Neurons are the cells that are an essential part of the nervous system and sends and receives nerve impulses from the external world to the brain and spinal cord and then to muscles. Neurons transmit signals between various parts of the nervous sytem.
If an individual experiencing tissue damage in his finger it will activate nociceptors that are special types of receptors for pain present in the skin. These receptors send signals or nerve impulses to the peripheral nerve to the spinal cord with the help of sensory neurons where neurotransmitters are released.
Chemical signals activate the nerve signals in the brain that are processed relayed to the frontal cortex for thinking, the somatosensory cortex for sensation, and the limbic system for the response.
What happens is that when the finger touches whatever hurt it, it sends a reaction wave to your nervous system and force the hand to move away from the object.
No, that is just the enzyme working at its maximum, the hardest it can. For example, the enzyme is still working at pH4, just not as hard as it is at pH6
