Inspiration and Expiration

Between the bony portions of the rib cage are two layers of intercostal muscles: the external intercostal muscles and the internal intercostal muscles (fig. 16.14). Between the costal cartilages, however, there is only one muscle layer, and its fibers are oriented in a manner similar to those of the internal inter-costals. These muscles are therefore called the interchondral part of the internal intercostals. Another name for them is the parasternal intercostals.

An unforced, or quiet, inspiration results primarily from contraction of the dome-shaped diaphragm, which lowers and flattens when it contracts. This increases thoracic volume in a vertical direction. Inspiration is aided by contraction of the parasternal and external intercostals, which raise the ribs when they contract and increase thoracic volume laterally. Other thoracic muscles become involved in forced (deep) inspiration. The most important of these are the scalenes, followed by the pec-toralis minor, and in extreme cases the sternocleidomastoid muscles. Contraction of these muscles elevates the ribs in an an-teroposterior direction; at the same time, the upper rib cage is stabilized so that the intercostals become more effective. The increase in thoracic volume produced by these muscle contractions decreases intrapulmonary (intra-alveolar) pressure, thereby causing air to flow into the lungs.

Quiet expiration is a passive process. After becoming stretched by contractions of the diaphragm and thoracic muscles, the thorax and lungs recoil as a result of their elastic tension when the respiratory muscles relax. The decrease in lung volume raises the pressure within the alveoli above the atmospheric pressure and pushes the air out. During forced expiration, the internal intercostal muscles (excluding the interchondral part) contract and depress the rib cage. The abdominal muscles also aid expiration because, when they contract, they force abdominal organs up against the diaphragm and further decrease the volume of the thorax. By this means, the intrapulmonary pressure can rise 20 or 30 mmHg above the atmospheric pressure. The events that occur during inspiration

Respiratory Physiology

Muscles of inspiration

Sternocleidomastoid Scalenes

External intercostals

Diaphragm

Muscles of expiration

Muscles of inspiration

Sternocleidomastoid Scalenes

External intercostals

Human Expiration

Internal intercostals

External abdominal oblique

Internal abdominal oblique Transversus abdominis Rectus abdominis

Diaphragm

Internal intercostals

External abdominal oblique

Internal abdominal oblique Transversus abdominis Rectus abdominis

■ Figure 16.14 The muscles involved in breathing. The principal muscles of inspiration are shown on the left, and those of expiration are shown on the right.

Table Í6.2

Mechanisms Involved in Normal, Quiet Ventilation and Forced Ventilation

Inspiration

Expiration

Normal, quiet breathing Contraction of the diaphragm and external intercostal

Relaxation of the diaphragm and external intercostals, plus

muscles increases the thoracic and lung volume,

elastic recoil of lungs, decreases lung volume and

decreasing intrapulmonary pressure to about -3 mmHg.

increases intrapulmonary pressure to about +3 mmHg.

Forced ventilation

Inspiration, aided by contraction of accessory muscles

Expiration, aided by contraction of abdominal muscles and

such as the scalenes and sternocleidomastoid,

internal intercostal muscles, increases intrapulmonary

decreases intrapulmonary pressure to -20 mmHg or

pressure to +30 mmHg or higher.

lower.

and expiration are summarized in table 16.2 and shown in figure 16.15.

