Comprehensive Guide to Arm Anatomy: Parts, Names & Diagram

Overview of Arm Anatomy

The upper extremity, or arm, is a key part of the upper body. Arm anatomy consists of 3 main parts: the upper arm, forearm, and hand. It spans from the shoulder to the fingers and contains 30 bones, along with nerves, blood vessels, and muscles. The brachial plexus supply the arm’s nerves. Starting at the shoulder, which is a ball-and-saucer joint. It is the upper extremity that allows significant movement due to a shallower socket. However, stability is compromised if we compare it with the hip joint. The elbow is often called a hinge joint, but its ability to pronate and supinate the forearm is enabled by the pivot joint formed by the radial head and radial notch on the ulna.

The wrist joint is categorized as ellipsoidal or condyloid, and there are intercarpal joints among the carpal bones, allowing limited movement. The interphalangeal joints in the fingers function as basic hinge joints. In this article, we will see all parts of the arm with their names, functions and their locations in the diagram.

Arm Anatomy Diagram

Arm Anatomy: Parts & Functions

Shoulder

The human shoulder comprises 3 bones: the clavicle (collarbone), scapula (shoulder blade), and humerus (upper arm bone).

These remarkable skeletal elements connect with an intricate network of muscles, ligaments, and tendons. This combination creates a very effective shoulder joint design.

Within this system, the glenohumeral joint with the acromioclavicular joint strengthens the overall splendor. The shoulder joint allows an inseparable connection between the humerus and the scapula.

Functionally, the shoulder joint is a good ball and socket splendor, releasing the great potential of circular rotations. A hinge-like extension elevates the arm to move freely.

Biceps

The biceps brachii muscle is located in the anterior compartment of the upper arm. What sets it apart is its dual-headed origin.

The short head originates from the coracoid process, while the long head arises from the supraglenoid tubercle of the scapula.

Unlike typical muscles, the biceps brachii display an exceptional capacity to traverse not one but two joints – the shoulder joint and the elbow joint. It facilitates interesting forearm flexion and supination actions.

The corkscrew is twisted into the cork with force by the biceps. The biceps attach to the brachialis and coracobrachialis muscles to form a trio within the anterior compartment of the upper arm.

It shares nerve supply, forming a collaboration that enhances their collective strength.

Read More – Ultimate Guide to Bicep Anatomy: Parts, Names, Functions & Diagram

Triceps

The triceps brachii is a strong muscle at the back of your upper arm. It helps straighten your elbow and has three parts: a long head, a lateral head, and a medial head. These parts come together into one tendon near your elbow.

The long head begins from a spot on your shoulder blade, while the lateral and medial heads start from your upper arm bone. They all connect to a bony part on your elbow called the olecranon process.

Its main job is to extend your forearm at the elbow. When your arm is slightly bent, the biceps usually have more power than the triceps.

Apart from straightening your arm, the triceps also help keep your elbow stable when your hand is doing delicate tasks like writing.

The triceps hang out in the back part of your arm, while muscles like the biceps and brachialis live in the front. There is a sort of barrier called the lateral intermuscular septum that separates these muscle groups.

Forearm

The forearm is the part between your elbow and wrist, made up of two bones called the radius and ulna. It is packed with muscles—20 in total—that help you do delicate movements with your arm, wrist, and fingers.

There are two main muscle groups in the forearm: the front one (for flexing) and the back one (for extending). Tough layers of tissue split these groups. They are like compartments that keep the muscles in place.

These muscles are a big deal for making your arm, wrist, and fingers move smoothly. They are split into two types: ones that do their job in the forearm itself (intrinsic) and others that handle finger movement (extrinsic).

The intrinsic muscles help rotate your forearm, while the extrinsic ones deal with bending and straightening your fingers.

One more muscle, the brachioradialis, goes from your arm to your wrist and helps to bend your elbow.

Hand

The hand is what we use to grab and hold things. Humans and some animals like monkeys and koalas have hands with fingers and a thumb.

Usually, there are five parts to our hand: four fingers and one thumb. Inside, 27 bones help the hand move. Some people might have a different number of tiny bones.

The bigger bones in the middle connect the fingers to the wrist bones. Overall, our hands are made up of small and big bones that help us do lots of different things!

Read More – Comprehensive Guide to Hand Anatomy: Parts, Functions & Diagram

Thumb

The human thumb is the most important part of our arm anatomy. It underwent millions of years of evolution. The first digit of the hand sits beside the index finger when the palm faces forward.

The thumb is one of the fingers of five fingers and is positioned as the outermost finger. It has two phalanges and an incredibly flexible joint, giving a wide range of movements and precise control.

Fingers

Fingers are standout digits found on the front limbs of most four-legged vertebrates, particularly those with handy limbs like humans and other primates.

Most animals with four limbs have five fingers, and if they are shorter than the metacarpals (the bones in the palm), we call them toes. On the flip side, if they are notably long, we call them fingers.

In humans, these fingers are bendy and opposable, making them essential for feeling things and pulling off delicate movements. This flexibility is a big deal for the hands, helping us grab and handle stuff with finesse.

Read More – Complete Guide to Finger Anatomy with Parts, Names, Functions & Diagram

Nails

Primates, including humans, have nails on their fingers and toes. These nails are like claws but made of a tough stuff called keratin. They are about 0.5 millimeters thick and a little curved.

Nails stick to the nail bed but separate at the tips so we can scratch stuff. They are also important for feeling things.

Nails have folds of skin around them: side ones called lateral nail folds and a bottom one called the proximal nail fold. There is a thin skin layer, the cuticle, protecting the lower part of the nail.

Read More – Complete Guide to Nail Anatomy with all Parts, Names & Diagrams

Joints

Shoulder Joint

The shoulder joint connects your arm to your body and can move in lots of ways. It is like a ball fitting into a socket.

