Some of the movements animals make are under conscious control, and are called voluntary movements. By contrast, other movements occur without the animal's conscious decision to do so. These types of movements are called involuntary movements or reflexes.
There are many different examples of voluntary movement. Humans walk, talk and lift things voluntarily. Additionally, humans have conscious control over their excretory functions, making them voluntary movements as well. Voluntary movements of other animals are similar. A flying bird, slithering snake and swimming fish are all exhibiting voluntary movements.
Involuntary movements include a variety of reflexes. For example, the human eyes exhibit several types of involuntary movement, such as the constriction of the pupil in bright light or the expansion of it in dim light. The movement of the heart muscle is involuntary for most animals. Doctors frequently check the involuntary movements of their patients as a component of a physical exam. For example, doctors may hit a patient’s knee with a small, plastic mallet. If the patient is healthy, the knee extends involuntarily, causing the patient’s leg to kick.
Some activities, such as eating food, feature both types of movement. Typically, chewing is a voluntary movement, while the muscular contractions of the esophagus and intestine are not under conscious control.