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A Gomphosis Joint Would Be Functionally Classified Assignment

JOINTS

A.  Describe the two systems for classifying joints.

B.Explain the structure of a fibrous joint, list the three types,and give examples of each type.

C.Give examples of cartilaginous joints.

D.Illustrate the structure of a synovial joint and explain theroles of the components of a synovial joint.

E.Classify synovial joints based on the shape of the bones inthe joint and give an example of each type.

F.Demonstrate the difference between the following pairsof movements: flexion and extension; plantar flexion and dorsiflexion; abduction and adduction; supination and pronation; elevation and depression; protraction andretraction; opposition and reposition; inversion and eversion.


joint, or an articulation, is a place where two bones come together. A joint is usually considered movable, but that is not always the case. Many joints exhibit limited movement, and others are completely, or almost completely, immovable.

  One method of classifying joints is a functional classification. Based on the degree of motion, a joint may be called a synar-throsis (sin′\ar-thrō′\sis; nonmovable joint), an amphiarthrosis (am′\fi-ar-thrō′\sis; slightly movable joint), or a diarthrosis (dı̄-ar-thrō′\sis; freely movable joint). However, functional classification is somewhat restrictive and is not used in this text. Instead, we use a structural classification whereby joints are classified according to the type of connective tissue that binds the bones together and whether there is a fluid-filled joint capsule. The three major struc-tural classes of joints are fibrous, cartilaginous, and synovial.

Fibrous Joints

Fibrous joints consist of two bones that are united by fibroustissue and that exhibit little or no movement. Joints in this group are further subdivided on the basis of structure as sutures, syn-desmoses, or gomphoses. Sutures (soo′\choorz) are fibrous joints between the bones of the skull (see figure 6.11). In a newborn, some parts of the sutures are quite wide and are called fontanels (fon′\tă-nelz′\), or soft spots (figure 6.37). They allow flexibility in the skull during the birth process, as well as growth of the head after birth. Syndesmoses (sin′\dez-mō′\sēz) are fibrous joints in which the bones are separated by some distance and held together by ligaments. An example is the fibrous mem-brane connecting most of the distal parts of the radius and ulna. Gomphoses (gom-fō′\sēz) consist of pegs fitted into sockets andheld in place by ligaments. The joint between a tooth and its socket is a gomphosis.



Cartilaginous Joints

Cartilaginous joints unite two bones by means of cartilage.Only slight movement can occur at these joints. Examples are the cartilage in the epiphyseal plates of growing long bones and the cartilages between the ribs and the sternum. The cartilage of some cartilaginous joints, where much strain is placed on the joint, may be reinforced by additional collagen fibers. This type of cartilage, calledfibrocartilage , forms joints such as the intervertebral disks.

Synovial Joints

Synovial (si-nō′\vē-ăl) joints are freely movable joints that con-tain fluid in a cavity surrounding the ends of articulating bones. Most joints that unite the bones of the appendicular skeleton are synovial joints, whereas many of the joints that unite the bones of the axial skeleton are not. This pattern reflects the greater mobility of the appendicular skeleton compared to that of the axial skeleton.


  Several features of synovial joints are important to their func-tion (figure 6.38). The articular surfaces of bones within synovial joints are covered with a thin layer of articular cartilage, which provides a smooth surface where the bones meet. The joint cav-ity is filled with fluid. The cavity is enclosed by a joint capsule, which helps hold the bones together and allows for movement. Portions of the fibrous part of the joint capsule may be thickened to form ligaments. In addition, ligaments and tendons outside the joint capsule contribute to the strength of the joint.

  A synovial membrane lines the joint cavity everywhere except over the articular cartilage. The membrane produces synovial\ fluid, which is a complex mixture of polysaccharides,proteins, lipids, and cells. Synovial fluid forms a thin, lubricating film covering the surfaces of the joint. In certain synovial joints, the synovial membrane may extend as a pocket, or sac, called a bursa (ber′\să; pocket). Bursae are located between structures that rub together, such as where a tendon crosses a bone; they reduce fric-tion, which could damage the structures involved. Inflammation of a bursa, often resulting from abrasion, is called bursitis. A synovial membrane may extend as a tendon sheath along some tendons associated with joints (figure 6.38).

Types of Synovial Joints

Synovial joints are classified according to the shape of the adjoin-ing articular surfaces (figure 6.39). Plane joints, or gliding joints, consist of two opposed flat surfaces that glide over each other. Examples of these joints are the articular facets between vertebrae.


