 Human beings, for better or for worse, have developed into the dominant species on this planet. Beyond our incredible capacity for imagination, cooperation and thought is our ability to make and to do. We are the only species that combines a powerful brain with an upper limb that can be used as a tool. The anatomy of the upper limb enables us to position our hand in space so that we can interact with our environment. Large movements of my shoulder joint and elbow position my hand and small movements in the hand are used for grasping. In this case, the apple. Let's take a closer look at the actual anatomy of the upper limb. Anatomical features of the upper limb provide us with strength, flexibility and precision. We'll start close to the body core of the shoulder and move towards the hand. The closer we are to the body core, the larger and more powerful our muscles are. As we move towards the hand, we trade strength for precision. Now we're the only species that doesn't use the upper limb consistently for walking. This has allowed us to specialize. In humans, the shoulder blade or scapula has moved to the back and is not anchored to the vertebral column. This allows for great mobility and allows us to extend reach into our environment. The scapula can rotate, move up and down and forward and backward. This mobility allows us to point our shoulder joint in multiple directions for a wide range of movement of our upper limb. Let's have a closer look at the architecture of the shoulder joint itself in the lab. These are the bones of the shoulder joint, the scapula and the humerus. Now you can see here that the head of the humerus is really large and it has to articulate with this tiny, articulate facet of the scapula. Now you can see right away, that's not stable. It's never going to hold together. So how are we going to stabilize it? Well, if we were to stabilize it with ligaments or bones, we would lose all mobility. So, along with the joint capsule, we stabilize it with muscles, which will allow the head of the humerus to be anchored, but now it can also move freely. Here are some of the muscles of the posterior scapula region. Three of the rotator cuff muscles can be seen in this position. This is supraspinatus, infraspinatus and pterus minor. For the last member of the rotator cuff, we need to look at the scapula from the front. Let's look at this on this pro-section. Here on the anterior surface is subscapularis. All of these muscles attach around the head of the humerus. They cuff the joint and provide rotation. While the shoulder joint provides large positioning movements of the entire upper limb, the elbow takes on a different function. It's the elbow that allows you to move your hand towards or away from your head. You can now pick up an object and examine it more closely, and you can eat it. The elbow allows for flexion and extension movements, as well as these movements that rotate the hand, pronation, and supination. The elbow is the articulation between three bones, the humerus, the radius, and the elbow. Flexion and extension occur between the bones of the forearm and the humerus. Flexion and extension of the elbow is provided by large muscles in the arm. The anterior compartment provides flexion, mainly with brachialis here and biceps here. The posterior compartment provides extension with triceps here. Pronation occurs when the radius rotates on the humerus and flips the hand over. Supination brings the hand back into position. These important movements of supination and pronation are provided by only four muscles. Pronation is mediated by pronator teres here and pronator quadratus. Pronator quadratus is deep to all of these muscles and wraps around these two bones, allowing for this movement. Supination is a powerful movement, and the most important supinator is biceps. Here, in the arm. The other supinator is located deep in the forearm and simply called supinator. As we move further towards the hand, our movements become smaller and more precise. The wrist is a very stable joint with limited mobility. If our wrist was floppy, the precise movements of our hand would be shaky. Movements of the wrist modify and stabilize the position of the hand itself, particularly obvious when grasping and unscrewing the lid of this honey jar. Let's have a look at the five muscles that stabilize and position the wrist. The wrist joint is the articulation between the radius of the forearm and the carpal bones of the hand. Side-to-side movements of the wrist are done by two flexor muscles in the anterior compartment of the forearm and three extensor muscles in the posterior compartment. Flexor carpial narus and extensor carpial narus are here on the ulnar or medial side, and they can pull the hand inward or adduct it. Flexor carpioradialis and extensor carpioradialis longus and brevis are on the radial or lateral side and in an opposing function, abduct the wrist outward. Together, they allow you to rotate your hand. Everything we've talked about so far was for one purpose, to position our hand. It is our first point of connection and tool for exploring and creating the world around us. We get a grasp on the world with our hand. When we grasp objects, we can do this with power or with precision. Power requires big muscles, but our hands are way too small for that, so our hands outsource the power of large muscles to the forearm. It's only their tendons that extend into the hand. In this dissection of the forearm and hand, large flexor muscles are located in the anterior compartment of the forearm and their tendons extend into the hand and attach to the bones of the fingers and thumb. In the same way, large extensor muscles in the posterior compartment also have tendons that project into the hand and attach to the posterior aspect of the fingers and thumb. However, the use of our hand is not just about power. We can perform remarkably delicate and precise movements as well. These movements are done by small muscles that are actually within the hand itself. These small muscles can modify movements generated by the large muscles of the forearm and make them more precise. This muscle here, a lumbar muscle, is one of the coolest hand muscles. It does something really unique. It allows us to do this movement, a combination of extension and flexion. We can do this because the muscle originates from a flexor tendon and extends around the finger to attach to an extensor tendon. Other muscles, such as these interosseae, can abduct and adduct the fingers. These remarkable movements of the thumb are generated by a specialized set of muscles here. These allow us to oppose the thumb to the other fingers, rotate it, abduct and adduct it. You know, we own nearly everything we make, do and hold with our hands to the muscles of our opposable thumbs. We may take it for granted, but this dexterity and opposability remains one of the main reasons for our dominance on this planet. Even with our intelligence, our imagination and creativity, we may never have realized our potential as a species without it.