Corpus: Flexor pollicis longus muscle
from latin: pollex - thumb
Definition
The flexor pollicis longus muscle, abbreviated as FPL, is a muscle that belongs to the deep layer of the flexor muscles of the forearm.
Anatomy
Origin
The muscle originates from the anterior surface of the radius and the palmar side of the interosseous membrane of the forearm. The origin surface may also extend to parts of the proximal ulna.
Insertion
The muscle fibers end in a flat tendon that runs beneath the flexor retinaculum through the carpal tunnel. It passes between the superficial head of the flexor pollicis brevis muscle and the oblique head of the adductor pollicis muscle to the thumb. The insertion point is the distal phalanx, i.e., the end segment of the thumb (Digitus I).
Variation
In about 40 % of people, an additional humeral head can be found, originating from the medial epicondyle of the humerus. In such cases, there is also a tendinous connection with the humeral head of the flexor digitorum superficialis muscle.
Innervation
The innervation of the flexor pollicis longus muscle is provided by the median nerve or the anterior interosseous nerve from the brachial plexus (segments: C6 - C8).
Function
The flexor pollicis longus muscle is responsible for the flexion (bending) and opposition movement of the thumb. Furthermore, it supports flexion at the wrist.