 Saddle joints consist of two saddle-shaped articulating surfacesoriented at right angles to each other. Movement in these joints can occur in two planes. The joint between the metacarpal bone and the carpal bone (trapezium) of the thumb is a saddle joint. Hinge joints permit movement in one plane only. They consist of a convex cylinder of one bone applied to a corresponding con- cavity of the other bone. Examples are the elbow and knee joints (figure 6.40a,b). The flat condylar surface of the knee joint is modified into a concave surface by shock-absorbing fibrocartilage pads called menisci (mĕ-nis′\sı̄). Pivot joints restrict movement to rotation around a single axis. Each pivot joint consists of a cylindrical bony process that rotates within a ring composed partly of bone and partly of ligament. The rotation that occurs between the axis and atlas when shaking the head “no” is an example. The articulation between the proximal ends of the ulna and radius is also a pivot joint.


 Ball-and-socket joints consist of a ball (head) at the end of one bone and a socket in an adjacent bone into which a portion of the ball fits. This type of joint allows a wide range of move-ment in almost any direction. Examples are the shoulder and hip joints (figure 6.40c,d). Ellipsoid (ē-lip′\soyd) joints, or condyloid (kon′\di-loyd) joints, are elongated ball-and-socket joints. The shape of the joint limits its range of movement nearly to that of a hinge motion, but in two planes. Examples of ellipsoid joints are the joint between the occipital condyles of the skull and the atlas of the vertebral column and the joints between the metacarpal bones and phalanges.

Types of Movement

The types of movement occurring at a given joint are related to the structure of that joint. Some joints are limited to only one type of movement, whereas others permit movement in several directions. All the movements are described relative to the ana-tomical position. Because most movements are accompanied by movements in the opposite direction, they are often illustrated in pairs (figure 6.41).

 Flexion and extension are common opposing movements. The literal definitions are to bend (flex) and to straighten (extend). Flexion occurs when the bones of a particular joint are moved closer together, whereas extension occurs when the bones of a particular joint are moved farther apart, such that the bones are now arranged somewhat end-to-end (figure 6.41a,b). An example of flexion occurs when a person flexes the forearm to “make a muscle.”

  There are special cases of flexion when describing movement of the foot. Movement of the foot toward the plantar surface (sole of the foot), as when standing on the toes, is commonly called plantar flexion. Movement of the foot toward the shin, as whenwalking on the heels, is called dorsiflexion.


 Abduction (ab-dŭk′\shun; to take away) is movement away from the median or midsagittal plane; adduction (to bring together) is movement toward the median plane (figure 6.41c). Moving the legs away from the midline of the body, as in the outward move-ment of “jumping jacks,” is abduction, and bringing the legs back together is adduction.

 Pronation (prō-nā′\shŭn) and supination (soo′\pi-nā′\shun) are best demonstrated with the elbow flexed at a 90-degree angle. When the elbow is flexed, pronation is rotation of the forearm so that the palm is down, and supination is rotation of the fore-arm so that the palm faces up (figure 6.41d).

 Eversion (ē-ver′\zhŭn) is turning the foot so that the plantar surface (bottom of the foot) faces laterally; inversion (in-ver′\zhŭn)is turning the foot so that the plantar surface faces medially.

 Rotation is the turning of a structure around its long axis, as in shaking the head “no.” Rotation of the arm can best be dem-onstrated with the elbow flexed (figure 6.41e) so that rotation is not confused with supination and pronation of the forearm. With the elbow flexed, medial rotation of the arm brings the forearm against the anterior surface of the abdomen, and lateral rotationmoves it away from the body.

 Circumduction (ser-kŭm-dŭk′\shŭn) occurs at freely movablejoints, such as the shoulder. In circumduction, the arm moves so that it traces a cone where the shoulder joint is at the cone’s apex (figure 6.41f\).

  In addition to the movements pictured in figure 6.41, several other movement types have been identified:

·            Protraction (prō-trak′\shŭn) is a movement in which astructure, such as the mandible, glides anteriorly.

·            In\retraction(rē-trak′\shŭn), the structure glides posteriorly.

 

·            Elevation is movement of a structure in a superior direction.Closing the mouth involves elevation of the mandible.

·            Depression is movement of a structure in an inferior direction.Opening the mouth involves depression of the mandible.

 

·                          Excursion is movement of a structure to one side, as inmoving the mandible from side to side.

·            Opposition is a movement unique to the thumb and littlefinger. It occurs when the tips of the thumb and little finger are brought toward each other across the palm of the hand. The thumb can also oppose the other digits.

·            Reposition returns the digits to the anatomical position.

  Most movements that occur in the course of normal activities are combinations of movements. A complex movement can be described by naming the individual movements involved.

