Unit X – The Neck and Shoulder Complex

 

 

Objectives:

At the completion of Unit 10 the student will be able to:

1.                  Identify the bony structures and key landmarks of the neck and shoulder complex.

2.                  Identify the key joint structures of the neck and shoulder region.

3.                  Discuss basic movement patterns of the shoulder complex

4.                  Describe the movement of the neck.

5.                  Identify the major muscles in the neck and shoulder region.           

We have already explored the trunk and pelvis portions of the spine. We will now look at the neck region briefly. Finally, we will complete an overview of the anatomy of the shoulder complex and its importance to dance. Because of the importance of understanding the lower spine and lower extremity in dance, a great deal more detail was provided in this course for those areas. Less detail will be given for the neck and shoulder areas.

The Neck:

Bony Structures of the Neck

The neck region is referred to as the Cervical Spine. It is the portion of the vertebral column that connects the head to the thorax or trunk.
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There are 7 cervical vertebrae. Cervical vertebrae 1and 2 (or C1 and C2) have special bony structures for supporting the movement of the skull. Cervical vertebrae 3-7 are more typical. Although the general structures of the cervical spine are similar to the bony structures of the lower spine, there are key differences. 
The typical cervical vertebrae (C3-C7) are smaller than the vertebrae in the thoracic or lumbar areas. The disc material between the bones is about half as thick. Also, the cervical vertebrae have more of a rectangular shape in the body of the bone. There are two lips on the superior surface of the body of the cervical vertebrae. These lips interlock with the vertebrae above it. The cervical vertebrae are designed to allow more range of motion than the thoracic or lumbar areas, but also provide good stability in the neck region. The spinous processes project posteriorly, the longest of which is C7.  
C7 is the prominent bony landmark you can feel at the base of your neck.
Cervical vertebrae C1 and C2 are different in structure than those below. C1 is called the atlas and is the pedestal on which the skull rests. It is called the atlas because of the image of atlas holding up the world. It does not have a body or a spinous process, but is more of a bony ring with two important facets on which the occiput of the skull rests. 
The occiput bone of the skull is the most posterior and inferior region of the skull. It has a large hole through which the spinal cord passes to merge with the brain. There are occipital condyles on the base of the skull that rest on the corresponding condyles on C1.  There is large hole in the middle of C1 for passage of the spinal cord, called the vertebral foramen.
©
Cervical vertebrae C2 is called the axis. It also has two superior facets on which C1 rests. C2’s key structure is a process called the dens or odontoid process, that extends superiorly from the bone. It fits into a hole or foramen in the C1 vertebrae above it
The two vertebrae form an interlocking structure that allows rotation of the skull on the top of the cervical spine. The dens rotates within C1 to allow this rotation. There are also several ligaments in this area that provide stability to these important structures.

 

Motions of the Cervical Spine

The typical vertebrae C3-C7 joints allow cervical flexion, extension, sidebending, and rotation in the neck region. C1, or the atlas, allows for slight flexion and extension of the skull on the neck. C2 or the axis allows for rotation of the upper cervical spine region.
Cervical Flexion – bending of the head forward or movement of the head toward the chest.  

C1, or the atlas, allows for slight flexion and extension of the skull on the neck

Cervical Extension – tipping the head backward so that the eyes look at the ceiling.
Sidebending – tipping the head toward the side so that the ear of one side moves toward the shoulder of that same side. This occurs both left and right.
Rotation – turning of the head left or right. The nose moves over the shoulder as the head rotates.       

C2 or the axis allows for rotation of the upper cervical spine region.

Muscles of the Neck

The muscles in the neck are divided into three groups:

  • the deep neck muscles

  • the posterior neck muscles and 

  • the anterior neck muscles.

Deep Neck Muscles

Between the base of the skull and the upper cervical vertebrae are a group of muscles called the suboccipitals. It is easy to remember this group name because it means “under the occiput” which is where these muscles are located. 
The suboccipitals are 4 short muscles that originate from processes on C1 and C2 and attach on the base of the occiput of the skull. These small muscles act to move the head on the top of the cervical spine through the motions of extension, rotation, and sidebending. Since they are small muscles they do not allow a lot of motion or produce a lot of force. They do, however, provide a great deal of precision of movement of the head on the neck and are important for regulating the correct orientation of the head on the neck.
If you as a dancer change position in space so that you are sideways or tipped from upright orientation, a key role of these suboccipital muscles is to support the head on the neck and provide stability for this body region, as well as help keep you oriented in space. 

