Unit IV – The Thoracic Cage/ Respiration & Breathing
Objectives: At the completion of Unit IV the student will be able to:
1.
2.
3.
4.
Name the primary anatomical structures of the thorax and thoracic cage.
Identify the structures applicable to respiratory function.
Describe the process of respiration, including the role of the diaphragm.
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. An important component of the thorax is the anatomical structures for
respiration (breathing). Breathing is a key element to understand and must be utilized
experientially for the dancer in all movement.
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 vertabrae. These bony and cartilagenous structures for the thoracic cage (rib
cage) which surrounds the thoracic cavity and supports the shoulder girdle. The thoracic
cavity contains the heart, 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.
Specific Bony Anatomy
There are three primary components of the thoracic cage:
1. The sternum
2. The thoracic vertabrae 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 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 – 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 fell in the middle of your chest. It houses the costal notches for
articulations with ribs 2-7.
The Xiphoid Process – This is the inferior most component of the sternum. It is a
small cartilagenous structure that varies in shape from pointed to blunt. It ossifies by age
40.
The Thoracic Vertabrae
The 12 thoracic vertabrae have the same bony components as the lumbar vertabrae
discussed in Unit III. They also have several additional special features:
1. Costal facets (flat spots for attachments) on the body of the vertabrae for articulation
with the ribs
2. Costal facets on the transverse processes for articulation with the tubercles of the ribs
3. Long spinouse processes
The attachment location of the rib to the vertabrae is called the costovertebral
articulation. This articulation is made up of the head of one rib and the costal facets on
the vertabrae of that rib and the vertabrae above.
For example: thoracic rib #7 articulates with the costal facets of the lower part of the
vertabrae T6 and the upper part of the vertabrae of T7.
The costotransverse joint articulation is the attachment of the the rib (example – T7
rib) with the facet on the transverse process of vertabrae 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 light weight 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 vertabrae, but not to the sternum so
they float on one end
Structure of Typical Rib – 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:
Posterior portion – This portion of the rib has a head and 2 facets for articulation
with the bodies of the thoracic vertabrae. 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 vertabrae and for attachment of
ligagments.
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 vesselts 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