The Biological Basis of Bone & Anatomical Directional   Terms

28 FEB http://thesebonesofmine.wordpress.com/category/diagenesis/

Be prepared for a long post!

The adult human skeleton  consists of more than 200 separate bones (often around

206) whilst the juvenile skeleton can have over 300 individual bones (predominately

in newborn babies) (White & Folkens 2005).  Over time certain bones fuse to others

(such as the os coxa or hip bone) to produce stable and protective environments

once the soft tissues have fully grown (ie the plates of the cranium once the brain

has fully grown).  In life, the skeleton can weight from between 12% to 20% of a

person’s weight.  Please click on the below picture to enlarge the general elements

in the human skeleton.

Basic Human Skeletal Elements.

The skeleton, and individual bones, both act as tissue and as organs (White &

Folkens 2005).  Primarily the skeleton acts as a mechanical component for the

musculoskeletal system.  They provide a framework for the organs and support for

the body by helping to anchor muscles, tendons and ligaments; as well as acting

as rigid levers for the muscles to help produce movement (White & Folkens 2005:

31).  Important physiological functions include the production of blood cells whilst

bone can also acts as a storage for calcium & fat deposits.

Traditionally skeletal elements are classed around 4 main groups- long bones, short

bones, flat bones, & irregular bones.  Bone is mainly consisted of a composite

material of Hydroxyapatite (mineral) &  Collagen (protein).  It is amongst the

strongest of biological materials- able to cope with high stress levels, bending

& contortion pressures.  The basic structure of living bone is provided below. 

The outer surface is the membrane called the Periosteum, the outer bone surface

is called Cortical bone (otherwise known as compact bone), the inner bone is

called Trabecular bone (spongy, shock absorbing), whilst in the long bones

a Medullary Cavity is often present (Mays 2008, Schwartz 2007).

Basic Long Bone Anatomy Diagram (Wikipedia).

Generalized Bone Growth (Baron

2008-http://www.endotext.org/parathyroid/parathyroid1/parathyroid1.html).

The growth of bones in the womb up until full maturity is directed by two

different processes.  Endochondral Ossification  is a process by which bones are

preceded by cartilage models.  Ossification is initiated before birth of the baby, and

is amongst one of a number of processes

ongoing. Intramembranous   Ossification   occurs when apposition of tissue within an

embryonic connective tissue membrane covering.  However, this is limited to the

Cranial (Frontal & Parietal) bones (White & Fokens 2005: 46).

Fusion of the epiphysis plates to the diaphysis plates in the long bones of the

skeleton (femora, tibia, humeri etc) occurs during late adolescence, and is often

used as an age estimator.  Anatomical directional terms and planes of reference are

used to give precise locations when discussing the human skeleton.  This is so that

when using this nomenclature it is obvious to all concerned about what is being

talked about; it is used to avoid ambiguity.  Below is a diagram outlining the main

terms.

Anatomical Planes (Wikipedia).

Standard Anatomical Directions.

The skeleton is often described of as composing of the appendicular & the axial

skeleton.  The appendicular skeleton is the locomotor of the body.  The appendicular

skeleton includes the elements and joints of the feet, leg & hip bones together with

the hand, arm and shoulder bones.  This allows an astonishing array of movement

and functions, although more rotation and general movement is permissible at the

shoulder joint because of its structure in comparison to the weight bearing hip and

knee joints (Schwartz 2007).  The axial skeleton holds the pelvic girdle, the ribcage,

the shoulder girdle & the cranium.  This houses all of the main organs of the body,

and supports the basic biological function of life as we know it.

Finally, I’ll quickly mention bone microstructure.  The basics of bone microstructure

include both Volkmann’s & Haversian canals- basic nutritional and blood supplies

for the bone.  At the micro level, bone is made of and replaced by

Osteons- including Osteocytes, Osteoblasts, Osteoids & Osteoclasts.  In living

persons the bone is covered by the periosteum, a living tissues that acts as a soft

tissues from which vessels bringing in and out blood etc moves through (White &

Folkens 2005).  Here is a guide depicting variation between human and

various animal microstructure, and how to recognise the variations.  But we will

leave those for now (and discuss them in  later post)- instead here is a tasty

transverse diagram of the insides of the microscopic structure of bone!

Bone Microstructure (Wikpedia 2011).

A full list of terms & directions are described here.  As we are in the business of

archaeology, the condition of the bone is dependent on two main processes post

burial/deposition Diagenesis & Taphonomic changes.  Diagenesis “is the cumulative

physical, chemical and biological environment; these processes will modify an

organic object’s original chemical and/or structural properties and will govern its

ultimate fate, in terms of preservation or destruction” (Wikipedia 2011).  Whilst

taphonomy is the study of decaying and decayed organisms. Thus the ”study

(of) taphonomic processes(can be used) to determine how plant and animal (as well

as human) remains accumulate and differentially preserve within archaeological

sites. This is critical to determining whether these remains are associated with

human activity. In addition, taphonomic processes may alter biological remains after

they are deposited at a site.” (Wikipedia 2011).

A discussion of tooth anatomy will follow in the next week or so, as teeth are a

distinct part of our bony body.  Various elements of the skeleton, ie the vertebral

column, will be discussed in separate posts for a more in depth study.  For the

moment it is important to grasp the fundamentals.  Terminology regarding subject

key words (terms such as ‘Bioarchaeology’ or ‘Physical Anthropology’) will be

discussed in the following post to decide what exactly they mean, and where they

came from.  Hopefully this short series of introduction posts will help broaden your

knowledge of Human Osteology…

o Please head over to Powered By Osteons blog to learn about the microbiology of

bone, including how Osteoblasts & Osteclasts work.

Bibliography:

Larsen, C. 1997. Bioarchaeology: Interpreting Behaviour From The Human

Skeleton. Cambridge: Cambridge University Press.

Mays, S. 1999. The Archaeology of Human Bones. Glasgow: Bell & Bain Ltd.

Schwartz, J. H. 2007. Skeleton Keys: An Introduction to Human Skeletal

Morphology. New York: Oxford University Press.

White, T. & Folkens, P. 2005. The Human Bone Manual. London: Elsevier Academic

Press.