Function & Anatomy of the Muscles of the Chest and Abdomen

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  • 0:07 Axial vs. Appendicular Muscles
  • 1:35 Muscles of the Chest
  • 4:42 Muscles of the Abdomen
  • 6:33 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

Did you know your body has a trunk? No, not like an elephant's trunk. Your trunk encompasses the chest, back and abdomen. In this lesson you'll learn about some of the main muscles of the chest and abdomen.

Axial vs. Appendicular Muscles

Ever think about what's underneath your skin? What would your face look like without skin covering it up? Or your chest? Or your back? Probably pretty gruesome, or maybe pretty cool, depending on who you are. Well, underneath all that skin that you're used to looking at every day are the muscles that do all the work of moving your body.

If you've been following some of our other lessons on muscle anatomy, you may recall that, just like the skeleton, the muscles of the body can be divided into two groups based on location. The appendicular muscles are attached to the appendicular skeleton. Those would be the muscles making up your arms, shoulders, hips and legs. And, the axial muscles are the muscles attached to your axial skeleton. So, that would be the muscles of your head, neck, chest, abdomen and back.

The axial muscles may not have as much range of motion as your appendicular muscles do, but they are important in providing support and protection for your internal organs. They also control facial expression, neck movement, spinal rotation and even breathing. That's because your axial muscles are found on your face, your neck and the trunk of your body. Did you know you had a trunk? Not a trunk like an elephant's - this one is made up of your chest, abdomen and back.

Muscles of the Chest

Let's take a look at some of the muscles of the chest and abdomen in this lesson. Muscles of the chest, also called the thorax, include both smooth muscles and skeletal muscles. You may recall from other lessons that smooth muscles are found in many of your internal organs and blood vessels. They are involuntary muscles, meaning they aren't under conscious control. For example, you don't have to think 'digest' to make your stomach digest food or to make your intestines move food through your body. Smooth muscles:

  • Have smaller individual muscle cells than skeletal muscles
  • Lack the striations (or stripes) that are visible on skeletal muscles (that's why they're called smooth muscles)
  • Contract slower than skeletal muscles do

The diaphragm is important for breathing.
Diaphragm Image

One of the main smooth muscles inside the chest is the diaphragm. Located between the upper chest and abdomen, the diaphragm is a dome-shaped muscle responsible for enabling us to breathe. It works together with muscles of the ribs to alter the pressure in the lungs as you breathe in and out.

On the outside of the ribs we have the skeletal muscles. Skeletal muscles make up most of your external muscles and are attached to the bones of your skeleton. These muscles are voluntary muscles, meaning that they are consciously controlled by you; you can choose to move them. For example, when you want to throw a ball, you have to think about the action; your arm doesn't just pick up and throw a ball without you knowing it. Skeletal muscles:

  • Have larger muscle cells (or fibers) than smooth muscles
  • Contract faster and with more force
  • Have striations on them that we don't see in smooth muscles

Location of the serratus muscles
Serratus Muscles

Skeletal muscles of the chest are attached to the ribs and sternum. These muscles also attach to the scapula, clavicle, vertebrae and neck. Muscles located in between your ribs are called intercostal muscles ('inter' because they are 'in-between'). To the sides of your rib cage are the serratus muscles, which originate on the ribs and insert at the back, along the scapula. Together with the pectoral and teres muscles, they assist in shoulder movements and in raising the arm, making them appendicular muscles.

The pectoral and teres muscles assist with shoulder movements and arm raises.
Pectoral Teres Muscles

Many muscles of the chest function to pull the body inward. What do I mean by inward? Well, imagine you're standing up straight, or you can just go ahead and stand up straight if you want. Now, hunch or pull your shoulders and arms toward your chest. This movement is pulling your upper body inward, toward the center of your chest, and is performed by the skeletal muscles of your chest.

Muscles of the Abdomen

Underneath the upper chest are axial muscles of the abdomen. These can be divided into the oblique and abdominus muscles. They surround the internal organs, providing a protective barrier between them and the external environment.

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