Posterior Neck Muscles

You will recall from the discussion of the thoracic and lumbar spine in Unit III, that there are long back extensor muscles that run the length of the spine.  These muscles are collectively known as the erector spinae. There are 3 components to the erector spinae group: 
  •  the iliocostalis (the most lateral)
  •  the longissimus and
  •  the spinalis (the most medial).
There are cervical components to these three muscle groups. 

The iliocostalis cervicis runs from the upper six ribs to the transverse processes of the lower cervical vertebrae. The longissimus capitis runs from transverse processes of the upper thoracic spine to the lower cervical vertebrae and inserts on the base of the skull. The longissimus cervicis runs from the transverse processes of the upper thoracic spine to the transverse processes of C2-C6. The spinalis capitis and semispinalis capitis lie closer to the middle of the spine and originate from the spinous processes and transverse processes of the lower cervical and upper thoracic vertebrae and attach on the base of the skull. 

Collectively these posterior muscle groups run from the upper thoracic spine and lower cervical spine to attach to either the upper cervical area or the base of the skull. The erector spinae muscle group in the cervical region primarily functions to extend the neck. If these muscles act on one side they can also produce some sidebending of the neck.

Anterior Neck Muscles

There are 3 key muscle groups in the anterior neck:
  • the longus colli and capitis
  • the scalenes and 
  • the sternocleidomastoid
©
The longus colli and capitis (the capitis lie beneath the longus colli and are not visible on the photo to the left) are the deeper muscles that lie along the front of the vertebrae running up and down. They attach to the various transverse processes from C1 to C7, as well as up to the occiput of the spine. When these muscle contract bilaterally they flex the head forward and straighten our the cervical spine curve. If they contract on one side they sidebend and rotate the head to that side.  
The scalene muscle group is located more laterally in the neck region. It is made up of 3 muscles – the anterior, medius, and posterior scalenes. The scalenes originate from the transverse processes from C2-C7 and attach to the superior surfaces of the first and second ribs below. The scalene muscle group is primarily responsible for producing side bending of the head on the neck.
The sternocleidomastoid muscle group is the largest and most superficial of the anterior neck muscles. It is visible through the skin. When you look at someone from the front, the two muscles that stick out on either side of the front of the neck and attach to the sternum below are the sternocleidomastoids. 

If you turn your head to one side you will see one side become more visible. 

The sternocleidomastoid or SCM has its origins on the sternum and on the clavicle. It passes superiorly and posteriorly to attach on the mastoid process of the skull. The mastoid process is the bony prominence you can feel just behind your ear. The SCM has several important functions in the neck region.  When the skull is fixed it pulls up on the sternum and clavical and assists with inspiration during breathing. When the thorax is fixed contraction of one SCM produces sidebending of the head to that side and rotation of the head to the opposite side. Bilateral contraction of SCM produces flexion of the head on the neck.

 

Try this now: While in a sitting position with your head upright and facing forward, tip you head to the left side. From that position now turn your nose toward the ceiling. The motions you just did were produced from your left sternocleidomastoid muscle. If you place your left hand on the left SCM as you repeat these motions you will feel the muscle contract under your hand. 

 

Relevance to the Dancer: It is important for the dancer to remember that the head and neck are the top of the chain that runs from the head to the base of the spine in the pelvic area. As the dancer moves through space he or she must have an appreciation for the connection between head and tail and how this connection provides fluidity and connectedness of motion. 
The head and neck are also intimately connected to the shoulder complex that provides arm motion in space. The dancer must be able to utilize the top to bottom connection in the spine and the connection of the spine and thorax to the large motions available at the shoulder.
We will now consider the shoulder complex to complete Unit X.

 

The Shoulder

Bony Structures of the Shoulder  

The shoulder is the area where the arm attaches to the thorax. Unlike several other joints we have discussed, it involves several bones and forms several joints that make up what is collectively called the shoulder complex. The shoulder complex produces a great amount of range of motion for arm movements.

