ELECTRICAL TRANSMISSION IN THE NERVE ::
Every excitable tissue including a nerve fibre has an established electrical potential called the membrane potential This results from the differences in concentrations of certain ions on either side of the membrance The difference is mainly due to positively charged sodium ions that are present in greater concentrations outside the nerve fibre and to potassium ions also positively charged that are in greater concentrations inside the nerve fibre The membrane is selectively permeable allowing potassium ions to diffuse freely but restricting the passage of sodium ions For Sodium to move across the membrane energy dependent carrier is required The energy is produced by the mitochondria of the neuron and the carrier involved is called the sodium potassium ATPase pump
In the resting neuron i.e. one that is not transmitting sodium ions are pumped to the outside while potassium ions are pumped into the fibre number of sodium ions transported out is greater than the number of potassium ions that move into the fibre and the membrane is polarized it has a negative charge on the inside and a positive charge outside the actual voltage of the membrane potential is about negative 80 mV
When a nerve is stimulated the permeability of the membrane is altered allowing sodium to enter causing the membrane to become suddenly positive inside and negative outside This is called depolarization
A ten thousandth of a second after depolarization the membrane again becomes impermeable to sodium ions but potassium ions can still move through the membrane Because of the high concentration of potassium inside many potassium ions diffuse outward carrying positive charges with them This once again creates a negative charge on the inside and a positive charge outside the membrane This process is called repolarization these changes in the membrane potentials causing depolarization and repolarization are described as the Action Potential
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