Unit IV – The Thoracic Cage/ Respiration & Breathing

 
 

 

Objectives: At the completion of Unit IV the student will be able to:

 1.      Name the primary anatomical structures of the thorax and thoracic cage.

2.      Identify the structures applicable to respiratory function.

3.      Describe the process of respiration, including the role of the diaphragm.

4.      Describe the relationship of the diaphragm and the iliopsoas and its its importance to the dancer.

 

 

Introduction:

We have explored the vertebral column and its muscle attachments and movements. Now we will consider the thorax and the thoracic cage areas and its relationship to the trunk and extremities. Other important aspects of the thorax are the anatomical structures for respiration (breathing). Breathing is a key element to understand, and must be utilized experientially for the dancer in all movements.

 

 

Overview of the Thorax

The thorax is the superior part of the trunk between the neck and the abdomen. It is formed by the 12 pairs of ribs, the sternum (breast bone), costal cartilages, and the 12 thoracic vertebrae. These bony and cartilagenous structures form the thoracic cage (rib cage) which surrounds the thoracic cavity and supports the shoulder girdle. The thoracic cavity contains the heart, the lungs, and some abdominal organs. The thoracic cage provides attachments for muscles of the neck, thorax, upper limbs, abdomen, and back. 

The thorax moves up and down to allow breathing, so it is one of the most dynamic regions of the body. The picture below shows the basic structures that form the thorax.

 
 

 
 

Specific Bony Anatomy  

 There are three primary components of the thoracic cage:

  1. The sternum

  2. The thoracic vertebrae and their intervertebral discs

  3. The ribs and costal cartilages

Let’s explore each of these in some detail now.

The Sternum

The sternum, or breast bone, is the flat, elongated bone that forms the midline of the anterior thoracic cage. It has 3 parts: the manubrium , the body, and the xiphoid process.

 
 

The Xiphoid Process – This is the most inferior component of the sternum. It is a small cartilagenous structure that varies in shape from pointed to blunt. It ossifies by age 40.

The Manubrium – is like the handle of the sword with the body of the sternum its blade. It is the superior most component of the sternum and has several important indentations.

      Indentations –

  • Jugular notch is the most superior aspect of  the manubrium that you can feel at the base of your throat

  • Clavicular notches – these are the left and right notches that articulate with the sternal end of the clavical (collar bone). These two bones form an articulation called the sternoclavicular joint.  There is a right and a left sternoclavicular joint.

  • Costal notches – these are small notches at the lower end of the manubrium that are attachments for the first ribs on the right and on the left.

The Body  - This is the longer, narrower portion of the sternum that extends down the front of the chest wall. The body is sometimes called the breast bone and is the hard structure you can feel in the middle of your chest. It houses the costal notches for articulations with ribs 2-7.

 
 

The Thoracic Vertebrae

The 12 thoracic vertebrae have the same bony components as the lumbar vertebrae discussed in Unit III. They also have several additional special features:

  1. Costal facets (flat spots for attachments) on the body of the vertebrae for articulation with the ribs.

  2. Costal facets on the transverse processes for articulation with the tubercles of the ribs

  3.  Long spinous processes

 The attachment location of the rib to the vertebrae is called the costovertebral articulation.  (The word costal refers to rib---therefore this is a "rib-vertebrae connection"). This articulation is made up of the head of one rib and the costal facets on the vertebrae of that rib and the vertebrae above.

 
  For example: thoracic rib #7 articulates with the costal facets of the lower part of the vertebrae T6 and the upper part of the vertebrae of T7. (See illustration to left)  
Looking through the rib cage to view the anterior thoracic spine with the corresponding rib attachments.

©

 

 The costotransverse joint articulation is the attachment of the rib  (example – T7 rib) with the facet on the transverse process of vertebrae T7.

 **This articulation structure will be important when we explore the movement of the ribs in the next section of this unit.

 
 

The Ribs

 The ribs are elongated, flattened, and twisted bones. They are very lightweight and resilient. There are 3 types of ribs:

  1.  True Ribs – ribs 1-7 ; these are attached directly to the sternum through their own costal cartilages.

  2.   False Ribs – ribs 8-10; their costal cartilages are joined to the rib just above them so their attachment to the sternum is indirect

  3.  Floating Ribs – ribs 11-12; these ribs attach to vertebrae, but not to the sternum so they float on one end

 
 

Illustration of true, false, and floating ribs in the rib cage  
 

Structure of Typical Ribs – Ribs 3-10 

A typical rib is twisted along its axis and has a sharp bend in the shaft called the costal angle. There are two main parts to the typical rib: the posterior portion and the body

 
  Posterior portion – This portion of the rib has a head and 2 facets for articulation with the bodies of the thoracic vertebrae. The neck of the rib is located just behind these facets and is a constricted section of the bone. The tubercle is a bony prominence for articulation with the transverse process of the thoracic vertebrae and for attachment of ligaments.  
 

