Shoulder + Thorax

BONES

Shoulder Bones: Our shoulders are made up of 3 bones which are the scapula (shoulder blade), clavicle (collar bone) and the humerus. 

Thorax Bones: Our thorax is made up of 3 main parts which are the sternum, ribs and vertebral column. 

Sternum - Is located at the front of the chest which protects the heart, lungs and major blood vessels. The manubrium, gladiolis (the body) and the xiphoid process are the 3 parts which make up the sternum. This bone has the shape of a necktie and the sides of this bone allow the ribs and clavicles to attach.

Ribs - Are described as flat bones which are curved and play a role in protecting the major thoracic organs. Ribs are classified into 3 main parts which are true ribs, false ribs and floating ribs. 

1. True ribs are the first seven sets of ribs which attach directly to the sternum on the anterior side, and also attach to the vertebral column on the posterior side.                                                                                                                                                                      
2. False ribs are the next three sets of ribs which attach to the vertebral column on the posterior side, and do not directly attach to the sternum on the anterior side. Instead they attach to the rib that is directly superior to them and they attach via costal cartilage.                                                                                                                                                                                            
3. Floating ribs are the last two pairs of ribs which attach to the vertebral column on the posterior side, but do not attach to the sternum or anything at all on the anterior side.

Vertebral Column - There are 5 sections that make up the vertebral column. 

1. Cervical Vertebrae: The cervical vertebrae bones are labelled as C1-C7, since there are 7 cervical vertebrae, and these bones are the smallest of the vertebrae.                                                                                                                                                                                                                                                                                                                                                           
2. Thoracic Vertebrae: The thoracic vertebrae bones are labelled as T1-T12, since there are 12 thoracic vertebrae.These bones protect many of our major internal organs and are therefore, a component of the thorax.                                                                                                                                                                                                                                                             
3. Lumbar Vertebrae: The lumbar vertebrae bones are labelled as L1-L5 since there are 5 lumbar vertebrae, which are located in the lower back.                                                                                                                                                                               
4. Sacrum: There are 5 fused bones that make up the sacrum. These 5 bones most often fuse during the teenage years, not at birth.                                                                                                                                                                                                             
5. Coccyx: There are 3-5 fused bones that make up the coccyx, but in some cases the bones aren't actually fused. The lowest portion of the tailbone is where the coccyx is located, and this bone also acts as an attachment point for ligaments and tendons.

LIGAMENTS

In our shoulders we have 6 ligaments that are there for support, and allow the shoulder to properly function. These ligaments are:

1. Glenohumeral Ligament - The glenohumeral ligaments are what make up the joint capsule of the shoulder. There is a superior glenohumeral ligament, a medial glenohumeral ligament and a inferior glenohumeral ligament.                               
2. Acromioclavicular Ligament - The acromioclavicular ligament attaches the acromion and the clavicle together.                          
3. Coracoacromial Ligament - The coracoacromial ligament attaches the coracoid to the acromion.                                               
4. Coracoclavicular Ligament - The coracoclavicular ligament is made up of 2 small ligaments which are called trapezoid and conoid ligaments. These ligaments, along with the acromioclavicular joint play a crucial role in allowing the scapula to stay attached to the clavicle. They could be ruptured, along with dislocation of the AC (acromioclavicular) joint, if the point of the shoulder was to be injured. However, these ligaments are extremely strong.                                                                     
5. Coracohumeral Ligament - The coracohumeral ligament attaches the humerus to the coracoid process of the scapula.          
6. Transverse Humeral Ligament - The long head of the biceps brachii muscle has a tendon, which is held by the transverse humeral ligament, in the groove between the greater and lesser tubercle on the humerus.                                         

BONE MARKINGS

There are 3 bone markings which play a vital role in the joints of the shoulder.

1. Coracoid Process: This bone marking is located on the superior anterior side of the scapula, on the lateral edge and has a hook-like shape. Along with the acromion, the coracoid process helps with stabilization of the shoulder joint.                                              
2. Glenoid Fossa/Cavity: This bone marking is located on the lateral angle of the scapula and has a shallow surface. It attaches the humerus to the glenoid cavity.                                                                                                                                                                                          
3. Acromion: This bone marking is located on the superior end of the scapula and it extends over the shoulder joint, laterally, along with the coracoid process. On the scapula the acromion is a bony process.  
   

MUSCLES:

Major Muscle Groups: The following muscle groups make up some of  the largest muscles in our bodies

1) Shoulder Muscle Groups: The rotator cuff muscle group is the main muscle group of the shoulder region, and the four following muscles are what make up this region.

Supraspinatus Muscle	Infraspinatus	Subscapularis	Teres Minor

2) Anterior Trunk Muscle Groups: The following muscles make up the anterior aspect of our trunk.

