Y1B4M1L4 Articulations, Joint Motion & Muscle Contraction PDF

Y1B4M1L4 ARTICULATIONS, JOINT MOTION & MUSCLE CONTRACTION III. JOINT MOTION A. KINEMATIC CHAIN ● A group of body segments connected by joints so that the segments operate together to provide a wide range of motion for a limb. ○ Some joints are linked together so that motion in one joint is accompan...

Y1B4M1L4 ARTICULATIONS, JOINT MOTION & MUSCLE CONTRACTION III. JOINT MOTION A. KINEMATIC CHAIN ● A group of body segments connected by joints so that the segments operate together to provide a wide range of motion for a limb. ○ Some joints are linked together so that motion in one joint is accompanied by motion in an adjacent joint. The change in functional structure of a joint will cause a change in function of a joint either immediately adjacent or distal to it. ● 2 types: ○ Closed ○ Open Joint Function: ● Effective function of the total structure is dependent on the integrated action of multiple joints, stability (synarthrodial joints) must be reached before mobility (diarthrodial joints) Figure 18. Bending Knee Lower Extremity) Kinematic Chain B. JOINT MOTION ● 3 types ○ Rolling → Rolling of one joint surface on another → Like a tire rolling on the road → E.g. knee - femoral condyles roll on the fixed tibial surface. ○ Sliding → Gliding of one component over another → Like a braked wheel skids → A pure translatory motion → E.g. proximal phalanx slides over the fixed ends of the metacarpals. ○ Spinning → Rotation of the movable element like when a top spins → A pure rotatory motion → E.g. radial head spins on the capitulum of the humerus in pronation/supination. Figure 17. Kinematic Chain CLOSED KINEMATIC CHAIN ● ● ● ● Distal part is fixed Proximal part is free to move Motion of other joints occur in a predictable manner. E.g. push up (upper extremity) whether wall or floor, motion occurs in the same manner (predictable). ● ● ● ● Proximal part is fixed Distal part is free to move Motion occurs in an unpredictable manner. E.g. waving hand (upper extremity) by abducting and adducting elevated hand, externally and internally rotating the arm with an elbow flex, flexing and extending the wrist or finger joints, or by simple pronation and supination (unpredictable). OPEN KINEMATIC CHAIN Arthrokinematics: ● Movement of joint surfaces in relation to the direction of movements of the distal end of the bone. Concave-Convex Rule: ● Ovoid joint (convex on concave joint) ○ The convex articulation surface moves in the opposite direction of the moving bone ○ Glide occurs in the direction opposite to the physiological movement ○ One surface is convex, the other is concave ○ Example: humerus-on-scapula motion - a shoulder abduction with inferior glide ● Sellar joint (concave on convex joint) ○ The convex articular surface moves in the same direction as the moving bone ○ Glide occurs in the same direction as the physiological movement ○ Each joint surface is both convex and concave ○ Example: tibia-on-femur motion – a knee flexion with posterior glide BARBON, CALIZO, DAQUIL, DULANA, LAYGAN, RODRIGUEZ, SOMBONG, TILOS, TUMACOLE | MG 4 6 of 22 Y1B4M1L4 ARTICULATIONS, JOINT MOTION & MUSCLE CONTRACTION C. JOINT MOTION CLOSE PACKED AND LOOSE PACKED POSITIONS Table 3. Comparison of Skeletal, Cardiac, and Smooth Muscle CLOSE PACKED POSITION ● ● ● ● ● ● Close-packed position (aka locked position) one in which joint surfaces are maximally congruent and compressed. Usually at the extreme end of a range of motion. Position of greatest stability and resistant to tensile forces causing separations. Little or no joint play is possible. Examples: extension of elbow, wrist, hip, knee, and interphalangeal joints In extension). LOOSE PACKED POSITION ● ● ● ● ● ● ● ● Loose-packed position (aka unlocked position) one in which joint surfaces are relatively free to move in relation to each other. Any position other than the close-packed position. The term is most used to refer to the position at which the joint structures are more laxed. Joint cavity has a greater volume than in other positions. The joint has a maximum amount of joint play. Movement in and out of the close-packed positions may be beneficial to joints because of the squeezing out of the fluid during each compression and imbibing of the fluid when compression is removed. An externally applied force such as that applied by a therapist or physician can produce movements of one articular surface on another and enable the examiner to assess the amount of joint play that is present. V. ORGANIZATIONAL LEVEL OF THE MUSCLE JOINT PLAY ● ● Movement of one articular surface on another Not under voluntary control IV. COMPARISON OF SKELETAL, CARDIAC, AND SMOOTH MUSCLE CELLS Table 2. Comparison of Skeletal, Cardiac, and Smooth Muscle (Ganongʼs 24th Ed) Smooth Muscle Cardiac Muscle Skeletal Muscle Spindle-shaped Branching Elongated, Tubular Non-Striated Striated Striated Central Uninucleus Central Uninucleus Multinuclear Peripheral) Involuntary Involuntary Voluntary Walls of internal organs (eg. GI tract) Walls of the heart Usually attached to the skeleton Figure 19. Skeletal Muscle Structure: Connective Tissue, Innervation and Blood Supply ● ● ● ● ● Skeletal muscle is composed of a orderly arrangement of connective tissue and contractile cells the muscles is made up of: Fascicles – bundles of individual muscle cells. Each fascicle is surrounded by a connective