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Where is the triceps?

Where is the triceps?

Where is the triceps?

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Triceps

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. It is the muscle principally responsible for extension of the elbow joint (straightening of the arm).

Structure

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.

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.

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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.

Where is the triceps?
Where is the triceps?

 

 

three fascicles

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. It has been suggested that each fascicle “may be considered an independent muscle with specific functional roles.”

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) 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.

Innervation

All three heads of the triceps brachii are classically believed to be innervated by the radial nerve. However, a study conducted in 2004 determined that, in 20 cadaveric specimens and 15 surgical dissections on participants, the long head was innervated by a branch of the axillary nerve in all cases.

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Variation

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.

Function

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 used for fine movements, e.g., when writing. It has suggested that the long head fascicle  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. sorigin 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.

Triceps brachii

he triceps brachii is a large, thick muscle on the dorsal part of the upper arm. It often appears as the shape of a horseshoe on the posterior aspect of the arm. The main function of the triceps is the extension of the elbow joint.

The Triceps brachii gets its name with tri referring to “three” muscle heads or points of origin (with Brachii referring to the arm). These include the: Medial head; Lateral head; Long head

Image 1: Triceps brachii muscle: Long head red; Lateral head yellow; Medial head green

The 3 minute video is on the anatomy of Triceps

Long head

  • Origin: infraglenoid tubercle of the scapula
  • Insertion: Posterior surface of the olecranon process of the ulna, capsule of the elbow joint and antebrachial fascia.
  • Action: Because it attaches to the scapula, the long head not only extends the elbow but will also have a small action on the glenohumeral joint. With the arm adducted, the triceps muscle acts to hold the head of the humerus in the glenoid cavity. This action helps prevent any displacement of the humerus. The long head also assists with the extension and adduction of the arm at the shoulder joint. The lateral head also active during extension of the forearm at the elbow joint when the forearm supinated or pronated.
  • Innervation: radial nerve
Where is the triceps?
Where is the triceps?

Lateral Head

  • Origin: posterior aspect of the humerus, superior to the radial groove
  • Insertion: Posterior surface of the olecranon process of the ulna, capsule of the elbow joint and antebrachial fascia.
  • Action: Strongest head of the three. It is active during extension of the forearm at the elbow joint when the forearm supinated or pronated.
  • Innervation: radial nerve

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Medial head

  • Origin: posterior aspect of humerus, inferior to the radial groove
  • Insertion: Posterior surface of the olecranon process of the ulna, capsule of the elbow joint and antebrachial fascia.
  • Action: As the medial head does not attach to the scapula and therefore has no action on the glenohumeral joint, whether with stabilization or movement. However, the medial head active during extension of the forearm at the elbow joint when the forearm supinated or pronated.
  • Innervation: radial nerve

Note: All the three heads of triceps brachii innervated by the four branches of the radial nerve (C7, C8). However, according to the cadaveric study it found that the medial head of triceps brachii innervated by the ulnar nerve. Some research reveals that the long head of triceps actually innervated by the axillary nerve.

The muscle supplied with oxygen and nutrients from the branches of the deep brachial artery.

Physiotherapy

The triceps reflex, elicited by sharply striking the triceps tendon, often used to test the function of the nerves of the arm. This reflex tests spinal nerves C6 and C7, predominately C7. The reflex tested by abducting the patient’s shoulder and elbow to 90 degrees. Then the triceps tendon tapped using a reflex hammer just proximal to the olecranon.

Axillary nerve damage can have an impact on the long head of the triceps brachii (LTB). Therefore, people with axillary nerve damage should undergo an assessment for the function of the LTB. If they demonstrate lost function, this shows a poor prognosis, and early repair at three months recommended.

Distal nerve

The triceps muscle can undergo reinnervation through a distal nerve transfer. Commonly used nerves for reinnervation include the flexor carpi ulnaris fascicle of the ulnar nerve and the posterior branch of the axillary nerve. Both of these nerves have shown to recover the function of the triceps muscle.

Ruptures of the triceps muscle are rare and typically only occur in anabolic steroid users. Distal triceps ruptures are also relatively uncommon. The injury typically occurs due to either a fall on an outstretched hand or a direct blow to the triceps tendon. The patient presents after a painful popping sensation with pain and swelling over the posterior elbow with the inability to extend the elbow against resistance.

trapezius muscle

trapezius muscle, large, superficial muscle at the back of the neck and the upper part of the thorax, or chest. The right and left trapezius together form a trapezium, an irregular four-sided figure. It originates at the occipital bone at the base of the skull, the ligaments on either side of the seven cervical (neck) vertebrae (ligamentum nuchae), and the seventh cervical and all thoracic vertebrae. It inserted on the posterior of the clavicle (collarbone) and on the spine of the scapula (shoulder blade). Its chief action is support of the shoulders and limbs and rotation of the scapula necessary to raise the arms above shoulder level.

erector spinae

erector spinae, a deep muscle of the back; it arises from a tendon attached to the crest along the centre of the sacrum (the part of the backbone at the level of the pelvis, formed of five vertebrae fused together). When it reaches the level of the small of the back, the erector divides into three columns, each of which has three parts. The muscle system extends the length of the back and functions to straighten the back and to rotate it to one side or the other.

Where is the triceps?
Where is the triceps?

soleus muscle

soleus muscle, a flat, broad muscle of the calf of the leg lying just beneath the gastrocnemius muscle. It arises from the upper portions of the tibia and fibula, the bones of the lower leg, and then joins with the gastrocnemius to attach via the Achilles tendon at the heel. Its major action is flexion of the ankle joint, particularly when the leg bent at the knee, thereby extending the foot downward.

Brachialis

The brachialis muscle lies deep to the biceps brachii, and found more distally than the other muscles of the arm. It forms the floor of the cubital fossa.

  • Attachments: Originates from the medial and lateral surfaces of the humeral shaft and inserts into the ulnar tuberosity, just distal to the elbow joint.
  • Function: Flexion at the elbow.
  • Innervation: Musculocutaneous nerve, with contributions from the radial nerve.

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