Person Centred Care 1

4PY019 Person Centred Care 1 Science for Pharmacy – Life Sciences Musculoskeletal Dr S. Anderson, University of Wolverhampton Scanned images from Tortora & Grabowski, 10th ed., 2003, John Wiley & Sons 1 The musculoskeletal system refers to a body’s locomotor system. This covers muscles, bones, joints and connective tissues. Muscles Muscle cells specialize in contracting, where they activity shorten, then they can relax, where they can lengthen by being stretched out. Muscles convert chemical energy (ATP) into mechanical energy. General arrangement of muscle fibres 2 There are three muscle types: • Skeletal muscle • Cardiac muscle • Smooth muscle Fibres are arranged differently, which allows them to perform particular functions. 3 1 Skeletal Muscle: • attaches to bone, skin or fascia, • striated: light & dark bands visible with microscope, • voluntary control (although can be subject to reflex movements). Three main functions of skeletal muscle: • movement, Origin • posture/muscle tone, • heat production. Insertion For movement, muscles pull on bones. As muscle fibres shorten, the bones to which they are attached move closer. Generally it is the insertion bone that moves. 4 Voluntary muscular movements are generally smooth and free of tremors and jerks. This is because muscles do not often work alone, but in teams. For movements to occur, muscles work as agonists and antagonists. The muscle that is activity contracting is the agonist, whereas the muscle that is relaxing and lengthening is the antagonist. From the diagram, when lifting the weight and the arm is flexing, the biceps is acting as the agonist and the triceps is the antagonist. When an arm extends, the triceps will be actively contracting (agonist) and the biceps will be relaxing (antagonist). 5 In a team of muscles that is contracting, the one muscle that is mostly causing the movement is the ‘prime mover’. The other muscles that are helping are the ‘synergists’. Types of muscle contractions: • concentric – occurs when the length of a muscle shortens as tension is being generated. • eccentric – occurs when a muscle lengthens as tension is being generated (muscles are acting as brakes, e.g. running downhill). • isotonic – occurs when a muscle changes length whilst generating tension. • isometric – occurs when a muscle’s length does not change when generating tension. 6 2 Muscles involved with maintaining body position (posture) use tonic contractions. Here only a few fibres in a muscle shorten together and then maintain position, so parts of the body can then be held in position. Some muscles are composed mostly of type I muscle fibres. These are slow-twitch fibres and resist fatigue. These fibres are largely found in postural muscles as they can hold position for long periods. They are oxidative/aerobic in nature. They contain lots of myoglobin (red) and mitochondria. Type IIb fibres have larger diameters and are more glycolytic/anaerobic. They can produce rapid, forceful contractions, but they fatigue quickly. They do not contain much myoglobin (white) or many mitochondria. Such fasttwitch muscles are utilized in sprinting, jumping, etc. 7 Type IIa fibre are intermediate, as they have many mitochondria, but they do not contain much myoglobin. They do not fatigue as quickly as type IIb, but they cannot generate as much explosive energy. These are fast oxidative muscles. Most skeletal muscles contain all three fibre types, but muscles adapt to demands by changing fibre composition. Some muscles can contain mostly type I fibres, others might be mostly type IIb, while others might be a mixed fibre type, so involved with both posture and rapid movements. Generally training can increase endurance, force or have an intermediate effect of the two. 8 Muscles produce heat when contracting. When cold, body temperature needs to be maintained. Shivering will help to maintain body temperature, as some of the heat generated by these contractions will be absorbed by the blood passing through these muscles and then distributed around the body. General muscular activity also helps to maintain body temperature under normal conditions. When exercising, losing heat through the skin and sweating helps to reduce the risk of muscles overheating and losing function. 9 3 Cardiac Muscle This forms the contractile tissue of the heart. It is striated muscle, of uninucleate, branching cells joining together at intercalated discs. It is autorhythmic and under involuntary control. Smooth Muscle Found in the GI tract, walls of arteries, arterioles, venules and veins, attached to hair follicles in the skin, in the walls of hollow organs, can form sphincters, etc. Non-striated. Involuntary. 10 Properties of Muscles: Excitability: respond to neurotransmitters. Conductivity: propagate electrical signals over membrane. Contractility: shorten & generate force. Extensibility: can be stretched without damage. Elasticity: return to original shape after being stretched. 11 Skeletal Muscle Fibre Anatomy Skeletal muscles fibres are long cylindrical cells (10-100 mm diameter and can be centimetres long!) with several nuclei (multinucleated) appearing just under the plasma membrane (sarcolemma). This is not so surprising as these fibres are made from many cells fused together (syncytium). The sarcoplasm (muscle cell cytoplasm) is filled with myofibrils and myoglobin (red-colored, oxygen-binding protein similar to haemoglobin). N.B. sarc- or sarco- denotes muscle or fleshy tissue. 