When a person is subjected to electric shock, how does the  electricity affect the human body?

How does the human body react to a severe electric shock

The human body contains body fluid mainly consisting of water, which gets electrolysed on passage of electric current in the event of an electric shock.

This can lead to other complex electric effects in the body as follows:

The effects on the human body can include burns, ventricular fibrillation, neurological effects etc. 

Heating due to resistance can cause extensive and deep burns. Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage divided by resistance) available from the source. Damage due to current is through tissue heating.

Current can cause interference with nervous control, especially over the heart and lungs. Repeated or severe electric shock which does not lead to death has been shown to cause neuropathy. Recent research has found that functional differences in neural activation during spatial working memory and implicit learning oculomotor tasks have been identified in electrical shock victims.

The famous Italian scientist Luigi Galvani in the 1780s, discovered that when an electric current was passed through a living tissue the nerves respond in a typical way that makes the muscular tissues contract and a twitching was observed

In fact, the symptom of such spasms has been recorded in more controlled experiments where a definite quantity of electric charge was deposited on the spinal cord of frogs and the frogs exhibited the same type of spasms in their muscles; more charge resulted in greater twitching of muscles.

In the human body also, the same effect takes place. In severe cases of such electric shock, the spasms can be so strong that the muscles of some critical organs like the heart can be thrown out of their characteristic rhythmic motion.

And the electric current can also disrupt the functioning of the brain. The combined effect can be fatal.