Neck, Chest & Back Muscles
Directions
- Print this PDF worksheet for a hardcopy guide as you work through this lesson.
- Within the lesson click the red linked headings to bring up the desired starting point within the cadaver for your work.
- Use the provided images on the worksheet to annotate and identify specific anatomical structures.
Let's identify four neck muscles responsible for head movement. Each of these have already been added to your specimen's skeleton.
- sternocleidomastoid (right & left) - Contracted together, this muscle pair extends the head and flexes the cervical region. This muscle has two heads. VH Dissector designates the "sternal head." You can easily see the "clavicular head" that simply is labeled as part of the entire muscle. Rotate your specimen to a lateral view;. The insertion point of the sternocleidomastoid is the temporal mastoid process. Kind of self explanatory, eh? Sterno-cleido-mastoid = Sternum & Clavicle & Mastoid. These anatomists are pretty clever!
- splenius capitis (right & left) - Rotate your specimen 180° to gain a posterior perspective. These muscles originate from cervical and thoracic vertebrae processes and insert onto the occipital bone and mastoid process of the temporal bone.
- semispinalis capitis (right & left) - Continuing your examination from the posterior perspective, dissect away the splenius capitis muscles to more fully reveal the semispinalis capitis. These muscles originate from the transverse processes of cervical and thoracic vertebra. The insertion is on the occipital bone.
- longissimus capitis (right & left) - Dissect away the semispinalis capitis to reveal the longissimus capitis. As you can see, these muscles also originate from thoracic and cervical vertebrae. The insertion is on the mastoid process of the temporal bone (you'll need to dissect away the sternocleidomastoid to see the insertion point).
All four of these muscles serve the common function of extending the head when contracted together or rotating the head if one side is contracted while the other is relaxed.
The hyoid bone is a very unique bone in that it does not articulate with any other bone. Instead, it is supported and suspended by muscles. Learn these muscles as two groups. The suprahyoids, those located superior to the hyoid bone and the infrahyoids, those located inferior to the hyoid bone. So you know what you are looking for in your specimen, here are the individual muscle names appropriately grouped.
suprahyoids - Generally speaking, these muscles elevate the hyoid bone.
- digastric
- mylohyoid
- stylohyoid
- geniohyoid (you need to dissect away the mylohyoid to get a better unobstructed view)
infrahyoids - Conversely, this muscle group depresses the hyoid bone.
- sternohyoid
- omohyoid
- sternothyroid
- thyrohyoid
Once again, you ONLY need to identify these muscles as suprahyoids and infrahyoids.
Chest and back muscles are largely responsible for movement of the pectoral girdle and arms (humerus). We'll start this study with some muscles best viewed from the anterior perspective. This group of muscles is visible on the left side of your specimen. Locate them on the right side in the cross-section and click on them with the highlight tool to add them to your specimen. As you will soon see, you are building from deep to superficial.
- pectoralis minor (right & left) - This deep muscle originates from the second through fifth ribs (variably) with the insertion on the scapular coracoid process. It abducts the scapula and rotates it downward.
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deltoid (right & left) - This muscle originates in three different places resulting in three different shoulder joint movements. The insertion is the deltoid tuberosity of the humerus.
- Anterior fibers originate from the acromial extremity of the clavicle which flex and medially rotate the arm at the shoulder joint.
- Lateral fibers originate from the scapular acromion which abduct the arm at the shoulder joint.
- Posterior fibers originate from the scapular spine and extend and laterally rotate the arm at the shoulder joint.
- pectoralis major (right & left) - This large, thick, fan-shaped muscle covers the superior thorax. It has two origins, the smaller clavicular head and a larger sternocostal head. The insertion is into the greater tubercle and intertubercular sulcus of the humerus. When contracted as a whole, this muscle adducts and medially rotates the arm at the shoulder joint. Contracting the clavicular head alone flexes the arm. Contracting the sternocostal head alone extends the arm.
Back muscles are generally antagonists of chest muscles and are equally responsible for pectoral girdle and arm movement. Identify and dissect each of the following paired muscles (right & left).
- trapezius - As you can see, this large, flat, triangular sheet of muscle extends from the skull and vertebral column medially to the lateral pectoral girdle. It extends the head and, depending on which part is contracted, variably manipulates the scapula.
- teres major - This muscle extends, adducts, and rotates the arm at the shoulder joint.
- teres minor - This muscle rotates, extends, and adducts the arm at the shoulder joint.
- latissimus dorsi - With its insertion on the humerus, the latissimus dorsi is known as the "swimmers muscle" for all its arm movements during that activity.
- infraspinatus - Named for its location in the scapular infraspinous fossa, this muscle laterally rotates and adducts the arm at the shoulder joint.
- subscapularis - Dissect away both scapulae. As the name implies, the subscapularis is deep to the scapula. It medially rotates the arm at the shoulder joint.
- serratus anterior - Known as the "boxer's muscle", the serratus anterior's origin is the superior eight or nine ribs with its insertion at the vertebral border and inferior angle of the scapula. Its named for the sawtooth appearance of its origins along the ribs. Serratus anterior abducts and rotates the scapula and elevates the ribs when the scapula is stabilized.
- levator scapula - Inserting on the superior vertebral border of the scapula, this muscle elevates the bone and rotates it downward.
- supraspinatus - With its insertion on the humerus, this muscle assists the deltoid in abducting the arm at the shoulder joint.
- rhomboid major & minor - These parallel muscles are used when forcibly lowering the raised upper limbs like driving a stake into the ground with a sledgehammer.
- erector spinae - The remaining three muscle groups visible on your specimen are collectively known as the "erector spinae". You are only responsible for knowing and identifying it as one BIG structure. :-)
Self-test Labeling Exercises