tissue called Perimysium Fig. 30 . Perimysium – binds fascicles Epimysium – binds entire muscles (external connective tissue). Endomysium – third connective tissue layer within the fascicle and binds muscle fiber. o Insulator BARBON, CALIZO, DAQUIL, DULANA, LAYGAN, RODRIGUEZ, SOMBONG, TILOS, TUMACOLE | MG 4 7 of 22 Y1B4M1L4 ARTICULATIONS, JOINT MOTION & MUSCLE CONTRACTION o o ● “Myelin sheath of muscle fibers” Separates and electrically insulates the individual muscle cells from each other All three connective tissue layers bind the muscle cells together providing strength and support to the entire muscle. They merge at the ends of the muscle and are continuous with the tendon. Figure 20. Components of a contractile cell of the muscle Figure 21. Internal Structure of a Fascicle 2 TYPES OF MYOFILAMENTS ● Each muscle cell is made up of myofibrils, which are made up of two types of filaments. ○ Thin Filament: → Composed of the protein actin. ○ Thick Filament: → Composed of the protein myosin. ● The striated appearance of the muscle fiber is created through a pattern of alternating bands in muscle fibers. ○ Dark A (anisotropic) bands – bisected by the H zone running through the center of which is the M line. → H zone - made of thick filaments ○ Light I (isotropic) bands – bisected by the Z disc → Z disc - point of connection between 2 neighboring actin filaments ● Sarcomere - the length between two Z discs; the contractile unit of the muscle. Figure 23. Thick and thin filaments Figure 22. Organizational levels of skeletal muscle ● A muscle fiber is not a single cell but a syncytium – special names for muscle fiber parts ○ Sarcolemma – plasma membrane ○ Sarcoplasmic reticulum – endoplasmic reticulum ○ Sarcosomes – mitochondria ○ Sarcoplasm – cytoplasm Figure 24. Thick and thin filaments BARBON, CALIZO, DAQUIL, DULANA, LAYGAN, RODRIGUEZ, SOMBONG, TILOS, TUMACOLE | MG 4 8 of 22 Y1B4M1L4 ARTICULATIONS, JOINT MOTION & MUSCLE CONTRACTION VI. ACTIVATION OF SKELETAL MUSCLE Figure 27. Motor Neuron ● Skeletal muscles are electrically insulated by endomysium. In order for the muscle cells to contract, each cell must be stimulated by the process of a motor neuron. Figure 28. Neuromuscular Junction Figure 25. Skeletal Muscle Activation for Contraction ● In order for skeletal muscle cells to contract, each cell must be stimulated by the processes of a motor neuron. ● A motor neuron comes from the anterior horn cells of the spinal cord. It exits through the intervertebral foramina and then goes distally as the motor neuron and gives off processes to the skeletal muscle cells. ● Neuromuscular junction – junction between the terminal of a motor neuron and a muscle fiber where action potential terminates. ● The terminals of motor axons (axon terminals) contain thousands of synaptic vesicles filled with acetylcholine (ACh). ● Synaptic cleft – separates axon terminal from motor end plate. Figure 29. Arrival of AP at Axon Terminal Figure 26. Motor Unit Consists of a Single Motor Neuron and the Muscle Fibers Innervated by it) BARBON, CALIZO, DAQUIL, DULANA, LAYGAN, RODRIGUEZ, SOMBONG, TILOS, TUMACOLE | MG 4 9 of 22 Y1B4M1L4 ARTICULATIONS, JOINT MOTION & MUSCLE CONTRACTION ● When an action potential arrives at the axon terminal, the voltage change of the membrane opens voltage regulated calcium channels, allowing calcium to enter the axon terminal. ● This ion exchange causes local depolarization of the motor end plate. Figure 33. Depolarization of motor end plate Figure 30. Synaptic Vesicles Fusion ● The calcium ions cause several synaptic vesicles to fuse with the membrane of the axon terminal. ○ These synaptic vesicles contain acetylcholine. ● When an action potential reaches the axon terminal, hundreds of these vesicles discharge their Ach onto a specialized area of postsynaptic membrane on the muscle fiber. ● This area contains a cluster of transmembrane channels that are opened by Ach and let sodium ions Na+) diffuse in. ● The interior of a resting muscle fiber has a resting potential of about 95 mV. ● The influx of sodium ions reduces the charge, creating an end plate potential. ● If the end plate potential reaches the threshold voltage (approximately 50mV), sodium ions flow in with a rush and an action potential is created in the fiber. ● No visible change occurs in the muscle fiber during the action potential. ● This period is called the latent period and usually lasts for 3 10 ms. Figure 31. Release of Acetylcholine ● Acetylcholine is then liberated from the vesicles via exocytosis into the synaptic cleft. ● Calcium ions are then pumped out of the axon terminal. Figure 34. Acetylcholine Breakdown Figure 32. Ach binding to receptor sites ● Events before latent period is over: ○ The enzyme acetylcholinesterase breaks down the Ach in the neuromuscular junction (at a speed of 25,000 molecules per second). ○ The sodium channels close, and the field is cleared for the arrival of another nerve impulse. ○ The resting potential of the fiber is restored by an outflow of potassium ions. ○ The brief 1 2 msec) period needed to restore the resting potential is called the refractory period. ● Ach binds to receptor sites of ion channels of the motor end plate, which causes the channels to open, permitting an influx of Sodium Na+) ions, and a small efflux of Potassium ions. BARBON, CALIZO, DAQUIL, DULANA, LAYGAN, RODRIGUEZ, SOMBONG, TILOS, TUMACOLE | MG 4 10 of 22