 The Body – This is the long, curved shaft of the bone; its anterior end attaches to the costal cartilage that then attaches to the sternum.

 

 

Structure of Atypical Ribs – Ribs 1-2, and 11-12

Several ribs have a slightly different structure than the typical ribs, due to their location in the thoracic cage. Ribs 1 and 2 are shorter, flatter, and tilted more forward than the others. Many important nerve trunks and blood vessels pass across rib 1 on the way to the arm.

Ribs 11  and 12 are short, floating ribs that do not attach anteriorly to the sternum, so they have no neck or tubercles.

Respiration – Rib Movement and Thoracic Cage Function for Breathing

The attachment of the ribs to the sternum and spine between T1 and T7 (true ribs) limits mobility of the thoracic spine in this area. There is a little mobility where the rib attaches to the cartilage before it attaches to the sternum. Ribs 8-10 (false ribs) have longer costal cartilages  which attach to other cartilage, so this area of the rib cage has more mobility. Ribs 11-12  (floating ribs) have no anterior attachment at all so the greatest mobility of the thoracic spine is in this area.  Due to these attachments, the upper ribs move differently from the lower ribs.

   As you breathe air in (inspiration) *see light pink * the thorax widens as the ribs elevate (move upward). The middle portion of the lower ribs moves more laterally when they elevate.  
 

Thoracic Wall Movement –

This motion of the thoracic wall resembles the movement of a bucket handle.  The bucket handle is attached to the bucket on each end and as it lifts it moves laterally and up, but in unison left to right.  This increases the lateral excursion or movement of the rib cage. When the upper ribs are elevated the anterior-posterior diameter of the thorax increases. This movement resembles that of a pump handle being pumped up and down.  

 
   
 

The combination of these movements allows the rib cage to increase in the anterior-posterior and the transverse diameters. During expiration (breathing out) the ribs move down and medially.

 
 

The Process of Respiration

 The diaphragm is the primary muscle for respiration. It is located within the lower aspect of the rib cage. Specifically, it has 3 origin areas - the xiphoid process of the sternum,  the inner surfaces of the lower 6 ribs, and a ligamentous structure called the arcuate ligaments that run from the bodies of the upper lumbar vertebrae up to T12.  The diaphragm then inserts into a thin, strong tendon called the central tendon or crura which spans the central portion of the muscle and is more anterior. This muscle forms  a dome shape in the rib cage and spans the space across the rib cage in a figure eight type of shape. This muscle separates the thoracic and abdominal cavities.

 
   
  Inspiration (Breathing in)  - with inspiration the diaphragm descends in the thoracic wall and presses against the abdominal organs below. This results in the thoracic cavity gaining in vertical diameter. There is also movement more laterally as the bucket handle movement of the ribs allows the expansion of the lungs outward.  This is an active movement that must overcome resistance for adequate intake of air.  
  Expiration – (Breathing out) – with expiration the diaphragm ascends back up to its resting position and the vertical space in the thoracic cavity decreases while the lateral movement pulls down and in.  Expiration occurs mostly from elastic recoil of the lungs when the inspiratory muscles relax, so it is a much more passive process. There can be increased expiratory work when there is increased exercise demand on the lungs or with singing.  
 

The Muscles of Respiration

 Inspiration -

The diaphragm is the primary muscle used for inspiration, but the internal and external intercostal muscles also play an important role in inspiration. The intercostal muscles are the small muscles that lie in diagonal patterns between the ribs. Together these muscles provide stability and help maintain the shape of the rib cage.

 
The external intercostals are located more externally on the rib cage and pass from the inferior border of the ribs to the superior border of the ribs below.
The internal intercostals are on the inner surface of the ribs and insert on the adjacent ribs below them.
Lateral view of the internal intercostals. ©
Expiration
  The primary muscles of expiration are the abdominal muscles, which were discussed in Unit III. The abdominals -  the transversus abdominis, the external and internal obliques can function to raise intra-abdominal pressure to meet the increased demands of breathing as when exercising or dancing and provide forced expulsion of air from the lungs. When this is needed the abdominals fire more actively to produce this motion. In resting breathing, the abdominals provide anterior holding support for the abdominal cavity.  
  The overall movement of the rib cage and trunk is impacted by the respiratory process. Upon inspiration the trunk and rib cage expand and open up so that the movement is more into relative extension  of the trunk or opening of the anterior aspect of the body. Similarly, expiration brings the trunk into relative flexion or forward  bent posture.  
   
