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The muscles of the thumb are nine skeletal muscles located in the hand and forearm. The muscles responsible for thumb flexion include the flexor pollicis longus, flexor pollicis brevis, and opponens pollicis. The flexor pollicis longus is a deep forearm flexor that originates from the forearm and inserts into the base of the distal phalanx of the thumb. The flexor pollicis brevis is a two-headed muscle that flexes, abducts, and adducts the thumb. The opponens pollicis is a small, triangular muscle that lies within the thenar eminence and flexes the thumb's metacarpal bone.
| Characteristics | Values |
|---|---|
| Definition | A muscle that contracts to perform flexion, a movement that decreases the angle between the bones converging at a joint. |
| Flexion | Decreasing the angle between two bones (bending). |
| Extension | Increasing the angle between two bones (straightening a bend). |
| Elbow Flexion | The biceps brachii, brachialis, and brachioradialis flex the elbow. |
| Knee Flexion | The hamstrings, gracilis, and sartorius flex and internally rotate the knee. |
| Forearm Flexion | The flexor group of the forearm flexes the wrist and the fingers. |
| Benefits | Muscle flexing can improve physical and mental health, including treating headaches, high blood pressure, digestive problems, anxiety, insomnia, and migraines. |
| Isometrics | Exercises such as planks and wall sits strengthen muscles by keeping them still in the face of resistance. |
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What You'll Learn
Flexor Pollicis Longus
The flexor pollicis longus (FPL) is a long muscle in the forearm and hand that is responsible for flexing the thumb. It is one of the deep flexors of the forearm, alongside the flexor digitorum profundus and pronator quadratus.
The flexor pollicis longus arises from a broad area on the radius and adjacent structures, such as the interosseous membrane and the lateral border of the coronoid process of the ulna. It then crosses three joints and inserts onto the distal phalanx of the thumb. This muscle is unique to humans, being either rudimentary or absent in other primates.
The main function of the flexor pollicis longus is to flex the thumb at the interphalangeal joint, which is essential for gripping. It is the only muscle that flexes this joint. The muscle also assists in flexing the wrist and is considered an extrinsic muscle of the hand due to its function in thumb movement.
The flexor pollicis longus receives dual blood supply. Its medial part is supplied by the anterior interosseous artery, a branch of the ulnar artery, while its lateral part receives blood from the radial artery. Additionally, the muscle is innervated by the anterior interosseous nerve, a branch of the median nerve.
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Flexor Pollicis Brevis
The flexor pollicis brevis (FPB) is a small, short, and broad intrinsic muscle of the hand. It is present on the radial border of the palm and is part of the thenar muscles, which act on the thumb. The FPB is composed of superficial and deep heads, which originate from different bones and ligaments in the hand. The superficial head is commonly blended with the opponens pollicis muscle, while the deep head can vary in size or even be absent.
The FPB flexes the thumb at the metacarpophalangeal joint and also produces flexion and medial rotation of the first metacarpal bone at the carpometacarpal joint. This action aids in the opposition of the thumb, allowing us to manipulate objects and create tools. The FPB receives its blood supply from branches of the radial artery, including the superficial palmar artery and branches of the princeps pollicis and radialis indicis arteries.
The innervation of the FPB varies, but it typically receives dual innervation from the median and ulnar nerves. The superficial head is usually innervated by the median nerve, while the deep head receives innervation from the deep branch of the ulnar nerve. However, in some cases, the superficial head can also receive innervation from the ulnar nerve, and the deep head can be absent or receive innervation from the recurrent branch of the median nerve.
The FPB can be activated by placing the palm facing up and the wrist in a neutral position. The thumb is then brought to touch the base of the little finger, and pressure is applied. This exercise helps to isolate and strengthen the FPB muscle.
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Opponens Pollicis
The opponens pollicis is a small, triangular, intrinsic muscle of the hand. It is one of the three thenar muscles, along with the abductor pollicis and flexor pollicis brevis. The thenar muscles are located on the radial (lateral) aspect of the hand, where they form an elevation named the thenar eminence.
