Question

learning goal 2:

1. list which muscles we use to breathe.
2. describe how these muscles work so that air is drawn into our bodies.

Explanation:

1. List which muscles we use to breathe.

The primary muscles of respiration are the diaphragm and the intercostal muscles (external and internal intercostal muscles). The diaphragm is a dome - shaped muscle that separates the thoracic cavity from the abdominal cavity. The external intercostal muscles are located between the ribs and help in inhalation, while the internal intercostal muscles can be involved in forced exhalation. Additionally, accessory muscles like the sternocleidomastoid, scalene muscles, and abdominal muscles (in forced exhalation) can be used in respiration, especially during labored breathing.

Inhalation (air drawn in):

1. Diaphragm: When we inhale, the diaphragm contracts. This contraction causes the diaphragm to flatten and move downwards towards the abdominal cavity. This increases the vertical dimension of the thoracic cavity.
2. External Intercostal Muscles: The external intercostal muscles contract, which pulls the ribs upward and outward. This increases the anterior - posterior and lateral dimensions of the thoracic cavity.
3. Effect on Volume and Pressure: As the volume of the thoracic cavity increases (due to the actions of the diaphragm and external intercostal muscles), according to Boyle's law ($P_1V_1 = P_2V_2$, where $P$ is pressure and $V$ is volume), the pressure inside the thoracic cavity (and thus in the lungs, as the lungs are connected to the thoracic cavity) decreases. The pressure inside the lungs becomes lower than the atmospheric pressure.
4. Air Movement: Since air moves from an area of higher pressure (atmosphere) to an area of lower pressure (lungs), air is drawn into the lungs.

Role of Accessory Muscles (during labored inhalation):

When we need to take in more air (e.g., during exercise or when having difficulty breathing), accessory muscles like the sternocleidomastoid and scalene muscles contract. The sternocleidomastoid pulls the sternum up, and the scalene muscles lift the upper ribs. This further increases the volume of the thoracic cavity, leading to a greater pressure drop and more air being drawn into the lungs.

Answer:

• Diaphragm: The main muscle for quiet breathing.
• External Intercostal Muscles: Assist in inhalation by elevating the ribs.
• Internal Intercostal Muscles: Involved in forced exhalation.
• Accessory Muscles (e.g., Sternocleidomastoid, Scalene Muscles): Used in labored inhalation.
• Abdominal Muscles (e.g., Rectus Abdominis): Used in forced exhalation.

2. Describe how these muscles work so that air is drawn into our bodies.