Which muscles assist in the process of quiet respiration without being the primary muscles used?

The accessory muscles are involved in quiet respiration, primarily assisting during increased levels of ventilation or when the primary muscles require support. While the diaphragm and intercostal muscles are the main muscles used during normal (quiet) breathing, the accessory muscles, which include muscles in the neck and shoulders such as the sternocleidomastoid and scalene muscles, can facilitate breathing when necessary, especially during times of exertion or respiratory distress.

Quiet respiration typically doesn’t call for these additional muscles under normal conditions; however, they become significant when airflow needs to be increased due to factors such as exercise, or if the primary muscles are compromised. Thus, while they are not the primary drivers of quiet respiration, they play a supportive role in ensuring that sufficient air can be drawn in or pushed out as required, making them essential in variations of breathing effort.