The opponens pollicis muscle originates from the flexor retinaculum of the hand and the tubercle of the trapezium bone. It passes downward and laterally, inserting into the whole length of the first metacarpal bone of the thumb on its radial side. This muscle is relatively short and slender and lies deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis.
The main function of the opponens pollicis muscle is to draw the thumb across the hand to touch the tips of the other digits. When the muscle contracts, it pulls the thumb medially towards the fingers, allowing the hand to cup objects. This movement is called the opposition of the thumb and takes place at the first carpometacarpal joint. The opposition of the thumb is a combination of actions, including flexion, internal rotation, and palmar abduction of the thumb, which together enable a pinch grip.
The opponens pollicis muscle is innervated by the recurrent branch of the median nerve (C8 and T1 roots) and, in some individuals, by the ulnar nerve. The blood supply to this muscle comes primarily from the superficial palmar arch, which arises from the radial artery. Additional blood supply is provided by several other arteries, including the deep palmar arch formed by the ulnar artery.
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Abductor Pollicis Brevis
The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb. It is a flat, thin muscle located just under the skin. It is a thenar muscle, contributing to the bulk of the palm's thenar eminence. The thenar muscles are a group of three muscles: abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. They form an elevation on the radial (lateral) aspect of the palm, named the thenar eminence.
The abductor pollicis brevis is inserted by a thin, flat tendon into the lateral side of the base of the first phalanx of the thumb, and the capsule of the metacarpophalangeal joint. The main action of this muscle is the abduction of the thumb at the carpometacarpal and metacarpophalangeal joints. This action happens in synergy with the abductor pollicis longus muscle. Abductor pollicis brevis also facilitates the movement of the thumb towards the fingertips in the carpometacarpal joint (opposition) and flexion in the metacarpophalangeal joint.
The abductor pollicis brevis is supplied by the recurrent branch of the median nerve (Roots C8-T1). It is commonly used in neuroscience studies related to muscle responses during various surgical procedures.
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Adductor Pollicis
The adductor pollicis is an intrinsic muscle of the hand, lying deep in the thenar muscles. It is the only muscle of the adductor compartment of the hand and does not form part of the thenar muscle group, which includes the abductor pollicis, flexor pollicis brevis, and opponens pollicis. The adductor pollicis is the most powerful of the intrinsic muscles of the hand.
The adductor pollicis has two heads: the oblique head and the transverse head. The oblique head originates from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the flexor carpi radialis. The transverse head, on the other hand, originates from the palmar base of the third metacarpal bone. The two heads converge into a single muscle belly as the fibres run laterally towards the thumb, forming the tendon of the adductor pollicis, which often contains a sesamoid bone.
The main function of the adductor pollicis is to adduct the thumb, which refers to bringing the thumb into a position of opposition at the centre of the palm or alongside the palm and index finger. This movement is critical for hand dexterity, as it is essential for functions that require pinching and gripping. The adductor pollicis also aids in the later stages of opposition of the thumb, allowing it to touch each fingertip of the same hand.
The adductor pollicis is innervated by the deep branch of the ulnar nerve (C8-T1). The deep palmar arterial arch, formed by the anastomosis of the radial artery and the deep palmar branch of the ulnar artery, provides vascularization to the muscle. The radial artery passes between the two heads of the adductor pollicis, forming the deep palmar arch.
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Frequently asked questions
The biceps brachii, brachialis, and brachioradialis are examples of flexor muscles in the human body. These muscles are responsible for flexing the elbow. The gracilis and sartorius muscles are also flexors, and they play a role in flexing and internally rotating the knee.
Flexing muscles is not just about displaying physical strength or building muscle mass. It can also have significant benefits for both physical and mental health. Flexing muscles can help treat headaches, high blood pressure, digestive issues, and insomnia. It can also be used as a relaxation technique to manage anxiety and depression.
Muscle flexing, also known as muscle contraction, involves creating tension that temporarily contracts the muscle fibres. Isometric exercises, such as planks and wall sits, strengthen muscles by keeping them still while they face resistance. These exercises are particularly useful for individuals with injuries that make traditional movements painful.