The bones that comprise the shoulder complex are:

  • the humerus
  •  the clavicle
  •  the scapula and 
  • the proximal aspect of the sternum. 

There is also connection to the posterior aspect of the thorax on the ribs. Let’s briefly explore these bones.

 

Humerus
The humerus is the long bone of the upper arm. Its counterpart in the lower extremity is the femur. The proximal end of the humerus is a ball shape with several important landmarks for muscle attachments. The head of the humerus is the medial ball shaped prominence that articulates with the scapula to form the actual shoulder joint. The greater tubercle is the lateral prominence and the smaller, more anterior prominence, is called the lesser tubercle

Both of these are important muscle attachments that will be discussed later in this unit.

 Between these two prominences is the bicipital groove. It is a ditch in which the biceps tendon lies. Just below the head of the humerus is the anatomical neck. The humerus has a long shaft just like the femur. On the shaft of the humerus is a roughened area called the deltoid tuberosity. This is the area where the deltoid muscle inserts on the humerus.

 The distal end of the humerus has several important structures that comprise the elbow joint. They will be mentioned briefly at the end of this unit.

 

Scapula
The scapula, or shoulder blade, is the flat triangular bone that lies on the upper portion of the back. It attaches to the ribs on its under surface and to the humerus laterally. It has several important landmarks because it is a very important muscle attachment area in the shoulder complex. Viewed from the posterior aspect the scapula has three borders – the medial or vertebral border nearest to the spine, the superior border across the top and the lateral or axillary border on the shoulder side.

There are two important angles to remember – the superior angle at the top inside corner of the scapula, and the inferior angle at the bottom point.

© The spine of the scapula is a prominent line of bone that runs from the medial border across the upper third of the scapula and form laterally into the acromion process. You can visibly see the spine of the scapula through the skin when you look at someone from the back.
The acromion is the wide, flat bony surface you can feel at the top of your shoulder. On the posterior surface of the scapula the area above the spine is called the supraspinous fossa, while the area below the spine is called the infraspinous fossa. These are also important for muscle attachments. 
If you look at the scapula on the lateral side where it attaches to the humerus you will see the glenoid cavity or fossa. This is the large, round and slightly indented surface that serves at the articulation for the humeral head. Just superior and anterior to the glenoid fossa is the coracoid process, which actually protrudes anteriorly. The anterior surface of the scapula is the surface that articulates with the ribs.
Clavicle and Sternum    
The scapula is the posterior aspect of the shoulder complex, and the humerus is the lateral component. 

The clavicle and the sternum form the anterior portion of the complex. The clavicle, or collarbone, is a flattened, elongated bone shaped like an S if viewed from above. 

The clavicle articulates medially with the manubrium or upper section of the sternum in the middle of the chest. It articulates laterally with the acromion process of the scapula. 

The clavicle transmits a lot of forces in the arm, but is not very strong, so it is the most frequently broken bone in the body. There are ligaments at each end of the clavicle that attach it to the other bones.

 

Joints of the Shoulder Complex

There are 4 major joints that comprise the shoulder complex. These joints starting anteriorly are:
  • the sternoclavicular joint
  • the acromioclavicular joint
  • the glenohumeral joint and 
  • the scapular thoracic joint.

 There is a left and right side of each of these joints.

 

Sternoclavicular Joint

The sternoclavicular joint is the articulation between the concave surface of the manubrium of the sternum and the medial end of the clavicle. The movements at this joint occur secondarily with the movements of the scapula.

 

Acromioclavicular Joint

The acromioclavicular joint is the articulation between the lateral end of the clavicle and the acromion process of the scapula. The clavicle articulates with a small oval surface on the medial aspect of the acromion process. 

There is a ligament at the attachment of these two bones called the acromioclavicular ligament which helps provide stability to the joint.   

Scapular Thoracic Joint  

The scapular thoracic joint is the broad articulation of the posterior surface of the scapula against the thoracic cage on its posterior aspect. This joint provides motion of the scapula across the thoracic cage. This is more of a floating joint supported by muscles and ligaments from thoracic area 2-7.
Glenohumeral Joint
The glenohumeral joint, or shoulder joint, is the articulation of the head of the humerus with the glenoid cavity of the scapula. The surface area of the head of the humerus is two times as large as the area of the glenoid cavity. The shoulder joint is not an inherently stable joint and must rely heavily on the glenoid labrum for stability.

