As you read this, muscles are contracting and relaxing regularly to move air in and out of your lungs. When you walk to the kitchen for a cup of coffee, muscles in your legs contract and relax in rhythmic sequence to move you forward. For animals to function, motor behaviours like breathing and walking must be reliably controlled by the nervous system. Muscles need to contract in the same order, for roughly the same duration, each time a breath or step is taken. There is a pattern of activity that must be maintained. But the system also has to be flexible enough to respond to changes in the environment, such as obstacles in your path that you have to step around. There are many open questions about how the nervous system controls rhythmic movements, permitting reliability and flexibility. What determines the timing of the motor pattern? Under what conditions can the timing be altered, and how? To what extent can these behaviours be recovered after injury?
|How does the nervous system produce the rhythmic sequence of movements required for walking?|
Image credit: Eadward Muybridge 1887, via Boston Public Library
Rhythmic motor pattern generation
|Example of a motor network, in which motor neurons are not part of the CPG. Image credit: E. McKiernan.|