JOINTS (ARTICULATIONS)

Transcription

1 CJ Shuster A & P I Note Series Articulations 1 JOINTS (ARTICULATIONS) - JOINTS or ARTICULATIONS - sites where 2 or more bones meet. Hold skeleton together & give it motility (by using muscles). All locomotion movement (i.e., movement through space) is causes by one bone moving with respect to another bone around a joint. - Articulations can be classified structurally or functionally. Synarthrotic I. FUNCTIONAL CLASSIFICATIONS 1) Synarthroses(is) - immovable joints; axial skeleton only. * sutures between bones of the skull or os coxae. 2) Amphiarthroses(is) - slightly movable joints, axial skeleton only. * joints between vertebrae Amphiarthrotic 3) Diarthroses(is) - freely movable joints. - limbs; appendicular skeleton mostly. *elbow, shoulder, knee, etc. II. STRUCTURAL CLASSIFICATIONS Diarthrotic - names indicate the tissue type that join the bones together. A. FIBROUS JOINTS -bones joined by fibrous tissue. No joint cavity. Most are synarthrotic, but a few are amphiarthrotic. 1) Sutures ( seams ) - wavy articulating bone interlocks with neighboring bone; junction between bone is filled with short connective tissue fibers. During adulthood, the fibrous tissue ossifies, fusing the bones. 2) Syndesmoses(is) - bones are connected to each other via a LIGAMENT (a band of fibrous connective tissue). Example: the connection between the tibia & fibula, and the radius & ulna. 3) Gomphoses(is) - peg-in-socket joint. Teeth held in sockets using the PERIODONTAL LIGAMENT.

2 CJ Shuster A & P I Note Series Articulations 2 B. CARTILAGINOUS JOINTS - bones joined by cartilage. No joint cavity. Synarthrotic or amphiarthrotic. 1) Synchondroses(is) - plate of hyaline cartilage unites bones. Give individual bones some flexibility (the epiphyseal plate is the only example). Become ossified at adulthood. 2) Symphyses(is) ( growing together ) - surface of bone covered with articular cartilage, which fuses with a fibrocartilage pad between the bones. Amphiarthrotic only. Intervertebral joints and pubic symphysis only. C. SYNOVIAL JOINTS - All freely moveables (diarthrotic), all joints of the limbs (in fact, most of the body). Characteristic structure: articulating bones are separated by a fluid-filled joint cavity. - Several distinct features: 1) articular cartilage - hyaline covers ends of epiphyses. = spongy cushions that absorb compression. 2) articular capsule - tissue capsule surrounding the cavity. 2 layers: inner synovial membrane, composed of loose connective tissue, covers all joint surfaces, & produces the fluid inside the cavity. Outer layer = fibrous connective tissue that is continuous with the periosteum. 3) joint cavity - filled with fluid. 4) synovial fluid - viscous fluid inside cavity; lowers friction. WEEPING LUBRICATION is the mechanism by which fluid is squeezed in & out of the cartilages during regular movement, lubricating & nourishing cells.

3 CJ Shuster A & P I Note Series Articulations 3 5) Many synovial joints (majority but not all) are strengthened by several ligaments. INTRINSIC or CAPSULAR LIGAMENTS are thickened parts of the fibrous capsule. EXTRINSIC or EXTRACAPSULAR or INTRACAPSULAR LIGAMENTS are distinct and lay outside or inside the capsule itself. 6) Some synovial joints (a minority) have pads of fibrocartilage separating the articulating surfaces of the bones (MENISCUS(I) or ARTICULAR DISKS). 7) Many synovial joins exhibit BURSAE ( purse ) & TENDON SHEATHS - bags of lubricant that reduce friction between adjacent bones in a joint. The fibrous membranes of the synovial membranes of adjacent bones fuse together, forming a sac filled with synovial fluid. BURSAE is a sac that often lay between tendons and bone, thereby protecting the tendon. A BUNION is an enlarged bursae at the base of the big toe TENDON SHEATH is an elongated bursae that wraps completely around the tendon, like a bun around a hot dog. Recall Bursitis & tendonitis from the Membranes of the body section.

