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An example of trapezius function is an overhead press. When activating together, the upper and lower fibers also assist the middle fibers (along with other muscles such as the rhomboids) with scapular retraction/adduction. The trapezius also assists in abduction of the shoulder above 90 degrees by rotating the glenoid upward.
The platysma muscle is a broad sheet of muscle arising from the fascia covering the upper parts of the pectoralis major muscle and deltoid muscle. Its fibers cross the clavicle, and proceed obliquely upward and medially along the side of the neck. This leaves the inferior part of the neck in the midline deficient of significant muscle cover. [1]
Triceps muscle is shown in green text. 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.
The accessory nerve is tested by evaluating the function of the trapezius and sternocleidomastoid muscles. [8] The trapezius muscle is tested by asking the patient to shrug their shoulders with and without resistance. The sternocleidomastoid muscle is tested by asking the patient to turn their head to the left or right against resistance. [8]
The two muscles most commonly inhibited during this first part of an overhead motion are the serratus anterior and the lower trapezius. [10] These two muscles act as a force couple within the glenohumeral joint to properly elevate the acromion process, and if a muscle imbalance exists, shoulder impingement may develop.
The trapezius evolved separately, but the other three muscles in this group evolved from the first eight or ten ribs and the transverse processes of the cervical vertebrae (homologous to the ribs). [7] Functional demands have resulted in the evolution of individual muscles from the basal unit formed by the serratus anterior.
The splenius capitis is deep to sternocleidomastoideus at the mastoid process, and to the trapezius for its lower portion. It is one of the muscles that forms the floor of the posterior triangle of the neck. The splenius capitis muscle is innervated by the posterior ramus of spinal nerves C3 and C4.
There are two rhomboid muscles on each side of the upper back: [1] [2] [3] Rhomboid major muscle; Rhomboid minor muscle; The large rhombus-shaped muscle, located under the trapezius muscle, in the upper part of the thoracic region of the back, and the small muscle, in the same way, participate in the movement of the scapula. [4]