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arms and hands anatomy lesson

Live Comfortably - June 29, 2023

Anatomy Lesson: The Arms & Hands, Our Hold on the World

By Leslie LaPlace

On a journey that began at the end of 2020 with the feet and ankles, we have finally arrived at our final Anatomy Lesson. As we wound our way from the legs, the hips, the core, the back and all the way up to the shoulders and neck, we’ve left one critical area of the body to explore. We use this area to hug loved ones, carry heavy bags, hold our phones, write our to-do lists and do countless other tasks all day long. Taking care of this area ensures that we’re able to pick up our kids, type emails to our coworkers and cook meals for ourselves and our loved ones. Let’s look at the bones and muscles of the arms and hands.

Basic Skeletal Structure of the Arms

If you remember from the last article on the shoulders and neck, the arm connects to the shoulder at the glenohumeral joint. There are only three bones in the arm itself. These bones are:

  • Humerus: The long bone that comprises the upper part of the arm, extending from the shoulder to the elbow. Many muscles and ligaments including the rotator cuff, , pectoralis major, latissimus dorsi and deltoid attach to this bone. The top of the bone is the ball of the ball and socket At the other end, it connects with the radius and ulna bones at the elbow joint.
  • Radius: The radius is one of the two bones that make up the lower part of the arm. It is located on the side closest to the thumb. The radius twists around the ulna as the hand moves. Muscles attached to the radius aid in moving the elbow, wrist and fingers. It’s common to break the radius in a fall because we use our hands and arms to brace ourselves.
  • Ulna: The ulna is the other bone that makes up the lower part of the arm. It runs parallel to the radius and is located on the side of the arm closest to the pinky finger. The ulna is stationary, not twisting as the radius does.

Basic Muscles of the Arms

Your upper arm and forearm (the area between your elbow and your wrist) contain more than 20 muscles. These muscles help you with small movements of your hands as well as bigger movements involving your whole arm. Some of these muscles are located deep inside your arm while others are closer to the surface of your skin and visible when you flex the muscle.

There are four main muscle groups, two in the anterior (front) area of the arm and two in the posterior (back) area of the arm.

Anterior arm muscles tend to be the flexors, which pull your arms inward toward your center. The two muscle groups that make up the anterior arm muscles are the biceps brachii and the forearm flexors.

  • Biceps Brachii, commonly referred to as biceps, are a muscle group that at one end attaches the shoulder to the elbow and at the other end bends the elbow to bring the forearm toward the upper arm.
  • Forearm Flexors are made up of eight muscles that run along the inside of the forearm. These muscles flex the wrist and fingers and rotate the forearm. Your forearm flexors work to help you grip things, climb or hang by your hands. While flexing your wrist is one way to strengthen the forearm flexors, overdoing it can lead to “golfer’s elbow”.

Posterior arm muscles perform the opposite function of anterior arm muscles: they pull your arms out and back. The two muscle groups that make up the posterior arm muscles are the triceps brachii and the forearm extensors.

  • Triceps Brachii, usually referred to as the triceps, run along the humerus. They straighten the elbow and help stabilize the shoulder joint.
  • Forearm extensors are 11 muscles that run along the top of the forearm. These muscles help you extend your wrist and fingers. Overuse of these muscles can result in “tennis elbow”.

Bones in the Hands

The bones of the hand can be divided into three categories: carpal bones, metacarpals and phalanges. Each hand is made up of 19 bones.

  • Carpal bones are the eight bones that make up the wrist. For the purposes of this article, I’ll highlight just two of those bones: the scaphoid and the trapezium.
    • The scaphoid helps to link the two rows of wrist bones together. It is key to the function of the wrist because of the way it interacts with the other wrist bones.
    • The trapezium is a saddle-shaped bone that stabilizes the thumb and allows it to move in multiple directions.
  • Metacarpals – There are five metacarpals, one for each finger. These are located in the middle part of the hand (within the palm) and connect your wrist to your fingers.
  • Phalanges are 14 bones that are found in the fingers of each. The thumb has two phalanges, which each other finger has three.

Muscles in the Hands

Two groups of muscles act on the hand: extrinsic muscles and intrinsic muscles.

  • Extrinsic muscles in the anterior and posterior of the forearm help the hand flex and grip.
  • Intrinsic muscles are located within the hand itself and control the hand’s fine motor functions.

There are 34 such intrinsic muscles in the hand. These muscles are grouped into four categories:

  • Thenar muscles control your thumb and are located in your palm at the base of your thumb.
  • Hypothenar muscles line the outer edges of your palm and control your pinky finger.
  • Interossei muscles are between the metacarpal bones in your palm. They help you stretch your fingers out and pull them in to form a fist (abduction and adduction).
  • Lumbrical muscles are worm-shaped muscles located at the base of your four non-thumb fingers that help you flex your fingers.

It’s All Connected

Thank you for coming with me on this journey through the body. I hope you found it both interesting and helpful, and that you now have a greater appreciation of the interconnectedness of our bones and muscles. The body truly is an amazing piece of machinery and I’ve only touched on the major muscles and bones in our Anatomy Lessons.

I also hope you also found the accompanying videos useful in developing an appropriate exercise routine to strengthen and protect each area of your body. Like any machine, the body needs oil and exercise and stretching help to keep joints lubricated and muscles working efficiently. And as an added bonus, you will feel better and more energized. Just make sure you move within your comfort zone to avoid hurting any of the muscles or bones that enable us to function every day!

Stay well!


Leslie LaPlace, Fitness Manager at Goodwin House Alexandria, is a self described recovering Software Development Project Manager. Leslie parlayed a lifelong love of and belief in the restorative power of exercise into a satisfying career working with adults ages 55 and older. She believes that staying active can help reduce aches and pains—It’s also a great anti-aging remedy. She has more than eight years’ experience working with seniors at Arlington County, The Jefferson, Goodwin House Bailey’s Crossroads and Goodwin House Alexandria. Leslie is a certified personal trainer and aquatic instructor who loves creating a positive and fun training experience. She believes that it’s never too late to improve your strength and balance!


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