Innervation
The Opponens pollicis and Abductor pollicis brevis are normally innervated by the median nerve. The Flexor pollicis brevis can be innervated by the median or ulnar nerve. The adductor pollicis is typically innervated by the ulnar nerve. There are normal variations. In a Cannieu-Riche anastomasis, fibers from the deep palmar branch of the ulnar nerve innervate the opponens pollicis and/or abductor pollicis brevis. Regardless of their final innervation, the nerves that reach the thenar muscles arise from the C8 and T1 roots, pass through the lower trunk of the plexus, and then through the medial cord of the plexus.
The ulnar nerve is exclusively responsible for the innervations of the hypothenar eminence. Both nerves contribute to the innervations of the midpalmar group.
Flexor Pollicis Brevis (FPB) is typically an ulnar-innervated muscle. Due to a common interconnection between the Median and Ulnar nerves in the hand (Riche-Cannieu interconnection), the Median nerve may innervate the FPB in 35% of people. It is innervated by the Ulnar nerve in 50% of people and by both the Median and Ulnar nerves in 15%.
The muscles in this location are usually innervated by the recurrent branch of the median nerve. They all control movement of the thumb.
The innervation of these muscles by the median nerve is unusual, as most of the intrinsic muscles on the palm of the hand are supplied by the ulnar nerve. The lateral two lumbrical muscles are the other exception.
Read more about this topic: Thenar Eminence, Muscles