NOTE: Lecture notes are intended to help the student organize their notes and facilitate assimilation of the material. They are in no way a substitute for the actual lectures; however, this material will be covered on exams!
Text Reference: CHAPTER 9
An ARTICULATION (JOINT) is a point of contact between two bones. Some joints are freely movable, while some are partially movable or even immovable. Some articulations, such as the sutures in the skull, are FIBROUS JOINTS held together by fibrous connective tissue (Fig. 9.1). Fibrous joints allow little or no movement. Sutures of the skull, for example, are completely immovable. Other examples of fibrous joints can be seen in Fig. 9.1. A second type of joint is a CARTILAGINOUS JOINT (Fig. 9.2). The joints between vertebrae are cartilaginous joints, because they are separated by intervertebral discs made of fibrocartilage. The joints between vertebrae are movable. Another cartilaginous joint is the pubic symphysis, which is slightly movable (Fig.9.2). The pubic symphysis contains a fibrocartilage disc to absorb compression. Another example of a cartilaginous joint is between a true (vertebrosternal) ribs and the sternum, because costal cartilage separates the bones. A third type of joint is the SYNOVIAL JOINT (Fig. 9.3). These joints are freely moveable, and include such joints as the shoulder, elbow, hip, and knee joints. SYNOVIAL JOINTS are defined as freely movable articulations with a joint space (synovial cavity) between the articulating bones (Fig. 9.3).
We will look at more detail of SYNOVIAL JOINTS. A joint in which there is a space between the articulating bones is called a SYNOVIAL JOINT. See FIG. 9.3. A SYNOVIAL JOINT is a freely movable joint. There is a small space between the articulating bones called the SYNOVIAL CAVITY, which contains synovial fluid. Covering the epiphyses (ends) of the bones at the synovial joint is ARTICULAR CARTILAGE, which is glassy-smooth hyaline cartilage that cushions the epiphyses where the bones come together at the joint. The synovial cavity is surrounded by an ARTICULAR CAPSULE, which consists of an outer FIBROUS CAPSULE lined with SYNOVIAL MEMBRANE. The outer fibrous capsule consists of dense irregular connective tissue, which is attached to the periosteum of the neighboring bones. The inner layer of the articular capsule is a SYNOVIAL MEMBRANE, a tissue membrane composed of areolar connective tissue with elastic fibers and some adipose tissue. The synovial membrane secretes a small amount of slippery SYNOVIAL FLUID into the synovial cavity. Synovial fluid has a viscous (thick), uncooked egg-white consistency. It becomes less viscous as it warms during joint activity. The synovial fluid lubricates the joint to reduce friction and prevents articular cartilage erosion. Synovial fluid also nourishes the articular cartilage (since the cartilage is avascular). Synovial fluid contains macrophages, white blood cells that consume microbes and cellular debris resulting from wear and tear during joint activity.
See FIG. 9.4 for the different kinds of synovial joints. You should know hinge joints, pivot joints, and ball-and-socket joints.
Synovial joints are reinforced and strengthened by LIGAMENTS, cords of dense irregular connective tissue that hold bone to bone. See FIGURES 9.11-9.16 for examples of ligaments.
Inside the synovial cavity of the TEMPOROMANDIBULAR JOINT (Fig. 9.11) and the KNEE JOINT (Fig. 9.15) are fibrocartilage pads called ARTICULAR DISCS. In the knee joint the articular discs are called the LATERAL & MEDIAL MENISCI (meniscus, singular). These discs allow 2 bones of different shapes to fit tightly at a joint, which helps maintain the stability of the joint. Since they are made of fibrocartilage, they are able to resist compression forces that would be experienced at the jaw and knee joints. The knee joint also contains a fat pad to cushion the joint.
See FIGS. 9.12 (shoulder joint), 9.13 (elbow joint), & 9.15 (knee joint) for examples of BURSAE. A bursa is a fluid-filled sac found between skin & bone, tendons & bone, muscles & bone, or ligaments & bone. Their functions are to cushion the bone and reduce friction between moving parts at joints. The wall of the bursa is connective tissue and the fluid inside is similar to synovial fluid.
TYPES OF MOVEMENTS AT SYNOVIAL JOINTS: (FIGS. 9.5-9.10, TABLE 9.2 &
Hand-out of joint movements)
1. FLEXION is a bending movement that decreases the angle of the joint and
brings the articulating bones closer together.
2. EXTENSION involves straightening the joint between articulating bones.
2a. HYPEREXTENSION is the extension of a joint beyond the
anatomical position.
NOTE: Flexion, extension & hyperextension of the head occurs between the occipital condyles of the skull and the superior articular facets of C1 (the atlas).
3. ABDUCTION is the movement of a bone away from the midline of the body
along a frontal plane.
4. ADDUCTION is the movement of a bone toward the midline of the body.
5. CIRCUMDUCTION consists of the movements of flexion, abduction, extension, and adduction performed in a succession so that the limb describes a cone in the air. The proximal end of the limb remains stable, while the distal end moves in a circle.
6. ROTATION is the turning of the bone around its long axis. It is the only movement allowed between C1 (atlas) and C2 (axis). It is a common movement at the hip and shoulder joints. In MEDIAL ROTATION, the anterior surface of the bone moves toward the midline. In LATERAL ROTATION, the anterior surface moves away from the midline.
7. INVERSION is the movement of the sole of the foot inward or medially.
8. EVERSION is the movement of the sole outward or laterally.
9. DORSIFLEXION is the flexion of the ankle so that the superior part of the
foot moves toward the shin.
10. PLANTAR FLEXION is the extension or straightening of the ankle so that you
are pointing your toes.
11. SUPINATION is the movement of the flexed forearm so that the palm is
turned anterior or superior.
12. PRONATION is the movement of the flexed forearm so that the palm is turned
posterior or inferior.
NOTE: The ulna and radius are parallel during supination, but the radius
crosses over the ulna during pronation.
13. PROTRACTION is the forward movement of the mandible or shoulder girdles
on a plane parallel to the ground.
14. RETRACTION is the movement of the protracted mandible or shoulder girdles
back along a plane parallel to the ground.
15. ELEVATION is the upward movement of a body part (mandible or shoulder
girdle).
16. DEPRESSION is the downward movement of a body part (mandible or shoulder
girdle).