Final answer:
A puncture to the thoracic cavity inhibits inhalation by introducing atmospheric pressure into the space, preventing the creation of negative pressure required for lung expansion and thereby affecting normal breathing.
Step-by-step explanation:
A puncture to the thoracic cavity, such as from a knife wound, can significantly inhibit inhalation. This is because inhalation relies on creating a negative pressure within the thoracic cavity relative to the atmosphere. During inhalation, the diaphragm contracts and the thoracic cavity expands, leading to a decrease in intrapleural pressure which allows air to enter the lungs. A puncture introduces atmospheric pressure into the intrapleural space, resulting in a loss of the negative pressure required for lung expansion. This condition is referred to as pneumothorax and it prevents normal involuntary breathing by failing to change the intrapleural pressure.