ ions quickly move
inside the fibre .So the inside the fibre now more
positively charge then the out side
The reversal of electric charges is called
Depolarization.

8. 3.REPOLARIZATION-
 When the cell membrane become depolarized. K+
ions automatically leave the cell until the cell is
back to its resting state is called repolarization.

9. 4.METABOLIC PUMP-
 The active transport of Na+ out of the cell and
the reestablishment of K+ concentration inside it
restores the cell to a resting state .
 The mechanism is called sodium-potassium
pump.

10. 5.ACTION POTENTIAL-
 Due to rapid flow of Na+ ,the potential decreases
first to zero and then rises to +45 to +50mv .This
potential difference is called Action potential
 It travels as a wave along the length of nerve
fibre in a particular direction. This wave is called
nerve impulse.

11. PROPAGATIONOF NERVE IMPULSE IN MYELINATED
NERVE FIBRE-
 In myelinated nerve fibre, the voltage gated ion
channels are found only at the nodes of Ranvier.
 The action potential can therefore jump large
distances from node to node.
 This process is called soltatory propagation.

12. CONCUSION-
nerve impulses are transmitted in one
direction only .The nerve fibre always have
a refractory period after a stimulus and the
nerve impulses obey the ‘all or none’
law .