12 4 Sarcoplasm contains large amounts of stored glycogen. The usual organelles are present, along with some unique features e.g., the sarcoplasmic reticulum (SR), T tubules and myofibrils. The SR is a form of endoplasmic reticulum, which forms a meshwork of interconnecting tubules that surrounds each myofibril and also forms end sacs (terminal cisternae). The SR regulates [Ca2+]i, by storing it at rest and then releasing it when a muscle is stimulated to contract. T tubules (transverse tubules) are from the sarcolemma forming hollow tubes that penetrate into the cell near the location of terminal cisternae. Muscle cells can have 1000s of T tubules. 13 Action potentials (coming from the NMJ) travel along the sarcolemma and continue down T tubules. Therefore T tubules conduct action potentials deep into muscle cells close to the terminal cisternae of the SR. This ensures that myofibrils in a muscle fibre contract at virtually the same time. Since T tubules are hollow, they contain extracellular fluid, so can aid the delivery of O2, glucose, etc. to the deeper parts of muscle cells. 14 Triads are successive groupings of three membranous structures: terminal cisternae-T tubule-terminal cisternae. 15 5 Myofibrils These are the contractile parts of muscle cells. Muscle cells contain hundreds to thousands of rodlike myofibrils, which run in parallel and extend the length of the cell. Myofibrils are often 1-2 mm in diameter and are densely packed together. Organelles like mitochondria appear squeezed in between. A myofibril is made up of small contractile units that are arranged in chains. These small contractile units are called saromeres (muscle segments). 16 Myofibril 17 Bands, Zones and Lines Skeletal muscles show striations (repeating dark and light bands). Dark bands are anisotropic (polarize visible light) and are called A bands. Light bands are isotropic (non-polarizing) and are called I bands. Each A band has a slightly lighter zone in the middle called the H zone (helle/bright), which is most visible in relaxed muscle. The middle of an H zone has a dark line called the M line. The middle of an I band also has a dark line called the Z line or disc. A sarcomere, the smallest contractile unit, is the region between two Z lines. 18 6 Looking more closely, there is an orderly arrangement of filaments or myofilaments (my- or myo- denotes muscle). Thick filaments extend the length of A bands. Thin filaments extend across I bands and partway into A bands. H bands appear less dense as here thin filaments do not overlap thick ones. 19 Actin and Myosin Thick filaments (~16 nm diameter) are mostly made of the protein myosin. A strand of myosin has a rodlike tail and two globular heads The heads are sometimes called cross bridges, as they link think and thin filaments during contractions. One thick filament within a sarcomere contains ~200 myosin molecules. Heads possess ATPase activity and split ATP for energy during contraction. 20 Thin filaments are mostly made of actin. Subunits (kidney bean shaped) of actin filaments contain sites to which myosin heads attach during contraction. Two strands of actin coil around each other to form a helical structure. Regulatory proteins are also present in thin filaments: • Tropomyosin is a protein that spirals around filament cores and when relaxed they block actin’s attachment sites for myosin. • Troponin binds to actin, tropomyosin and Ca2+ ions. Both these proteins help control actin myosin interactions and thus muscle contraction and relaxation. 21 7 Other Proteins Associated with Muscle Titin: a stretchy protein that attaches thick filaments to Z disc. It can stretch to 4x resting length & spring back. It helps to stabilize sarcomeres. Myomesin: connects to titin and adjacent thick filaments. Nebulin: inelastic protein that aligns thin filaments. Dystrophin: links thin filaments to sarcolemma & transmits tension generated to tendons. 22 The Sliding Mechanism of Actin and Myosin Filaments • Myosin cross bridges pull on thin filaments. • Thin filaments inward. slide • Z Discs come toward each other. • Sarcomeres shorten. • Muscle fibres shorten. • Muscle shortens. • Thick & thin filaments do not change length. 23 The Neuromuscular Junction Skeletal muscles are under somatic control. Motor neurons are long and myelinated, so they can quickly carry action potentials long distances. Nerve terminals release acetylcholine (ACh) into the NMJ. 24 8 Ca2+ V.O.C. Ca2+ vesicle neurotransmitter terminal action potential Presynaptic nerve neuron synaptic cleft vesicle fusion postsynaptic membrane agonist receptor binding receptor receptor activation response Postsynaptic membrane 25 Released ACh will bind to nicotinic ACh receptors (nAChR) on the postsynaptic membrane (motor end plate) that is under the nerve terminal. Two ACh molecules open each nAChR, which allows Na+ ions to diffuse in, causing depolarization and generating action potential. an 26 Synaptic clefts are tiny and filled with basal lamina (gel-like glycoprotein rich substance) and the sarcolemma that forms the motor end plate is highly folded, so increasing its surface area to pack in large numbers of nAChRs. As the sarcolemma is polarized at rest, motor end plate potentials causes depolarization, spreads and conducts down T tubules to the triad regions. At rest the concentration of free [Ca2+]i is very low, but now the SR quickly releases (>1 ms) lots of Ca2+ ions into the sarcoplasm. This Ca2+ binds to troponin, which alters its conformation to shift tropomyosin. Myosin cross bridges attach and pull the thin filaments towards the centre of the sarcomere. 