Victor Forge
The forearm is a complex part of the body, with many muscles to remember. There are several tricks to help you remember the names of the forearm muscles. One is to use mnemonics, such as All 3 deep flexors have a word starting with 'P', or SEPIA, which stands for Supinator, Extensor Pollicis (longus and brevis), (extensor) Indices, Abductor (pollicis longus). Another is to use the rule of three, for example, there are three muscles for wrist extension: ECRB, ECRL, and ECU. A final method is to associate a pose or action with a particular muscle, for example, the muscle that extends the little finger can be remembered by thinking of Dr. Evil's pose with his little finger at his mouth in the Austin Powers movies.
| Characteristics | Values |
|---|---|
| Number of forearm muscles | 12 (4 Superficial + 3 Mobile wad + 5 Deep) |
| Number of deep flexors with a word starting with "P" | 3 (flexor digitorum Profundus, flexor Pollicis longus, Pronator quadratus) |
| Extensors with a "P" in them | 5 (abductor Pollicis longus, extensor Pollicis brevis, extensor Pollicis longus, extensor indicis Proprius, PIN) |
| Rule of threes for extensors | 3 wrist extensors (ECRB, ECRL, ECU), 3 finger extensors (EDC, EIP, EDM), 3 muscles for the thumb (EPL, EPB, APL) |
| Rule of threes for flexors | 3 wrist flexors (FCR, PL, FCU), 3 finger flexors (FDS, FDP, FPL), 2 pronators (PT, PQ) |
| Nerve supply for flexor muscles | Anterior interosseous branch of median nerve (AIN) except Flexor digitorum profundus of ring and little fingers, which is supplied by the ulnar nerve |
| Brachioradialis | A paradoxical muscle; its origin and innervation are characteristic of an extensor muscle, but it is actually a strong flexor of the forearm |
| FCU | A large muscle with insertion onto 3 bones on the ulnar aspect of the wrist (pisiform, hamate hook, and 5th metacarpal base) |
| Posterior forearm muscles | SEPIA (Supinator, Extensor Pollicis (longus and brevis), (extensor) Indices, Abductor (pollicis longus) |
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What You'll Learn
- The Rule of Threes: 3 muscles for wrist extension, 3 muscles for finger extension, 3 muscles for the thumb
- Extensor muscles with a 'P' are deep extensors
- The mnemonic 'SEPIA' helps remember muscles in the deep posterior compartment
- The mnemonic 'PAD DAB' helps remember palmar and dorsal hand muscles
- Brachioradialis is a paradoxical muscle
The Rule of Threes: 3 muscles for wrist extension, 3 muscles for finger extension, 3 muscles for the thumb
The forearm muscles can be a tricky bunch to remember, but the Rule of Threes is a great way to keep them straight in your head.
Three muscles for wrist extension:
First up, we have the wrist extensors:
- ECRB (Extensor Carpi Radialis Brevis) – this inserts into the lateral dorsal surface of the third metacarpal bone and is responsible for extending and abducting the wrist.
- ECRL (Extensor Carpi Radialis Longus) – this inserts into the dorsal surface of the second metacarpal bone and also helps to extend and abduct the wrist.
- ECU (Extensor Carpi Ulnaris) – this is supplied by the ulnar artery and assists in wrist extension.
Three muscles for finger extension:
Now, on to the finger extensors:
- EDC (Extensor Digitorum Communis) – this is one of the main extensors responsible for extending the fingers.
- EIP (Extensor Indicis Proprius) – this is the extensor for the index finger.
- EDM (Extensor Digitorum Minimi) – this is the extensor for the little finger, allowing for more independent movement of this finger.
Three muscles for the thumb:
Finally, we have the thumb muscles:
- EPL (Extensor Pollicis Longus) – this inserts on the base of the distal phalanx of the thumb and works with the EPB to extend the distal phalanx.
- EPB (Extensor Pollicis Brevis) – this inserts into the base of the thumb to extend and abduct the thumb at the MCP joints.
- APL (Abductor Pollicis Longus) – this is supplied by the posterior interosseous artery, a branch of the ulnar artery, and assists in thumb movement.
So there you have it, the Rule of Threes for the forearm muscles! A handy way to keep all those muscles straight in your head.
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Extensor muscles with a 'P' are deep extensors
When it comes to the forearm muscles, there are several tricks and mnemonics to help you remember the various muscles and their functions.
One such mnemonic relates to the deep extensors: "Extensor muscles with a P are deep extensors". This refers to the muscles with names containing the letter 'P':
- Abductor Pollicis Longus (APL)
- Extensor Pollicis Brevis (EPB)
- Extensor Pollicis Longus (EPL)
- Extensor Indicis Proprius (EIP)
These muscles are located in the deep compartment of the posterior forearm, with the exception of the supinator, which lies in the floor of the cubital fossa. They act on the thumb and index finger, and are innervated by the radial nerve.
Another helpful relation to keep in mind is the rule of threes for extensors:
- Three muscles for wrist extension: ECRB, ECRL, and ECU
- Three muscles for finger extension: EDC, EIP, and EDM
- Three muscles for the thumb: EPL, EPB, and APL
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The mnemonic 'SEPIA' helps remember muscles in the deep posterior compartment
The forearm has 12 muscles in total, which can be divided into 4 superficial, 3 mobile wad, and 5 deep muscles. The mnemonic SEPIA helps remember the muscles in the deep posterior compartment of the forearm:
Supinator: The Supinator, like the Pronator Teres, originates from the epicondyle (the lateral epicondyle in the Supinator, and the medial epicondyle in the Pronator Teres).
