The purpose of our synovial joints (a freely movable joint) is to reduce friction and produce synovial fluid. Surrounding each of our synovial joints is a synovial membrane, which is what actually produces the synovial fluid. The synovial fluid resides in a synovial cavity, an area between the membrane and the bones that “lubricates joint surfaces and nourishes articular cartilages.” (Quotes come either from Professor Diamond or from my $40 barely used copy of Human Anatomy & Physiology, sixth edition, by Elaine N. Marieb. Most definitely a helpful resource and companion to Marian C. Diamond’s UC Berkeley lectures.)
This science of joints is known as arthrology (art = joint, ology = study of), and arthritis (itis = inflammation) is what it is called if any of those joints become inflamed.
Our joints come in handy for helping us to move and consist of “the junction of two or more bones.” I use my joints all the time when doing yoga, and at one time or another have moved every single joint in my body. Think about all the ways in which joints can be moved:
• flexion is the easiest to do and moves at a decreasing angle, such as flexing our arms and biceps
• extension is the opposite of flexion and consists of moving at an increasing angle, such as our triceps
• adduction is when we bring a limb toward our midline
• abductor is when we bring a limb away from our midline
• circumduction is when we move our joints in a circular motion
To facilitate this joint movement, our bodies have four types of joints, each with the ability to move the associated bones. The hinge joint increases and decreases angles; when you flex or extend your elbows and knees you are using your hinge joints. Another type of joint is the ball and socket, which consists of a “head” (the ball) in a “depression” (a cavity). The humerous (arm) fits into the glenoid cavity in this manner, and the femur (thigh) fits into the acitabulum.
The pivot joint lets one bone move around another, as happens in the forearm when the head of the radius pivots around the ulna. The saddle joint is prevalent in our fingers, where the convex end of the metacarpals fit into the concave end of the carpals.
Those may be the joints, but what are the threads? This morning I took a yoga class with Deb, who I first met five years ago on a brisk sunny February afternoon in Central Park when we were introduced by a mutual friend at The Gates. Deb often talks about the adductors and abductors, and this morning she mentioned our synovial fluid. She has been incorporating anatomical terms into yoga class for as long as I can recall, and it is no small delight to tie together my physical yoga practice with my study of anatomy.
In addition to our joints, our skeleton also consists of cartilage and bone. As Professor Diamond explains, bone is a connective tissue with cells, fibers, calcified matrix and lots of blood vessels. Cartilage is also a connective tissue with cells and fibers but with a firm, pliable matrix and no blood vessels. It gets nutrients by diffusion. It is important to note that bone is not calcified cartilage; they are different entities.
@!brainbits: Marian Diamond’s Human Anatomy lec#7 – “We all need an hour of exercise everyday!”
@brainbits: Bone is NOT calcified cartilage! Our bones develop by removing cartilage and laying down bone. (Thanks Marian Diamond!)