 The glenoid labrum is a fibrocartilagenous ring that functions like a washer to seal the joint. The labrum is located between the glenoid cavity and the head of the humerus.  

 

Movements of the Shoulder Complex

Because the shoulder is not a stable joint is has a great deal of motion in many directions. The glenohumeral joint, in combination with the movements of the scapula, allow combinations of movements to occur together. The glenohumeral joint, or shoulder joint, movements include:
Flexion – the arm lifts in an anterior direction away from the body. If this motion is completed the arm is raised completed overhead.

Extension – the arm moves posteriorly away from the body to the back. There is considerably less shoulder extension compared to shoulder flexion.

Abduction – the arm moves to the side away from the body. Beyond 90 degrees of abduction the arm starts to move back toward the body but is still called abduction. In order for full shoulder abduction to occur there must be external rotation of the arm to allow the humerus to clear out from under the large acromion process.

Adduction – the arm moves toward the midline of the body. The arm may be away from the body in an abducted position and then move toward the midline. This is adduction. Also, if the arm is at the side and then passes in front of the trunk to cross midline, this is also called adduction.

External Rotation  – the humerus rotates on its axis to move the greater tubercle toward the midline of the body. Internal Rotation – the humerus rotates on its axis to move the greater tubercle away from the midline of the body.

 

Internal and External rotation are both more easily visualized when the elbow is bent to 90 degrees. The point of bend of the elbow should remain fixed while the humerus rotates above it.  
Horizontal abduction and adduction – When the shoulder is flexed to 90 degrees the arm can be moved across the body toward or away from midline. 
© The movement toward  midline is called horizontal adduction, while the movement away from midline is horizontal abduction.

 

Movements of the Scapula

The scapula also has several available motions that combine with the shoulder motion for upper extremity movement. These include:

Elevation – with elevation the scapula as a whole slides up the thoracic cage in a superior direction; imagine lifting your shoulders toward your ears.

 Depression – with depression the scapula as a whole slides down the thoracic cage in a inferior direction; imagine pushing your shoulder down toward the floor.

Protraction – the scapula abducts on the thoracic cage or slides away from the midline of the body

 Retraction – the scapula adducts on the thoracic cage or slides toward the midline of the body; with retraction the two scapula draw together in the back and come closer to the spinous processes of the spine.

 

Downward Rotation – when the scapula rotates downward, the inferior angle of the scapula moves toward the midline of the body.

 Upward Rotation – when the scapular rotates upward, the inferior angle of the scapula moves away from the midline of the body.

 

 

Scapular-Humeral Rhythm

Because of the intimate connection between the joints of the shoulder complex they work in concert together to provide the motion in the upper extremity. This combined motion combination is referred to as the scapular humeral rhythm because there is a specific and predictable rhythm to the sequence and timing of the motions at the different joints and the firing of the muscles that produce these motions. We will consider  this only briefly for this course, but in depth exploration of this biomechanical area is complex and interesting.
 

Imagine this: The scapular, the humerus, and the clavicle are the dancers. These dancers are touching one another and as one moves the others must move also in a pattern. 

The humerus moves first and begins to move away from the body into abduction. As it moves its connection to the scapula pulls the scapula into upward rotation on the thoracic cage. The humerus and scapula are also connected to the clavicle in front and as the scapula upwardly rotates the acromion moves and pulls the clavicle up and rolls it posteriorly. 

All three of the dancers are moving together, and in concert, but are not performing the same motions. It is the combination movements of these three bones and their associated joints that give the shoulder complex its incredible movement potential. There are many motion combinations that occur as part of this scapular-humeral rhythm.

 

The Capsule and Ligaments of the Shoulder

Since the bony structures of the shoulder do not provide for joint stability, the stability of the joint must be gained in other ways. There are several important structures that provide stability at the shoulder.
The first is a structure located inside the shoulder capsule that was mentioned above – the glenoid labrum. The labrum is a fibrocartilaginous ring that functions much like a washer to seal the head of the humerus to the glenoid cavity. The labrum is the deepest support structure in the shoulder and can be damaged or torn from pinching mechanisms in the joint.

