Thieme Dissector Volume 1 (eBook)

Introduction to Dissection

Anatomy is one of the basic subjects in medical education. It deals with the structure of human body. A sound knowledge of this subject provides better understanding of the clinical subjects. The subject of anatomy is best studied by dissection. It will be appropriate to say that dissection forms an integral part of teaching or learning anatomy. It gives you an opportunity to explore, observe, and learn about structures/organs. The experience that you gain in the dissection room is unmatched. It cannot be compared to learning through books, illustrations, CDs, and DVDs that are available to learn the subject. Dissecting a cadaver improves your skill of handling the tissues and instruments that you will be trying later when you start practicing on living subjects. It gives you an understanding about the relationship of various structures to each other and helps you know what is normal and what is anomalous. It offers an anatomical basis of tests that you may do, various signs and symptoms that you encounter in a patient, variations that you may see in some subjects, and overall better understanding of many disease processes. It is well said that the cadaver is the best teacher of anatomy. Once it is accepted, it is our duty to treat the cadaver with the same respect and dignity which is offered to a living patient.

Preservation of the Cadavers

It is done by embalming the cadaver with the embalming fluid which contains a strong fixative. Subsequently, the cadaver is submersed in the preservative fluid. When the cadaver is partly dissected, proper care should be taken by wrapping it so that it is kept moist, or else the cadaver will desiccate and once the part is dry it cannot be restored. Therefore, expose only the part which is to be dissected. Ideally, all the parts of the body should be periodically inspected and moistened during the dissecting session.

Anatomical Terms

It is essential to get familiar with many anatomical terms which are repeatedly used to describe structures, organs, parts, etc. Some of them are given in the following paragraphs.

Anatomical Position

It is the position of the body with the person standing erect, feet approximated (together), toes pointing forward, arms hanging by the side of the body, palms facing forward, and the eyes looking at horizon (Fig. 1).

All the descriptions in anatomy are provided assuming the body is in anatomical position, though the cadaver is lying horizontally on the dissection table. Its relationship with the neighboring structures is essential when you study the structure; remember that the description applies assuming the structure is in anatomical position. The frequently used terms can be put into two groups: the terms of positions and the terms of movements.

Terms of Positions (Fig. 2)

1.Anterior: It means nearer to the front of the body.

2.Posterior: It means nearer to the back.

3.Ventral and dorsal are used in the case of trunk instead of anterior and posterior, respectively.

4.In the hand, palmar means anterior and dorsum means posterior. In the foot, the terms used are dorsum for the upper side and plantar for the sole of the foot.

5.Median: It means in the middle.

6.Medial: It means nearer the median plane.

7.Median plane: It is an imaginary plane bisecting the body into nearly two equal halves.

8.Lateral: It means away from the median plane; for example, there are two forearm bones, the radius is on the lateral side and the ulna is on the medial side. In the bones of the leg, the tibia is on the medial side and the fibula is on the lateral side.

9.Superficial: It means nearer to the skin of surface.

10.Deep/Profundus: It means deeper (as compared to superficial) from the surface.

11.Proximal (nearer to): It indicates relative position of the structure.

12.Distal (further from): For example, elbow is distal to the shoulder but proximal to the wrist.

13.Superior/Cephalic: The term refers to the position of the part which is nearer to the head.

14.Inferior/Caudal: It means nearer to the feet.

Anatomical Planes

There are four imaginary planes (Fig. 3) that pass through the body in anatomical position:

1.Median/Sagittal plane: A vertical plane which passes through the center of the body and divides it into two equal halves.

2.Paramedian/Parasagittal plane: Any vertical plane which is parallel to the median plane.

3.Coronal plane: Any vertical plane perpendicular to the median plane.

4.Transverse/Horizontal plane: Any plane at right angle to coronal and sagittal planes.

Terms of Movements

1.Flexion: It means forward bending of the trunk and folding of limbs.

2.Extension: In case of the trunk, it is backward or posterior bending and in limbs it is straightening.

3.Dorsiflexion: It is the movement of the foot toward the dorsum. It occurs at the ankle joint.

4.Plantar flexion: It is the movement of the foot toward the sole. It also occurs at the ankle joint.

5.Adduction: The movement toward the median plane.

6.Abduction: The movement away from the median plane.

7.Lateral flexion: It is movement of the trunk in the coronal plane.

8.Pronation and supination: These are movements involving the forearm and occur at the radioulnar joints (joints between the forearm bones, the radius and ulna). In anatomical position, the forearm is supinated and the palm faces forward. In pronation, the palm faces backwards/posteriorly.

9.Inversion and eversion: These movements involve the foot and occur at the subtalar and calcaneocuboid joints (joints of the tarsal bones, the bones of the foot). In inversion, the medial border of the foot is raised so that the sole faces medially. In eversion, the lateral border of the foot is raised and the sole of the foot faces laterally.

10.Rotation: The term signifies the movement where the part of the body is turned around its own longitudinal axis. In the limbs, it can be medial or lateral rotation at a particular joint, for example, the shoulder joint.

Structures That Are Encountered in Dissection

The body surface is covered by the skin, beneath which lies the superficial fascia and still deeper lies the deep fascia.

Skin

The skin consists of the outer, avascular, stratified, keratinized epithelium, the epidermis, and inner vascular, dense, fibrous tissue, the dermis. Dermis has protrusions into the epidermis. This increases the area of contact between them; thus, the two are firmly bound together.

Superficial Fascia

It consists of fat-filled fibrous mesh, connecting the dermis (of the skin) with the deep fascia. In the region of the scalp, palms of the hands, soles of the feet, and the back of the neck, the superficial fascia is dense. Hence, in these places the skin is firmly bounded to the underlying deep fascia. In other parts of the body, the superficial fascia is loose and elastic so that the skin can move freely.

The amount of fat in the superficial fascia varies. It is scanty in the nipple and areola of the breast and absent in some parts of the external genital organs. The subcutaneous fat is responsible for the rounded contours of the body and differs in its distribution in males and females. The superficial fascia contains the cutaneous blood vessels, lymphatics, and nerves.

At this stage, it is pertinent to understand how to differentiate between arteries, veins, and nerves. To accomplish this task, students should know the relationship of these structures to each other. It is well said, “Your eyes see the things that your mind knows.” Therefore, students are advised to go through the text to learn about the relationship between arteries, veins, and nerves.

Blood Vessels

The blood vessels comprise arteries and veins (Fig. 4). The arteries convey blood (oxygenated) from the heart to the tissues under high pressure. The arteries can be categorized as follows: (a) Large or elastic arteries, for example, the aorta, resist high internal pressure and their elastic recoil smoothens the intermittent systolic pumping action of the heart producing a continuous flow of blood. (b) The medium-sized arteries are also called muscular or distributing arteries. Their lumen is controlled by the sympathetic nerves, which determines...