Introductory Anatomy: Terminology

Dr. D.R.Johnson, Centre for Human Biology

What is anatomy?

Anatomy is the study of the structure of the body. Derived from the Greek to cut up: the Latin 'to cut up' gives us dissect.

Structure determines function and vice versa. Understanding the links between structure and function is intellectually more satisfying than learning lists, and makes long term retention easier. The abnormal patterns seen in disease are also related to anatomy: the transmission of stress from outstretched hand to trunk determines the location of skeletal fractures. The structure of the mouth determines the route of puss from a dental abscess. During your course we shall continually stress both the relationship between structure and function and the relationship between structure and disease.

Subdivisions

Under the general heading of anatomy are several subdivisions.
Embryology examines development of adult structure from fertilised ovum
Cytology deals with the structure of individual cells
Histology deals with aggregations of cells, tissues, or aggregations of tissues, organs
Neuroanatomy deals with the elaborate connections of nerve cells
Gross anatomy deals with those structures that can be seen without a microscope.

Methods of study

Dissection of a fixed cadaver is the most important tool of anatomists. The dissection may be done by you, the students (and you will have opportunities to practice this skill during the course) or by someone else on your behalf, to produce prosections which show particular regions or features. Prosections save you time, but I suspect that dissection leaves a longer lasting impression of structure.

Living anatomy is the observation of the living body at rest or in action. This has both drawbacks and plus points. Our own bodies (or those of colleagues) are always available to see and feel, and we are younger and more muscular than dissecting room specimens, who are a. dead from natural causes and hence b. usually old and c. embalmed. Some of your patients will be old, but few will be dead or embalmed. So the examination of a patient is an exercise in living anatomy. Living anatomy is sometimes called surface anatomy, because that is what we see - so the obvious drawback is that some parts cannot be seen or felt in the living.

But instruments do exist to allow us to extend the view from the outside on patients. These are usually called -scopes: endoscopes, proctoscopes, bronchoscopes etc. all allow further examination. Nowadays these are often fibre optic devices aided by computer visualisation, and can allow a good view of the gall bladder or the inside of the knee joint.
We can also add a range of indirect imaging techniques. The first of these was probably radiology, the directing of a beam of x-rays at a subject and the measurement of the intensity of what passes through, usually by means of darkening a photographic plate. Different tissues absorb radiation to different degrees, and the pattern of densities can record position shape and size of bones, fat, gas filled structures and so on. Interpretation is often a little difficult because structures at some distance from the source are magnified as the rays diverge and all structures are in focus, and so appear piled on top of each other in two dimensions. A plain radiograph can be enhanced by filling relevant bits of the patient with contrast medium, which is opaque to x-rays. This can be injected into a blood vessel or swallowed to outline parts of the gut.

Radio isotope imaging is a variant of this where the contrast medium is replaced by a radio labelled substance avidly taken up by the target tissue - for instance radio iodine can be used to target the thyroid gland. Tomography, is a newer technique in which source and photographic plate are moved in relation to the subject. Computer Assisted Tomography (CAT) is an even more sophisticated technique in which both x- ray source and detector (replacing film) are moved around the body, producing a data stream which is interpreted by a computer as a series of images equivalent to cross sections through the body at fixed intervals. The drawback is of course that X rays are now known to be harmful, inducing mutation and tissue damage.

Alternatives include:

• ultrasound which reflects from boundary layers between tissues of different densities
• magnetic resonance imaging (MRI) produces images according the atomic structure of their major components, by subjecting them to a strong collapsing magnetic force. Again pictures equivalent to cross sections of the body are produced.

We must also not neglect comparative anatomy. Man is an animal and his structure is often more easily understood with reference to his relatives. For instance the skull contains air sinuses: two alternative theories suggest that these may a. reduce weight and b. act as resonators for the voice. Comparative anatomy tells us that other vertebrates have sinuses, even those which make no sounds. Birds such as geese, which make long migratory flights, have extensive sinuses, in the skull and elsewhere.

Vocabulary

Anatomy has a very specialised vocabulary, much of it inherited from Latin, Greek and Arabic, and used in a very precise way. Medical students usually double their vocabulary during training, and most of the new words will come in the next two years.
There is a standard list of terms, in Latin, which has the disadvantage that virtually no-one uses it. More often we use an anglicised version of these names. Our clinical colleagues either use alternative versions or outdated ones (depending on when they trained). And on top of this is the so-called eponymous nomenclature, calling things after their discoverer, or your boss or folk hero. This is frowned upon as it is unhelpful - Madonna's ligament or Minogue's disease doesn't tell us much about it.

Major parts of the body

Anatomical usage follows general for most of the main parts, head neck, trunk. The limbs are a little different. The Anatomist calls these the upper and lower limbs, and arm means between shoulder and elbow, and leg between knee and ankle. We subdivide the trunk into thorax, above the diaphragm and abdomen, below it.

The anatomical position.

For descriptive purposes the body is always imagined to be in the anatomical position, standing erect, arms by sides, palms of hands facing forwards. In this position directions are given by superior, inferior, anterior, posterior. These are equivalent to the zoologists cephalad, caudad, ventral and dorsal. Thus the eyes are always superior to the mouth, even if the patient is lying down or standing on his head. These terms are not quite equivalent to above, below, in front of and behind. To a layman an acrobats feet are above her head when she is dangling from a trapeze: to an anatomist they are inferior.

