Lab 19: Elbow and Wrist Joint | Muscles of the Posterior Arm | Nerve and Vessel Review
By the end of this lab, students will be able to:
- Identify and describe the components of the elbow joint
- Identify and describe the joints of the forearm, and wrist.
- Identify and describe the muscles of the posterior forearm.
Terms to Know
Wrist and Hand Joints
Muscles of the Posterior Forearm
Today you will review the elbow and wrist joints, as well as the muscles of the posterior forearm using wet specimens, plastinates, and the Visible Body App. You will also have a chance to review the nerves of the upper extremity. Keep in mind that all structures are not visible using all tools, and that is OK. Also, take advantage of the opportunity to use other lab atlases and images to identify these structures. Before you start, here are a few things to keep in mind about structures you will be identifying today:
- Posterior Forearm: The muscles of the posterior compartment of the forearm generally contain muscles that extend the wrist. These extensors originate from the area of the lateral epicondyle of the humerus. Palpate your lateral epicondyle and move your fingers to the mass of muscle just distal to it. Extend your wrist, and you should feel this extensor mass contract. The posterior compartment also contains a muscle that abducts the thumb, as well as the supinator muscle. The supinator muscle works with the biceps brachii to supinate the hand. Supination makes the palm face forward in anatomical position. You can remember the position of a supinated hand by thinking that, in the supinated position, you can hold a cup of soup.
- Hand: The muscles of the hand can be divided into a few groups. The thenar muscles are those that act on the thumb, and the hypothenar muscles are those that act on the 5th digit. Both the thenar and hypothenar muscles are completely located within the hand and contain an abductor, flexor, and opponens muscle. The opponens muscles act on the thumb or 5th digit to make these digits touch. The thumb also has a muscle that acts to adduct it, called adductor pollicis, but the fifth digit does not have a counterpart to this muscle. All muscles containing the word “pollicis” act on the thumb, and all muscles that contain the words “digiti minimi” act on the 5th digit.
Activity 1: Cadaveric Specimins-The Elbow and Wrist Joints and Muscles of the Posterior Forearm
As you are exploring the muscles of the posterior forearm, especially those crossing the wrist and hand joints, you should gently pull on these tendons to watch how they move the wrist and digits.
- Begin by examining the elbow joint. The elbow is constructed of three separate joints: the humeroulnar joint between the humerus and ulna, the humeroradial joint between the humerus and radius, and the proximal radioulnar joint between the radius and ulna proximally. The ligaments of these joints are best seen on the iPads, but you may be able to appreciate them on one of the upper extremity dissections. Often these ligaments are blended into the surrounding capsule, so they can be difficult to define. However, you may be able to appreciate the ulnar or radial collateral ligaments on either side of the joint or the annular ligament surrounding the head of the radius.
- Observe the muscles of the posterior forearm. The names of these muscles tell a lot about their location and/or function. They tend to extend the wrist or digits, and most originate on the lateral epicondyle of the humerus. This compartment can be divided into superficial and deep layers, each with five muscles. We won’t ask you which layer a muscle is located in. However, sometimes breaking the muscles into smaller groups can be helpful for learning.
- On the radial side of the forearm, observe the extensor carpi radialis longus and extensor carpi radialis brevis muscles. Don’t confuse these with the brachioradialis, which sits partially superficial to these. The brachioradialis has an origin that is proximal to the lateral epicondyle, while these muscles originate on or near the lateral epicondyle. Both extensor carpi radialis longus and brevis cross the wrist and act to extend it, the difference between the longus and brevis muscles is in the tendon length and position. Extensor carpi radialis longus has a longer tendon and is just superficial to the extensor carpi radialis brevis. The extensor carpi ulnaris (only one on this side) extends the wrist and inserts on the ulnar side of it.