 

Relevance to Dance  

The dancer can use the action of respiration or “breath” to assist in movement intention. If a dancer wants to move toward the ground or an inward contracted posture, active exhalation will use the abdominals to assist in hollowing the abdominal cavity to bring the dancer into a more flexed posture.  Conversely, the dancer can use inspiration to open up the chest and lift the arms for a more extended posture.

Take a minute and try this now. Experiment with inhalation and exhalation as you move from more flexed trunk positions to more open and extended trunk positions. How does breathing facilitate or hinder this motion?

 

 
 

Accessory Muscles of Respiration

The accessory muscles of respiration are muscles in the trunk and lower neck that can be called into action to assist with breathing. These muscles usually have other primary functions and only assist with respiration under certain circumstances – usually when more deep or rapid breathing is needed.  

The accessory muscles include the scalenes and  the sternocleidomastoid muscles in the neck, the serratus anterior, and the pectoral muscles in the upper trunk, the upper trapezius and latissimus dorsi muscles of the trunk, and the erector spinae muscles of the back. There are also some smaller, deeper muscles which lie against the rib cage which can also be recruited to assist with respiration. Some of the trunk muscles were discussed in Unit III. The neck muscles will be discussed in more detail in Unit X .

 
    Some examples of accessory muscles of respiration.  
 

Factors Affecting Respiration

When an individual is at rest, the diaphragm and the intercostal muscles produce inspiration. The act of expiration is primarily passive. The lungs fill only partially and provide adequate oxygenation for the body to maintain function in the resting state. The action of the abdominals and the accessory muscles is usually minimal, unless there is some disease state that affects respiration. 

However, when there are other factors introduced, more of the respiratory muscles are called into action. Respiration can be impacted by changes in body position, emotional state, activity level, and even tight corset garments around the abdominal area. There is no clear interaction that always occurs. It depends on the needs of the body at the time.

 

 
 

Respiration or Breathing and the Dancer

 For the dancer, the words of Peggy Hackney are important:

“ We breathe automatically, but breath can be influenced by and is reflective of changes in consciousness, feelings, and thoughts… The key element in usefulness of medical-scientific information to increase movement facility is the degree to which it facilitates a more lively moving image of physiological or neuromuscular connections within the body.” (pgs. 51 & 60,  Making Connections; Gordon and Breach pub.)

 In other words, understanding the anatomical mechanics of breathing can empower the dancer to use those breathing mechanics in a way that facilitates desired movements and different movement qualities.   

 

 
 

Upper-Lower Connectivity and Respiration

 

 
When one thinks about breathing it is usually thought of as an upper body activity since the mouth and lungs take in the air. However, after considering the important role of the diaphragm and the abdominals in respiration it is clear that there is a key central core component for respiration.
The diaphragm connects down into the lumbar spine via the crura muscle.
It also interdigitates with the abdominal muscles and the iliopsoas muscle (psoas major) to form the abdominal wall. These muscles  make an important connection to the lower body. We have not discussed the iliopsoas  muscle, but it is an important part of the upper-lower connectivity concept for the body.
 

The Iliopsoas and Its Role in Connectivity

 
  The iliopsoas is composed of two muscles – the psoas major and the iliacus. The psoas major originates on the transverse process of all lumbar vertebra and the sides of the discs in this area also. It inserts on the lesser trochanter of the femur. The iliacus component of the muscle originates in the iliac fossa of the pelvis and inserts on the lateral aspect of the psoas major at the lesser trochanter. 

We will discuss this muscle in more depth when we consider the pelvis region, and again when we explore the hip.  The iliopsoas is a powerful hip flexor of the femur and an important part of the pelvic floor, as well as a major element in postural alignment. Its central location in relation to the diaphragm cannot be ignored.

  • It is important to remember that the iliopsoas, in combination with the the quadratus lumborum, and the diaphragm  form a kinetic chain to integrate  upper and lower body activity through the use of breath.
 
 

Later in the course, in Units XI and XII, we will consider how this upper-lower connectivity is important for body movement and limb-torso connections, weight shifts, and other movement phrases.

This ends the course material for Unit IV.    Return to Blackboard to proceed to Unit V.