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Ecology & Evolutionary Biology

BIO 210 Oct 3/2011 Chapter 9: Articualtions  Because bones of skeleton are fairly inflexible, movements only occur at articulations or joints where 2 bones interconnect. 9.1 Joints are categorized according to their range of motion or anatomical organization  2 classification methods used to categorize joints on is functional scheme because it is bacsed on the amount of movement possible; range of motion. Each functional group further subdivided:  Immovable joint is synarthrosis. Can be fibrous or cartilaginous, depending on nature of connection  Slightly movable joint is amphiarthrosis which is either fibrous or cartilaginous depending on the nature of the connection between opposing bones  Freely movable joint is diarthrosis are subdivided according to nature of movement permitted. nd  2 classification theme relies solely on anatomical organization of joint, without regard to degree of movement permitted. In this framework joints classified as bony, fibrous or synovial.  2 classification themes loosely correlated. 9.2 Synovial joints are freely movable containing synovial fluid  Synovial joints are freely movable and classified as diarthroses. Synovial joint surrounded by 2 layered joint capsules also called articular capsule.  Joint capsule contains an inner synovial membrane and an outer fibrous capsule. Membrane does not coverarticulatinf surfaces within the joint. Articular Cartilages  In normal circumstances bony surfaces at synovial joint cannot contact eachother because special articular cartilages cover articulating surfaces.  Articular cartilages resemble hyaline cartilages however articular cartilages have no prichondrium and matrix contains more water than that of other cartilages.  Surface of articular cartilages are slick and smooth which reduces friction. Even when pressure apllied smooth articular cartilages don’t touch because they are separated by thin film of synovial fluid within the joint cavity.  Normal synovial joint cannot continue if articualr cartilages damaged, matrix begins to break down. Exposed surface changes from smooth slick, gliding surface to rough abrasive surface of bristly collagen fibres which increases friction Synovial fluid  Resembles interstitial fluid but contains high [] of proteoglycans secreted by fibroblasts of synovial membrane  Synovial fluid within the joint has 3 primary functions:  Lubrication: articular cartilages act like sponges filled with synovial fluid. When compressed some fluid comes out and into sac between opposing surfaces. When compression stops sunovial fluid oulled back into articular cartilages  Nutrient distribution: synovial fluid in joint muscles circulates continuously to provide nutrients and waste disposal route for chondrocytes of articular cartilages. Circulates when the joints move and compression and re-expansion of articular cartilages pump synovial fluid into and out of cartilage matrix. As synovial fluid flows through areolar tissue of synovial membrane, waste products are absorbed and additional nutrients are obtained by iddufsion across capillary walls.  Shock absorption: synovial fluid cushions joint subjected ti compression from shocks, Accessory structures  Synovial joints have variety of accessory structure including pads or cartilage (fat), ligaments,tendons and bursae. Cartilages and fat pads  Several joint including knees, menisci and fats pads lie between opposing articualr surfaces. Menisci pad of fibro cartilage located between opposing bones within a synovial joint.  Menisci (articular discs) may subdivide a synovial cavity, channel flow of synovial fluid or allow for variations in shapes of articular surfaces.  Fat pads localized masses of adipose tissue covered by layer of synovial membrane. Commonly superficial to joint capsule. Protect articualr cartilages and act as packaging material for joint. Ligaments  Capsule that surrounds the entire joint in cts with the periostea of articulating bones. Accessory ligaments support, strengthen, and reinforce synovial joints.  Intristic ligaments or capsular ligaments are localized thickenings of the joint capsules.  Extrinsic ligaments are separate from the joint capsule. Maybe located on either inside or outside the joint capsule and are called intracapsular or extracapsular ligaments.  Ligaments strong. In sprain ligament is stretched at which some of the collagen fibers are torn but ligament as a whole survives and joint is not damaged.  Broken bone heals quicker than torn ligaments because ligaments have no direct blood supply and thus must derive substances by diffusion. Tendons  Tendons passing across and around a joint may limit the joint’s range of motion and provide mechanical support of it. Bursae  Are small, fluid filled pockets in CT. Have a synovial fluid and are linked by synovial membrance.  Maybe connected to the joint cavity or separate from it. Form where a tendon or ligament rubs against tissues.  Synovial tendon sheaths are tubular bursae that surround tendonds where they cross bony surfaces.  Bursae may also appear deep to the skin, covering a bone or lying within other CT exposed to friction or pressure.  Bursae that develop in abnormal locations or because of abnormal stress care called adventitious bursae. Factors that stabilize Synovial Joints  Synarthrosis is the strongest type of joint and permits no movement. Diarthrosis is weaker but permits a broad range of movement.  Movement beyind its normal range of motion will damage any mobile diarthrosis.  Several factors responsible for limiting the range of motion, stabilizing the joint and reducing the chance of injury:  Collagen fibers of joint capsule and any accessory, extracapsular or intracapsular ligaments.  Shapes of articulating surfaces amd menisci, which may prevent movement in specific directions.  Presence of other bones, skeletal muscles or fat pads around the joint.  Tension in tendons attached to the articulating bones.  When skeletal muscle contartcs and pulls on a tendon, movement in a specific direction maybe either encourage or opposed.  The more stable the joint the more restricted its range of motion.  Shoulder joint, most mobile synovial joint relies only on the surrounding ligaments, muscles, and tendons fore stability. Fairly weak.  