  When the bones of a joint are forcefully pulled apart and the ligaments around the joint are pulled or torn, a sprain results. A separation exists when the bones remain apart after injury to ajoint. A dislocationis when the end of one bone is pulled out ofthe socket in a ball-and-socket, ellipsoid, or pivot joint.

 Hyperextension is usually defined as an abnormal, forcedextension of a joint beyond its normal range of motion. For example, if a person falls and attempts to break the fall by putting out a hand, the force of the fall directed into the hand and wrist may cause hyperextension of the wrist, which may result in sprained joints or broken bones. Some health professionals, however, define hyperextension as the normal movement of a structure into the space posterior to the anatomical position.

The Joints

Let's Come together

THE JOINTS

  Joints can be classified into structural categories or they can be classified into functional categories.

The structural classification of joints takes in account what types of tissues are present in the joint and/or if a joint cavity exists.

The 3 Structural Categories of Joints Are...
  1. fibrous joints
  2. cartilaginous joints
  3. synovial joints 
The 5 Functional Categories of Joints Are...
  1. synarthroses (syn = together, arthro = joint), which are immovable joints
  2. amphiarthroses (amphi = on both sides), slightly movable joints
  3. diarthroses (dia = through, apart), or freely movable joints
  4. cartilaginous joints
  5. synovial joints (Only synovial joints have a joint cavity)
  •  Freely movable joints predominate in the limbs.
    • ​Synovial joints are freely movable. 
  • Immovable and slightly movable joints are largely restricted to the axial skeleton.
    • Immovable and slightly movable joints are much more stable than moveable joints. This means they are less prone to injury.
    • In general, fibrous joints (such as cranial sutures) are immovable.
    • However, cartilaginous joints have both rigid and slightly movable examples. 

Fibrous Joints

There are three types of fibrous joints.
  1. sutures
  2. syndesmoses
  3. gomphoses
Properties of fibrous joints.
  • Most fibrous joints are "fixed" or "immovable".
  • They have no joint cavity.
  • They are connected via fibrous connective tissue.

   Sutures are immovable joints that are completely filled with very short, interconnecting fibers, that appear like stitches or sutures. This type of joint is found only in the skull and nowhere else in the body.  The immovable nature of the sutures "fixes" the cranial bones in position as a protective adaptation that protects the brain. 

 Syndesmoses are immovable joints that are held together with ligaments. Between the fibula and tibia at the ankle.

     In syndesmoses, the bones are connected by ligaments and bands of fibrous tissue. The syndesmoses may have some very slight movability , depending on the length of the cords or bands of fibrous tissue that it is composed of.  The longer the fibrous tissue, the more movability is possible. The cords and bands of fibrous tissue found in syndesmoses are always shorter than those found in sutures. 

The only example is the articulation of a tooth with its bony alveolar socket. The term gomphosis comes from the Greek gompho, meaning “nail” or “bolt,” and refers to the way teeth are embedded in their sockets (as if hammered in). The fibrous connection in this case is the short periodontal ligament

Cartilaginous Joints

   As you might expect, cartilaginous joints contain cartilage. They do not have a cavity and are slightly mobile.
  There are two types of cartilaginous joints.
1) Synchondroses
2) Symphyses

Synchondrosis ​

    The term "synchondrosis" means “junction of cartilage”.  These joints are joined via plates of hyaline cartilage. Virtually all synchondrosis joints are synarthrotic (immovable).
Examples of synchondroses include...
  1. The epiphyseal plates (epiphyseal lines) in long bones of children. Epiphyseal plates are temporary joints and eventually become synostoses.
  2. Another example of a synchondrosis is the immovable joint between the costal cartilage of the first rib and the manubrium of the sternum. 

Symphyses ​

Synovial Joints

Plane or Gliding Joint

A plane joint or gliding joint, is formed from flattened articulation surfaces. This structures allows the bones to glide past one another in any direction.

Hinge Joints

Hinge Joints Allow for Flexion and Extension

Hinge joints provides a stable and smooth structure that allows for the motions of flexion and extension. ​
  • Flexion = Flexion is the bending movement that decreases the angle of the joint and brings the articulating bones closer together.
  • Extension = Extension is the reverse of flexion and occurs at the same joints. It increases the angle of the joint . It typically straightens a flexed limb or body part. 


Pivot Joints

    In addition to the hinge joint formed between the ulna and the humerus, the elbow joint also has a pivot joint that is formed between the humerus and the radius. 
    Pivot joints allow for rotational motion.  The pivot joint between the radius and the humerus, allows for 2 unique movements that are only possible in the forearms and hands, and are not possible anywhere else in the body. These movements are called pronation and supination.​. 


