Medical students have to experiment with dead human bodies.

Answer

It is never permissible. It is haraam. The human body has to be compulsorily buried. Rasulullah (Sallallahu alayhi wasallam) said that breaking the bones of a mayyit is just like breaking the bones of a living person.

Once when Rasulullah (Sallallahu alayhi wasallam) saw a Sahaabi leaning against a grave, rebuking him, our Nabi (Sallallahu alayhi wasallam) said: "Do not inconvenience the inmate of the Grave."

There are other Ahaadith also which confirm that the 'dead' person has perception and is aware of what is being done to him/her. Whether the person is interred under ground, cremated, drowned or devoured by a lion, he is alive in the state of Barzakh.