An action potential occurs when a stimulus causes the membrane of a neuron to depolarize, reversing the electrical charge from negative to positive. Normally, sodium levels are higher outside the cell and potassium levels are higher inside. When depolarization occurs, sodium rushes into the cell, making the outside more negative. This action potential then automatically propagates along the axon from node to node in myelinated fibers or point to point in unmyelinated fibers.

1. ACTION POTENTIAL
PREPARED BY FATIMA SUNDUS

7. • Sodium inside the cell is 14meqL and out
side is 142
• Potassium inside is 140 and outside is 4

9. • We know that the inside of the nerve membrane is
negative with respect to the outside (RMP=—90 mv)
• When an effective stimulus (threshold or
suprathreshold) is applied, the electrical charge on
the membrane is reversed: at the active part of the
nerve fibre the outside becomes negative as
compared to the corresponding region in the interior.
This is called DEPOLARIZATION and forms the
Action Potential.

18. • Once an action potential is initiated at the axon
hillock, no further triggering event is necessary to
activate the remainder of the nerve fiber. The impulse
is automatically conducted throughout the neuron.
• in an Unmyelinated Nerve Fiber an Action Potential
travels from POINT TO POINT. At the nodes of Ranvier,
there are an increased number of Sodium channels
present

21. CONDUCTION OF AP IN A MYELINATED NERVE FIBER:
In a Myelinated Nerve Fiber an Action Potential
travels by SALTATORY Conduction, which is in a
jumping manner from one Node of Ranvier to
the next Node of Ranvier.