The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three
thenar muscles. It lies deep to the
abductor pollicis brevis and lateral to the
flexor pollicis brevis.
Structure
The opponens pollicis muscle is one of the three
thenar muscles. It originates from the
flexor retinaculum of the hand
The flexor retinaculum (transverse carpal ligament, or anterior annular ligament) is a fibrous band on the palmar side of the hand near the wrist. It arches over the carpal bones of the hands, covering them and forming the carpal tunnel.
Struc ...
and the tubercle of the
trapezium. It passes downward and laterally, and is inserted into the whole length of the
metacarpal bone of the thumb on its radial side.
Innervation
Like the other thenar muscles, the opponens pollicis is innervated by the
recurrent branch of the median nerve. In 20% of the population, opponens pollicis is innervated by the
ulnar nerve.
Blood supply
The opponens pollicis receives its blood supply from the
superficial palmar arch
The superficial palmar arch is formed predominantly by the ulnar artery, with a contribution from the superficial palmar branch of the radial artery. However, in some individuals the contribution from the radial artery might be absent, and instea ...
.
Function
''Opposition of the thumb'' is a combination of actions that allows the tip of the thumb to touch the tips of other fingers. The part of apposition that this muscle is responsible for is the flexion of the thumb's metacarpal at the first
carpometacarpal joint
The carpometacarpal (CMC) joints are five joints in the wrist that articulate the distal row of carpal bones and the proximal bases of the five metacarpal bones.
The CMC joint of the thumb or the first CMC joint, also known as the trapeziometa ...
. This specific action cups the palm. Many texts, for simplicity, use the term ''opposition'' to represent this component of true apposition. In order to truly appose the thumb, the actions of a number of other muscles are needed at the thumb's
metacarpophalangeal joint
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow c ...
. Note that the two opponens muscles (opponens pollicis and opponens digiti minimi) are named so because they oppose each other, but their actions appose the bones.
Additional images
Image:Gray426.png, The muscles of the thumb
Image:Musculusopponenspollicis.png, The muscles of the right hand. Palmar surface.
File:Dissection of hand.jpg, Opponens pollicis muscle
Image:Gray219.png, Bones of the left hand. Volar surface.
Image:Gray422.png, Transverse section across the wrist and digits.
File:Slide1MAI.JPG, Muscles of hand. Cross section.
References
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Muscles of the upper limb