Articulations and Body Movement PDF

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The goal of the lecture is understand rare exceptions of every bone and joint. Topics also discussed include --- classification of joints, synovial joints and their movements, and selected synovial joints. ...

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Articulations and Body Movements With rare exceptions, every bone in the body is connected to, or forms a joint with, at least one other bone. Articulations: Joints, perform functions for the body o Hold the bones together o Allow the rigid skeletal system some flexibility so that gross body movements can occur. Classification of Joints  Classified structurally and functionally. o Structural classification is based on the type of connective tissue between the bones and the presence or absence of a joint cavity.  Fibrous: adjoining bones connected by dense fibrous connective tissue; no joint cavity  EX: between the tibia and fibula, tooth in a bony socket  Synarthroses and Amphiarthrosis functional classifications  Cartilaginous: Adjoining bones united by cartilage; no joint cavity  EX: Intervertebral discs between adjacent vertebrae and the anterior connection between the pubic bones  Synarthroses and Amphiarthroses functional classifications.  Synovial Joints: Adjoining bones covered in articular cartilage; separated by a joint cavity and enclosed in an articular capsule lined with a synovial membrane.  EX: Between the carpals of the wrist, elbow joint, shoulder joint  Diarthrosis functional classifications only. o Functional classification focuses on the amount of movement allowed at the joint  Synarthroses: immovable joints  Amphiarthroses: slightly movable joints  Diarthroses: freely moveable joints  Types of Joints o Joints to the left of the skeleton are cartilaginous joints – joints above and below the skeleton are fibrous joints. o Joints to the right of the skeleton are synovial joints  Joint between costal cartilage of rib 1 and sternum  Intervertebral discs of fibrocartilage connecting adjacent vertebra  Fibrocartilaginous pubic symphysis connecting the pubic bones anteriorly  Dense fibrous connective tissue connecting interlocking skull bones  Ligament of dense regular connective tissue connecting the inferior ends of the tibia and fibula  Shoulder joint  Elbow joint  Wrist joint Synovial Joints  Joints in which the articulating bone ends are separated by a joint cavity containing synovial fluid.  All synovial joints are diarthroses, or freely movable joints. Most joints in the body are synovial joints.  Typically have the following structural characteristics o Joint (articular) cavity: a space between the articulating bones that contains a small amount of synovial fluid o Articular cartilage: Hyaline cartilage that covers the surface of bones forming the joint o Articular capsule: two layers that enclose the joint cavity.  The tough external layer is the fibrous layer composed of dense irregular connective tissue.  The inner layer is the synovial membrane composed of loose connective tissue o Synovial fluid: A viscous fluid, the consistency of egg white, located in the joint cavity and the articular cartilage.  This fluid acts as a lubricant, reducing friction. o Reinforcing ligaments: Some joints are reinforced by ligaments.

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Most ligaments are capsular ligaments, which are thickenings of the fibrous layer of the articular capsule.  Some ligaments are extracapsular, found outside the articular capsule.  Intracapsular ligaments are found within the articular capsule. o Nerves and blood vessels: Sensory nerve fibers detect pain and joint stretching.  Most of the blood vessels supply the synovial membrane. o Articular discs: Pads composed of fibrocartilage (menisci) may also be present to minimize wear and tear on the bone surfaces. o Bursa and tendon sheath: Sac filled with synovial fluid that reduces friction where ligaments, muscles, skin, tendons, and bones rub together.  A tendon sheath is an elongated bursa that wraps around a tendon like a bun around a hot dog.  Types of Synovial Joints o The many types of synovial joints can be subdivided according to their function and structure.  Shapes of the articular surfaces determine the types of movements that can occur at the joint.  Determine the structural classification of the joints o Plate: Flat or slightly curved bones o Hinge: A rounded or cylindrical bone fits into a concave surface on the other bone o Pivot: A rounded bone fits into a sleeve (a concave bone plus a ligament) o Condylar: An oval condyle fits into an oval depression on the other bone o Saddle: Articulating surfaces are saddle shaped; one surface is concave, the other surface is convex o Ball-and-socket: The ball-shaped head of one bone fits into the cup-like depression of the other one. o Articulating bones  Intercarpal joint  Elbow  Proximal radioulnar joint  Metacarpophalangeal joint  Carpometacarpal joint of the thumb  Shoulder Movements Allowed by Synovial Joints  Every muscles of the body is attached to bone (or other connective tissue structures) at two points o Origin: stationary, immovable, or less moveable bone o Insertion: movable bone.  Body movement occurs when muscles contract across diarthrotic synovial joints o When the muscle contracts and its fibers shorten, the insertion moves toward the origin o The type of movement depends on the construction of the joint and on the placement of the muscle relative to the joint.  Most common types:  Flexion, extension, and hyperextension of the neck  Flexion, extension, and hyperextension of the vertebral column  Flexion and extension at the shoulder and knee, and hypertension of the shoulder  Abduction, adduction, and circumduction of the upper limb at the shoulder  Rotation of the head and lower limb  Pronation and supination of the forearm  Dorsiflexion and planter flexion of the foot  Inversion and eversion of the foot o Flexion: A movement, generally in the sagittal plane, that decreases the angles of the joint and reduces the distances between the two bones  Typical of hinge joints (bending the knee or elbow) but is also common at ball-and-socket joints (bending forward at the hip) o Extension: A movement that increases the angle of a joint and the distance between two bones or parts of the body; the opposite of flexion. 

