Guide to Forearm Anatomy with Parts, Names, functions & diagram

Overview of Forearm Anatomy

The forearm is the part of your arm between your elbow and wrist. It is the lower part of your arm. Forearm anatomy consists of various bones, muscles, joints, and nerves. Inside the forearm, there are two bones called the radius and ulna, connected by an elastic tissue called the interosseous membrane. On the outside, your forearm has muscles that help you move your wrist, fingers, and elbow. Some muscles bend your wrist and fingers (flexors), some straighten them out (extensors), and others help you turn your hand palm up or palm down. In the middle of your forearm, there is a line dividing it into two sections. The back part holds the muscles that straighten your fingers and wrist, and the radial nerve controls it. The front part holds the muscles that bend your fingers and wrist, mainly controlled by the median nerve.

The ulnar nerve also goes through your forearm. Overall, your forearm muscles are bigger on the front because they fight against gravity when you lift things.

In this article, we will see all the different parts of forearm anatomy to understand their functions and names.

Forearm Anatomy Diagram

Parts of Forearm

Muscles

Flexor Muscles
- Flexor Digitorum Profundus
- Flexor Digitorum Superficialis
- Flexor Carpi Ulnaris
- Flexor Carpi Radialis
Extensor Muscles
- Extensor Carpi Radialis Longus
- Extensor Carpi Radialis Brevis
- Extensor Digitorum
- Extensor Carpi Ulnaris
- Extensor Digiti Minimi
Pronator Muscles
- Pronator Teres
- Pronator Quadratus
Supinator Muscle
Other Muscles
- Brachioradialis
- Anconeus
- Palmaris Longus
- Extensor Indicis

Bones

Ulna
Radius

Joints

Elbow Joint
Radioulnar Joints

Nerves

Median Nerve
Radial Nerve
Ulnar Nerve

Blood Vessels

Brachial Artery
Ulnar Artery
Radial Artery

Forearm Muscle Anatomy – Flexor

The forearm has two bones: the radius on the outer side and the ulna on the inner side. There are two muscle groups: one in the front for bending your arm and one in the back for straightening it. Together, these muscles are in total twenty. They help move your elbow, wrist, and fingers. They are crucial for making precise movements with your upper limb.

Flexor Digitorum Profundus

It is a strong muscle in your forearm that helps you grip things tightly. It is called the flexor digitorum profundus. You can feel it as a big bump on the back of your forearm near the inner side.

It is the main muscle responsible for gripping because its tendons start lower down your arm compared to other muscles in the forearm.

Flexor Digitorum Superficialis

The flexor digitorum superficialis is a big muscle in the front of your forearm. It has two parts: one starts from your elbow and the other from your radius bone. These parts join together to form four tendons that connect to your fingers.

This muscle helps you bend your fingers at the middle and first knuckles. It also helps bend your wrist. It gets its signals from the median nerve and blood supply from arteries in your arm.

Flexor Carpi Ulnaris

The flexor carpi ulnaris is a muscle on the inner side of your forearm. It has two parts: one starts from the inner elbow and the other from the upper part of the inner forearm.

These parts come together to form a strong tendon that attaches to the wrist bones and the base of your little finger.

This muscle is unique because it is controlled by the ulnar nerve, which runs down the inner side of your arm. It gets its blood supply from a nearby artery.

Its main job is to bend your hand at the wrist. It also helps move your hand sideways toward your metacarpal bone 5.

Flexor Carpi Radialis

The flexor carpi radialis is a forearm muscle that helps move your hand and wrist. It starts from the inside of your elbow and runs down the inside of your forearm to a tendon in your wrist.

From there, it connects to the base of your second and third metacarpal bones. The median nerve controls it. It gets its blood supply from branches of the ulnar and radial arteries.

When it tightens, it bends your wrist downward (flexion) and moves it sideways towards your thumb side (abduction). It also helps turn your palm down (pronation), but not as much as other muscles in the forearm.

Palmaris Longus

The palmaris longus muscle is one of the outer muscles on the front side of your forearm. It starts from a medial epicondyle of the humerus. It runs down to the middle of your forearm, where it turns into a tendon.

This tendon then travels toward your wrist, passing over a flexor retinaculum, and attaches to a palmar aponeurosis.

