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The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of
muscles of the thumb The muscles of the thumb are nine skeletal muscles located in the hand and forearm. The muscles allow for flexion, extension, adduction, abduction and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: The ext ...
. The skin overlying this region is the area stimulated when trying to elicit a
palmomental reflex The palmomental reflex (PMR) or Marinesco-Radovici Sign or Kinn reflex or Marinesco Reflex is a primitive reflex consisting of a twitch of the chin muscle elicited by stroking a specific part of the palm. It is present in infancy and disappears as t ...
. The word thenar comes .θέναρ
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Structure

The following three muscles are considered part of the thenar eminence: * Abductor pollicis brevis abducts the thumb. This muscle is the most
superficial Superficial may refer to: *Superficial anatomy, is the study of the external features of the body *Superficiality, the discourses in philosophy regarding social relation *Superficial charm, the tendency to be smooth, engaging, charming, slick and ...
of the thenar group. *
Flexor pollicis brevis 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. Origin and insertion The muscle's superficial head arises from the distal edge of the f ...
, which lies next to the abductor, will flex the thumb, curling it up in the palm. (The
Flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is un ...
, which is inserted into the distal phalanx of the thumb, is not considered part of the thenar eminence.) * 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 human hand dexterity comes from this action. Another muscle that controls movement of the thumb is
adductor pollicis In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment benea ...
. It lies deeper and more distal to flexor pollicis brevis. Despite the name, adductor pollicis is chiefly responsible for rotation and opposition. This muscle is not in the thenar group of muscles, and is supplied by the ulnar nerve instead.


Nerve supply

The opponens pollicis and abductor pollicis brevis are normally innervated by the
median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...
. The flexor pollicis brevis has two heads a superficial and a deep. The 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 adductor pollicis is typically innervated by the ulnar nerve. There are normal variations. In a Cannieu-Riche anastomosis, 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 The hypothenar muscles are a group of three muscles of the palm that control the motion of the little finger. The three muscles are: * Abductor digiti minimi * Flexor digiti minimi brevis * Opponens digiti minimi Structure The muscles of hypot ...
. Both nerves contribute to the innervations of the midpalmar group. Print. The muscles in this location are usually innervated by the
recurrent branch of the median nerve The recurrent branch of the median nerve is the branch of the median nerve which supplies the thenar muscles. It is also occasionally referred to as the thenar branch of the median nerve, or the thenar muscular branch of the median nerve. Struct ...
. 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.


Additional images

File:Slide8PPP.JPG, Thenar eminence File:Hand dissection 5.jpg, Carpal tunnel and thenar and hypothenar eminences File:Thenar eminence comparison anterior.jpg, Comparison, anterior File:Thenar eminence comparison posterior.jpg, Comparison, posterior File:Thenar eminence comparison thumbs.jpg, Comparison facing thumbs


See also

*
Hypothenar eminence The hypothenar muscles are a group of three muscles of the palm that control the motion of the little finger. The three muscles are: * Abductor digiti minimi * Flexor digiti minimi brevis * Opponens digiti minimi Structure The muscles of hypot ...


References


External links

* {{DEFAULTSORT:Thenar Eminence Hand Muscles of the upper limb