The spinal cord conveys information to and from the brain. However, the spinal cord is more than an information pipe. As you saw in Key Concept 44.4, the spinal cord carries out integrative functions as well. The knee-jerk reflex (see Figure 44.14) is an example of a circuit between the PNS and the spinal cord that controls a simple behavioral function. That simple circuit can be built on to control more complex behaviors such as the withdrawal reflex, which involves readjusting tension in many muscles on both sides of the body to coordinate movement and maintain balance.