4 CJ Shuster A & P I Note Series Articulations 4 - there are several types of synovial joints, based on how the joint rotates or turns. 1) ball-and-socket large round condyle ( head ) of one bone articulates with deep concave surface of another. Shoulder & hip. 2) hinge joints - rounded condyle fits into a curved groove-like fossa on the other bone; motion is like a door hinge. Many examples: elbow, knee, jaw. 3) pivot joints - rounded condyle protrudes into a sleeve-like ring of bone. Best example: odontoid process of axis fits into atlas vertebrae. 4) plane joints - articular surface is flat, allowing slipping or gliding motions. Best example: joints between bones in wrist and ankles. 5) condyloid oval-shaped condyl of one bone articulates in an oval ( elliptical ) fossa on another. Wrist articulating with the radius. 6) saddle joints 2 concave surfaces articulate. Rare; best example is base of thumb. Allows our thumb to be opposable.

5 CJ Shuster A & P I Note Series Articulations 5 III. MOVEMENTS OF SYNOVIAL JOINTS - joints cause movement by allowing muscle to pull bone towards each other ORIGIN - ATTACHED TO THE IMMOVABLE BONE. BELLY - CENTRAL PORTION OF THE MUSCLE. INSERTION -ATTACHED TO THE BONE THAT MOVES. * NOTE: in body movement, one bone always move towards another. Movement Terms: - several ways in which we can describe movements caused by the contraction of the muscle. * Does it bring bones together (make an angle formed at the joint smaller) or does it move bones away from each other (widen an angle)? * Does it move a body part towards or away from the trunk of the body? * Does it turn a bone? 1) Terms referring to the angle of the joint: (a) flexion - decreases the angle of a joint; brings 2 bones together. (b) extension - increases the angle of a joint; moves 2 bones farther apart. (c) dorsiflexion - ankle only - pointing toes up (superior surface of foot moves towards shin). (d) plantar flexion - ankle only - pointing toes down (standing on ones s toes). 2) Terms referring to movement towards or away from body: (a) abduction - moving limb away from midline of body. (b) adduction - moving a limb towards the midline (think of adding it to the body). (c) protraction - move bone anteriorly along the transverse plane (think of jutting out your jaw). (d) retraction - move bone posteriorly along the transverse plane (bring your jaw back in). (e) elevation & depression - moving a bone superiorly & inferiorly along a frontal plane (your jaw is elevated & depressed when you chew). 3) Turning a bone: (a) circumduction - moving a limb so that it describes a cone in space. (b) rotation - turn a bone around it s own axis. (c) supination - forearms only - turn palms superior (or anterior in correct anatomical position). (d) pronation - forearms only -turn palms inferior (or posterior in correct anatomical position). (e) inversion - foot only - turn sole medially. (f) eversion - foot only - turn sole laterally.

6 CJ Shuster A & P I Note Series Articulations 6 IV. Kinesiology The study of movement (Kinetics). How our skeleton, joints and muscles work together to form a movement. (See summary at the end for what will be on the exam. It is not that much!) A. Lever Systems The operation of most skeletal muscles involves leverage using a lever to move an object ( load ). A lever is a rigid bar that moves on a fixed point called the fulcrum, when a force is applied to it ( effort ). In the first image, you are seeing the fulcrum, load and effort. In our example, the effort is pushing down on the right side to lift the load on the left. But there are other kinds, as well. B. Lever mechanics: Power Versus Speed A lever allows a given effort to move a heavier load, or to move a load farther and faster. Levers always sacrifice power for speed (and vic-a-versa). 1. Mechanical Advantage: The load is close to the fulcrum and the effort is applied far from the fulcrum (in other words, a relatively short out arm ) Power lever - a small effort exerted over a relatively large distance can move a large load over a small distance. For example, a person can lift a car with a power lever or jack. The car moves up only a small distance with each downward push of the jack handle, but relatively little muscle effort is needed. 2. Mechanical disadvantage: the effort is applied close to the fulcrum, and the load far away from the fulcrum (in other words, a relatively long out arm ) Speed lever - the lever will be very fast, but not able to move much load.

