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Axial Muscles: Trunk Muscles Anatomy & Support

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  • 0:05 Trunk Muscles
  • 1:22 Cervical Trunk Muscles
  • 1:52 Thoracic Trunk Muscles
  • 2:42 Abdominal Trunk Muscles
  • 5:01 Lesson Summary
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

The trunk, or torso, of the human body contains several important muscle groups that aid in breathing and provide support to other parts of our anatomy. This lesson explores the location and function of the major axial muscles.

Trunk Muscles

Believe it or not, when I was in college, I did hundreds of sits-ups every day to get a 'six-pack' of abdominal muscles. These sits-ups, along with other similar exercises, work our oblique (that is, not straight) as well as our rectus (or straight) muscles located in the body wall of our trunk. These oblique and rectus muscles are axial muscles, as they're located in the middle, or the axis, of the body.

A transverse section of the abdominal muscles
transverse view of abdominal muscles

Most people will think of trunk muscles as being located anteriorly (that is, in the front) in the belly area of the abdomen. But, if we look at a transverse section of the abdominal area (above), we see that these muscles run from the vertebral column in the back, around the abdomen, all the way to the ventral midline in the front. Due to their attachments, trunk muscles help to flex the vertebral column, compress abdominal contents, and even help with breathing, or ventilation. These muscles can be categorized based on their location; that is, the cervical region, thoracic region, and abdominal region. We will identify the oblique and rectus muscles in each of these areas of the trunk.

Muscles in the trunk are categorized by their location.
Trunk Muscle Catagories

Cervical Trunk Muscles

Cervical or neck trunk muscles include the anterior, middle and posterior scalene muscles. Scalene muscles originate on the cervical vertebrae and insert on the first two ribs. These muscles work in pairs, and when they do so, they elevate the rib cage, expanding the thoracic cavity during forced breathing, as occurs with blowing out candles and exercise.

Thoracic Trunk Muscles

We have two sets of muscles located in between the ribs of the thoracic wall. These muscles layer on top of each other and are named accordingly.

The deep muscles attach to the inside of the ribs, and they're termed the internal intercostal muscles. Due to their attachment, the internal intercostal muscles are used for exhalation, as they depress the ribs, forcing the air out of the lungs.

The external intercostal muscles are superficial to the internal intercostal muscles, and they attach to the outside of the ribs. Due to their attachment, the external intercostals are used for inhalation, as they elevate the ribs, thus helping to pull air into the lungs.

Abdominal Trunk Muscles

The muscles located in the wall of the abdomen
Abdominal Trunk Muscle

Moving down and along the trunk, we can see the muscles within the body wall of our abdomen. The oblique muscles are named for their position relative to each other. Let's take a look at them. The external oblique muscles are the most superficial, and their fibers run downward towards the midline on each side. Deep to the external obliques are the internal oblique muscles with fibers running at oblique angles to the external oblique fibers. These muscles attach to the linea alba, or 'white line,' which is a connective tissue separating the right and left sides of the front part of the body. Together, the oblique muscles compress the abdomen, thus containing and providing support for the abdominal contents.

Let me make a quick note. Let's go back to the external oblique fibers. As I told you, their fibers run downward on an angle towards the midline. So, if you think of yourself as sticking your hand in your pockets which are on the outside of your pants, your fingers are running in the same direction that the external oblique muscle fibers run. Perhaps that'll help. Let's move on.

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