- Extensor digitorum extends to the distal phalanx of digits 2-5 and extends the MCP, DIP, and PIP of these digits. Note that there is only one extensor digitorum muscle, so there is no other descriptor in the name (e.g. superficialis, profundus, brevis, or longus. Observe the small angled dense connective tissue connecting the tendons of extensor digitorum in the hand. This is called the juncturae tendinae. It functions to coordinate and distribute force across the extensor tendons. Try extending your ring finger (4th digit) while keeping the other digits in a fist. You are not able to extend that finger without moving the others because of the juncturae tendinae. However, you can extend your 5th digit much farther while the others are flexed. That is because of the extensor digiti minimi muscle. This muscle acts to extend the fifth digit. In this tissue, it appears that this muscle has blended with the extensor digitorum muscle. Be sure to observe this muscle in laminated or atlas/PAL images.
- You may also notice that you can extend your 2nd digit (pointer finger) while flexing your other digits. That is because another muscle extends this digit: extensor indices. Another deep muscle of the posterior forearm is the supinator, which acts to supinate the forearm. This muscle is deep and more difficult to find, but it can be observed running from the lateral epicondyle to the shaft of the radius.
- The other muscles of the deep posterior forearm act on the thumb. Abductor pollicis longus acts to abduct the thumb, while extensor pollicis brevis and longus act to extend the joints of the thumb. The extensor pollicis brevis tendon sits between the abductor pollicis longus and extensor pollicis longus tendons.
- Observe the dense connective tissue running over the extensor tendons. This is called the extensor retinaculum. Like the flexor retinaculum, this structure holds the extensor tendons in place and provides a mechanical advantage with extension.
- Observe the wrist. Though you may not be able to see the joints, you should be able to feel for the distal radioulnar, radiocarpal, midcarpal, Intercarpal, and carpometacarpal joints. Feel these joints as you move the wrist. These may be easier to feel on the deep dissection.
Activity 2: Visible Body app
First, explore the muscles and joints of the posterior forearm and wrist using the iPads.
- Click on the Regions tab and scroll to 9. Cubital Fossa. Under the systems tab 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 today. While under the systems tab, at the very top, 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 for 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. Some muscles are deep to others, thus you will have to remove the more superficial muscles in order to see the deep muscles. Some of the joints will not be specifically listed in the app, however you will be able to see the three ligaments of the elbow listed as well as the extensor retinaculum on the wrist.
- You will be asked to identify the origins, insertions, actions, and innervations of these muscles (this will be listed in the app after you have highlighted the structure and click the book). However, you may not need to know certain specifics for each muscle. Follow what is in the muscle charts for the specifics of what you need to know for each muscle. If you would like to see the muscle(s) in action, there are two means to see this, the first is to click on the red pin when you have highlighted the muscle, this will drop down motion videos. The second way to see muscle actions is to go back to the home screen of the app and select the Muscle Actions tab. From here, you will be able to see motions of the shoulder and within those motion sequences, you can individually select muscles to see their action.
- Elbow Joint
- Humeroulnar joint
- Ulnar collateral
- Humeroradial joint
- Radial collateral
- Proximal radioulnar joint
- Wrist and Hand Joints
- Distal radioulnar joint
- Radiocarpal joint
- Midcarpal joints
- Intercarpal joints
- Extensor Retinaculum
- Muscles of the Posterior Forearm
- Superficial Layer
- Extensor carpi radialis longus
- Extensor carpi radialis brevis
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
- Deep Layer
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
- Extensor indicis
- Superficial Layer
- Click on the Muscle Animations tab (on the home page) and scroll to forearm and wrist motions to view the muscles that act on the forearm and wrist. Explore the animations of forearm pronation/supination, wrist extension/flexion, wrist abduction/adduction, finger extension/flexion, thumb extension/flexion and opposition.
Activity 3: Review of Nerves and Vessels of the Upper Extremity
Take the extra time in this lab to review the brachial plexus and vasculature of the upper extremity. Now that you know more of the muscles, try identifying a muscle and then find the nerve that innervates it. Then identify the nerves and point out the muscles that they innervate. Also review the vasculature of the upper extremity.