Pectorals	Pectoralis Major	Pectoralis Minor
The pectoralis major and the pectoralis minor make up a large part of the chest. Both these muscles, along with others, help to perform adduction of the humerus, arm flexion at the shoulder joint, and medial rotation of the shoulder.

Abdominal Muscles	Picture
Abdominal muscles help protect our internal organs. There are many muscles in the abdomen that control movements such as trunk rotation, drawing the ribs towards the pelvis, and stabilizing the core. Some of the main abdominal muscles are, the Rectus Abdominus, Transverse Abdominus, Internal Oblique and External Oblique.

3) Posterior Trunk Muscle Groups:  The following muscles make up the posterior aspect of our trunk.

	Role of this muscle	Picture
Latissimus Dorsi	This muscle is often called the 'lat muscle' and it is the widest muscle of the body. The Latissimus Dorsi covers the majority of the back and assists/controls movements such as medial rotation at the shoulder joint, extension at the shoulder joint, and adduction of the humerus. The lats work with the pecs, in a synergistic fashion to perform many movements of the upper body.
Trapezius Muscle	This muscle is a diamond shaped muscle of the upper back. The trapezius helps to stabilize the scapula, as well elevate the shoulders.

Major Muscles: There are 7 main muscles in the shoulder region that we are going to focus on.

Muscle Names	Description	Picture
Supraspinatus	This muscle is one of the four rotator cuff muscles and can abduct the arm at the shoulder up to 15 degrees, but only when it is the main agonist. The supraspinatus muscle is a small muscle of the upper back which assist the deltoid muscle in producing abduction, up to 90 degrees.
Infraspinatus	This muscle is also another one of the four rotator cuff muscles which is a thick triangular muscle. The infraspinatus muscle is in charge of stabilizing the shoulder joint, and externally rotating the humerus.
Subscapularis	This muscle is again, one of the four muscles of the rotator cuff and is a large triangular muscle. The subscapularis muscle aids the humerus with medial rotation and depression at the glenohumeral joint. During shoulder movements, this muscle also helps stabilize the head of the humerus.
Teres Minor	This muscle is the final rotator cuff muscle and is in charge of producing external rotation of the shoulder joint. The teres minor muscle helps the shoulder with two specific movements, which are adduction and extension.
Teres Major	This muscle attaches to the scapula and the humerus and is a thick muscle of the shoulder joint. The teres major muscle is in charge of internally rotating and adducting the arm.
Deltoid	This muscle is located at the top of the arm and at the top of the shoulder, and has a round and triangular shape. The deltoid muscle has 3 heads that work together, in order to produce abduction of the shoulder joint.
Coracobrachialis	This muscle attaches to the coracoid process of the scapula and is located on the top of the arm, on the medial side.The coracobrachialis muscle assists in two movements at the shoulder joint, which are flexion and adduction.

ORIGINS AND INSERTIONS

TENDONS

Rotator Cuff Tendons:

In our shoulder, the 4 rotator cuff muscles (Supraspinatus, Infraspinatus, Subscapularis and Teres Minor) all attach to our humerus, through these tendons. These 4 tendons allow stabilization to our 4 rotator cuff muscles.

The 4 tendons are: 

1. Supraspinatus tendon
2. Infraspinatus tendon
3. Subscapularis tendon
4. Teres minor tendon

Biceps Tendons:

In our biceps muscle, there are 2 tendons which attach at the shoulder that are called the short head and long head. The long head tendon of the biceps brachii muscle, attaches to the glenoid and goes through the glenohumeral joint. This tendon is a very important tendon. The short head tendon of the biceps brachii muscle attaches to the coracoid process, which is located on the shoulder blade.

JOINTS

There are 4 joints in the shoulder which are the:

1. Glenohumeral Joint - This joint is the main joint of the shoulder and attaches the proximal head of the humerus with the glenoid fossa (area of the scapula).                                                                                                                              
2. Acromioclavicular Joint - This joint is also called the AC joint and it is located at the top of the shoulder. It attaches the acromion of the scapula and the clavicle together.                                              
3. Sternoclavicular Joint -  This joint is also called the SC joint and it attaches the manubrium of the sternum to the medial side of the clavicle.                                                                                                                                                                                                                                                                      
4. Scapulothoracic Joint - This joint is located on the posterior side of the body and is where the scapula and ribs meet, at the back of the chest.                                                                                                                                                                                                                                              

MOVEMENTS

The different kinds of movements that occur in the shoulder are abduction and adduction, flexion and extension, internal/medial rotation and external/lateral rotation, elevation, depression and circumduction. As you can see the shoulder is a very freely movable joint and can move in a variety of ways. This is because the shoulder is a synovial ball-and-socket joint, and because of this the shoulder is able to move in so many different ways.