Extensor Carpi Radialis Longus (ECRL): The ECRL is part of the Mobile Wad of Henry. It can be felt between the thumb and index finger just distal to the lateral epicondyle.
Pronator Quadratus: All three deep flexors have a word starting with "P". The other two are the Flexor Digitorum Profundus and the Flexor Pollicis Longus.
Indicis Proprius (EIP): The EIP is one of the three muscles for finger extension, the other two being the Extensor Digitorum Communis (EDC) and the Extensor Digitorum Minimi (EDM).
Abductor Pollicis Longus (APL): The APL is one of the three muscles for thumb extension, the other two being the Extensor Pollicis Brevis (EPB) and the Extensor Pollicis Longus (EPL).
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The mnemonic 'PAD DAB' helps remember palmar and dorsal hand muscles
The human hand is a complex structure, with many muscles, bones, and ligaments working together to allow for a wide range of movements. It can be challenging to remember the names and functions of all the muscles in the hand and forearm, but thankfully, there are some useful mnemonics to help. One such mnemonic is PAD DAB, which helps us remember the palmar and dorsal hand muscles.
The "P" in PAD stands for the palmar interossei. The palmar interossei are unipennate muscles that adduct the fingers, bringing them towards the midline. The "A" represents adduction, the action of pulling something towards the midline or axis of the body. The "D" in DAB stands for the dorsal interossei. These muscles are bipennate and permit the abduction of the phalanges, moving them away from the midline. The "AB" in DAB stands for abduction, the opposite of adduction, which is the action of moving something away from the midline or axis of the body.
The intrinsic muscles of the hand can also be remembered with the mnemonic "PAd DAb FOAL/LOAF". This helps us remember the muscles in their relative palmar anatomical position from lateral to medial. The letters stand for: Abductor Pollicis Brevis, Flexor Pollicis Brevis, Opponens Pollicis, Adductor Pollicis, Opponens Digiti Minimi, Flexor Digiti Minimi, and Abductor Digiti Minimi.
The hand and forearm muscles can also be grouped by anatomy and function. The extrinsic muscles of the hand originate in the forearm and are located on the anterior and posterior aspects of the forearm, with flexors positioned anteriorly and extensors posteriorly. The anterior forearm muscles include the flexor carpi radialis, palmaris longus, and flexor carpi ulnaris, which are all innervated by the median nerve, except for the flexor carpi ulnaris, which is innervated by the ulnar nerve. The posterior forearm muscles include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, and extensor digiti minimi, which are all innervated by the radial nerve.
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Brachioradialis is a paradoxical muscle
The forearm has 8 muscles in total, consisting of 4 superficial muscles, 1 intermediate muscle, and 3 deep muscles. One of the superficial muscles is the brachioradialis, which is considered a paradoxical muscle.
The brachioradialis is a fusiform muscle located in the lateral part of the posterior forearm. It is the most superficial muscle on the radial side of the forearm. It forms the lateral side of the cubital fossa and is often fused proximally with the brachialis. The muscle fibres course inferiorly down the radial part of the anterior forearm, forming a thick tendon in the middle of the forearm. This tendon then continues across the remainder of the forearm, inserting near the wrist, just proximal to the styloid process of the radius. The muscle is also known as the supinator longus.
The brachioradialis is a paradoxical muscle because, despite being anatomically part of the posterior forearm muscles, which are known to be forearm extensors, its fibre orientation enables it to flex the forearm. This is especially true when the forearm is semi-pronated, with the palm perpendicular to the ground. In this position, the brachioradialis is a powerful forearm flexor, working in synergy with the biceps brachii and brachialis. When the forearm is pronated, the brachioradialis tends to supinate as it flexes, and when the forearm is supinated, it tends to pronate as it flexes.
The brachioradialis is one of the first muscles to recover innervation following an injury to the radial nerve in the radial groove, making it important to check for radial nerve recovery. To stretch the brachioradialis muscle, extend the elbow, interlace the fingers of both hands, and use the other hand to flex the wrist of the affected arm and inwardly rotate the arm so the hand is facing outwards.
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Frequently asked questions
A good way to remember the muscles of the posterior forearm is to use the acronym SEPIA: Supinator, Extensor Pollicis (longus and brevis), (extensor) Indices, Abductor (pollicis longus).
There are 12 muscles in the forearm (4 superficial, 3 mobile wad, and 5 deep).
All the flexor muscles of the forearm are supplied by the median nerve, except for one and a half. A good way to remember this is with the acronym PAD DAB: palmar hand muscles adduct, dorsal hand muscles abduct.
All the extensor muscles of the forearm are supplied by the radial nerve. A good way to remember the names of the extensor muscles is to use the Rule of 3: 3 muscles for wrist extension, 3 muscles for finger extension, and 3 muscles for the thumb.
The components of the Mobile Wad of Henry are Brachioradialis, ECRL, and ECRB. A good way to remember this is that Brachioradialis is a paradoxical muscle. Its origin and innervation are characteristic of an extensor muscle, but it is actually a strong flexor of the forearm.
