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Deltoid Muscle


ATTACHMENTS

This muscle has got a proximal and a distal attachment.

  1. Proximal attachment: Proximally this muscle has got three attachment points, one point for each portion of deltoid i.e. anterior, posterior and middle. The anterior fibers of deltoid are attached to the lateral one third of Clavicle. The middle mulitpennate fibers are attached to the Acromion process of Scapula. The posterior unipennate fibers are attached to the Spine of Scapula.

  2. Distal attachment: The fibers from all three parts of Deltoid move down making the round counter of shoulder, attaching into one single point. That point is the Deltoid tuberosity of Humerus and is termed as the distal attachment of Deltoid.

NERVE SUPPLY

Axillary nerve is the major nerve innervating this muscle. This nerve is a part of Brachial plexus of the nerves of upper limb and its root values are C5-C6.

BLOOD SUPPLY

The blood supply of this muscle comes from the Deltoid branch of Thoracoacromial artery i.e. a branch of Axiallry artery.

ACTIONS

As said earlier, this muscle can act as a whole or its parts can contract individually. The major function of this muscle is abduction. However, all the movements associated with this muscle are discussed as follows:

  1. When the anterior part contracts: When the anterior or Clavicular part of Deltoid contracts result is flexion and Medial rotation of Arm.

  2. When the middle part contracts: When the middle or Acromial part contracts result is abduction of arm.

  3. When the posterior part contracts: When the posterior or Spinal part contracts result is extension and lateral rotation of arm.

  4. When the muscle contracts as a whole: When the muscle contracts as a whole result is abduction of arm. In this process the main function is performed by the middle part while the anterior and posterior parts of Deltoid serve to steady the motion of arm.

During the first 15 degrees of abduction, Deltoid is assisted by the Suprapinatus muscles. After the initial 15 degrees assistance by Suprapinatus muscle, Deltoid becomes a fully effective abductor.

CLINICAL POINTS

  1. Deltoid is the muscle of choice, in addition to gluteus muscles, for an intra muscular injection.

  2. The loss of counter of Deltoid muscle means the damage of Axiallry nerve supplying it.

  3. To test the function of Deltoid as an abductor or the function of Axillary nerve, the person is asked to abduct his/her arm against resistance. After 15 degrees of motion Deltoid muscle can be appreciated in case of normal muscle function and intact Axiallry nerve.


ATTACHMENTS

This muscle has got a proximal and a distal attachment.

  1. Proximal attachment: Proximally this muscle has got three attachment points, one point for each portion of deltoid i.e. anterior, posterior and middle. The anterior fibers of deltoid are attached to the lateral one third of Clavicle. The middle mulitpennate fibers are attached to the Acromion process of Scapula. The posterior unipennate fibers are attached to the Spine of Scapula.

  2. Distal attachment: The fibers from all three parts of Deltoid move down making the round counter of shoulder, attaching into one single point. That point is the Deltoid tuberosity of Humerus and is termed as the distal attachment of Deltoid.

NERVE SUPPLY

Axillary nerve is the major nerve innervating this muscle. This nerve is a part of Brachial plexus of the nerves of upper limb and its root values are C5-C6.

BLOOD SUPPLY

The blood supply of this muscle comes from the Deltoid branch of Thoracoacromial artery i.e. a branch of Axiallry artery.

ACTIONS

As said earlier, this muscle can act as a whole or its parts can contract individually. The major function of this muscle is abduction. However, all the movements associated with this muscle are discussed as follows:

  1. When the anterior part contracts: When the anterior or Clavicular part of Deltoid contracts result is flexion and Medial rotation of Arm.

  2. When the middle part contracts: When the middle or Acromial part contracts result is abduction of arm.

  3. When the posterior part contracts: When the posterior or Spinal part contracts result is extension and lateral rotation of arm.

  4. When the muscle contracts as a whole: When the muscle contracts as a whole result is abduction of arm. In this process the main function is performed by the middle part while the anterior and posterior parts of Deltoid serve to steady the motion of arm.

During the first 15 degrees of abduction, Deltoid is assisted by the Suprapinatus muscles. After the initial 15 degrees assistance by Suprapinatus muscle, Deltoid becomes a fully effective abductor.

CLINICAL POINTS

  1. Deltoid is the muscle of choice, in addition to gluteus muscles, for an intra muscular injection.

  2. The loss of counter of Deltoid muscle means the damage of Axiallry nerve supplying it.

  3. To test the function of Deltoid as an abductor or the function of Axillary nerve, the person is asked to abduct his/her arm against resistance. After 15 degrees of motion Deltoid muscle can be appreciated in case of normal muscle function and intact Axiallry nerve.
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