It gets its signals to move from a nerve called the median nerve, and its blood supply comes from an artery called the anterior ulnar recurrent artery.

The main job of the palmaris longus muscle is to work with other muscles in the front of your forearm to help you bend your hand at your wrist. It also helps steady your elbow and gives a little bit of strength to bend your fingers at the joints.

Forearm Muscle Anatomy – Extensor

Extensor Carpi Radialis Longus

The extensor carpi radialis longus is a long muscle in your forearm on the side of your thumb. It starts from a lateral supracondylar ridge of the humerus and the lateral intermuscular septum of the arm. Then, it narrows down into a tendon that connects to the base of your second finger’s hand bone.

This muscle gets its signals from the radial nerve in your neck and upper back. Blood comes to it mainly from a big artery in your arm, with a little help from another artery.

It helps pull your hand back and away from your body and also helps with bending your elbow. It is important for things like grabbing and holding objects.

Extensor Carpi Radialis Brevis

The extensor carpi radialis brevis is a muscle that starts from a lateral epicondyle of the humerus on the outer side of your elbow. Its fibers run down towards your wrist and the tendon attaches to the back of the bone in the base of your third finger.

This muscle gets its signals from a nerve called the deep branch of the radial nerve. It relies mainly on the radial artery in your arm for energy and nutrients.

The main job of the extensor carpi radialis brevis is to help straighten and move your hand away from your body at the wrist joint.

Extensor Digitorum

The extensor digitorum is a long muscle in your forearm that helps you straighten your fingers and wrist. It starts from a lateral epicondyle of the humerus via the common extensor tendon on your elbow. It runs down to your second to fifth fingers.

Its main job is to straighten your fingers at the middle and end joints, and it also helps with straightening your wrist.

Extensor Carpi Ulnaris

The extensor carpi ulnaris muscle is located on the inside of your forearm. It starts from a lateral epicondyle of the humerus via the common extensor tendon on your elbow and runs down to your wrist.

Further, it attaches to the metacarpal bone of the 5th digit. It is powered by a nerve that comes from your spine and gets its blood supply from nearby arteries.

The extensor carpi ulnaris muscle’s main job is to move your hand sideways toward your metacarpal bone (ulnar deviation). It also helps with stretching your hand out, working alongside other muscles.

Extensor Digiti Minimi

The extensor digiti minimi is a thin muscle near the outer side of your forearm. It starts from a lateral epicondyle of the humerus via the common extensor tendon. It stretches down to connect to your digit 5 finger.

This muscle helps straighten your pinky finger at the joint closest to your hand, but it can also help with other movements of the pinky.

It gets its power from a nerve in your arm and its blood from nearby arteries. Overall, it plays a role in straightening your pinky finger and extending your wrist.

Brachioradialis

The brachioradialis muscle in your forearm is important for bending your elbow and stabilizing during hammering. It connects from the bottom end of your radius bone to a ridge on the outer part of your upper arm bone (humerus).

Depending on your forearm position, this muscle can rotate your forearm inward (pronation) and outward (supination).

The brachioradialis works best when you bend your elbow with your forearm positioned halfway between fully turned inward and outward.

When you bend your forearm inward, the brachioradialis muscle helps to turn it outward (supinate) as it bends. When your forearm is already turned outward (supinated), it is easier to bend it by turning it inward (pronate). It allows for quicker movements when lifting weights slowly.

Forearm Anatomy – Pronator Muscles

Pronator Teres

The pronator teres muscle is one of the outer forearm muscles. It has two parts: the humeral head starts from the medial supracondylar ridge of the humerus (inside of the upper arm bone), and the ulnar head from a coronoid process of the ulna(lower arm bone).

These parts come together to form a tendon that attaches to a pronator tuberosity on the lateral side of the radius bone.

This muscle gets signals from the median nerve and blood from the brachial, radial, and ulnar arteries. Its main job is turning the palm downward by rotating the forearm at the top joint near the elbow. It also helps in bending the forearm at the elbow.

Pronator Quadratus

The pronator quadratus is a square-shaped muscle in the lower part of the forearm. It helps to turn the hand so the palm faces downwards.

Its fibers run across the arm and connect from the front of the lower quarter of the ulna to the lower quarter of the radius.

