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What Does the Deltoid Muscle Do? - Definition & Function

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  • 0:04 The Muscular System
  • 0:43 What Is the Deltoid Muscle?
  • 1:15 Parts of the Deltoid Muscle
  • 2:26 Lesson Summary
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Lesson Transcript
Instructor: Justine Fritzel

Justine has been a Registered Nurse for 10 years and has a Bachelor's of Science in Nursing degree.

There are over 600 muscles in the human body. Do you know what the deltoid muscle is? In this lesson, we will learn where the deltoid muscle is and what it does.

The Muscular System

The human body is an amazing creation. It's made up of several different systems, one of which is the muscular system. The muscular system includes all of the muscles in the body, which is over 600!

Some muscles you are able to control, like moving your leg. Other muscles work without you thinking about them, like breathing. The largest muscles are the buttocks and the smallest muscle is inside your ear. The strongest muscle is in your jaw but the hardest working muscle is your heart.

If you didn't have muscles, gravity would just pull you to the earth in a heap on the ground. Your muscles work against gravity to maintain your position.

Let's learn more about one muscle in particular, the deltoid muscle.

What is the Deltoid Muscle?

The deltoid muscle is a round muscle that moves and stabilizes your shoulder joint. The deltoid muscle is named after the Greek letter delta-- Δ --. The deltoid resembles an inverted version of this letter because it's wider at the top and narrows at the bottom.

Our shoulders allow us to do so many things with our arms. Your ability to reach up or out in front of your body is because of your shoulders. You couldn't scratch your nose or feed yourself if you didn't have shoulders to give you movement.

The deltoid is a large and strong muscle. It's further divided into three parts that we will learn more about next.

Parts of the Deltoid Muscle

Anterior means front and, therefore, the anterior deltoid is found at the front of the shoulder and allows you to flex your arm at the shoulder joint and rotate the shoulder inward. The anterior deltoid attaches to the collarbone. Hang your arm at your side and then raise it in front of you. This is an example of flexion at the shoulder joint thanks to the anterior deltoid. Now, hang your arm at your side again and then rotate your entire arm in towards your body. That was the anterior deltoid at work again.

The middle deltoid is the middle part of the deltoid and attaches to the shoulder blade. The middle deltoid also aids in a process called abduction, which is the action of moving your shoulder out and away from your body. Once again, hang your arm at the side of your body. Lift it straight out to the side and up. This is abduction and the work of your middle deltoid.

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