Cognitive Science: An Introduction/Control of the Body

Movement of the body is known as "motor control." Muscles are controlled directly by neurons. Axons from neurons connect to muscle fibers, which contract when a signal is received. The amount of contraction depends on the amount of neurotransmitters present.

Moving upstream from this, we have the motor cortex, which is the part of the brain that more or less initiates muscle movement. Controlling the motor cortex is the premotor cortex, which is what decides which motor actions to take. It does this by taking input from multiple sources. The cortical regions represent the judgments, memory, and beliefs that are relevant to motor action. The other inputs are sub-cortical: the reward system, the emotional systems, and the motor basal ganglia all contribute, too. The motor action that the pre-motor cortex decides on is a function of all of these inputs. The basal ganglia represents habits and other automatic behaviors. This is why you sometimes do things you don't want to do. The better judgment comes from the cortical areas, like "I shouldn't eat that cake." But your reward system wants you to eat the cake, or the basal ganglia might have encoded in it a habit to eat cake every afternoon. Sometimes these subcortical processes take control. The ability of your cortical areas to win over the subcortical areas is a decent approximation of what we colloquially call "willpower" or "self-control."