Working of Neurons
Neurons are excitable cells because of their polarised state. Different types of ions are present on the neural membrane. These membranes have channels which are selectively permeable to different ions.
STEP 1 - Resting phase.
The membrane is comparatively more permeable to potassium ions (K+)
Nearly impermeable to Sodium ions (Na+) present outside the neuron
Impermeable to negative charge proteins present inside the neuron
Hence - Neuron has high concentration of K and negative proteins but less concentration of Na compared to the outside.
This causes a concentration gradient -- Outside positive , Inside negative.
This gradient is maintained actively by the sodium-potassium pump which transports 3 Na+ outside and 2 K + inside the neuron.
STEP 2 - Stimulus
When stimulus is applied there is a sudden influx of Na inside the neuron.
This causes reversal of polarity at that point, outside negative, inside positive
This is called Deplorisation and marks te start of nerve impulse.
At sites imediately ahead, the inside of neuron is negative and outside is still positive.
This causes flow of current from postive to negative
This results in the flow of impulse.
