Firstly, the message would be carried by the peripheral nervous system which is responsible to take all information from outside the central nervous system (brain and spinal cord) to it. Within this peripheral nervous system, the part of it that would be used is the somatic nervous system<span> which is</span><span> associated with voluntary control of the body through </span><span>skeletal muscles, allowing him to stop running and rest because he/she felt his/her knee was sore.</span>
Since biochemical function is determined largely by specific enzymes (proteins), different sets of genes must be turned on and off in the various cell types. This is how cells differentiate.
