Textbook of Anatomy (Volume 1) Inderbir Singh
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1Upper Extremity2

Some Essential TermsCHAPTER 1

 
THE SUBJECT OF ANATOMY
Anatomy is the science that deals with the structure of the human body. Different aspects of the subject are as follows:
  1. Gross anatomy or morphological anatomy is the study of structure that can be seen by naked eye.
  2. Microscopic anatomy or histology is the study of structure that can be observed only under a microscope.
  3. Cytology is the study of details of the structure of cells.
  4. Histochemistry is the study of chemical processes going on in cells and tissues.
  5. Ultrastructure is the study of tissues using an electron microscope. It provides very high magnification.
  6. Embryology is the study of the development of tissues and organs before birth.
  7. Applied anatomy or clinical anatomy is the study of aspects of anatomy that are useful in diagnosis and treatment of disease.
 
MAIN SUBDIVISIONS OF THE HUMAN BODY
For convenience of description the human body is divided into a number of major parts.
  1. The uppermost part of the body is the head. The face is part of the head.
  2. Below the head, there is the neck.
  3. Below the neck, there is the region that we call the chest. In anatomical terminology the chest is referred to as the thorax. The thorax is in the form of a bony cage within which the heart and lungs lie.
  4. Below the thorax, there is the region we commonly refer to as ‘stomach’ or ‘belly’.
    1. Its proper name is abdomen. The abdomen contains several organs of vital importance to the body.
    2. Traced downwards, the abdomen extends to the hips. A part of the abdomen present in the region of the hips is called the pelvis.
  5. The thorax, the abdomen, the neck, and the head together form the trunk.
  6. Attached to the trunk, there are the upper and lower limbs, or the upper and lower extremities.
 
