Athena Vale
The human thumb's ability to touch the tips of the other fingers is a complex movement called thumb opposition. This is a combination of flexion, adduction, and medial rotation at the first carpometacarpal joint. Opposition of the thumb is a fundamental function of the human hand, allowing for precision and dexterity when performing tasks that require fine motor control. The muscles that create this movement are the thenar eminence muscles, which are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
| Characteristics | Values |
|---|---|
| Opposition of the thumb | The ability to bring the pad of the thumb into contact with the pads of the fingers on the same hand |
| Muscles involved | Opponens pollicis, adductor pollicis, abductor pollicis brevis, flexor pollicis brevis, extensor pollicis brevis, abductor pollicis longus, flexor digitorum superficialis, flexor digitorum profundus, and lumbrical muscles |
| Function | Allows the hand to cup objects and perform a pincher grip |
| Innervation | Recurrent branch of the median nerve (C8 and T1 roots) and occasionally the ulnar nerve |
| Blood supply | Superficial palmar arch |
| Anatomical snuff box | Formed by the tendons of the extensor pollicis longus and extensor pollicis brevis |
| Thenar eminence | Group of four muscles on the palm at the base of the thumb, including opponens pollicis, adductor pollicis, abductor pollicis brevis, and flexor pollicis brevis |
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What You'll Learn
The opponens pollicis muscle
The nerve innervation of the opponens pollicis muscle may come from the ulnar nerve in some cases, with the ulnar nerve made up of spinal roots C8 and T1. However, the muscle is typically innervated by the recurrent branch of the median nerve. The opponens pollicis receives its blood supply from the superficial palmar arch.
Understanding the anatomy of the thumb is important for nursing students, as it plays a critical role in providing client care. The opposition of the thumb is a seemingly simple action that sets humans apart in the animal kingdom, allowing for precision and dexterity when performing tasks requiring fine motor control.
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The abductor pollicis brevis
The main function of the abductor pollicis brevis is the abduction of the thumb at the carpometacarpal joint. It is the most lateral and the most superficial of the thenar muscles, located underneath the skin. It runs from the scaphoid and trapezium carpal bones, and from the flexor retinaculum to the proximal phalanx of the thumb. The majority of muscle fibres originate from the broadest origin area located on the flexor retinaculum. Two smaller origins are located on carpal bones; the first is found on the tubercle of the scaphoid, while the second is on the tubercle of the trapezium bone. After originating from these locations, the muscle fibres form a single muscle belly that runs distally and radially (laterally) towards the thumb.
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The flexor pollicis brevis
The muscle bellies of the superficial and deep heads of the flexor pollicis brevis travel inferiorly and converge to a single tendon. This tendon contains a sesamoid bone and inserts onto the lateral aspect of the base of the proximal phalanx of the thumb. The flexor pollicis brevis receives its blood supply from the superficial palmar branches of the radial artery and the princeps pollicis artery. The superficial head is innervated by the median nerve, while the deep head is innervated by the ulnar nerve (C8-T1). Due to a common interconnection between the median and ulnar nerves in the hand (Riche-Cannieu interconnection), the median nerve may innervate the flexor pollicis brevis in 35% of people.
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The adductor pollicis
The main function of the adductor pollicis is the adduction of the thumb, which is the movement of the thumb towards the index finger from an abducted position. This movement is essential for functions that require pinching and gripping. The adductor pollicis also aids in the later stages of opposition of the thumb, which is a combination of adduction, medial rotation, flexion, and adduction of the thumb so that it can touch each fingertip of the same hand.
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The first dorsal interosseous muscle
The main function of the first dorsal interosseous muscle is to abduct the index, middle, and ring fingers away from the hand's midline (or the ray of the middle finger). This muscle also assists in flexion at the metacarpophalangeal joints and extension at the interphalangeal joints of the index, middle, and ring fingers. The first dorsal interosseous muscle also assists in adduction of the thumb and can rotate the index finger slightly at the metacarpophalangeal joint.
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Frequently asked questions
Thumb opposition is the ability to bring the pad of the thumb into contact with the pads of the fingers on the same hand.
The opponens pollicis muscle is the main muscle involved in thumb opposition. It originates from the flexor retinaculum of the hand and the tubercle of the trapezium, and is inserted into the whole length of the metacarpal bone of the thumb on its radial side. The abductor pollicis brevis, flexor pollicis brevis, and first dorsal interosseous muscles also influence thumb movement.
The opponens pollicis muscle allows the thumb to touch the tips of the other fingers, enabling the hand to cup objects and perform a pincher grip.
