ARTICULATIONS
A.CLASSIFICATION OF JOINTS
What is an articulation?
An articulation (joint) is a point of contact between bones, between
cartilage and bone, or between teeth and bones.
What determines a joint’s function?
A joint’s structure determines its function(s).
Name the four factors that influence the range of motion allowed at any particular joint?
1.tightness of fit between bones
2.precise manner in which the bones fit together
3.tightness of the tissues that bind the bones of the joint together
4.position of the ligaments, muscles, and tendons surrounding the
joint
1.STRUCTURAL CLASSIFICATION
Name the structural classification of joints and give a brief description of each.
Fibrous – There is no joint cavity. the bones are held tightly
together by dense fibrous connective tissue.
Cartilaginous – There is no joint cavity. The bones are held
together by a bridge of cartilage.
Synovial – There is a joint cavity present. the bones are held
together loosely by a surrounding capsule of connective tissue and by various ligaments.
2.FUNCTIONAL CLASSIFICATION
Name the functional classification of joints and give a brief description of each.
Synarthrosis – This is an immovable joint.
Amphiarthrosis – This is a slightly movable joint.
Diarthrosis – This is a freely movable joint.
B.DIARTHROSES (FREELY MOVABLE JOINTS)
1.STRUCTURE OF A DIARTHROSIS
Describe each of the following components of a synovial joint:
Joint cavity – The distinguishing anatomical feature of a diarthrosis
is the synovial (joint) cavity, a fluid-filled space that separates the articulating bones.
Articular cartilage – There is articular cartilage (hyaline type) that
covers the surfaces of the bones at their point of articulation, but does not bind the bones together.
Synovial fluid – Synoviocytes, lining the inside surface of the
synovial membrane, secrete synovial fluid into the joint cavity for lubrication of the articular cartilages and the nourishment of the cartilage cells.
Articular capsule – The sleeve-like articular capsule surrounds the
joint, uniting the two bones by forming a sac-like structure that incorporates the ends of each bone.
outer layer – The outer layer of the articular capsule is the
fibrous capsule. It is formed of dense irregular connective tissue that blends with the periostea of the two bones and provides flexibility with resistance to dislocation.
inner layer – The inner layer of the articular capsule is the
synovial membrane. It is composed of synoviocytes, areolar tissue, and adipose tissue.
Describe each of the following:
Accessory ligaments – In addition to the ligaments formed by
thickenings of the fibrous capsule, most synovial joints have accessory ligaments as well. These are not an integral part of the fibrous capsule.
extracapcular – Extracapsular ligaments lie outside the
articular capsule and bridge the two bones.
intracapsular – Intracapsular ligaments lie within the articular
capsule and bridge the two bones. They are excluded from the joint cavity by wraps of the synovial membrane.
Describe the articular discs (menisci) of cartilage found in the knee and shoulder joints. What are their functions?
Inside the shoulder and knee joints are pads of fibrocartilage called the articular discs (menisci). these pads lie between the articular bone surfaces in addition to the articular cartilages and are attached to the fibrous capsule by ligaments.
They serve to:
1.allow the ends of the articulating bones to fit more closely
together;
2.give more stability to the joint by giving a better fit between
the bones; and
3.direct the flow of synovial fluid to areas with greatest friction.
What are bursae?
Associated with may synovial joints are synovial membrane-lined, synovial fluid-filled sacs called bursae.
Where are they found?
Bursae are strategically located between moving parts. In general, they are found between skin and bone, tendon and bone, muscle and bone, ligament and bone, or articular capsule and bone.
What is their function?
Their function is to reduce the great amounts of friction that are
generated between moving parts during various motions.
2.CONTACT AT A DIARTHROSIS
Several factors contribute to keeping the articular surfaces of bones in a synovial joint in contact. These factors, in turn, determine the type and extent of motion that is possible at the joint.
Identify these five factors.
1.structure or shape of the articulating bones
2.strength and tension of the joint ligaments
3.arrangement and tension of muscles around the joint
4.apposition of soft parts
5.hormones (relaxin)
3.MOVEMENT AT A DIARTHROSIS
Identify each of the four major movement types allowed by synovial joints and give a brief description of each.
Gliding – Gliding movements are the most simple. One surface
moves back-and-forth and/or side-to-side over another without angular or rotary motion. Examples would be those joints between the carpal bones and those between the tarsal bones. The ribs glide on the vertebrae and the clavicle glides on both the sternum and the scapula.
Angular – Angular movements are those in which the angle
between the articulating bones changes. There are five.
Flexion – Flexion decreases the angle between the two
articulating bones.
Extension – Extension increases the angle between the
articulating bones.
Hyperextension – Hyperextension continues the extension
movement beyond the anatomical position.
Abduction – Abduction refers to movement away from the
body’s midline.
Adduction – Adduction refers to movement towards the
body’s midline.
Rotation – Rotation movements are movements of a bone in a
single plane about its own longitudinal axis. In medial rotation the anterior surface of the bone or extremity rotates towards the midline. Lateral rotation is just the opposite.
Circumduction – Circumduction movements are those in which the
distal end of the bone moves in a circle while the proximal end remains relatively fixed in position. This is really a combined movement of flexion-extension and abduction-adduction. The shoulder joint and hip joint are capable of circumduction.
4.SPECIAL MOVEMENTS AT DIARTHROSES
List the five pairs of special movements allowed by diarthroses and give a brief description of each.
Elevation vs depression – Elevation is an upward movement of a
body part, while depression is a downward movement. The mandible and the shoulder do these movements.
Protraction vs retraction – Protraction is a movement forward on a
plane parallel to the ground, as in thrusting the mandible forward. The shoulders can also be protracted. Retraction is the opposite movement.
Inversion vs eversion – Inversion is the movement of the sole of the
foot inward (medially) so that the soles face each other. Eversion is movement of the sole outward (laterally) so that the soles face away from each other.
Dorsiflexion vs plantar flexion – Dorsiflexion involves bending the
ankle in the direction of the dorsum (top) of the foot, as in trying to stand on your heels. Plantar flexion is bending the ankle in the direction of the plantar surface (sole) of the foot, as in standing on your toes.
Supination vs Pronation – Supination is a movement of the forearm
in which the palm of the hand is turned anteriorly (anatomical position). Pronation is the movement that turns the palm posteriorly.
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