Introduction

In this lab, you will view the muscles of the anterior forearm and hand and the joints of the hand.

Lab Activity 1: Muscles of the Anterior Forearm-Donor Tissue

Muscles of the anterior compartment, or anterior aspect of the forearm, are generally flexors of the wrist or fingers. The flexors originate from a flexor mass with its proximal attachment point on the medial epicondyle of the humerus. Palpate your medial epicondyle and then move your fingers to the mass just distal to the medial epicondyle. Flex your wrist, and you should feel this flexor mass contract. The anterior compartment also contains pronators of the arm. From anatomical position, this motion would be turning your hand so that your thumb points medially and your hand faces backward. If you imagine holding a glass of water, pronation would also be the motion of turning your wrist and hand to pour the water out of the glass. The names of these muscles often tell a lot about their location and/or function.

The anterior compartment can be divided into three layers. We won’t ask you specifically which layer a muscle is located in. However, sometimes breaking up these muscles into smaller groups can be helpful for learning them.

Superficial layer:

• Observe the brachioradialis. This muscle originates in the brachium, or arm, and inserts onto the styloid process of the radius.
• The pronator teres inserts onto the mid-shaft of the radius. It is the shortest muscle originating from the medial epicondyle.
• Flexor carpi radialis and flexor carpi ulnaris both cross only the wrist joints and act to flex the wrist (flexor = flex and carpi = wrist). They insert on the side of the wrist nearest the bone that is part of their name.
• The palmaris longus is a very small muscle and weak flexor of the wrist. It is not present in 10-20% of the population.

Intermediate Layer:

• Flexor digitorum superficialis (FDS) crosses the wrist, MCP, and PIP joints of digits 2-5 in the hand. Notice how this tendon splits and inserts on the middle phalanx of these digits.

Deep Layer:

• First observe flexor digitorum profundus (FDP). Observe how it is deep (profundus) to the FDS. Both of these muscles act to flex the MCP and PIP joints of the digits. However, observe how FDP runs deep to the tendon of FDS through its split in the digits and continues distally to insert on the distal phalanx of digits 2-5. Therefore, only FDP will flex the DIP of the digits.
• The flexor pollicis longus muscle sends its tendon across the IP joint of the first digit to insert on the distal phalanx of digit 1, the thumb. Therefore, it flexes the MCP and IP joints of the thumb.
• Finally, very deep on the anterior aspect of the distal forearm, observe pronator quadratus. This muscle sits just anterior to the interosseus membrane, which you can observe proximal to this muscle.

Observe how the tendons of these muscles run underneath a thick sheet of connective tissue. This is called the flexor retinaculum. This helps to hold these flexor tendons in place and create a mechanical advantage, increasing the force these muscles can produce. The median nerve, which you will observe in the next lab, also runs deep to the retinaculum. The space that these tendons and the median nerve runs through is commonly called the carpal tunnel. Irritation of the median nerve in this place and is called carpal tunnel syndrome. Note that the palmaris longus is the only muscle whose tendon does not travel through the carpal tunnel but, instead, travels superficial to the flexor retinaculum. If you forcibly squeeze your thumb and fingertips together, tensing your palm while flexing your wrist slightly, you can see this tendon clearly in the wrist area if you have this muscle.

Observe the muscles of the hand. These are best viewed on the deep dissection.

• The thenar and hypothenar muscles act on the thumb and fifth digits, respectively. Each has a flexor, abductor, and opponens muscle. Notice that the flexor pollicis brevis and abductor pollicis brevis muscles have been cut so that you can observe the deeper opponens pollicis muscle. On the hypothenar side, the flexor digit minimi muscle has been cut so that you can see the opponens digiti minimi muscle. Abductor digiti minimi has been preserved.
• The adductor pollicis muscle is part of the deep muscles of the hand. You can move the tendons near the thumb to the side to observe this muscle on the palmar aspect of the hand. It may be helpful to observe this muscle in the digital atlas or laminated image first. Notice that there are two heads. One runs from the thumb horizontally across the hand, while the other runs from the same origin obliquely across the palm. These two heads create a “7” shape. This muscle acts to adduct the thumb.
• Observe the lumbricals, which attach to the flexor tendons within the hand. These thin muscles help you form an “L” with your 2^nd-5^th digits (if you turn your palm upwards). They flex the metacarpophalangeal joints while extending the proximal interphalangeal distal interphalangeal joints.
• On the dorsal aspect of the hand, you can observe the dorsal and palmar interossei. Though their names specify directionality, you can see both from the dorsal aspect of the hand. You will need to observe fiber direction for these muscles to determine which is which. You can remember their actions by remembering DAB and PAD: Dorsal interossei ABduct the digits and Palmer interossei ADduct the digits. Therefore, by looking at the fiber directions, you can understand if that interossei would be pulling the fingers medially or laterally with respect to the midline of the hand. The middle (3^rd) digit can only abduct, so it has only dorsal interossei on either side. For the other digits, the interosseus muscle on the medial aspect of the digit with its fibers running proximally towards the midline are palmar interossei. The interosseous muscle on the lateral aspect of the digit with its fibers running distally towards the midline are dorsal interossei.

Lab Activity 3: Anterior Forearm and Hand – Visible Body App

First, explore the muscles and joints of the anterior forearm and wrist using the iPads.

• Click on the Regions tab and scroll to 9. Cubital Fossa. Click on Systems at the bottom left if the systems column is not already present on the left side of the screen. Click on the arterial, venous, nervous, and lymphatic systems twice to remove them since we will not be looking at these systems in this lab. At the very top of the systems column, you have the option to select a region. Scroll to the left and for shoulder/arm, click the muscle twice, so you only have the bones on the left side of the body and muscles on the right side of the body.
• Explore the muscles and joints of the forearm and hand listed in the Terms to Know. Some of these muscles will be deep to others. Thus you will have to remove the more superficial muscles to see the deep muscles. Some of the joints may not be specifically listed in the app.
• You will be asked to identify the origins, insertions, actions, and innervations of these muscles (this will be listed in the app after highlighting the structure and clicking the book). However, you may not need to know certain specifics for each muscle. Follow what is on the posted muscle charts for the specifics of what you need to know for each muscle.
• Two view the actions of the muscles. You can click on the Muscle Actions tab on the home page, then click on the motion you would like to view.