27 9 Excitation - Contraction Coupling Relaxed Contraction 28 The Contraction Cycle 29 Muscle Relaxation ACh is hydrolysed by acetylcholinesterase (AChE) enzymes found on the surface of the motor end plate and in the basal lamina to form acetic acid and choline. Motor end plate potentials stop. Ca2+ release from the SR stops. Active transport pumps Ca2+ ions back into sarcoplasmic reticulum. Tropomyosin-troponin complexes shield myosin binding sites on actin. 30 10 Muscle Fibre Bundle Arrangements Circular: muscle bundles are arranged in concentric rings. This muscle arrangement surrounds external body openings, which they close by contracting. A general term for such muscles is ‘sphincters’. Examples include muscles surrounding the mouth and eyes. Convergent: muscle bundles that have a wide origin, and converges towards a single tendon. The pectoralis major is an example. A SI 31 Parallel: the long axis of the muscle bundles runs parallel to the long axis of the muscle. Examples include the biceps brachii and sartorius muscles. Pennate: muscle bundles are short and attach obliquely to a central tendon (like a feather). Bundles attaching to one side of the tendon are ‘unipennate’ (extensor digitorum longus); bundles attaching to opposite sides are ‘bipennate’ (rectus femoris). A SI 32 Axial & Appendicular Skeleton Skeleton: rigid framework of connected bones that gives form to the body, protects and supports soft tissues, and provides attachments for muscles Anterior view and a system of levers essential for locomotion. Cranium The human skeleton consists of 206 named bones. The axial skeleton consists of 80 bones and is divided into the skull, vertebral column and bony thorax regions. Skull Facial bones Mandible Sternum Bony thorax Rib Vertebral column Vertebra Sacrum Coccyx A SI 33 11 Posterior view Clavicle The appendicular skeleton consists of the bones of the limbs and their girdles. Yoke-like pectorial girdles attach the upper limbs to the body trunk. The pelvic girdle secures the lower limbs. Scapula Humerus Upper limb Radius Ulna Carpals Metacarpals Phalanges Femur Lower limb Tibia Fibula Tarsals Metatarsals Phalanges A SI 34 Articulations (joints) • Sites where two or more bones meet. • Hold the skeleton together. • Give the skeleton flexibility. Classification of Joints Functional (amount of joint movement) – • Synarthroses: immovable e.g. skull sutures. • Amphiarthroses: slightly movable e.g. vertebrae. • Diarthroses: freely movable e.g. shoulder, ankle. or Structural (material binding the bones together) – • Fibrous: generally immovable. • Cartilaginous: rigid or slightly movable. • Synovial: freely movable. 35 Fibrous Joints Sutures: Seams that occur between bones of the skull. Interlocking edges. Bones fuse into a single unit by adulthood. Syndesmoses: Bones connected together by a cord or sheet of fibrous connective tissue. The joint has ‘give’, but no true movement. For example the distal tibiofibular joint. Gomphoses: Tooth peg-in-socket joint. Cartilaginous Joints Synchondroses: Cartilage bars or plates that connect together bones. Allow bone growth in epiphyseal plates. Symphyses: Compressible and resilient cartilage pads. Permits limited movement. For example intervertebral joints. 36 12 Synovial Joints General structure – Articular cartilage: glassy smooth, spongy cartilage cushions cover opposing bone surfaces. Joint cavity: filled with synovial fluid. Articular capsule: double layered capsule enclosing the joint cavity. Outer layer is a tough flexible fibrous capsule. Synovial membrane: composed of loose connective tissue, lining the fibrous capsule and all non-cartilage covered surfaces. Synovial fluid: small amount of slippery fluid occupies all free spaces in the joint capsule. Reduces friction within the joint. Bone Ligament 37 Synovial Joint Movements Gliding: flat/nearly flat bone surfaces glide or slip over one another, resulting in a displacement. Gliding joints occur at intercarpal and intertarsal joints, and between flat articular processes of the vertebrae. Angular: increase or decrease the angle between two bones. Such movements include flexion (decrease angle), extension (increase angle), abduction (moving away from medial plane), adduction (moving towards medial plane) and circumduction (cone shaped movements). Rotation: turning a bone around its own long axis. Such movements occur around the hip and shoulder joints, as well as between the first two cervical vertebrae. 38 Levers A lever is a rigid bar that moves on a fixed point (fulcrum) when a force is applied to it. The applied force (effort) is used to move a resistance (load). Type 1 lever: Effort Load Fulcrum 39 13 Type 2 lever: L Type 3 lever: L 40 Some health problems associated with the musculoskeletal system Muscular dystrophy: any one of a group of genetic conditions that causes a progressive weakness and degeneration of skeletal muscles. Sarcolemma can tear during muscle contraction, leading to degeneration of individual muscle fibres and atrophy of muscles. Myasthenia gravis: a progressive autoimmune condition, in which nAChRs are destroyed in the NMJ, causing muscle weakness. Rheumatoid arthritis: an autoimmune and inflammatory condition that may affect the joints of the fingers, wrists, feet, ankles, etc in a symmetrical pattern. Osteoporosis: loss of bony tissue, resulting in bones at a higher risk of fracture. 41 In summary, some of the things we have seen are: • Some characteristics and functions of muscles. • Structure of muscle fibres. • The NMJ and the coupling of excitation and contraction. • The overall structure of the skeleton. • Types of skeletal joints. 42 14