Question

actions of these muscles .

muscle                         origin                                            insertion                     action

Sternocleidomastoid	Manubrium and medial portion of clavicle		When both contract: When one contracts:
Erector Spinae
Serratus Anterior
Pectoralis major	Clavicle, sternum, and costal cartilage of first six ribs
deltoid	Lateral third of clavicle; acromion and spine of scapula
Trapezius	Occipital protuberance and spinous processes of C7 thru T12		Action on scapula: When scapula is fixed:

Answer 1

MUSCLE NAME	ORIGIN	INSERTION	ACTION
STERNOCLEIDO MASTOID	The manubrium and medial portion of the clavicle	Mastoid process of the temporal bone, superior nuchal line	WHEN ONE CONTRACT- contralateral cervical rotation, ipsilateral cervical flexion WHEN BOTH CONTRACT -cervical flexion, the elevation of the sternum, and assists in forced inhalation.
ERECTOR SPINAE	Spinous processes of T9-T12 thoracic vertebrae, the medial slope of the dorsal segment of the iliac crest	spinous processes of T1 and T2 thoracic vertebrae and the cervical vertebrae	EXTEND THE VERTEBRAL COLUMN
SERRATUS ANTERIOR	fleshy slips from the outer surface of upper 8 or 9 ribs	costal aspect of medial margin of the scapula	protracts and stabilizes scapula, assists in upward rotation.
PECTORALIS MAJOR	Clavicular head: anterior surface of the medial half of the clavicle. Sternocostal head: anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle	Lateral lip of the bicipital groove of the humerus	Clavicular head: flexes the humerus Sternocostal head: horizontal and vertical adduction, extension, and internal rotation of the humerus Depression and abduction of the scapula
DELTOID	the anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula	DELTOID TUBEROSITY OF HUMERUS	shoulder abduction, flexion and extension
TRAOEZIUS	Occipital protuberance and spinous processes of C7 thru T12	nuchal ligament, medial superior nuchal line, posterior border of the lateral one-third of the clavicle, acromion process, and spine of scapula	Rotation, retraction, elevation, and depression of scapula