If extension proceeds beyond anatomical position (bends the trunk backward), it is termed hyperextension. o Abduction: Movement of a limb away from the middle of the body, along the frontal plane, or the fanning movement of fingers or toes when they are spread apart o Adduction: Movement of a limb toward the midline of the body or drawing the fingers or toes together  Opposite of abduction o Rotation: Movement of a bone around its longitudinal axis without lateral or medial displacement.  Rotation, a common movement of ball-and-socket joints, also describes the movement of the atlas around the dens of the axis. o Circumduction: A combination of flexion, extension, abduction, and adduction commonly observed in ball-and-socket joints like the shoulder. The limb as a whole outline a cone. o Pronation: Movement of the palm of the hand from an anterior or upward-facing position to a posterior or downward-facing position. The distal end of the radius rotates over the ulna so that the bones form an X with pronation.  During supination, the radius and ulna are parallel. o Supination: Movement of the palm from a posterior position to an anterior position (the anatomical position)  Opposite of pronation  During supination, the radius and ulna are parallel. o Refer to movements of the foot:  Dorsiflexion: A movement of the ankle joint that lifts the foot so that it’s superior surface approaches the shin.  Plantar flexion: A movement of the ankle joint in which the foot is flexed downward as if standing on one’s toes or pointing the toes.  Inversion: A movement that turns the sole of the foot medically.  Eversion: A movement that turns the sole of the foot laterally  Opposite of inversion. Selected Synovial Joints  The Hip and Knee Joints o Both joints are large weight-bearing joints of the lower limb, but they differ substantially in their security.  The Hip Joint o A ball-and-socket joint, so movements can occur in all possible planes. o Movements are definitely limited by its deep socket and strong reinforcing ligaments, the two factors that account for its exceptional stability. o Acetabular labrum: the deeply cupped acetabulum that receives the head of the femur is enhanced by a circular rim of fibrocartilage  Because the diameter of the labrum is smaller than that of the femur’s head, dislocations of the hip are rare. o Ligament of the head of the femur: Short ligament runs from the pit-like fovea capitis on the femur head to the acetabulum where it helps to secure the femur. o Strong ligaments that spirals posteriorly, arranged so they can “screw” the femur head into the socket when a person stands upright.  Iliofemoral  Pubofemoral anteriorly  Ischiofemoral  The Knee Joint o The knee is the largest and most complex joint in the body. o Three joints in one allows:  Extension, flexion  Little rotation o Tibiofemoral joint: actually, a biocondyloid joint between the femoral condyles above and the menisci (semilunar cartilages) of the tibia 

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 Functionally a huge joint  Very unstable one made slightly more secure by the menisci Some rotation occurs when the knee is partly flexed, but during extension, the menisci and ligaments counteract rotation and side-to-side movements Femoropatellar joint: intermediate joint anteriorly The knee is unique in that it is only partly enclosed by an articular capsule  Anteriorly, where the capsule is absent, are three broad ligaments that runs from the patella to the tibia below and merge with the capsule on either side.  Patellar ligament  Medial patellar retinacula  Lateral patellar retinacula Extra capsular ligaments are crucial in reinforcing the knee  Fibular and tibial collateral ligaments (prevent rotation during extension)  Oblique popliteal  Arcuate popliteal ligaments The knees have a built-in locking device that must by “unlocked” by the popliteus muscles before knees can be flexed again. The anterior and posterior cruciate ligaments are intracapsular ligaments that cross (cruci = cross) in the notch between the femoral condyles  Help prevent anterior-posterior displacement of the joint and overflexion and hyperextension of the joint....