Using the Sectra table, you will identify the muscles of the pectoral region and arm. Bolded terms are in the objectives for this lab.
The upper limb
“The upper limb is divided into four regions: shoulder (pectoral girdle), arm (brachium), forearm (antebrachium), and hand (manus). The upper limb is structured for mobility so we can place our hands, which are grasping organs, in a large area of space. Some of the muscles that control the upper limb are extrinsic, meaning they extend into the other regions of the body, specifically the anterior thorax and the back.” – Grant’s Dissector 16th ed.
Review the bones of the upper limb in the VH Dissector:
- Identify bones of the axial and appendicular skeleton where muscles of the upper limb attach: sternum, clavicle, ribs, and humerus
- Rotate the model image with one finger, or use two fingers to move the image around and zoom in and out.
Muscles of the pectoral region
Begin your virtual dissection of the muscles of the pectoral girdle and arm (select this button at any time to start over):
As you identify and dissect muscles, you should review their origin, insertion, innervation, and action(s). If you are having trouble finding structures, you can search for them by selecting the Anatomy tab, typing the name of the structure in the search box, and selecting the sun icon next to the listed structure. You can dissect these structures by selecting the eye icon.
- Identify the pectoralis major and deltoid muscles
- Note that the pectoralis major has two heads: the clavicular head and the sternocostal head. The model will identify both heads as the “clavicular” (MPR)
- Identify the deltopectoral triangle and deltopectoral groove and note their borders (these spaces are not selectable on the model)
As you highlight a structure, note that the structure will also be highlighted in the multiplanar reconstructed (MPR), or cross-sectional images in the leftmost pane. All structures should be identified on the MPR images. Using three fingers, scroll through the MPR images to understand the three-dimensional relationships between different structures as you work though the lab. Structures that are difficult to identify in the MPR images will have additional links to assist you.
- Dissect the deltoid and pectoralis major on both sides
- Identify the pectoralis minor and serratus anterior muscles (MPR)
- Rotate the model to the posterior side and identify the latissimus dorsi and teres major (MPR)
- Dissect the latissimus dorsi on one side to observe the scapular attachment of serratus anterior
Q1: List the muscles that adduct the arm. What nerves innervate these muscles? (answer)
Muscles of the Arm
For the remaining muscles, use the left upper limb of the model only:
- Dissect the deltoid and review the muscles of the rotator cuff, including subscapularis (MPR)
- Identify the biceps brachii (MPR)
- Biceps brachii has both a long head laterally and short head medially. The model will identify both as the short head
The transverse humeral ligament passes superficial to the tendon of the long head of biceps brachii (this will not be visible on the model).
The biceps brachii inserts on the radius via the biceps brachii tendon. The bicipital aponeurosis is an extension of the biceps tendon that broadens medially and attaches to the antebrachial fasica.
- Dissect the biceps brachii
- Identify the coracobrachialis and brachialis muscles
- Rotate the arm to view the posterior side and identify the triceps brachii muscle. The long head is positioned most medially of the three heads of triceps brachii, while the lateral head and medial head are named for their position relative to the radial groove of the humerus. The medial head is deep to the other heads of triceps brachii, and will not be visible on the model (MPR)
Use the MPR pane to understand the relationship between muscles in the anterior and posterior compartments of the arm.
Q2: What nerve innervates the triceps brachii? review the path of this nerve through the spinal roots, trunks, divisions, and cords of the brachial plexus.(answer)
End of Sectra activity
Answers to activity questions
Below are answers to questions asked during the activity. Clicking the ‘back to lab’ link below each answer will take you back to the question (you may need to scroll up a little to view the question again).
Q1: List the muscles that adduct the arm. What nerves innervate these muscles?
- Pectoralis major (lateral and medial pectoral nerves)
- Latissimus dorsi (thoracodorsal nerve)
- Teres major (lower subscapular nerve)
- Coracobrachialis (musculocutaneous nerve)
Q2: What nerve innervates the triceps brachii? review the path of this nerve through the spinal roots, trunks, divisions, and cords of the brachial plexus.
- The triceps brachii is innervated by the radial nerve
- C5-T1 –> superior, middle, and inferior trunks –> all posterior divisions –> posterior cord –> radial nerve