MUSCLES OF THE PECTORAL GIRDLE

Objectives

At the end of this demo the student should be able to:

•Explain the different muscles attached to the pectoral girdle and to which group they belong.

•Explain the attachments ,innervations and blood supply of the muscles.

COURSE OUTLINE:

INTRODUCTION:

•Muscles of the pectoral girdle broadly are divided into

  1. Ant.axioappendicular group
  2. Post.axioappendicular group

1. Ant.axioappendicular muscles

Also called thoracoappendicular or pectoral muscles

Four muscles

•Pectoralis major

•Pectoralis minor

•Subclavius

•Serratus anterior

Pectoralis major

•Large fan shaped

•Covers superior part of thorax

•Has clavicular and sternocostal heads

•Its inferior border forms Ant. Axillary fold

•Pectoralis major and adjacent deltoid forms the narrow deltopectoral groove in which cephalic vein runs

•Pectoralis major along with clavicle forms clavipectoral or deltopectoral triangle

Pectoralis minor

•Lies beneath Pectoralismajor

•An imp.landmark for structures in axilla

•With coracoid process makes a bridge beneath which vessels and nerves pass

Subclavius

•Lies almost horizontally when the arm is in anatomical position

•Located inferior to clavicle and affords some protection to the subclavian vessels and the superior trunk of brachial plexus if clavicle fractures

Serratus anterior

•saw toothed appearance,also called boxer’s muscle

•Overlies lateral part of thorax and forms medial wall of axilla

•Holds scapula against thoracic wall while doing push-ups

Attachments of muscles of ant.axioappendicular group:

Post.axioappendicular muscles

•Also called scapulohumeral muscles

•Divided into 3 groups

  1. Superficial post. Appendicular(extrinsic shoulder) muscles;trapezius and latissimus dorsi
  2. Deep post. Appendicular(extrinsic shoulder) muscles;levator scapulae or rhomboids
  3. Scapulohumeral(intrinsicshoulder)muscles; deltoid, teres major ,and the 4 rotator cuff muscles(supraspinatus,infraspinatus,teres minor and subscapularis)

Trapezius

•Large,triangular muscle,covers the posterior aspect of neck and superior half of trunk

•Have 3 types of fibres

•Superior fibres;elevate scapula

•Middle fibres;retract scapula

•Inferior fibres;depress scapula

Latissimus Dorsi

•Widest muscle of the back

•Climbing muscle

•Large fan shaped muscle passes from trunk to humerus

Levator Scapulae

•Sup.third lies deep to sternocleidomastoid,while inf.third lies deep to trapezius

Rhomboids

•Major and minor

•Forms oblique equilateral parrallelogram

•Lies deep to trapezius

Scapulohumeral (intrinsic shoulder)muscles

  • Deltoid

•Supraspinatus

•Infraspinatus

•Teres major and minor

•subscapularis

•Deltoid

•Thick ,powerful,coarse textured forming rounded contour of the shoulder

•Shaped like delta

•Has unipennate ant.and post.parts

•Multipennate middle part