This joint lets you move your arm in many directions: forward, backward, away from your body, toward it, and even in circles. It is super flexible but not very stable because the bones don’t support it much.

The shoulder relies on muscles, ligaments, and tendons to keep it steady. But because it is so flexible, it is easy to hurt this joint. That is why shoulder injuries are common.

Elbow Joint

The elbow joint is where your upper arm bone (humerus) meets the bones in your lower arm (radius and ulna). It is a special kind of joint that lets you move your arm in different ways.

Inside, there’s a smooth surface on the bones covered with a slippery fluid that helps them glide smoothly. This fluid keeps things moving without any trouble.

Around the joint, there’s a tough covering like a capsule, and inside, there’s a lining that keeps everything running smoothly. This joint is kind of like a hinge—it mainly moves back and forth, like a door opening and closing.

Wrist Joint

The wrist joint is called the radiocarpal joint. It links the lower part of the forearm bone (radius) with three small wrist bones. It is the main part of the wrist but includes nearby joints, too.

In this joint, the end of the radius bone smoothly connects with the scaphoid and lunate bones. However, the link with the triquetral bone involves a disk between them.

The radiocarpal joint lets your wrist move in different ways: bending forward (flexion), backward (extension), moving sideways away from your body (abduction), and towards your body (adduction).

This joint’s structure and job are super important for wrist movement and keeping it steady.

Read More – Wrist Anatomy: Ultimate Guide to Parts, Names, Functions & Diagram

Metacarpophalangeal (MCP) Joints

The MCP joints link the bones of the palm to the fingers. There are five of these joints, one for each finger, linking a big hand bone to the first finger bone.

The spherical tops of the hand bones fit into the curving bottoms of the finger bones to form these joints. They allow your fingers to flex, extend, separate, come together, create circles, and spin slightly.

MCP joints are critical for hand usage because they provide strength and flexibility to your fingers. Ligaments, joint capsules, and surrounding muscles and tendons all contribute to smooth and easy-to-control motions.

Interphalangeal (IP) Joints..

The interphalangeal joints in your hand are like hinges between the bones (phalanges) of your fingers. They let your fingers bend towards your palm.

Each finger, except the thumb, has two sets of these joints. The “proximal interphalangeal joints” are between the first two bones of your fingers. The “distal interphalangeal joints” are between the last two bones.

These joints are pretty similar in structure, but there are some tiny differences. For instance, the way certain parts are attached and the flexibility of the joints vary slightly. The distal joints are a bit smaller and don’t move as much as the proximal ones.

Arm Muscle Anatomy

Your upper arm and forearm have over twenty muscles. These muscles help you to move your arms, hands, fingers, and thumbs.

Some muscles are for tasks like sewing, while others help with bigger actions like throwing a ball or doing push-ups.

Some muscles are deep inside your arm, while others are closer to your skin. You can see these muscles when you flex.

Tendons are soft tissues that connect these muscles to the bones in your arm and shoulder. They let you do things like straighten your elbow, lift your arms, and do all sorts of movements.

Anterior Compartment Muscles

The upper arm houses three muscles in its front area. The biceps brachii has two parts, long and short heads, found at the top. Below them, there are coracobrachialis and brachialis muscles nestled under the biceps.

Biceps Brachii

The biceps brachii is a front-arm muscle made of two parts. One part starts near the shoulder blade, and the other shares its start with another muscle near the same spot.

Both parts join into one and attach to the radius bone in the forearm. It gets signals from the musculocutaneous nerve and gets blood from the brachial artery.

It is mainly responsible for bending the elbow and turning the palm up. It also helps bring the arm forward. The longer part also helps keep the shoulder steady.

Brachialis

The brachialis muscle is in the front of your arm and helps you bend your elbow. It connects the upper arm bone to the forearm bone.

It gets messages from nerves in your arm and is supplied with blood from certain arteries. This muscle is key for bending your arm at the elbow.

Coracobrachialis

The coracobrachialis muscle sits on the inner side of your upper arm. It is attached to the shoulder blade and the upper arm bone.

This muscle is good at pulling your arm closer to your body and a bit at bending your arm at the shoulder. The nerves that make it work come from the neck area, and it gets its blood supply from certain branches of an artery in the arm.

Posterior Compartment Muscles

The back part of the upper arm houses a special muscle called the triceps brachii and Anconeus. These are the 2 muscles found in this particular compartment.

Triceps Brachii

The triceps brachii is a big muscle in the back of your arm. It has three parts, each starting from a different place but joining together at the same endpoint.

One part starts from the shoulder blade, another from the lower part of your upper arm bone, and the third from the upper part of your upper arm bone. They all come together and connect to the back of your elbow and the covering of your lower arm.

Anconeus

The anconeus muscle is a little helper at the back of your elbow. It links the bumps on your upper arm and forearm. You are assisting the larger triceps muscle in straightening your elbow and keeping the joint stable. Nerves from your neck (C7-C8) run the show for this muscle, and it gets its blood from an arm artery.

Read More-

Lower Limb

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Upper Limb

• Comprehensive Guide to Hand Anatomy: Parts, Functions & Diagram
• Shoulder Anatomy: Ultimate Guide to Parts, Names, Functions & Diagram
• Ultimate Guide to Bicep Anatomy: Parts, Names, Functions & Diagram
• Complete Guide to Finger Anatomy with Parts, Names, Functions & Diagram
• Wrist Anatomy: Ultimate Guide to Parts, Names, Functions & Diagram
• Complete Guide to Nail Anatomy with all Parts, Names & Diagrams

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External Sources-

• Wikipedia
• KenHub
• Optometrists
• Cleveland Clinic
• American Academy of Ophthalmology