The shoulder capsule of the glenohumeral joint attaches to the scapula, on the outer rim of the glenoid cavity. It goes all the way up to the coracoid process of the scapula superiorly and encircles the origin of the long head of the biceps muscle. On the humerus it attaches to the anatomical neck. The capsule is loose and has many folds, especially inferiorly where it is weakest. This looseness in the capsule allows for the humerus to move through many degrees of motion. 

There are two main ligaments that provide additional support to the capsule. The coracohumeral ligament runs from the border of the coracoid process to the greater tubercle. The three portions of the glenohumeral ligament are anterior on the capsule. They run from the border of the glenoid cavity to the lesser tubercle and anatomical neck of the humerus.   
The rotator cuff muscles of the shoulder provide additional dynamic support to the shoulder joint. These muscles will be discussed in the next section. The shoulder capsule is weakest in the anterior-inferior direction. A common type of shoulder injury is dislocation of the shoulder joint in which the humeral head moves anteriorly and inferiorly out of the joint. This can result in damage or tearing to the ligaments and capsule of the shoulder joint.
The acromioclavicular joint has the acromioclavicular ligament that runs from the lateral end of the clavicle to the superior surface of the acromion. This ligaments provides stability to the joint. Another common shoulder injury is separation of the clavicle from the acromion – called and AC separation. This can result in damage to the ligament and deformity to the AC joint.

Muscles of the Shoulder

The muscles of the shoulder can be divided into three primary groups:
  • the superficial muscles acting on the shoulder
  •  the deeper rotator cuff muscles of the shoulder and
  •  the muscles primarily acting on the scapula. 

Once these muscles have been described a brief overview of their functions together for performing motions will be listed.

Deltoid

The Deltoid is the bulky muscle that gives the shoulder its rounded shape on top. It has a good bit of muscle bulk and also serves as a shock absorber for the joint. The Deltoid is tear-shaped and originates from the spine and acromion of the scapula and the lateral third of the clavicle and inserts on the deltoid tuberosity of the lateral side of the humeral shaft. It is divided into the anterior portion that originates from the clavicle, the middle portion on the acromion, and the posterior components arising from the spine of the scapula.

 These components of the muscle contribute to different movements at the joint. The overall main action of the deltoid is to abduct the arm. The anterior portion of the deltoid contributes to flexion and medial rotation of the arm, while the posterior portion contributes to extension and lateral rotation of the arm.

 

Pectoralis Major and Minor
The pectoralis major is the large muscle that forms the bulk of the anterior trunk. The pectoralis major is divided into two sections – the clavicular and sternal sections. 

The clavicular section originates from the anterior portion of the clavicle, while the sternal section originates from the sternum and costal cartilages 1-6. Both sections start from a fan shape medially and narrow in to attach together on the bicipital groove of the humerus. 

Contraction of the entire pectoralis major produces adduction and medial rotation of the arm.

The pectoralis minor is a small muscle located deep to the pectoralis major muscle. It originates on ribs 3-5 and inserts on the coracoid process of the scapula anteriorly. When the ribs are fixed it pulls the scapula forward and down, and can act as a stabilizer for the scapula. When the scapula is fixed it assists in inspiration by elevating the ribs.
Latissimus Dorsi  

The latissimus dorsi is the wide superficial muscle of the back. It originates from the sacral and iliac crests, thoracolumbar fascia, the spinous processes of T7-T12, and the posterior surfaces of the lower ribs. It starts as a broad muscle medially and narrows as it passes laterally and superiorly. It passes around the medial side of the humerus and attaches on the bicipital groove of the humerus.

 The primary actions of the latissimus dorsi are extension, adduction, and  medial rotation of the arm.

 

The Rotator Cuff Muscles

The rotators cuff muscles are the deeper shoulder muscles that provide increased stability to the shoulder joint. 

They are four in number and can be remembered as the “SITS” muscles for the letter of the first name of each muscle and how they attach:

  • supraspinatus

  • infraspinatus

  • teres minor

  • subscapularis.

 
Supraspinatus

The supraspinatus originates from the supraspinous fossa on the posterior scapula. The tendon passes under the acromioclavicular joint and attaches to the most superior point on the greater tubercle of the humerus.

 The primary function of the supraspinatus is abduction of the shoulder. The supraspinatus fires early in the abduction motion to set the humeral head in the glenoid cavity.