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Responses

  • Frederick
    Is the transversus thoracis an inspiration muscle?
    3 years ago
  • Jodi
    What muscles elevate the ribs during forced inspiration?
    3 years ago
  • conner
    Is transversus thoracis involved with inspiration or expiration?
    3 years ago
  • RICHARD
    Do scalenes have inspiration or expiration?
    3 years ago
  • tuomas
    What is the most important muscle of inspiration?
    3 years ago
  • Merimac
    What are the muscles of inspiration and expiration?
    3 years ago
  • Andreas
    What thoracic muscles elevate the ribs during forced inspiration?
    3 years ago
  • MAIRE
    Are the scalenes and the sternocleidomastoids involved in passive inspiration?
    3 years ago
  • Janne
    How could expiration be aided by thoracic?
    3 years ago
  • kerstin
    What muscles are involved in deep inspiration?
    3 years ago
  • Amparo
    What are the steps involved in quiet inspiration and expiration?
    3 years ago
  • rowan
    What muscles are involved in forced inspiration?
    3 years ago
  • Sarah
    When the diaphragm and the external intercostals muscles contract intraalveolar pressure?
    3 years ago
  • selam
    What are the muscles involved in inspiration and expiration?
    3 years ago
  • maria teresa
    Which muscles increase inspired volume?
    3 years ago
  • anna maria
    What muscle are involved in forced expiration?
    3 years ago
  • alice
    Which muscles contract to decrease thoracic volume and raise intrapulmonary pressure?
    3 years ago
  • DIANA
    What is the increase in thoracic volume in diaphragm?
    3 years ago
  • Peter
    How is rectus abdominis used in expiration?
    3 years ago
  • selam
    What muscle contract in forceful exhalation?
    3 years ago
  • saba
    Does internal lung volume increase or decrease during diaphragm contraction?
    3 years ago
  • sofia
    Does contraction of internal intercostal muscles increase thoracic volume or pressure?
    3 years ago
  • NICOLE
    Which muscles provide for normal/quiet expiration?
    3 years ago
  • jago
    What muscle is involved in normal and forced inspiration?
    3 years ago
  • Semhar Kiros
    How is the sternocleidomastoid muscle involved in inspiration?
    3 years ago
  • Donnie
    What respiratory muscles increase thoracic volume?
    3 years ago
  • Anja
    Is quiet inspiration a passive process?
    3 years ago
  • Maria Teresa
    What muscle increases thoracic volume?
    3 years ago
  • melissa boffin
    What muscles contract in quiet expiration?
    3 years ago
  • ponto
    Are scalenes involved in forced inhalation?
    3 years ago
  • dirk
    How is inspiration and expiration caused in internal intercostals?
    3 years ago
  • ensio
    What muscle is involved in increasing thoracic volume?
    3 years ago
  • Miranda
    Why is the diaphragm and thesternocleidomastoid muscles used on forceful inspiration?
    3 years ago
  • Alfrida
    How is the sternocleidomastoid muscle involved in forced inspirations?
    3 years ago
  • Albano Toscani
    How is the ribs a part of inspiration and expiration?
    3 years ago
  • immacolata
    Why is Inspiration and Expiration so important to humans?
    2 years ago
  • KIRSTIN
    What is inspiration and expiration in biology?
    2 years ago
  • mimosa
    Does the internal intercostals increase or decrease the thoracic volume?
    2 years ago
  • brigitte fuerst
    Which organs are involved in expiration and inspiration?
    2 years ago
  • Pupetta
    What happens to the intercostal muscles and diaphragm with inspiration and expiration?
    2 years ago
  • JULIANE BUSCH
    How does the contraction and relaxation of the diaphragm muscle cause inspiration and expiration?
    2 years ago
  • cara
    What Is forced Inspiration and Expiration?
    2 years ago
  • bucca
    What muscle is used for forcable inspiration?
    2 years ago
  • stefan
    Is intrapulmonary volume increase the 3 rd step of inspiration?
    2 years ago
  • zula
    What muscle of the thorax is contracted during forced expiration.?
    2 years ago
  • rihanna
    How does the diaphragm affect inspiration and expiration?
    2 years ago
  • Iiro
    How is forced inspiration produced?
    2 years ago
  • settimio
    What about forsed inspiration and expiration?
    2 years ago
  • philipp
    How does diaphragmcontribute to inspiration and expiration?
    2 years ago
  • Niko
    Which muscle elevates the ribs during forced inspiration, as during strenuous exercise?
    1 year ago
  • ibrahim
    Which muscle contracts during forced expiration?
    1 year ago
  • viljo
    How insoiration and expiration works in human?
    1 year ago
  • sharon
    What muscles contract during forced expiration?
    9 months ago
  • Mathias
    Why is expiration a passive process?
    4 months ago
  • heike
    What intercostals increase or decrease alveolar pressur and expiration?
    3 months ago

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