Ball-and-Socket Joints

1.  Shoulder (Glenohumeral) Joint

   The shoulder or glenohumeral joint is the most freely moving joint of the body. However, in order for this freedom of movement to exist, the shoulder joint itself has sacrificed stabilization. Even though ball-and-socket joints have the potential to be very stable, in the case of the glenohumeral joint, the glenoid cavity of the scapulae is much too shallow to stabilize the large head of the humerus it articulates with. In fact, the glenoid cavity is only about one-third the size of the humeral head and adds only minimal stability to the joint. 


  • The coracohumeral ligament provides helps support the weight of the upper limb anteriorly. 
  • Three glenohumeral ligaments provide minor support. 
  • The “superstabilizer” is the tendon of the long head of the biceps brachii muscle of the arm. This tendon secures the head of the humerus against the glenoid cavity.


   Rotator cuff muscles and tendons encircle the shoulder joint adding to its stability.  The rotator cuff muscles include the subscapularis, supraspinatus, infraspinatus, and teres minor. The rotator cuff is a common area of injury due to vigorous circumduction. ​

The Hip (Coxal) Joint 

Temporomandibular Joint

      The temporomandibular joint (TMJ), or jaw joint, is the articulation of the mandibular condyles (located on the mandible) and the mandibular fossa (located on the temporal bones). This joint is a modified hinge joint that lies just anterior to the ear. 

     Temporomandibular joint dysfunction (TMD or

   Some of the long bones in the body such as he radius and ulna in the forearm and the tibia and fibula of the lower leg are joined by a syndemosis (singular) or syndemoses (plural). Syndesmoses are considered slightly movable (or amphiarthrodial). 

  A gomphosis is a "peg-in-socket" fibrous joint.​ The term gomphosis comes from a word meaning “nail”. This type of articulation found between our teeth and the bony sockets they sit in. The tooth is held into place in its socket through the periodontal ligament.

  The term symphysis means “growing together". The bone of these joints are connected using fibrocartilage. Fibrocartilage is strong. resistant and is a good shock absorber. These joint permit only a limited amount of movement. The surface of the fibrocartilage is covered with a layer of hyaline cartilage, to act as articular cartilage for the bony articulation points. ​
​ Examples of symphases include...
  1. the intervertebral joints
  2. the pubic symphysis of the pelvis 

    Synovial joints are joints in which the articulating bones are separated by a fluid-filled joint cavity.  
​      Synovial joints are freely movable diarthroses. These types of joints are found in almost all of the joints in the limbs, and also make up the majority of the joints in your entire body, 

Gliding joints are found between the carpal bones of the wrist.


Gliding joints are found between the tarsal bones of the ankle; and between the tarsals and the metatarsals of the foot.


Gliding Movements :  Gliding motion is permitted by joints that have with relatively flat articulating surfaces. These are the "plane joints" or "gliding" joints of the body. The movements arises from the nearly flat articulating surfaces of bone that "glide" across each other. The direction of the "gliding" motion can be either back-and-forth or side-to-side.
  • Gliding occurs at the following regions:
    • intercarpal joints
    • intertarsal joints
    • between the vertebrae 
  Hinge joints are located in our phalanges, ankles, elbows, and knees. Hinge joints are formed between two or more bones where the bones can only move along one axis to flex or extend.
​   The elbow joint has a hinge joint formed between the distal end of the humerus the proximal end of the ulna.
The elbow joint has a hinge joint formed between the distal end of the humerus the proximal end of the ulna.
The elbow joint has a hinge joint formed between the distal end of the humerus the proximal end of the ulna.
Pronation and supination are movements only found in the forearms and hands, that allow for the rotation of the hands.
  • Supination is when the hand is rotated toward the direction of the thumb, which results in the palms facing superiorly.
  • Pronation is when the hand is rotated in the opposite direct of the thumb, which results in the palms facing inferiorly. 
The elbow joint has a pivot joint formed between the distal end of the humerus the proximal end of the radius.
Ball-and-socket have the most freedom of motion. There are only two ball-and-socket joints in the entire body.
  1. The shoulder joints
  2. The hip joints

Ball-and-Socket Joints Allow for Circumduction of the Limbs.

The circular (or, more precisely, conical) movement of a body part, such as a ball-and-socket joint or the eye. It consists of a combination of flexion, extension, adduction, and abduction. "Windmilling" the arms and rotating the hand from the wrist are examples of circumductive movement.


​The hip (coxal) joint is a much more stable ball-and-socket joint, compared to the shoulder joint. In the hip joint, the acetabulum creates a deeply cupped surface of articulation for the head of the femur, which gives the joint added stability. However, the tradeoff is that the range of motion is more limited than that of the shoulder joint.


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