Name
Lab Section
Shoulder Complex Muscles
Purpose:
To learn the actions, proximal attachments, and distal attachments of the muscles
that act on the clavicle, scapula, and humerus at the glenohumeral,
acromioclavicular, and sternoclavicular articulations.
Equipment:
Textbook, Flash Anatomy Cards, or other resource for muscle actions & attachments
Handout – Learning Muscle Attachments (from web page)
Handout – Rules to Remember (from web page)
Articulated skeleton (to be provided by instructor)
Disarticulated skeleton (to be provided by instructor)
Background Information
As you begin your study of muscle attachments for muscles, know that I will use the terms proximal
and distal attachments rather than origins and insertions. The reason for this is that literally defined,
origin means the fixed bone and insertion means the moving bone. When a muscle contracts and attempts
to shorten, it exerts force on all the bones to which it attaches. The bone that is more stable will not
move, and the bone that is freer to move for whatever reason will move. Usually, the distal bone is lighter
than the proximal bone and is, therefore, freer to move. Since the distal bone is usually the bone that
moves, attachments on the distal bone were called the insertion points. However, you must understand
that either bone (proximal or distal) can potentially move. If the distal bone becomes more fixed, or
stable, then the proximal bone will move. An example of this would be in a pull-up, where contraction of
the biceps brachii, an elbow flexor, cause elbow flexion by pulling the humerus up to the forearm. This is
opposite what we usually associate with elbow flexion, where the forearm moves toward the stationary
humerus as in a curl motion. In the case of the pull-up, the attachment of the bicep on the forearm would
become the origin and the attachment on the scapula would become the insertion – in other words, they
would be reversed from what we normally consider the origin and insertion. Therefore, to keep things
simple, I will use the terms proximal and distal attachment rather than origin and insertion
For this lab, you are to learn the actions and attachments for the muscles of the shoulder complex.
The shoulder complex consists of two distinct and anatomically independent units: the shoulder girdle
and the shoulder (glenohumeral) joint. While they are functionally interdependent in many ways, these
two units can also function independently of each other. Therefore, you should learn them and their
muscles as individual units at this time. The functional interdependence of these two units will be
presented to you later in this course if you are taking the course for 3 credits.
We will first discuss the shoulder girdle. The shoulder girdle consists of the scapula and clavicle, and
the joints that connect these bones to the thorax [the sternoclavicular (SC) joint and the scapulothoracic
(ST) joint] and to each other [the acromioclavicular (AC) joint]. Therefore, movements of the shoulder
girdle (the scapula and clavicle) are not a result of motion about a single joint. Instead, movement of the
shoulder girdle is the summation of movements that occur at all three joints – the AC, SC, and ST.
Individually, these joints are classified primarily as nonaxial joints, which means that they do not allow
rotation. At this time, we will not learn about these joints individually, but you should understand that the
shoulder girdle movements that you learn are a result of motion about 3 joints simultaneously. When we
consider the movements of all of these joints together, linear and angular movements of the shoulder
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girdle can be defined in all 3 planes. In the frontal plane, the linear movements of elevation/depression
occur, and the angular movements of upward and downward rotation occur. In the sagittal plane, the
angular movements of upward & downward tilt occur. In the transverse plane, the angular movements of
protraction and retraction occur.
There are 6 muscles that are devoted to causing and controlling movements of the scapula
and/or the clavicle: the subclavius, the serratus anterior, the rhomboids (rhomboid major and
rhomboid minor), the trapezius, the pectoralis minor, and the subclavius. While the rhomboid
major and rhomboid minor are considered two separate muscles anatomically, you can learn
them as one muscle since their functions are identical. On the other hand, while the trapezius
muscle is considered one muscle anatomically, you should learn it as three muscles (upper,
middle, and lower trapezius) since each portion has a different function from the other portions.
As you study the attachment sites for the shoulder girdle muscles, remember that a muscle that
causes shoulder girdle movements must attach distally to the scapula or clavicle in order to be
able to cause that bone to move. Therefore, proximal attachments (usually origins) must be on
the thorax (ribs or vertebrae), and distal attachments (usually insertions) must be on the scapula
or clavicle.
The shoulder (or glenohumeral) joint is the articulation formed between the head of the
humerus and the glenoid fossa of the scapula. It is classified as a triaxial joint, allowing
movement in all three planes: flexion, extension, hyperextension in the sagittal plane; abduction,
adduction in the frontal plane; and medial rotation, lateral rotation, horizontal adduction, and
horizontal abduction in the transverse plane. Because it does permit frontal and sagittal plane
motions, it also permits circumduction. Muscles on the front will typically cause flexion, while
muscles on the back will typically cause extension and hyperextension. Muscles on the lateral
aspect of the shoulder will typically cause abduction while muscles on the medial aspect of the
shoulder will typically cause adduction. Transverse plane motions must be understood by
examining the line of pull of the muscle relative to the superior-inferior axis of the humerus. As
you study the attachment sites for the hip muscles, remember that a muscle that causes shoulder
joint movements must cross the shoulder joint. Therefore, proximal attachments (origins) must
be on the scapula, clavicle, or thorax, and distal attachments (insertions) must be on the humerus,
radius, or ulna. You should not confuse shoulder girdle muscles with shoulder joint muscles if
you will remember that shoulder girdle muscles do not cross the shoulder joint and, therefore,
cannot have attachments on the humerus or below.