This muscle has two heads: the superficial head starts from the front lower part of the ulna’s shaft and attaches to the front lower part of the radius’s shaft and its front section. The deep head also begins from here but attaches closer to the notch of the ulna.

It is unique because it is the only muscle that connects solely from the ulna to the radius. Blood comes to it from the anterior interosseous artery.

When the pronator quadratus tightens, it pulls the radius outer side towards the ulna and rotates the hand downward. Its deep fibers help keep the bones of the forearm together.

Supinator Muscle

The supinator is a muscle in the back of your forearm. It works with other muscles like the brachioradialis and the forearm extensors.

This muscle wraps around the top part of the radius bone, connecting it to the ulna bone. Because it crosses the forearm, the supinator helps to turn the palm of your hand up, a movement called supination.

When you turn your hand the other way, with the palm facing down, the pronator quadratus muscle does the work, called pronation.

The supinator’s main job is to rotate the radius bone laterally at the elbow, making the radius and ulna bones parallel and turning your hand palm up.

Anatomy Forearm Muscles – Other

Anconeus

The anconeus is a small, triangular muscle located at the back of the elbow. It runs from the lower end of the humerus (the upper arm bone) to the upper part of the ulna (one of the forearm bones).

This muscle is part of the group that helps extend the wrist and fingers, along with muscles like the brachioradialis, extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris.

The anconeus helps straighten the arm at the elbow. It stabilizes the elbow joint by supporting the back of the joint and the ulna.

Extensor Indicis

The extensor indicis is a muscle in the back of the forearm. It is part of a group of muscles that help move the wrist and fingers.

You can feel it by pressing firmly on the bone on the pinky side of your wrist while straightening your index finger.

Its main job is to straighten the index finger at the joints closest to the hand. Unlike other fingers that share muscles for movement, the index finger has its muscle dedicated to this action.

It also plays a minor role in bending the wrist backward.

Forearm Anatomy – Bones

Ulna

The ulna is one of the two long bones in the forearm. It is positioned on the inner side opposite the thumb, running from the elbow to the wrist. It is longer and thinner than the radius.

At the elbow, the ulna has a prominent bony projection called the olecranon process. It fits into the humerus to form a hinge joint and prevent the arm from overextending.

Towards the wrist, the ulna tapers and features a notch that accommodates the head of the radius. Additionally, there is a small bump called the ulnar tuberosity, where various muscles attach.

Radius

The radius is one of the bones in your forearm. It plays a critical role in moving your arm and wrist. It also supports important muscles, tendons, ligaments, and blood vessels.

If you break your radius, you might need surgery to fix it and physical therapy to regain strength and movement.

Because the radius is connected to many muscles and nerves, an injury to it can impact these as well.

Your radius has several important functions:

Helping your forearm and wrist move, bend, and rotate.
Supporting seven muscles.
Stabilizing your arm, wrist, and hand.

Forearm Anatomy – Joints

Elbow Joint

The elbow is the portion where the upper arm meets the forearm and forms a joint crucial for bending and straightening the arm. It comprises bones like the humerus, radius, and ulna.

This joint acts like a hinge, enabling us to move our forearm and hand towards and away from our body. Muscles like the biceps and triceps help with bending and straightening the arm.

In humans and other primates, this area is called the elbow. However, in other animals, it is referred to as the forelimb joint. The elbow’s range of motion goes from completely straight (0 degrees) to bent (150 degrees).

Overall, the function of the elbow is to position our hand accurately by adjusting the length of our upper limb.

Radioulnar Joints

The proximal radioulnar joint (PRUJ) is a synovial pivot joint in the forearm. It is the joint where the rounded head of the radius fits into the radial notch of the ulna.

This unique setup allows the radius to pivot around the ulna and enables the forearm to rotate. It is essential for twisting motions like turning your palm up or down.

The distal radioulnar joint (DRUJ) is another synovial pivot joint located at the opposite end of the radius and ulna. It features an articular disc that provides cushioning between the bones and is secured by the palmar and dorsal radioulnar ligaments.

The DRUJ also allows for rotation and movement of the forearm. It works in tandem with the PRUJ to support a wide range of hand and wrist activities.

Complete Guide to Forearm Anatomy: Parts, Names, Functions & Diagram