 

Infraspinatus

The infraspinatus originates from the infraspinous fossa on the posterior scapula. It insets on the greater tubercle of the humerus just posterior and inferior to the insertion of the supraspinatus muscle.

 The primary action of the infraspinatus is lateral rotation of the shoulder.

 

Teres Minor

The teres minor originates from the lateral border of the scapula on the posterior surface and inserts on the greater tubercle of the humerus just below the insertion of the infraspinatus. 

The primary action of the teres minor is lateral rotation of the shoulder.

 

Subscapularis

The subscapularis originates from the anterior surface of the scapula (under the scapula next to the rib cage) and inserts on the lesser tubercle of the humerus. 

The primary actions of the subscapularis are medial rotation and adduction of the arm.

 

The four muscles of the rotator cuff function collectively to reinforce the glenohumeral joint on three sides. Their main function is to help keep the head of the humerus in the glenoid cavity during various movements, especially during abduction . The anterior-inferior portion of the shoulder joint has less reinforcement and the capsule is more loose in this region, making it more vulnerable for dislocations or strains.

Scapular Muscles of the Shoulder Complex

The trapezius is the large, superficial muscle that forms the visible diamond shape at the base of the neck and top of the shoulder. It originates on the base of the occiput of the skull, the nuchal ligament, and the spinous processes of C7, T1-T12. The insertion is divided into three regions – the upper fibers insert on the posterior aspect of the clavicle, the middle fibers insert on the acromion and spine of the scapula, and the lower fibers insert on a tubercle at the medial end of the scapular spine.
The muscle begins as a wide fan from the neck to the mid-back and narrows to attach on the scapula. When the entire trapezius contracts it adducts the scapula toward the spine.  When the lower fibers of the trapezius (lower trapezius) contract they depress and downwardly rotate the scapula.
When the upper fibers of the trapezius (upper trapezius) contract they elevate and upwardly rotate the scapula and elevate the clavicle.

Prolonged suspension of the arms can result in tightness and spasm in the upper trapezius. The middle and lower trapezius fibers act to stabilize the scapula and can often be weak.

Levator Scapulae

The levator scapulae originates from the transverse processes of C1-C4 and inserts on the superior angle of the scapula. It elevates the scapula and rotates it downward. It can also act as a neck muscle when the scapula is fixed. 

This muscle is frequently tight and sore because of postural stresses. Most people can reach and find the spot at the top inside corner of the scapula. This area is frequently tender to touch.

 

Rhomboids

The rhomboids originate from the spinous processes of C7 and T1-T5 and insert on the medial border of the scapula. The rhomboids primary action is to adduct the scapula toward the spine. They can also function with levator scapulae to downwardly rotate the scapula.

 

Serratus Anterior

The serratus anterior is a broad, thin muscle that covers the lateral rib cage. It originates from the upper eight or nine ribs and inserts along the entire medial border of the scapula. It helps hold the scapula in place and function for abduction and rotation. When the arm is pushing against something the serratus anterior is very active.

 

Teres Major
The teres major originates from the posterior surface of the inferior angle of the scapula and inserts on the medial aspects of the bicipital groove of the humerus, next to latissimus dorsi. Its primary function is extension, adduction, and medial rotation of the arm.

 

Brief Recap of Muscles Functioning at the Shoulder and Scapula:

  • Shoulder Flexion – anterior deltoid, pectoralis major

  • Shoulder Extension – posterior deltoid, latissimus dorsi, teres major

  • Shoulder Abduction – middle deltoid, supraspinatus

  • Shoulder Adduction – latissimus dorsi, pectoralis major, teres major

  • Lateral Rotation – infraspinatus, teres minor, posterior deltoid

  • Medial Rotation - subscapularis, latissimus dorsi, pectoralis major, teres major

 

Relevance to the Dancer: As you can see, the shoulder complex is intricate and complex in its workings. It is important for the dancer to understand the key differences between the shoulder and the hip. The hip is a very stable joint with less available range of motion. It is designed to bear the weight of the body and provide stability for the lower leg. The shoulder is usually a non-weight bearing joint and has much more available range of motion for movements of the arms. The trunk must be a stable midline so that the arms can move freely in space. There is a connection between the center stability or core support of the spine or trunk and the stability of the scapula on that trunk that allows the arms to have maximum motion.

