Muscles Of Respiration Flashcards
What happens during inspiration?
Contraction
Diaphragm - flattens, extending the superior/inferior dimension of the thoracic a cavity
External intercostal muscles - elevates the ribs and sternum superiorly and anteriorly, extending the anterior/posterior dimensions of the thoracic cavity
Define Boyles Law
Volume of gas is inversely proportional to pressure
Example
Volume of thoracic cavity increases - volume of lungs increases = pressure within lungs decreases
Volume of thoracic cavity decreases - volume of lungs decreases = pressure within the lungs increases
Does the volume increase in the lungs or decrease as a result of inspiratory muscles?
Increase
Does the volume increase in the lungs or decrease as a result of expiratory muscles?
Decrease
What is the process of passive expiration?
Relaxation
Diaphragm - relaxes returning to resting position, domes superiorly. Reduces superior/inferior dimension of the thoracic cavity
External intercostal muscles - relax to depress the ribs and sternum. Rescues the anterior/posterior dimensions of the thoracic cavity
Internal intercostals - contract. Pull ribs inferiorly, and pull the sternum inferiorly and posteriorly. Decreasing the anterior/posterior lateral dimensions of the thoracic cavity
What is forced breathing?
Active mode of breathing which utilises additional muscles to rapidly expand and contract the thoracic cavity volume e.g. during exercise
What is the mode of active inspiration?
Contraction of accessory muscles
(Act to increase volume)
What does scalenes muscle do in active inspiration?
Elevates the upper ribs
What does sterncleidmastoid muscle do in active inspiration?
Elevates the sternum
What does pectoralis major and minor muscle do in active inspiration?
Pull ribs outwards
What does serratus anterior muscle do in active inspiration?
Elevates the ribs (when the scapulae are fixed)
What does latissimus Doris muscle do in active inspiration?
Elevates the lower ribs
What is active expiration?
Utilises the contraction of several thoracic and abdominal muscles
(Act to decrease volume of the thoracic cavity)
What does anterolateral abdominal wall do in active expiration?
Increase the intra-abdominal pressure, pushing the diaphragm further upwards into the thoracic cavity
What do the internal and innermost intercostal do in active expiration?
Depresses the ribs
When does the pressure inside the lung rise?
During the expiration phase of breathing
Do muscles contract or relax during expiration?
Relax
Do muscles contract or relax during inspiration?
Contract
Which nerve provides motor innervation to the diaphragm?
Phrenic
What does the scalenes do in active inspiration?
Elevate the upper ribs
What does the sternocleidomastoid do during active inspiration?
Elevates the sternum
What does the pectoralis major and minor do during active inspiration?
Pull the ribs outwards
What does the serratus anterior do during active inspiration?
Elevates the ribs (when the scapulae are fixed)
What does the latissimus dorsi do during active inspiration?
Elevates the lower ribs
What does the anterolateral abdominal wall do during active expiration?
Increase the intra-abdominal pressure, pushing the diaphragm further upwards into the thoracic cavity
What does the internal intercostal do during active expiration?
Depresses the ribs
What does the innermost intercostal do during active expiration?
Depresses the ribs
What are the muscles of active expiration
Anterolateral abdominal wall
Internal intercostal
Innermost intercostal
What are the muscles of active inspiration?
Scalenes
Sternocleidomastoid
Pectoralis major and minor
Serratus anterior
Latissimus dorsi
What type of muscle and shape is the diaphragm
Broad, thin, domed sheet of skeletal muscle
What does the diaphragm separate
Thoracic and abdominal cavities
What is the superior (thoracic) surface adjacent to
Parietal pleura
What do apertures in the diaphragm allow
Passage of structures between the abdomen and thorax (e.g. the aorta, inferior vena cava and oesophagus)
What is the function of the diaphragm
Mechanics of breathing (ventilation)
Where is the diaphragm attached
Xiphoid process
Costal margin (and to the tips of the 11th and 12th ribs)
Lumbar vertebrae
What is the central part of the diaphragm
Not muscular
Fibrosis = central tendon
What innervates the left and right sides of the diaphragm
Left and right phrenic nerves
Somatic nerves
Formed in the neck by fibres from the C3, C4 and C5 spinal nerves
Motor and sensory fibres
What are the 5 key principles of the mechanics of breathing
Muscles move the thoracic cage and change the dimensions of the thoracic cavity
Dimensions of the thoracic cavity determine the intrathoracic volume
Changes in intrathoracic volume alter intrathoracic pressure
Pressure changes inside the thorax drive inspiration and expiration
Different muscles are involved in normal, vigorous and forced ventilation
During ventilation what are the three planes that the dimensions the thoracic cavity changes in
Vertically - due to contraction and relaxation of the diaphragm
Laterally - due to the contraction of the intercostal muscles which move the ribs
Antero-posteriorly (AP) - due to the movement of the sternum secondary to the movement of the ribs
What is the role of the pleural fluid
Creates surface tension between the pleura lining the thoracic cavity and the visceral pleura on the surface of the lungs
What does surface tension caused by the pleural fluid do
Keeps the lungs and thoracic wall together
Between the two pleural membranes keeps them in contact with each other - prevents the lung from collapsing away from the thoracic wall
In normal (quiet breathing) what is active and passive
Inspiration is active (mainly driven by diaphragm)
Expiration is passive
In vigorous breathing (exercise) what muscles become important
Intercostal muscles
What muscles do active expiration use
Internal intercostal muscles
In vigorous or forced breathing (e.g. exacerbation of asthma) what muscles contribute
Accessory muscles
What are the accessory muscles
Sternocleidomastoid
Pec major
Pec minor
Serratus anterior
What is involved in inspiration
Diaphragm contracts
External intercostals
What is involved in expiration - passive
Diaphragm relaxes
External intercostals relax
What are the muscles of active inspiration
Scalenes
Sternocleidomastoid
Pectoralis major and minor
Serratus anterior
Latissimus dorsi
What are the muscles of active expiration
Anterolateral abdominal wall
Internal intercostals
Innermost intercostals