7 CJ Shuster A & P I Note Series Articulations 7 C. Lever Classes: Where are the in, out & fulcrum located relative to each other? Depending on the relative position of the three elements effort, fulcrum, and load a lever belongs to one of three classes. 1. In a first-class lever, the effort is applied at one end of the lever and the load is at the other, with the fulcrum somewhere between. These can either be at a mechanical advantage or disadvantage. * Seesaws and scissors are first-class levers. 2. In a second-class lever, the effort is applied at one end of the lever and the fulcrum is located at the other, with the load between them. Second-class levers are levers of strength, because in is always longer than out, but speed and range of motion are sacrificed for that strength. * A wheelbarrow demonstrates this type of lever system. 3. In a third-class lever, the effort is applied between the load and the fulcrum. These levers are speedy and always operate at a mechanical disadvantage, because out is always longer than in. * Think of tweezers and forceps.

8 CJ Shuster A & P I Note Series Articulations 8 D. Levers systems in our Bodies * For our bodies, all force is down due to gravity Inertia things do not want to move. Energy (ATP) must be appled. In the human body, the joints are fulcrums, and the bones act as levers. Muscle contraction provides the effort that is applied at the muscle s insertion point on the bone. But, muscles can only pull due to the structure of the sarcomere. The load is the weight of the body (or body part) itself, along with overlying tissues and anything else you are trying to move with that lever (say, a ball in your hand). Regardless of type, all levers follow the same basic principles discussed in the previous section: Effort farther than load from fulcrum = lever operates at a mechanical advantage Effort nearer than load to fulcrum = lever operates at a mechanical disadvantage In general, our skeleton gives up mechanical advantage for speed. Third-class levers are the most common type within our body. 1. Uncommon in the body. See skull image. Some first-class levers in the body operate at a mechanical advantage, but most, such as the action of the triceps muscle when bringing your fist down or moving your head up and down, operate at a mechanical disadvantage (for speed). 2. Second-class levers are rarest in the body, only example is the act of standing on your toes. All second-class levers in the body work at a mechanical advantage because the muscle insertion is always farther from the fulcrum than the load. 3. Most skeletal muscles of the body act in third-class lever systems. An example is the activity of the biceps muscle of the arm, lifting the distal forearm and anything carried in the hand. Third-class lever systems permit a muscle to be inserted very close to the joint across which movement occurs, which allows rapid, extensive movements (as in throwing a ball) with relatively little shortening of the muscle. Muscles involved in third-class levers tend to be thicker and more powerful.

9 CJ Shuster A & P I Note Series Articulations 9 - Sometimes, to give our third-class levers more strength, we have a relatively short muscle cross two joints. A good way to think about this: If I want to hit you several times rapidly, I use a ruler while moving my wrist. Relatively long out arm, but not moving a lot of weight. If I want to hit you harder, I use a rod by moving my elbow. Relatively short out arm, and I move more weight, but you might be able to get away because it is slower. And if I really want to hit you hard, I move a bat down by moving just my shoulder, like swinging an axe, which lengthens my in arm even farther. But that is much slower. You are probably not sticking around that long. If I want both, I add another joint! If I swing a bat, one muscle moves both my shoulder and elbow. Both speed and strength! Summary of what to know from the kinesiology section: Know the definition of kinesiology. Know the basic parts of a lever: fulcrum, load and effort. I never ask about the relative lengths of the in arm and out arm, but I ask about mechanical advantage versus speed.why do you use a jack to lift your car, but a shovel to lift dirt? Know the names of the 3 classes of lever systems. Know which are at a mechanical advantage or disadvantage (or a mix of the two). I never ask about the position of the fulcrum relative to the effort and the load. Understand that our body fights inertia, and that all resistance on our skeleton is down due to gravity. In our bodies, most of our joints are third-class lever systems with fairly short muscles, and are therefore fairly fast but not real strong, like the biceps brachii crossing the elbow. These muscles tend to be widder and bulkier, to give them more strength. We have very few (if any) second-class levers, but standing on your big toe is an example. The Axis and the Triceps brachii extending the elbow are first-class levers. Sometimes, out body has a fairly short muscle cross two joints to have both speed and strength. See the swinging a baseball bat example. V. HOMEOSTATIC IMBALANCES OF JOINTS The student should be familiar with the following: Sprains Bursitis Tendonitis Arthritis Osteoarthritis Rheumatoid arthritis *autoimmune disease *pannus Gouty arthritis