Other dimensions are referred to the midline - median, medial or lateral, or to their closeness to the body surface, superficial or deep. In the limbs structures near the trunk are proximal, those further away are distal. We have a problem with the hands and feet: the palms of the hands resemble the soles of the feet and the thumb is equivalent to the great toe. But the palmar surface of the hand faces anteriorly and the back is dorsal. In the foot we defy logic and call the inferior surface plantar (equivalent to palmar) and the superior surface dorsal, even though it faces upwards. But we are still not out of the wood because the great toe is medial but the thumb is lateral. To get around this the term preaxial is often used to describe the thumb or great toe side. Postaxial is the little toe or little finger side. The axis referred to runs to the tip of the middle finger or the second toe.
The other small problem, the penis, is described in it's erect position, so that its dorsal surface faces anteriorly and superiorly when detumescent.

We also need to define planes, mutually at right angles. The horizontal plane is clear enough: the other two are a little less so. The sagittal plane (L. sagitta, an arrow) probably refers to the sagittal suture which runs from anterior to posterior in the newborn skull, and has an arrowhead in the form of the frontal fontanelle. Coronal is also difficult since it means crown, and I always think of a crown as being horizontal. But this is an older usage, as in the crown of an arch or a tooth, or the road, meaning something more like a halo.
Once again these refer to the anatomical position.

Now that we can describe the body at rest we can also deal with movement.
abduction is movement of any part away from the midline in the coronal plain
adduction is return to the midline flexion is moving anything in the sagittal plane
extension is straightening it again.
lateral flexion is bending in the coronal plane
rotation occurs around a vertical axis, or the main axis of the limb. If we rotate the head to the right we end up facing right. For the limbs we still use the displacement of the anterior aspect i.e. lateral rotation moves the palm laterally. The shoulder is a good joint to illustrate movement because it is so free. The slide shows what we can do, and how we describe it.

Hand and foot again pose problems because of their distinctive orientation. The hand has a rather unusual movement whereby the thumb can be brought to lie medially: in fact this crosses the bones of the forearm. The anatomical position of the hand is called supine, the reverse prone, so this movement is pronation reverse supination.
Abduction and adduction of the digits are refereed to the axis of the hand or foot, which remember pass through the middle finger and the second toe. We also have a thumb problem. Finger nails are posterior, but that of the thumb lies at right angles to the others. The thumb normally lies with its palmar surface facing medially. Flexion and extension are thus in a coronal plane while abduction and adduction are sagittal. The thumb also has another important movement, opposition which brings its palmar surface in contact with the palmar surface of the fingers.
The feet also bring problems, so we talk of dorsiflexion and plantar flexion and, a unique foot movement inversion and eversion as the soles are made to point towards each other or away.

Variability in anatomy

One important fact which an anatomist must recognise is that no two of us, even identical twins are exactly alike. The structure of the body varies with

• age
• race
• sex
• genetic diversity
• environmental history (especially during growth)

The anatomy in most textbooks is the commonest pattern in adults, usually from Europe or N America. Good texts will give variations if common. Remember the body is always right: often a bizarre variant never seen before will work well for 70 or 80 years. In one year we had difficulty finding a text book pair of kidneys, because they are so variable. Because of this variation you should always look at a number of bodies, prosections or colleagues.
Age. Although this is a whole field in itself it is important to recognise the commonest changes due to age, since you will be looking mainly at aged cadavers and young, fit adults. Bear in mind that an 80 year old will differ in these respects:

connective tissue - less elasticity - wrinkles
cartilage - less elasticity - degenerative changes such as osteo-arthritis with associated changes. Costal cartilages often replaced by bone: bony spurs develop in unusual places.
bone - becomes brittle, reduced in size with less activity
muscle - ditto, plus deposition of fat.
heart and blood vessels - arteries become tortuous, walls become furred up with atheroma. Left ventricle is enlarged as consequence of load. Veins often varicose.
nervous system - Often small strokes will cause paralysis and reduction in size of some muscles.
Race- This is a tricky one because of its emotive content, and because of the difficulty in defining race since the invention of the bicycle, steamship, jumbo jet etc. have done much to cause intermingling. Carefully noting the distinction between racism and Racialism we can say that there are obvious differences in skin and hair colour, hair type, eye colour, etc. and some subtle but small differences in anatomical measurements.
Sex - The two sexes obviously differ in their reproductive organs: they also differ in many other respects: although variability is quite large within a sex height, weight and muscle mass will differ significantly. Males also have narrower hips and broader shoulders. Females have more dermal fat, distributed differently. Facial and body hair also differs.
Genetic and other variation - congenital anomalies - There is quite a high level of genetic and environmental variation which leads to the presence of extra fingers, a single kidney, or an extra rib or so. This may be genetical or due to the exposure of the fetus to something unpleasant during pregnancy - x-rays, medicaments, viruses. Superimposed upon this is the variation due to habit - a regular swimmer will have a better developed upper body than his or her classmates: a smoker may have inferior lung capacity.

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