SOME COMMONLY USED DESCRIPTIVE TERMS
  1. The study of anatomy is like the learning of a new language. The learning of anatomical terms is the basic foundation on which all subsequent studies in various subjects of the medical curriculum depend.
  2. Of all the terms to be learnt the most fundamental are those used for precise descriptions of the mutual relationships of various structures within the body.
  3. In describing such relationships, we usually use terms like ‘in front’, ‘behind’, ‘above’, ‘below’, etc. However, in a study of anatomy, such terms are found to be inadequate; and the student's first task is to become familiar with the specialised terms used.
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Anatomical Position
  1. In describing relationships within the body, we presume that the person is standing upright, looking directly forward, with the arms held by the sides of the body, and with the palms facing forwards.
  2. This posture is referred to as the anatomical position. We will now consider some descriptive terms one by one.
    1. When structure A lies nearer the front of the body as compared to structure B, A is said to be anterior to B (1.1).
      The opposite of anterior is posterior. In the above example, it follows that B is posterior to A.
    2. When structure C lies nearer the upper end of the body as compared to structure D, C is said to be superior to D (1.1). The opposite of superior is inferior. In the above example D is inferior to C.
    3. The body can be divided into two equal halves, right and left, by a plane passing vertically through it. The plane separating the two halves is called the median plane (1.2).
      1. When a structure lies in the median plane it is said to be median in position (e.g., G in 1.2).
      2. When structure E lies nearer the median plane than structure F, E is said to be medial to F.
      3. The opposite of medial is lateral. In the above example F is lateral to E.
    4. In the anatomical position the palm faces forwards and the thumb lies along the outer side of the hand. Starting from the side of the thumb (or first digit) the fingers are named:
      1. Index finger (second digit)
      2. Middle finger (third digit)
      3. Ring finger (fourth digit)
      4. Little finger (fifth digit).
    5. Various combinations of the descriptive terms mentioned above are frequently used.
      1. For example, each eye is anterior to the corresponding ear; and is also medial to it. Therefore, the eye can be said to be anteromedial to the ear.
      2. The tip of the nose is inferior and medial to each eye: we can say the nose is inferomedial to the eye.
    6. We must now consider terms that are sometimes used as equivalent to some of the terms introduced above.
      1. The anterior aspect of the body corresponds to the ventral aspect of the body of four-footed animals. Hence, the term ventral is often used as equivalent to anterior. (However, we shall see later that the two terms are not always equivalent e.g., in the thigh).
      2. In the hand, the palm is on the anterior or ventral aspect. This aspect of the hand is often called the palmar aspect.
      3. The opposite of ventral is dorsal. The back of the hand is the dorsal aspect, or simply the dorsum, of the hand.
      4. In the case of the foot, the surface towards the sole is ventral: it is called the plantar aspect. The upper side of the foot is the dorsum of the foot.
      5. While referring to structures in the trunk the term cranial (= towards the head) is sometimes used instead of superior; and caudal (= towards the tail) in place of inferior.
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        1.1: Scheme to explain the terms anterior, posterior, superior, and inferior
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        1.2: Scheme to explain the terms medial, lateral and median
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      6. In the limbs, the term superior is sometimes replaced by proximal (= nearer) and inferior by distal (= more distant). Using this convention the phalanges of the hands are designated proximal, middle and distal.
      7. In the case of the forearm (or hand), the medial side is often referred to as the ulnar side, and the lateral side as the radial side.
      8. Similarly, in the leg (or foot) we can speak of the tibial (=medial) or fibular (= lateral) sides.
In addition to the terms described above there are some terms that are used to define planes passing through the body.
  1. We have already seen that a plane passing vertically through the midline of the body, so as to divide the body into right and left halves, is called the median plane. It is also called the mid-sagittal plane.
  2. Vertical planes to the right or left of the median plane, and parallel to the latter, are called paramedian or sagittal planes (1.3).
  3. A vertical plane placed at right angles to the median plane (dividing the body into anterior and posterior parts) is called a coronal plane or a frontal plane (1.4).
  4. Planes passing horizontally across the body (i.e., at right angles to both the sagittal and coronal planes) and dividing it into upper and lower parts, are called transverse or horizontal planes (1.5).
  5. There are innumerable oblique planes intermediate between those described above.
  6. Sections through any part of the body in any of the planes mentioned above are given corresponding names. Thus, we speak of:
    1. Median sections
    2. Sagittal sections
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      1.3: Scheme showing median and paramedian planes
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      1.4: Scheme showing a frontal or coronal plane
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      1.5: Scheme showing a horizontal or transverse plane
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    3. Coronal or frontal sections
    4. Transverse sections
    5. Oblique sections.
 
