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Mound at the base of the thumb formed by the intrinsic group of muscles
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
.
[1]
The skin overlying this region is the area stimulated when trying to elicit a
palmomental reflex
. The word thenar comes from
Ancient Greek
θ?ναρ
(thenar)
'palm of the hand'.
[2]
Structure
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The following three muscles are considered part of the thenar eminence:
[3]
Another muscle that controls movement of the thumb is
adductor pollicis
. 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.
[4]
Nerve supply
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The opponens pollicis and abductor pollicis brevis are normally innervated by the
median nerve
.
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
. Both nerves contribute to the innervations of the
midpalmar group
.
[5]
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.
Additional images
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See also
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References
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External links
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