Lab 1 Pre-Lab Exercise:
PLEASE WATCH THIS INTRODUCTORY VIDEO PRIOR TO CLASS
The process of identifying structures before going to lab is also critical to your success in lab.
1. Review the basic structure of the skin [Histology site]. Return to Dr. Cabrey’s lecture and your histology textbook for a review.
The epidermis is composed of a stratified, keratinized epithelium; underneath is the dense, irregular connective tissue of the dermis. Beneath the dermis is a loose connective tissue, containing varying numbers of fat cells, called the hypodermis -- or in gross anatomical terms, the superficial fascia. You will be able to distinguish somewhat dermis and epidermis in lab and to a greater degree the former two from hypodermis.
- Observe how the skin on the back of your own hand moves freely over the underlying structures.
- Compare the mobility of the skin on the back of your hand with that on your palm.
Consider what you have learned about thick and thin skin in microanatomy. The superficial fascia allows for mobility, and also functions in fat storage. Where the skin is mobile, it can be separated easily from underlying muscle along the plane of the loose connective tissue of the superficial fascia. Always strive to locate this plane when skinning.
The deep fascia is more immobile; it encloses and binds together the underlying muscle tissue. Deep fascia is inelastic, and like tendons (muscle-to-bone), ligaments (bone-to-bone), and aponeuroses (broad tendons) is composed largely of collagen fibers. Its inelasticity explains why it is poorly developed over much of the thorax and abdomen, which must expand and contract in breathing. Deep fascia defines one muscle from another, passing between adjoining muscles to form intermuscular septa attached to the underlying bones. On the palms and soles, superficial fascia becomes dense and tightly bound to the deep fascia.
Atlas images related to histology of the skin:
2. Surface anatomy of the back
Surface features of the back are used to locate muscle groups, identify major bony landmarks, determine regions of the vertebral column, and to approximate the position of the spinal cord. These features are also used to locate organs that occur posteriorly in the thorax and abdomen. With the help of your teammates and using the images below, find the following surface anatomy landmarks of the back.
3. Identifying bony landmarks
In the midline of the back, there is a median furrow overlying the tips of the spinous processes of the vertebrae. Flex your head anteriorly and feel the prominent spinous process of C7 (7th cervical vertebra). Superiorly to this prominence is the nuchal groove (site of the nuchal ligaments) in the neck. These ligaments attach to the external occipital protuberance, which you can palpate at the back of your head. Inferiorly to this protuberance and below the skull, is the spinous process of C2. The spinous process of C2 is the most superior vertebral protuberance that can be palpated (C1 has no spinous process). Most of the other cervical vertebrae might be difficult to palpate because they are obscured by soft tissue (e.g., nuchal ligaments). Inferiorly to C7, you should be able to count the spinous processes of the twelve thoracic vertebrae (T1-T12). In some individuals the transverse processes of the thoracic vertebrae can also be palpated. Inferior to the thoracic vertebrae, count the five spinous processes of the lumbar vertebrae (L1-L5) and the five sacral processes (S1-S5). The tip of the coccyx (Co1-Co3 or 4), which is also the end of the vertebral column, is palpable between the gluteal masses.
You can palpate the spine of the scapula if you follow laterally the spinous process level of T3. Find the inferior angle of the scapula around the spinous process of T7. The medial end of the spine of the scapula also overlies the 4th rib, the 8th rib lies just below the inferior angle of the scapula, the 11th rib is the lowest rib crossed by the margin of latissimus dorsi. The horizontal line between the highest point of the iliac crest of the pelvis (on each side) crosses through the spinous process of L4. The spinous process of L3 and L5 can be palpated above and below respectively. Depressions indicate the site of the posterior superior iliac spines, which usually lie at the level of the sacro-iliac joints and/or S2 spinous process.
The spinous processes do not always lie at the same horizontal plane as their corresponding vertebral bodies. For example, in the thoracic region, the processes are long and slope downwards. The tips of their processes therefore lie at the level of the vertebral body below.
4. Identifying major muscles
To help you identify the major muscles of the back, abduct your arms (away from midline) so that your scapulae rotate superiorly on the thoracic wall (rib cage). You will see that there is a median furrow that separates two longitudinal bulges formed by the contracted erector spinae group of muscles. The superficially located trapezius and latissimus dorsi muscles connecting the upper limbs to the vertebral column are also visible. The trapezius muscle has three parts: descending (above the scapula), transverse (towards the spine of the scapula) and ascending (below the spine of the scapula). The latissimus dorsi can be found below the trapezius extending all the way to the iliac crests. The latissimus dorsi muscle winding around the lateral border of the teres major muscle forms the posterior axillary (armpit) fold. Finally, the rhomboid muscles, which are deep to the trapezius, can be accentuated when retracting the scapulae. In order to retract your scapulae, place your hands behind your head and push your elbows towards the back (see image below).