Question

Assertion: During inspiration, the volume of thorax increases. Reason: This happens due to the relaxation of diaphragm and inspiratory muscles.

Short answer

Both the assertion and reason are correct and the reason is the correct explanation of the assertion.

Step-by-step solution

Define the Terms

Firstly, it's important to understand what certain terms mean. \(\textbf{Inspiration}\) in the context of biology refers to the process of breathing in. The \(\textbf{thorax}\) is the part of the body between the head and the abdomen, which contains the lungs and the heart. The \(\textbf{diaphragm}\) is a sheet of internal muscle that extends across the bottom of the thoracic cavity. \(\textbf{Inspiratory muscles}\ include muscles like the diaphragm and external intercostals that assist with inspiration.

Describe the Process of Inspiration

During inspiration, the diaphragm and external intercostals contract. When this contraction happens, the volume of the thoracic cavity increases. This reduction in pressure allows air to flow into the lungs since air flows from areas of high pressure to areas of low pressure.

Connect the Parts

So we can conclude that during the inspiration process, the volume of the thorax increases, which indeed happens due to the contraction of the diaphragm and inspiratory muscles. Therefore, both the assertion and reason are correct and the reason is the correct explanation of the assertion.

Key concepts

Thoracic Cavity

The thoracic cavity is a crucial part of the human anatomy located between the neck and the abdomen. It houses significant organs such as the lungs and heart. Understanding the structure of the thoracic cavity provides insight into the breathing process. This cavity is protected by the rib cage, consisting of ribs and a series of internal and external muscles known as intercostals. These muscles play an important role during breathing, as they assist in changing the volume of the thoracic cavity.

During inspiration, or inhaling, the intercostal muscles contract alongside the diaphragm to increase the volume of the thoracic cavity. This increase in volume leads to a drop in pressure within the cavity compared to the outside atmosphere, allowing air to rush into the lungs. The coordinated action of the chest wall and the diaphragm ensures that the lungs can efficiently fill with air.

Diaphragm Function

The diaphragm is a dome-shaped muscle that sits at the base of the thoracic cavity. This muscle is essentially the main engine driving the inspiration process.

When we inhale, the diaphragm contracts and flattens, moving downward. This contraction increases the volume of the thoracic cavity, creating a vacuum that allows air to enter the lungs.

The diaphragm also works in concert with other muscles to improve lung expansion. It is assisted by the external intercostals, which lift the ribs upwards and outwards, further increasing lung volume. This dual-action is crucial as it facilitates larger breaths and efficient gas exchange in the lungs. Therefore, understanding the diaphragm's function is key to comprehension of the breathing mechanism and ensures our body gets the oxygen needed to function properly.

Muscle Contraction in Breathing

Breathing relies heavily on the contraction and relaxation of muscles within the thoracic region. During the process of inspiration, a combination of muscle movements allows for efficient air intake. The diaphragm and external intercostal muscles are the primary muscles involved.

As the diaphragm contracts, it flattens downward, increasing the thoracic cavity's vertical volume. Meanwhile, the external intercostal muscles, which lie between the ribs, contract to pull the ribcage upward and outward, expanding the ribcage horizontally.

• This dual muscular activity effectively increases the total volume of the thoracic cavity.
• Consequently, the pressure inside the cavity drops below atmospheric pressure, leading to air flowing into the lungs until pressure equilibrium is restored.

This beautiful orchestration of muscle contraction is vital for maintaining adequate respiratory function and ensuring that the body receives sufficient oxygen to meet its metabolic needs.