When reinforcing structure cannot protect a joint from extreme stresses, a dislocation or luxation results.  In dislocation articulating surfaces are forced out of position. Displacement can damage the articular cartilages, tear ligaments, or distort joint capsule. 9.3 Anatomical and functional properties of synovial joints enable various skeletal movements.  To understand human movement, you must be aware of the relationship between structure and function at each articulation.  To describe human movement, you need a frame of reference that enables accurate and precise communication Describing Movement  Pencil is a bone while the desk is an articular surface.  Hold pencil upright and push pencil across the surface. Kind of movement called gliding. Can slide fir ro backwards or side to side.  Tip held in position, move eraser end of the pencil forwards and backwards, from side to side or at some intermediate angle. Called angular movement.  Any angular movement can be descrbed with the reference to the same axes and the angular change.  Movement which corresponds to the path of yoru arm when you draw a large circle on a whiteboard. The term is called circumduction  If you keep the shaft vertical and the point at one location you can still spin the pencil around its longitudinal axis called rotation. Several articulations permit partial rotation but none and rotate freely.  An articulation that permits movement only along 1 axis is called monoaxial. In pencil if an articulation permitsonly angular movement in forward backward plane or prevents nay movement other than rotation around it’s longitudinal axis, it is monoaxial.  If movement occur along the 2 axes the articulation is biaxial. Pencil undergo angular movement in the forwards- backward and left right planes but not rotation it is biaxial.  Most mobile joints permit a combination of angular movement and rotation. Joints are said to be triaxial. Joint that permit gliding only allow small amounts of movement. Types of movement at synovial joints Gliding Movement  In gliding, 2 opposing surfaces slide past one another. It occurs between surfaces of articulating carpal bones between tarsal bones and between calvicles and sternum.  Movement can occur in any direction but amount of movement is slight and rotation is prevented by capsule and associated ligaments. Angular movement  Examples inclide flexiom, estension, abduction, adduction, and circumduction Flexion and extension  Flexion is movement in the anterior-posterior plane that decreases angle between articulating bones  Extension occurs in same plance, but it increases the angle between articulating bones. Tehse terms usually applies to movements of long bones of limbs but also used to describe movement of axial skeleton.  Extension reverses the movement, returning you to anatomical position. During anatomical position everything is at full extension.  Flexion of shoulder joint or hip bones moves limbs anteriorly and extension moves it posteriorly.  Extension past the anatomical position is called hyperextension. Abduction and adduction  Abduction is movement away from longitudinal axis of body in frontal plane.  Swinging upper limg to side is abduction of limb. Moving back to anatomical position is adduction.  Adduction of wrist moves hell of hands and fingers towards body, abduction move them farther away.  Spreading fingers or toes = abduction; bringing them together is adduction. Circumduction  Moving you arm in a loop. Drawing a circle. Rotation  Rotation of head may involve left rotation or right rotation.  Limb rotation maybe described by reference to longitudinal axis of trunk. During medial rotation (internal or inward rotation), anterior surface of limb turns towards the long axis of the trunk.  Reverse movement is called lateral rotation (external or outwards rotation).  Proximial articulation between radius and ulna permist rotation of radial head. As shaft rotates, distal ephiphysis of radius rolls across anterior surface of ulna. Movement called pronation, turns the wrist and hand from palm facing front to back.  Opposing movement when paln is turned anteriorly is supination. Special movements  Inversion is a twisting movement of foot that turns sole inwards, elevating medial edge of sole. Opposite movement is eversion.  Dorsiflexion is flexion at the ankle joint and elevaton of the sole, as when you dig in your heel. Plantar flexion the opposite movement extends ankle joint and elevates heel, as when you stand on tippy toe.  Opposition a movement of thumb towards surface of palm of other fingers. Enables you to grasp and hold objects between thumb and palm. Involves movement at the first carpometacarpal and metacarpophalangeal joints. Flexio at 5 meracarpophalangeal joint can assist this movement. Reposition returns thumb and fingers from opposition  Protraction is a moving body part anteriorly in the horizontal plane. Retraction is reverse movement. Protract your jaw when you garsp your upe rlip with your lower teeth and you retract your jaw when you return it to normal position.  Elevation and depression occur when a structure moves in a superior or an inferior direction. Depress mandible when mouth opened. Elevate mandible as you close it.  Lateral flexion occurs when your vertebral column bends to the side. Movement is most pronounced in the cervical and thoracic regions. Type of synovial joints  Synovial joitns described as gliding, hinge, pivot, condylar, saddle, and ball and socket joints.  Gliding joints (plane joints) have flattened or slightly curved faces. Relatively flat articular surfaces slide across one another, but amount of movement is slight. Roation possible but ligaments prevent it  Hinge joints permit angular movement in a single plane.  Pivot joints also a monaxial, nut only permit rotation.  Condylar joint an oval articualr face nestles within a depression in the opposing surface. All angular movements occurs around 2 axes, allowing of rflexiona nd extension, and abduction and adduction.  Saddle joints fit together like a rider and a saddle. Each articulr face is concave along 1 axis and convex among another. Arrangement permits angular movement, including circumdation., but
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