Enzymes, which are biological catalysts that aid in chemical reactions, by lowering the energy of activation or barrier, are affected by changes in PH, as increasing or decreasing PH, would result in higher or fewer concentrations of H+, which depending on the amount can undergo hydrogen bonding and other interactions that may cause changes to specific areas of the enzyme, specifically the active site. These changes can slow the activity of the enzyme in catalyzing reactions.
When petting a dog, mechanoreceptors in the skin of your hand send signals to the sensory neuron. The sensory neuron connects to your spinal cord and through your brain.
