Muscle on the back of the upper arm
The
triceps
, or
triceps brachii
(
Latin
for "three-headed muscle of the arm"), is a large
muscle
on the
back
of the
upper limb
of many
vertebrates
. It consists of 3 parts: the medial, lateral, and long head.
[1]
It is the muscle principally responsible for
extension
of the
elbow joint
(straightening of the arm).
Structure
[
edit
]
The long head arises from the
infraglenoid tubercle
of the
scapula
. It extends distally anterior to the
teres minor
and posterior to the
teres major
.
[2]
The medial head arises proximally in the
humerus
, just inferior to the
groove of the radial nerve
; from the dorsal (back) surface of the humerus; from the
medial intermuscular septum
; and its distal part also arises from the
lateral intermuscular septum
. The medial head is mostly covered by the lateral and long heads, and is only visible distally on the humerus.
[2]
The lateral head arises from the dorsal surface of the humerus, lateral and proximal to the
groove of the radial nerve
, from the
greater tubercle
down to the region of the lateral intermuscular septum.
[2]
Each of the three fascicles has its own motorneuron subnucleus in the motor column in the spinal cord. The medial head is formed predominantly by small type I fibers and motor units, the lateral head of large type IIb fibers and motor units and the long head of a mixture of fiber types and motor units.
[3]
[4]
It has been suggested that each fascicle "may be considered an independent muscle with specific functional roles."
[3]
The fibers converge to a single tendon to insert onto the
olecranon
process of the
ulna
(though some research indicates that there may be more than one tendon)
[5]
and to the posterior wall of the capsule of the elbow joint where
bursae
(cushion sacks) are often found. Parts of the common tendon radiates into the
fascia
of the forearm and can almost cover the
anconeus muscle
.
[2]
Innervation
[
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]
All three heads of the triceps brachii are classically believed to be innervated by the
radial nerve
.
[6]
However, more recent studies observed that in around 14% of individuals the long head of the triceps brachii was innervated by the
axillary nerve
, and in 3% it received dual innervation from both the radial nerve and axillary nerve.
[7]
[8]
Variation
[
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]
A
tendinous
arch is frequently the origin of the long head and the tendon of
latissimus dorsi
. In rare cases, the long head can originate from the lateral margin of the scapula and from the capsule of the shoulder joint.
[2]
Function
[
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]
The triceps is an
extensor
muscle of the elbow joint and an antagonist of the
biceps
and
brachialis
muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, e.g., when writing. It has been suggested that the long head fascicle is employed when sustained force generation is demanded, or when there is a need for a synergistic control of the shoulder and elbow or both. The lateral head is used for movements requiring occasional high-intensity force, while the medial fascicle enables more precise, low-force movements.
[3]
With its origin on the scapula, the long head also acts on the shoulder joint and is also involved in
retroversion
and
adduction
of the arm. It helps stabilise the shoulder joint at the top of the
humerus
.
[2]
Training
[
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]
The triceps can be worked through either isolation or compound elbow extension movements and can contract statically to keep the arm straightened against resistance.
Isolation movements include cable push-downs,
lying triceps extensions
and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the
push up
,
bench press
,
close grip bench press
(flat, incline or decline),
military press
and
dips
. A closer grip targets the triceps more than wider grip movements.
Static contraction movements include pullovers, straight-arm pulldowns and bent-over lateral raises, which are also used to build the deltoids and
latissimus dorsi
.
Ruptures of the triceps muscle are rare, and typically only occur in anabolic steroid users.
[9]
Clinical significance
[
edit
]
| This section
needs expansion
. You can help by
adding to it
.
(
February 2014
)
|
The
triceps reflex
, elicited by hitting the triceps, is often used to test the function of the nerves of the arm. This tests spinal nerves C6 and C7, predominantly C7.
[10]
History
[
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]
Etymology
[
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]
It is sometimes called a three-headed muscle (Latin literally three-headed,
tri
- three, and
ceps
, from
caput
- head), because there are three bundles of muscles, each of different origins, joining at the elbow. Though a similarly named muscle, the
triceps surae
, is found on the
lower leg
, the triceps brachii is commonly called the triceps.
