Which group is primarily responsible for expiration?

The ventral respiratory group is primarily responsible for expiration. This group of neurons, located in the medulla oblongata, plays a crucial role in the rhythmic pattern of breathing. During expiration, the ventral respiratory group sends signals to the expiratory muscles, primarily the internal intercostals and abdominal muscles, to facilitate the contraction necessary for forced expiration.

While other structures, such as the pneumotaxic center and apneustic center in the pons, help regulate the rhythm and depth of breathing, they are not directly responsible for the act of expiration itself. The medulla oblongata houses the ventral respiratory group along with other centers that coordinate overall respiratory function, but it is specifically the ventral respiratory group that handles the active process of expiration.