Thoracic Wall and Respiratory Muscles Quiz

What is the primary muscle involved in normal respiration?

• Internal intercostal

• Diaphragm

• Sternocleidomastoid

• Transversus thoracis

Answer explanation

The diaphragm is the primary muscle responsible for normal respiration. It contracts to create a vacuum that allows air to flow into the lungs, making it essential for breathing, unlike the other muscles listed.

Which muscles are primarily active during forced expiration?

• Scalene

• Serratus anterior

• Internal intercostals

• External intercostals

Answer explanation

During forced expiration, the internal intercostals are primarily active as they help depress the ribs and reduce the thoracic cavity volume, facilitating the expulsion of air. The other muscles listed are not primarily involved in this process.

What is the function of the serratus posterior superior muscle?

• Depresses ribs

• Elevates ribs 2-4

• Stabilizes the diaphragm

• Supports abdominal muscles

Answer explanation

The serratus posterior superior muscle primarily functions to elevate the ribs, specifically ribs 2-4, aiding in inhalation. This makes 'Elevates ribs 2-4' the correct choice.

Which structure passes through the aortic hiatus of the diaphragm?

• Inferior vena cava

• Esophagus

• Aorta

• Phrenic nerve

Answer explanation

The aorta is the major artery that carries blood from the heart and passes through the aortic hiatus of the diaphragm. The inferior vena cava and esophagus pass through different openings, while the phrenic nerve does not pass through the diaphragm.

What happens to the thoracic cavity during inspiration?

• Volume increases

• Diaphragm relaxes

• Pressure increases

• Volume decreases

Answer explanation

During inspiration, the diaphragm contracts and moves downward, increasing the thoracic cavity's volume. This decrease in pressure allows air to flow into the lungs, making 'volume increases' the correct answer.

Which muscle is NOT considered an accessory muscle of respiration?

• Serratus anterior

• Sternocleidomastoid

• Rectus abdominis

• Pectoralis major

Answer explanation

The rectus abdominis is primarily involved in flexing the spine and is not an accessory muscle of respiration. In contrast, the serratus anterior, sternocleidomastoid, and pectoralis major assist in expanding the thoracic cavity during breathing.

What is the role of the internal intercostal muscles during expiration?

• Stabilize the diaphragm

• Depress ribs

• Assist in inhalation

• Elevate ribs

Answer explanation

During expiration, the internal intercostal muscles contract to depress the ribs, aiding in the expulsion of air from the lungs. This action reduces the thoracic cavity volume, facilitating exhalation.

Which of the following muscles is involved in forced inspiration?

• Serratus posterior inferior

• Scalene

• Subcostals

• Transversus thoracis

Answer explanation

The scalene muscles assist in forced inspiration by elevating the first two ribs, increasing thoracic volume. The other muscles listed are not primarily involved in this process.

What is the primary action of the diaphragm during quiet inspiration?

• Flattens

• Elevates ribs

• Contracts abdominal muscles

• Expands thoracic cavity

Answer explanation

During quiet inspiration, the diaphragm primarily flattens, increasing the volume of the thoracic cavity and allowing air to flow into the lungs. This action is essential for effective breathing.

Which nerve innervates the diaphragm?

• Accessory nerve

• Intercostal nerve

• Phrenic nerve

• Vagus nerve

Answer explanation

The diaphragm is primarily innervated by the phrenic nerve, which originates from the cervical spinal cord (C3-C5). This nerve is crucial for diaphragm contraction and thus plays a key role in respiration.