Historically, the plural form of
triceps
was
tricipites
, a form not in general use today; instead,
triceps
is both
singular
and
plural
(i.e., when referring to both arms).
Other animals
[
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]
In the horse, 84%, 15%, and 3% of the total triceps muscle weight correspond to the long, lateral and medial heads, respectively.
[11]
Many mammals, such as dogs, cattle, and pigs, have a fourth head, the accessory head. It lies between the lateral and medial heads.
[3]
In humans, the
anconeus
is sometimes loosely called "the fourth head of the triceps brachii".
Additional images
[
edit
]
-
Animation. Close up.
Long head.
Lateral head.
Medial head.
-
Still image. Anterior view.
-
Muscles on the dorsum of the scapula, and the triceps brachii.
-
Movement of biceps and triceps when arm is flexing
See also
[
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]
References
[
edit
]
- ^
Casadei, Kyle; Kiel, John; Freidl, Michael (2020).
"Triceps Tendon Injuries"
.
Current Sports Medicine Reports
.
19
(9): 367?372.
doi
:
10.1249/JSR.0000000000000749
.
PMID
32925376
.
S2CID
221567814
.
- ^
a
b
c
d
e
f
Platzer W (2004).
Color Atlas of Human Anatomy, Vol. 1: Locomotor System
(5th ed.).
Thieme
.
ISBN
3-13-533305-1
.
- ^
a
b
c
d
Lucas-Osma AM, Collazos-Castro JE (September 2009). "Compartmentalization in the triceps brachii motoneuron nucleus and its relation to muscle architecture".
The Journal of Comparative Neurology
.
516
(3): 226?39.
doi
:
10.1002/cne.22123
.
PMID
19598170
.
S2CID
25918513
.
- ^
See the article "
Skeletal striated muscle
" for a discussion of type I and type II muscle fibers.
- ^
Madsen M, Marx RG, Millett PJ, Rodeo SA, Sperling JW, Warren RF (November 2006). "Surgical anatomy of the triceps brachii tendon: anatomical study and clinical correlation".
The American Journal of Sports Medicine
.
34
(11): 1839?43.
doi
:
10.1177/0363546506288752
.
PMID
16735585
.
S2CID
11671310
.
- ^
Bekler H, Wolfe VM, Rosenwasser MP (January 2009).
"A cadaveric study of ulnar nerve innervation of the medial head of triceps brachii"
.
Clinical Orthopaedics and Related Research
.
467
(1): 235?8.
doi
:
10.1007/s11999-008-0535-6
.
PMC
2600974
.
PMID
18850256
.
- ^
Wade, Michael D.; McDowell, Arthur R.; Ziermann, Janine M. (2018).
"Innervation of the Long Head of the Triceps Brachii in Humans-A Fresh Look: INNERVATION OF THE LONG HEAD OF THE TRICEPS BRACHII"
.
The Anatomical Record
.
301
(3): 473?483.
doi
:
10.1002/ar.23741
.
PMID
29418118
.
S2CID
3676096
.
- ^
Erhardt, Alexandra J.; Futterman, Bennett (2017-01-01).
"Variations in the Innervation of the Long Head of the Triceps Brachii: A Cadaveric Investigation"
.
Clinical Orthopaedics and Related Research
.
475
(1): 247?250.
doi
:
10.1007/s11999-016-5146-z
.
ISSN
1528-1132
.
PMC
5174069
.
PMID
27830483
.
- ^
Keener JD, Sethi PM (November 2015). "Distal Triceps Tendon Injuries".
Hand Clinics
.
31
(4): 641?50.
doi
:
10.1016/j.hcl.2015.06.010
.
PMID
26498552
.
- ^
"The Precise Neurological Exam: Deep Tendon Reflexes"
. New York University School of Medicine.
- ^
Watson JC, Wilson AM (January 2007).
"Muscle architecture of biceps brachii, triceps brachii and supraspinatus in the horse"
.
Journal of Anatomy
.
210
(1): 32?40.
doi
:
10.1111/j.1469-7580.2006.00669.x
.
PMC
2100266
.
PMID
17229281
.
External links
[
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]