Welcome to the second video of the fourth module, all about how we reconstruct aspects of activity from the skeleton. Before we can proceed to the case studies, we need a quick lesson about the musculoskeletal system, or MSK, as it's abbreviated. And that's because, what we are, in fact, most interested in inferring from the features that we see on the bone are the actions of the overlying muscles and joints. Muscles, bones, the joints between bones, cartilage, tendons, and ligaments, all types of connective tissue constitute the musculoskeletal system. So while in archaeology we only the bones left, usually at least, it's the interaction of all connective tissues that is important to reconstruct the types of activities that people commonly engaged in. So let's first talk about muscles. There are three types of muscles, cardiac, smooth and skeletal. Only the skeletal muscles can be moved consciously and they're the focus of the rest of this video. Muscles are innervated, meaning they are containing nerves. And this them the ability to contract, to bring about movement. Skeletal muscles are attached to bones and arranged in opposing groups around joints. There are around 650 muscles in the human body, almost all of which are paired, one on the right and one on the left, so giving us over 300 pairs of muscles. And as with bones, the muscles can be categorized into anatomical groups, so muscles related to the head and neck, muscles of the torso or trunk, muscles or the upper and lower limb, etc. And to bring about almost any movement, usually a group of muscles work together. Seldom is just a single muscle. Usually one muscle is main force or prime mover and others help to fine tune that movement. So especially important for osteoarchaeologists is how muscles are attached to bones, and that's via tendons. Perhaps you know of probably the most famous one, the Achilles tendon. This is a tendon on the back of the leg and it's the thickest in the human body. It attaches your calf muscles to your calcaneus or heel bone. Achilles heel refers to someone's vulnerability or downfall and relates to the mythical story of Achilles, who was slain during the Trojan War by a poisoned arrow to his heel. A tendon is a tough flexible band of fibrous connective tissue that binds muscle fibres to the bone's ends. Each muscle is labelled as having an origin and an insertion tendon site, relative to the particular movement of the joint or body part in question. An easy way to think about this is that the origin site is the one that does not move or at least moves very little, compared to the insertion site which is the site that moves more when the muscle contracts. It's also useful to know what a ligament is. Our ligaments is a band of dense fibrous elastic tissue that connects bones together in order to form a joint. It functions to help prevent dislocation and limit the range of movement of a joint. There are specific terms used to describe movements, for example, flexion versus extension, abduction versus adduction, lateral versus medial rotation. This figure depicts several of the most common movement terms that you may hear us use. There's a short list defining these terms in course documents that you can consult, if interested. The last thing we need to cover before diving into the case study is joints. And that's because the appearance, specifically the degradation of joints, can be a useful clue about activity patterns in past populations. So as you know, a joint or an articulation is location where two bones connect, but in some cases, the bones don't connect directly. The body's joints can be classified according to their structure or their function. Structural classification divides joints according to the type of binding tissue that is involved. There are three classifications. A fibrous joint, these joints are joined by tense connective tissue and include the cranial sutures. A cartilaginous joint, which are joined by cartilage, like where the ribs are joined to the breastbone, or sternum. And a synovial joint, like the knee, in which bones are not directly joined, rather they're connected in a fibrous capsule that's filled with synovial fluid. They're the most common and most movable type of joint in the body. The ends of bones in a synovial joint are covered in a layer of smooth articular cartilage and this functions to absorb shock and reduce friction during movement. It's this latter type that's especially useful to osteoarchaeologists, because we can see evidence of its degeneration and the degeneration can be brought about by strenuous repetitive activity. In summary, in this video you've learned about the different components of the musculoskeletal system, muscles, tendons, ligaments, and joints. And this will be important as we move ahead with our case studies. Our first case study is coming up next and looks at how musculoskeletal markers called entheses reveal differences in the labour patterns of rural farming men and women from 19th century Netherlands.
