Thenar eminence
| Thenar eminence | |
|---|---|
 The mucous sheaths of the tendons on the anterior surface of the wrist and digits. | |
 Transverse section across the wrist and digits. (Muscles of thumb labeled at upper left.) | |
| Details | |
| Nerve | median nerve |
| Actions | control movement of the thumb |
| Identifiers | |
| Latin | eminentia thenaris |
| TA98 | A01.2.07.023 |
| TA2 | 306 |
| FMA | 61520 |
| Anatomical terms of muscle | |
The thenar eminence is the body of muscle on the palm of the human hand just beneath the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex.
Muscles
The muscles in this location are usually innervated by the recurrent branch of the median nerve. They all control movement of the thumb.
The following three muscles are considered part of the thenar eminence:[1]
- Abductor pollicis brevis abducts the thumb. This muscle is the most proximal of the thenar group.
- Flexor pollicis brevis, which lies next to the abductor, will flex the thumb, curling it up in the palm.
- Opponens pollicis lies deep to abductor pollicis brevis. As its name suggests it opposes the thumb, bringing it against the fingers. This is a very important movement, as most of our dexterity comes from this action.
The muscles of hand can be remembered using the mnemonic, "A OF A OF A" for, Abductor pollicis longus, Opponens pollicis, Flexor pollicis brevis, Adductor pollicis (thenar muslces) and Opponens digiti minimi, Flexor digiti minimi, Abductor digiti minimi (Hypothenar muscles). [2]
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.
Another muscle that controls movement of the thumb is adductor pollicis. It lies deeper and more distal to flexor pollicis brevis. Despite its name, its main action is mainly rotation and opposition. It is not in the thenar group of muscles, so is supplied by the ulnar nerve.[3]
Nerve 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 lateral 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.
Article text.[4]
Mnemonic
A good way to remember what muscles are in the thenar eminence is "OAF"; oafs have big thenar eminences. 'O' = opponens, 'A' = abductor, 'F' = flexor. There is only one opponens. The other two muscles each have a long partner and thus are called "brevis."
Meat-LOAF: the "M" in the word "Meat" helps you remember that the LOAF muscles of the hand are innervated by the Median Nerve
ABOF (pronounced "above") the Law muscles. The law states muscles of the hand are supplied by ulnar nerve. However, ABOF the Law muscles are supplied by MEDIAN nerve. 'AB' = abductor, 'O' = Opponens, 'F' = Flexor, Law 'L' = Lateral Lumbricals (2).
MAINTAINER --Main(Median nerve) --Tainer(thenar muscles)
See also
Additional images
References
- ^ "Intrinsic Muscles of the Hand - Wheeless' Textbook of Orthopaedics". Retrieved 2008-01-16.
- ^ "Medical mnemonics". LifeHugger. Retrieved 2009-12-19.
- ^ "Applied MSK anatomy of the hand". Retrieved 2008-01-16.
- ^ [Van De Graaff, Kent M. Human Anatomy. 3rd ed. Dubuque: Wm C Brown, 1992. Print.],additional text.
External links
- lesson5mus&tendonsofhand at The Anatomy Lesson by Wesley Norman (Georgetown University)