Describe the action of the intercostal muscles during inspiration.

The external intercostal muscles contract and the internal intercostal muscles relax, pulling the rib cage upwards and outwards.

What happens to the diaphragm during inspiration?

The diaphragm contracts and flattens, increasing the volume of the thoracic cavity.

Explain how the increase in thoracic volume during inspiration causes air to enter the lungs.

The increase in thoracic volume decreases pressure in the lungs below atmospheric pressure, creating a pressure gradient that causes air to flow into the lungs.

Describe the action of the intercostal muscles during expiration.

The external intercostal muscles relax and the internal intercostal muscles contract, moving the rib cage downwards and inwards.

What happens to the diaphragm during expiration?

The diaphragm relaxes and returns to its domed shape, decreasing the volume of the thoracic cavity.

Explain how the decrease in thoracic volume during expiration causes air to leave the lungs.

The decrease in thoracic volume increases pressure in the lungs above atmospheric pressure, creating a pressure gradient that causes air to flow out of the lungs.

OCR A-Level Biology H420

Cell Structure

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Exchange Surfaces

Ventilation and lung volumes

3 things to know
Components 01 and 03

Overview

The intercostal muscles and diaphragm during inspiration and expiration, elastic recoil, and tidal volume, vital capacity and breathing rate from a spirometer trace.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

Explain mammalian ventilation.

Key term

Define tidal volume.

Key term

Define vital capacity.

Questions from this subtopic

Each one with the model answer underneath.

1
Describe the action of the intercostal muscles during inspiration.
Model answer
The external intercostal muscles contract and the internal intercostal muscles relax, pulling the rib cage upwards and outwards.
2
What happens to the diaphragm during inspiration?
Model answer
The diaphragm contracts and flattens, increasing the volume of the thoracic cavity.
3
Explain how the increase in thoracic volume during inspiration causes air to enter the lungs.
Model answer
The increase in thoracic volume decreases pressure in the lungs below atmospheric pressure, creating a pressure gradient that causes air to flow into the lungs.
4
Describe the action of the intercostal muscles during expiration.
Model answer
The external intercostal muscles relax and the internal intercostal muscles contract, moving the rib cage downwards and inwards.
5
What happens to the diaphragm during expiration?
Model answer
The diaphragm relaxes and returns to its domed shape, decreasing the volume of the thoracic cavity.
6
Explain how the decrease in thoracic volume during expiration causes air to leave the lungs.
Model answer
The decrease in thoracic volume increases pressure in the lungs above atmospheric pressure, creating a pressure gradient that causes air to flow out of the lungs.

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