STRUCTURES CONSTITUTING THE HUMAN BODY
When we dissect up any part of the body we encounter various elements.
  1. The basic framework of the body is provided by a large number of bones that collectively form the skeleton. As bones are hard they not only maintain their own shape, but also provide shape to the part of the body within which they lie.
  2. In some situations (e.g., the nose or the ear) part of the skeleton is made up, not of bone but of, a firm but flexible tissue called cartilage.
  3. Bones meet each other at joints, many of which allow movements to be performed. At joints, bones are united to each other by fibrous bands called ligaments.
  4. Overlying (and usually attached to) bones we see muscles.
    1. Muscles are what the layman refers to as flesh. In the limbs, muscles form the main bulk.
    2. Muscle tissue has the property of being able to shorten in length. In other words muscles can contract, and by contraction they provide power for movements.
    3. A typical muscle has two ends, one (traditionally) called the origin, and the other called the insertion.
    4. Both ends are attached, typically, to bones.
  5. The attachment of a muscle to bone may be a direct one, but quite often the muscle fibres end in cord like structures called tendons which convey the pull of the muscle to bone. Tendons are very strong structures.
  6. Sometimes a muscle may end in a flat fibrous membrane. Such a membrane is called an aponeurosis.
  7. When we dissect a limb we find that the muscles within it are separated from skin, and from each other, by a tissue in which fibres are prominent. Such tissue is referred to as fascia.
    1. Immediately beneath the skin the fibres of the fascia are arranged loosely and this loose tissue is called superficial fascia.
    2. Over some parts of the body the superficial fascia may contain considerable amounts of fat.
    3. Deep to the superficial fascia the muscles are covered by a much better formed and stronger membrane. This membrane is the deep fascia.
    4. In the limbs, and in the neck, the deep fascia encloses deeper structures like a tight sleeve.
  8. Membranes similar to deep fascia may also intervene between adjacent muscles forming intermuscular septa. Such septa often give attachment to muscle fibres.
  9. Running through the intervals between muscles (usually in relation to fascial septa) there are blood vessels, lymphatic vessels, and nerves.
    1. Blood vessels are tubular structures through which blood circulates.
    2. The vessels that carry blood from the heart to various tissues are called arteries.
    3. Those vessels that return this blood to the heart are called veins.
    4. Within tissues, arteries and veins are connected by plexuses of microscopic vessels called capillaries.
  10. Lymphatic vessels are delicate, thin walled tubes. They are difficult to see. They often run alongside veins.
  11. Along the course of these lymphatic vessels small bean-shaped structures are present in certain situations. These are lymph nodes.
  12. Lymphatic vessels and lymph nodes are part of a system that plays a prominent role in protecting the body in various ways that you will study later.
  13. Running through tissues, often in the company of blood vessels, we have solid cord like structures called nerves.
    1. Each nerve is a bundle of a large number of nerve fibres.
    2. Each nerve fibre is a process arising from a nerve cell (or neuron).
    3. Most nerve cells are located in the brain and in the spinal cord.
    4. Nerves transmit impulses from the brain and spinal cord to various tissues. They also carry information from tissues to the brain.
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    5. Impulses passing through nerves are responsible for contraction of muscle, and for secretions by glands. Sensations like touch, pain, sight and hearing are all dependent on nerve impulses travelling through nerve fibres.
  14. Bones, muscles, blood vessels, nerves etc., which we have spoken of in the previous paragraphs are to be seen in all parts of the body. In addition to these many parts of the body have specialized organs, also commonly called viscera.
  15. Some of the viscera are solid (e.g., the liver, or the kidney), while others are tubular (e.g., the intestines) or sac like (e.g., the stomach).
  16. The viscera are grouped together in accordance with function to form various organ systems.
    1. Some examples of organ systems are the respiratory system responsible for providing the body with oxygen.
    2. The alimentary or digestive system responsible for the digestion and absorption of food.
    3. The urinary system responsible for removal of waste products from the body through urine; and the genital system which contains organs concerned with reproduction.
  17. From the discussions in the previous paragraphs, it will be clear that in the study of the anatomy of any part of the body we have to consider the following:
    1. The skeletal basis of the part including bones and joints.
    2. The muscles and fasciae.
    3. The blood vessels and nerves.
    4. The lymph nodes and their areas of drainage.
    5. Viscera present in the region.
 
HOW MUSCLES ARE NAMED
  1. The human body contains a very large number of muscles, and each has a name. The student spends a great deal of time learning these names.
  2. A muscle may be named on the basis of its action, its shape and size, and the region in which it lies.
  3. The name of a given muscle usually consists of two or more words based on these characteristics.
  4. How muscles are named will be clear from the following examples.
 
Some Names Based on Region
  1. The region on the front of the chest is called the pectoral region. There are two muscles in this region. The larger of the two is called the pectoralis major. The smaller one is called the pectoralis minor.
  2. The region of the buttock is called the gluteal region. It contains three large muscles that are given the names gluteus maximus (largest), gluteus medius (intermediate in size) and gluteus minimus (smallest).
  3. In each of the above examples note that the first word in the name refers to the region concerned, and the second to relative size.
 
