Flexor pollicis brevis muscle

Flexor pollicis brevis muscle
Flexor pollicis brevis muscle
	The muscles of the left hand. Palmar surface. (Flexor pollicis brevis visible at center right, near thumb.)
Details
Origin	trapezoid, flexor retinaculum
Insertion	thumb, proximal phalanx
Nerve	median nerve, deep branch of ulnar nerve (medial head)
Actions	Flexes the thumb at the first metacarpophalangeal joint
Antagonist	Extensor pollicis longus muscle, Extensor pollicis brevis muscle
Identifiers
Latin	musculus flexor pollicis brevis
TA98	A04.6.02.055
TA2	2522
FMA	37378
	Anatomical terms of muscle [edit on Wikidata]

The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part.

The muscle

The muscle's superficial part arises from the distal edge of the flexor retinaculum of the hand and the tubercle of the trapezium, a bone in the wrist. It passes along the radial side of the tendon of the flexor pollicis longus, and, becoming tendonous, is inserted into the radial side of the base of the proximal phalanx of the thumb; in its tendon of insertion there is a sesamoid bone.

The deeper (and medial) portion of the muscle is very small, and arises from the ulnar side of the first metacarpal bone between the oblique part of the adductor pollicis and the lateral head of the first dorsal interosseous muscle, and is inserted into the ulnar side of the base of the first phalanx with the adductor pollicis.

The deep (medial) part of the flexor brevis pollicis is sometimes described as the first palmar interosseous muscle. When this muscle is included, the total number of palmar interossei is four. Otherwise, there are only three palmar interossei.

Innervation

The flexor pollicis brevis is mostly innervated by the recurrent branch of the median nerve (C8, T1). The deep part is often innervated by the deep branch of the ulnar nerve.