The teres minor muscle is a skeletal muscle that belongs to the shoulder musculature. It forms part of the rotator cuff, which holds the humerus at the shoulder. Damage to the teres minor muscle or its nerve can affect the stability of the cuff and increase the likelihood of dislocation of the shoulder (dislocation).

What is the teres minor muscle?

The teres minor muscle is a striated skeletal muscle that undergoes voluntary human control. It extends between the scapula and humerus and is part of the rotator cuff (muscle tendon cap), which secures the humerus to the shoulder and stabilizes the joint.

The shoulder joint needs this additional support, since it only has a relatively flat socket, from which the condyle can easily pop out. Dislocations (dislocations) are therefore particularly frequent at this joint. Together with the teres major muscle, the teres minor muscle also surrounds the axial gap. He is also known as a small round muscle and is one of the shoulder muscles. Above it lies the deltoid muscle (deltoid muscle), which extends as a triangle between the clavicle, scapula and humerus.

Anatomy & Construction

The teres minor muscle originates from the scapula, where the marginal margin of the scapula represents the outer margin of the bone. On the upper arm, the muscle attaches to the humerus. There is a larger protrusion in the side of the bone, which the anatomy refers to as the tuberculum majus humeri.

The infraspinatus muscle and the supraspinatus muscle, which, like the teres minor muscle, belong to the rotator cuff, are also involved here. The fourth muscle of this unit is the subscapularis muscle; this, however, does not start at the tuberculum majus humeri, but at the tuberculum minus, a smaller projection of the humerus. Between the two bony prominences runs a pit in which the tendon of the biceps brachii muscle finds support.

The teres major muscle or large circular muscle is also important for the stability of the shoulder. Like the teres minor, he is also responsible for a number of arm movements. The contracting command is obtained by the teres minor muscle via the axillary nerve, which also innervates the teres major muscle and the deltoid muscle.

Function & Tasks

The teres minor muscle is a striated muscle consisting of a large number of muscle fibers, which in turn are grouped into bundles. A muscle fiber is a muscle cell, unlike other cells, however, contains several cell nuclei, since the classical unit with a nucleus in a membranumh├╝llten cell does not exist in the muscle tissue. Instead, the fine structure within the muscle fiber forms myofibrils that stretch longitudinally through the fiber.

Their transverse sections (sarcomeres) are characterized by a change of actin / tropomyosin filaments and myosin filaments. Z-disks delimit the sarcomeres from each other. When the muscle contractes, the fine filaments of the striated musculature slide into each other; the myosin filaments have heads that allow them to dock to the complementary filament. When they then fold down, they pull the filaments together, thereby shortening the length of the muscle fiber.

This process is made possible by calcium ions originating in the sarcoplasmic reticulum. The sarcoplasmic reticulum is a tube system that surrounds the myofibrils in the muscle fiber. If an electrical nerve signal (action potential) reaches the muscle, it first crosses a synapse and triggers the so-called end plate potential in the muscle: an electrical charge shift in the muscle cell. This endplate potential spreads through the sarcolemma, the T tubules, and finally the sarcoplasmic reticulum.

Nerve cells whose job it is to control muscles are called motor neurons. They not only irritate a single muscle fiber, but several simultaneously. The ratio varies from muscle to muscle: fine movements require a lower ratio than coarse; For example, a motoneuron irritates about 700 muscle fibers on the biceps.

Contractions of the teres minor muscle contribute to various arm movements. The muscle is active when a person pulls the previously splayed arm back to the trunk (adduction) and when he turns it outwards (external rotation). In addition, the teres minor muscle is involved in retroversion; this movement stretches the arm backwards away from the body.

Diseases

Often, complaints related to the teres minor muscle are related to problems with the rotator cuff. Rotator cuff rupture is a tear of the tendons that attach the muscles of the cuff to the bone. Basically, both a single tendon and multiple tendons may tear at the same time. Particularly often the tendon of the supraspinatus muscle is affected.

Functional impairments of the teres minor muscle can also be caused by lesions on the axillary nerve, which supplies the muscle with neuronal signals. A possible cause of damage to the axillary nerve is a fracture of the upper arm on the Collum chirurgicum. This site breaks very easily and can also damage the axillary nerve. Even during bone healing, a lesion of the nerve is possible: to repair the fracture, the body forms new bone tissue, which builds a callus above the fracture site as a callus.

In addition, dislocation can damage the axillary nerve if it overstretches when the joint is distended. In both cases, impairment of the axillary nerve causes the nerve tract to no longer provide motor signals to the teres minor muscle and other muscles as usual.

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