Some Names Based on Shape
  1. Muscles that are straight are given the name rectus (compare with ‘erect’). One such muscle present in the wall of the abdomen is called the rectus abdominis. Another in the thigh is called the rectus femoris. (Femoris = thigh—that is why the bone of the thigh is the femur).
  2. Over the shoulder there is a strong triangular muscle called the deltoid (after the Greek letter delta, which is shaped like a triangle).
  3. A quadrilateral muscle present in the lumbar region is called the quadratus lumborum.
  4. Most muscles have a fusiform shape. The central thicker part is muscular and is called the belly. The ends are usually tendinous.
  5. Some muscles have two (or more) bellies each with a distinct origin (or head). A muscle having two heads is given the name biceps.
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  6. There is one such muscle in the arm and another in the thigh. The one in the arm is the biceps brachii (brachium = arm) and that in the thigh is the biceps femoris.
  7. On the back of the arm, there is a muscle that arises by three heads. It is called the triceps.
  8. On the front of the thigh, there is a muscle that has four heads. It is called the quadriceps femoris. (Distinguish carefully between quadriceps and quadratus).
 
Some Names Based on Action
  1. Muscles that produce flexion may be named flexors; and those that cause extension may be called extensors.
  2. Similarly, a muscle may be an abductor, an adductor, a supinator or a pronator.
  3. In each case, the word indicating action is followed by another word indicating the part on which the action is produced. For example, on the back of the forearm there is a muscle that is an extensor of the digits: it is called the extensor digitorum.
  4. Sometimes, we can have more than one muscle that qualifies for such a name. In that case we add a third word indicative of position.
    1. On the front of forearm there are two muscles that produce flexion at the wrist (or carpus).
    2. One of them, which lies towards the medial (or ulnar) side is called the flexor carpi ulnaris (= ulnar flexor of the carpus).
    3. The second muscle lies towards the lateral (or radial) side and is called the flexor carpi radialis.
  5. Sometimes, it is necessary to add a fourth word to the name. On the back of the forearm there are two radial extensors of the wrist: we call the longer one the extensor carpi radialis longus and the shorter one is named the extensor carpi radialis brevis.
  6. On the medial side of the thigh, there are three muscles that adduct it. Because of variations in size they are called the adductor longus, the adductor brevis, and the adductor magnus (magnus = largest).
  7. Appreciation of these principles, used in naming muscles, can go a long way in easing the burden of remembering the names of muscles and their actions.
 
SOME FEATURES OF JOINTS
  1. Joints are formed where two (or more) bones meet.
  2. Some joints are merely bonds of union between different bones and do not allow movement. Joints of the skull (sutures) belong to this category.
  3. Some joints allow slight movement, while some (like the shoulder joint) allow great freedom of movement.
  4. In describing movements, we use certain terms that the student must understand clearly.
    1. Movements at any joint can take place in various planes.
      1. Movements taking place in a sagittal plane are referred to as flexion (= bending), and extension (= straightening).
      2. For example, when we bend the upper limb at the elbow joint so that the front of the forearm tends to approach the front of the arm this movement is called flexion (1.6).
      3. Straightening the limb at elbow is called extension.
      4. Bending the neck forwards is flexion of the neck, and straightening it, is extension. Similarly, when we bow, the vertebral column is being flexed, and when the body is made upright the spine is being extended.
    2. Movements in the coronal plane are referred to as abduction (= taking away) or adduction (= bringing near).
      1. When a limb is moved laterally so that it moves away from the trunk it is said to undergo abduction (1.7).
      2. For example, such a movement takes place at the shoulder joint when the upper limb is raised sidewards.
      3. A similar movement takes place at the hip joint. Adduction and abduction can also take place at the wrist and at some other joints.
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        1.6: Diagram to explain the movement of flexion of the forearm
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        1.7: Diagram to explain the movement of abduction of the arm
    3. Some joints allow rotatory movements.
      1. When the forearm is rotated so that the palm comes to face forwards, the movement is called supination.
      2. The opposite movement is called pronation.
      3. Side-to-side movements of the neck are also rotatory movements.
      4. The movement of the arm performed by a cricketer in bowling is a rotatory movement at the shoulder.
      5. Note that during this movement the hand moves in a circle. This movement is, therefore, called circumduction.
    4. When the foot is turned so that the sole looks somewhat inwards, the movement is called inversion. The opposite movement is called eversion.