Biomedical Engineering Reference
In-Depth Information
Red marrow produces blood cells, while the yellow marrow is a store of adipose tissue for
future energy needs.
Bone is relatively inflexible, and the only way that movement can occur is at the joints
between the bones. There are three types of joints in the body that are each classified
based on the range of movement that they permit. The first type of joint allows no move-
ment between the neighboring bones and are termed synarthroses joints. The bones do not
rotate about each other because the edges are typically in contact and may even be fused
together. These joints are very strong and can be considered an extension of the bone itself.
This type of joint is commonly found between the bones that compose the skull. In some
sense, the bones are not individual anymore because they fuse to one another. The second
type of joint, the amphiarthroses joint, allows some movement between the neighboring
bones. These joints are still relatively strong and typically connected by collagen fibers or
cartilage. This type of joint can be found between the radius and the ulna or the tibia and
the fibula within the limbs. These bones rotate slightly around each other but do not have
a great deal of free motion.
The third type of joint, the diarthroses joint, allows a wide range of motion depending
on the structure of the joint. This type of joint is surrounded by an articular capsule and a
synovial membrane. The synovial membrane runs along the interior portion of the articu-
lar capsule. Synovial fluid (which will be discussed in
Sections 11.2
and
11.3
) fills the
space in between the two bones. There are six types of diarthroses joints, depending on
the exact nature of the movement that the joint allows. The first joint type is the gliding
joint, which typically allows translation in one or more directions. The bones that are in
contact with each other are typically flat or slightly rounded, allowing for the translational
motion without rotation. Movement within these joints (as well as rotation) is restricted by
the ligaments that anchor the bones. An example of this type of joint is the joint that is
formed from the connection between the clavicle and the manubrium. The second type of
joint is the pivot joint, which typically only allows rotation about one axis. It is normal for
the bones in these joints to be touching each other and for a small piece of ligament con-
nected to the first bone wraps around the second bone. An example of this type of joint is
between the atlas and the axis within the neck. The last joint that allows motion in one
direction is a hinge joint. This joint also allows rotation about the joint that connects the
bones but not translation. The elbow and the knee are two examples of a hinge joint.
The remaining types of diarthroses joints allow more degree of freedom in their move-
ment than the first three described. The first of these joints is the ellipsoid joint, which
allows rotation in two planes. Typically, one bone has a convex protrusion which fits
within a concave depression of a second bone. An example of this type of joint is found
between the metacarpal and phalanges bones within the hand (i.e., finger joints). The next
type of joint, the saddle joint, also allows rotation within two planes. One of the bones is
shaped like a saddle and the second bone is shaped like a rider's lower body surrounding
a saddle. This is also a concave surface facing a convex surface. This type of joint allows
the movement of the thumb about the trapezium. The last type of joint is the ball-and-
socket joint, which allows for three-dimensional rotation about the joint. In this type of
joint, the end of one bone is shaped as a ball and the other bone is concave. The ball fits
within the concave depression and is held in place by ligaments. The shoulder and hip
joints are examples of ball-and-socket joints.
Search WWH ::
Custom Search