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Procedures to be completed prior to lab:
1. Review the bony markings listed below for the scapula, vertebra, sternum, clavicle, radius,
ulna, and humerus. (Resource: BIOL 120 Lab Manual, or Flash Anatomy Cards – Bones)
Scapula
Acromion process
Articular facet of acromion process
Lateral (axillary) border
Coracoid process
Glenoid fossa
Inferior angle
Infraglenoid tubercle
Infraspinous fossa
Root of the scapular spine
Suprascapular notch
Spine of scapula
Supraspinous fossa
Subscapular fossa
Superior angle
Superior border
Supraglenoid tubercle
Medial (vertebral) border
Sternum
Xiphoid process
Manubrium
Clavicular notch
Body
Ulna
Olecranon process
Humerus
Anatomical neck
Body
Deltoid tuberosity
Head
Intertubercular (bicipital) groove
Lesser tubercle (or tuberosity)
Greater tubercle (or tuberosity)
Surgical neck
Clavicle
Conoid tubercle
Sternal end
Acromial end
Vertebra
Atlas (C1)
Axis (C2)
Coccyx
Sacrum
Body
Lamina
Pedicle
Spinous process
Transverse process
Vertebral arch
Vertebral foramen
Radius
Radial tuberosity
2. Review the joint actions of the shoulder girdle and glenohumeral joint. On a separate sheet of paper,
define the following terms for shoulder girdle (scapular) movements): elevation, depression,
abduction (protraction), adduction (retraction), upward tilt, downward tilt, upward rotation, and
downward rotation.
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3. Use the Handouts – Learning Muscle Attachments & Rules to Remember – and your Flash Anatomy
Cards or other resource to review diagrams, actions, and attachments of the following muscles:
Shoulder Girdle (Acromioclavicular, Sternoclavicular, and Scapulothoracic Joints):
Upper trapezius (I and II)
Middle trapezius (III)
Lower trapezius (IV)
Levator scapula
Rhomboids (major & minor)
Subclavius
Serratus anterior
Pectoralis minor
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Coracobrachialis
Anterior deltoid
Middle deltoid
Posterior deltoid
Biceps brachii (short head)
Biceps brachii (long head)
Shoulder (Glenohumeral Joint):
Pectoralis major (sternal)
Pectoralis major (clavicular)
Latissimus dorsi
Teres major
Triceps brachii (long head)
Procedures to be completed during the lab session:
1. Use the bones, muscle models, and muscle diagrams to help you study these muscles and their
attachments and actions. Strive to understand why each muscle has the action(s) that it has by
applying concepts previously learned (torque and lines of pull).
2. Attempt to locate and palpate the superficial muscles on your lab partner. This will aid you in
learning the location and actions of each of these muscles.
Study Questions
1. What are the posterior muscles of the shoulder girdle?
2. Which muscle would be considered the latissimus dorsi's little helper?
3. Which four muscles make up the rotator cuff group? What is their primary function at the shoulder
joint as a group?
4. On what aspect of the arm would you expect to find muscles that flex the humerus?
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Summary of Muscle Actions:
Shoulder Girdle
Elevation
Upper trapezius
Rhomboids
Levator scapula
Depression
Lower trapezius
Pectoralis minor
Pectoralis major
Latissimus dorsi
Subclavius
Abduction/Protraction
Serratus anterior
Pectoralis minor
Pectoralis major
Latissimus dorsi
Adduction/Retraction
Middle trapezius
Rhomboids
Lower trapezius
Levator scapula
Upper trapezius
Upward rotation
Serratus anterior
Upper trapezius
Lower trapezius
Downward rotation
Rhomboids
Pectoralis minor
Levator scapulae
Flexion
Anterior deltoid
Pectoralis major (C)
Biceps brachii
Coracobrachialis
Extension
Pectoralis major (S)
Latissimus dorsi
Teres major
Posterior deltoid
Triceps brachii (L)
Hyperextension
Posterior deltoid
Latissimus dorsi
Triceps brachii (L)
Adduction
Latissimus dorsi
Pectoralis major
Teres major
Triceps brachii (L)
Coracobrachialis
Abduction
Deltoid (all parts)
Supraspinatus
Lateral rotation
Infraspinatus
Teres minor
Posterior deltoid
Medial rotation
Subscapularis
Latissimus dorsi
Pectoralis major
Anterior deltoid
Teres major
Horizontal adduction
Pectoralis major
Anterior deltoid
Horzontal abduction
Posterior deltoid
Infraspinatus
Teres minor
Upward tilt
Pectoralis minor
Shoulder