 

The Elbow and Hand - a quick overview

For this Anatomy course you will not be spending much time exploring the elbow and hand, since this area is of less concern for the dancer. A brief anatomical overview of these two body areas will follow.

Bony Structures of the Elbow  

The distal end of the humerus has several important bony landmarks that form part of the elbow joint. The medial side of the humerus has a protrusion called the medial epicondyle and the lateral side a similar protrusion called the lateral epicondyle. These are both important muscle attachment sites. Just below the  medial epicondyle is a pulley shaped area called the trochlea. Below the lateral epicondyle is a rounded area called the capitulum. Both the trochlea and the capitulum articulate with the forearm bones to form the two elbow joints.

 

The forearm bones are the radius and the ulna

The ulna has at its proximal end at the trochlear notch that articulates with the trochlea of the humerus to form the main elbow joint. This joint produces the motions of flexion and extension of the elbow (bending the elbow and straightening the elbow). 

The radius bone has a rounded radial head at its proximal end. This radial head articulates with the capitulum on the distal end of the humerus. This joint produces the motions of supination and pronation at the elbow. 

Supination is the action of turning the palm up toward the ceiling. Imagine the motion you would do to balance a bowl of soup in the palm of your hand. Pronation is the action of turning the palm toward the floor so that you are looking at the backside of your hand.

 

Muscles of the Elbow

The two primary muscle groups that produce flexion and extension at the elbow are the biceps brachii and the triceps. 
Biceps Brachii
The biceps brachii has two origins. The long head arises from the tubercle above the glenoid cavity of the scapula and travels through the shoulder joint, between the greater and lesser tubercles in the bicipital groove and then merges into the body of the muscle. The short head of the biceps arises from the coracoid process of the scapula. These two head meet distally and merge to insert on the radial tuberosity and bicipital aponeurosis. 
The biceps brachii’s main function is elbow flexion, although it performs some supination. Two smaller muscles, the brachialis and the brachioradialis attach on the distal aspect of the humerus and onto the ulna and radius to assist the biceps brachii with elbow flexion.
The triceps brachii is the major elbow extender. It has three origins. The long head arises from the tubercle below the glenoid cavity, the lateral head arises from the lateral shaft of the humerus, and the medial or deep head arises from the posterior-inferior humerus. These three sections join in the body of the muscle to attach onto the olecranon of the ulna.

Muscles of Pronation and Supination

There are several long muscles that originate above the elbow, cross the elbow joint and attach at various places along the radius or ulna.

 Generally, the origin of the muscles of pronation is on the medial epicondyle of the humerus. The long muscles that originate in this area all work together to produce pronation of the forearm. The lateral epicondyle is the origin of the muscles that produce supination of the forearm.

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© Picture on the left shows anterior view of right arm in pronation.  Notice the distal end of the radius on the thumb  side. © Picture on the left shows the same view except now the hand has supinated or palm is now up. Notice how the radius has "crossed over" the ulna and now you are looking at the back of the hand.

The Hand

The hand is an intricate set of bones and muscles that work together to perform very complex and fine motor activities. The specifics of the bony structures for the hand will not be discussed in this course. It is helpful to consider, however, that the overall structure of the bones of the hand is similar to the structure of the foot which has been discussed in a previous unit. Some of the long muscles of the forearm attach to the hand. Other long muscles originate on the radius and ulna and pass into the hand region. Finally, there are small intrinsic muscles of the hand that perform the intricate movements between the hand bones. Overall, there is flexion and extension at the wrist. Flexion is bending the fingers and wrist toward the anterior surface of the forearm. Extension is moving the fingers and wrist toward the posterior surface of the forearm.
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The wrist also produces radial deviation in which the hand moves toward the radial side of the hand, or ulnar deviation in which the hand moves toward the ulnar side of the hand. There is also flexion and extension of the various joints of the fingers to allow the hand to open and close in either a flat hand position or a fist.
The complexity of the upper extremity provides a great deal of available motion options for the upper body. When these extremity motions have as their base a stable trunk or core, the range of movement possibilities is endless. 

This concludes Unit X. Return to Blackboard to complete Quiz #5 on Unit X.