Unit IV The Thoracic Cage/ Respiration & Breathing
completion of Unit IV the student will be able to:
1. Name the primary anatomical structures of the thorax and thoracic cage.
the structures applicable to respiratory function.
the process of respiration, including the role of the diaphragm.
the relationship of the diaphragm and the iliopsoas and its its importance
to the dancer.
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.
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:
explore each of these in some detail now.
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.
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.
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:
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
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.||
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.
ribs are elongated, flattened, and twisted bones. They are very lightweight and resilient. There are 3 types of ribs:
|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
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.
11 and 12 are short, floating
ribs that do not attach anteriorly to the sternum, so they have no neck or
Rib Movement and Thoracic Cage Function for Breathing
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.|
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.
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.
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
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
is an active movement that must overcome resistance for adequate intake of
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 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.||©|
|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.|
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
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.
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
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.)
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.
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.