Using the Sectra table, you will identify the muscles of the back and scapular region. Bolded terms are in the objectives for this lab.
The back
“The back is the posterior aspect of the trunk and extends from the base of the skull to the tip of the coccyx. The back contains three groups of muscles: the superficial muscles of the back, the intermediate muscles of the back, and the deep muscles of the back. All of these muscle groups attach to the vertebral column, which forms the axis of the trunk, supports the weight of the body, transmits forces generated by movement, and provides a protective bony covering for the spinal cord and nerve roots.” – Grant’s Dissector 16th ed.
Review the skeletal system in the VH Dissector:
- Identify the bones of the axial and appendicular skeleton where muscles of the back attach: scapula, occipital bone, vertebral column, and ilium
- Rotate the model image with one finger, or use two fingers to move the image around and zoom in and out
Superficial muscles of the back
Begin your virtual dissection of the superficial and deep back (select this button at any time to start over):
First, “skin” the model cadaver by selecting the skin tool and reducing the transparency to zero. You will notice that some muscles and bones are missing from the model to make this dissection easier.
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 following superficial muscles of the back: trapezius and latissimus dorsi
- Note that trapezius has 3 parts: descending, transverse, and ascending fibers
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 trapezius and latissimus dorsi on both sides. Dissection removes the muscle from the model only, not the MPR images (if you highlight the muscle again in the MPR images, it will reappear on the model)
- Identify the following superficial muscles of the back deep to trapezius: rhomboid major, rhomboid minor, and levator scapulae (MPR)
Q1: What is the triangle of auscultation? Describe its borders. (answer)
Intermediate and deep muscles of the back
- Dissect the rhomboid major, rhomboid minor, and levator scapulae on both sides
The intermediate muscles of the back are the serratus posterior muscles. The serratus posterior superior muscle is deep to the rhomboid muscles and the serratus posterior inferior muscle is deep to the latissimus dorsi muscle. They will be only partly visible on the model (incompletely rendered).
- Identify the following deep muscles of the back: erector spinae muscle group. These muscles are deep to the thoracolumbar fascia (not visible on the model)
- There are three muscles in the erector spinae muscle group: spinalis, longissimus, and iliocostalis. The model will label all three muscles as “iliocostalis cervicis” – know that they are all erector spinae muscles (MPR)
The splenius, semispinalis, and multifidus muscles are also muscles of the deep back.
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.
Muscles of the shoulder and posterior arm
- Identify and dissect the deltoid on both sides. It has several parts named for their bony attachments – the model will identify the entire muscle as the “acromial part”, but all parts can be individually selected in the MPR images
- Identify the teres major (both sides) and triceps brachii (left side only) (MPR)
- Identify the four rotator cuff muscles: supraspinatus, infraspinatus, teres minor, and subscapularis (MPR)
- You will need to rotate the model around to identify the subscapularis, on the anterior side of the scapula (visible on the right side only)
Identify the following anatomical spaces and which muscles form them (spaces will not be selectable on the model): quadrangular space, triangular space, and triangular interval
Q2: What are the borders of the quadrangular space, triangular space, and triangular interval? What neurovascular structures are associate with each space? (answer)
Q3: What muscle(s) is/are affected by injury to the axillary nerve? Describe the motions of the affected muscle(s). (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: What is the triangle of auscultation? Describe its borders.
- The triangle of auscultation is an area where the intercostal space (space 6) is not covered by any intrinsic or extrinsic muscle of the back, so it is an appropriate spot to auscultate the lungs
- Muscular borders: latissimus dorsi, trapezius, and rhomboid major
Q2: What are the borders of the quadrangular space, triangular space, and triangular interval? What neurovascular structures are associate with each space?
- Quadrangular space
- Borders: teres minor (superior), teres major (inferior), long head of triceps brachii (medial), surgical neck of humerus (lateral)
- Neurovascular structures: axillary nerve, posterior circumflex humeral artery
- Triangular space
- Borders: teres minor (superior), teres major (inferior), long head of triceps brachii (lateral)
- Neurovascular structures: circumflex scapular artery
- Triangular interval
- Borders: teres major (superior), long head of triceps brachii (medial), humerus (lateral)
- Neurovascular structures: radial nerve, deep brachial artery
Q3: What muscle(s) is/are affected by injury to the axillary nerve? Describe the motions of the affected muscle(s).
- Deltoid: abducts the humerus, flexes and medially rotates the humerus (anterior fibers only), extends and laterally rotates the humerus (posterior fibers only)
- Teres minor: adducts and laterally rotates the humerus