Muscles, Histology, Physiology, Biochemistry PDF

Assessment muscles Histology of muscles: 288228 1. Histological structure and localisation of smooth muscle tissue Are small elongated spindle shaped cells with finley tapered ends. These cells do not have a striated appearance because they do not contain muscle sarcomeres. Instead, arrays of acti...

Assessment muscles Histology of muscles: 288228 1. Histological structure and localisation of smooth muscle tissue Are small elongated spindle shaped cells with finley tapered ends. These cells do not have a striated appearance because they do not contain muscle sarcomeres. Instead, arrays of actin filaments, connected to dense bodies, surround myosin filaments in a less well- organized fashion. They are specialized for slow, prolonged contractions. Contraction of smooth muscle is triggered by a variety of impulses, including mechanical (passive stretching), electrical (depolarization at nerve endings), and chemical (hormones acting by a second messenger) stimuli. Smooth muscle cells in different organs have different functions. The contractile function of vascular smooth muscle regulates the luminal diameter of the small arteries - arterioles. Thereby contributing significantly to setting the level of blood pressure. In the digestive tract, smooth muscle contracts in a rithmic peristaltic fashion, rhythmically forcing foodstuffs through the digestive tract as the result of phasic contraction. SMooth muscle are also found in urinary tract Of all the muscle types, smooth muscle cells have the greatest capacity for regeneration.They can divide and increase in number. Numerous cells called pericytes, which lie along the small blood vessels can divide and generate new smooth muscle cells. Smooth muscle cells can also hypertrophy 2. Histological structure and localisation of skeletal muscle tissue Skeletal muscle fibers are the largest cells in the body, with a single cell stretching from one end of the muscle to the other. SKeletal muscle fibers contain thousands of nuclei, which are required to maintain a cell of this size. These muscle fibers are single, multinucleated cells. The nuclei are found at the cell periphery, and there is approximately one nucleus every 3μm along the fiber length. Multinucleated skeletal muscle fibers are formed by the fusion of many mononucleated cells (myoblasts) together during development, and growth. The structural and functional subunit of the muscle fiber is the myofibril. It is composed of precisely aligned myofilaments: Myosin- containing thick filaments and actin- containing thin filaments. In longitudinal sections, muscle fibers have a stripes appearance. These strips result from the arrangement of repeating units called sarcomeres in series along the fiber. In skeletal muscle, sarcomeres are about 2.5μm long. A fiber, 30 cm long, contains 120 thousand sarcomeres arranged end to end. Sarcomeres are the smallest contractile unit of started muscle. The arrangement of thick and thin filaments gives rise to the density differences that produce the cross- stations of the myofibril. The light-staining isotropic I band contains mainly thin filaments attached to both sides of the Z line, and the dark-staining anisotropic A band contains mainly thick filaments. The actomyosin cross-bridge cycle represents a series of coupled biochemical and mechanical events between myosin heads and actin molecules that lead to muscle contraction. Muscle fiber (myofibers) are terminally differentiated and do not undergo mitosis. But satellite cells, which are skeletal muscle stem cells, can repair damaged muscle fibers. These cells lie under the basal lamina of the muscle fibers. When the muscle is damaged, they are stimulated to divide to generate new myoblasts, which fuse and repair the damaged muscle fiber 3. Histological structure and localisation of cardiac muscle tissue Cardiac muscle is striated and has the same type and arrangement of contractile filaments as skeletal muscle. Cardiac muscle cells (cardiac myocytes) are short cylindrical cells with a centrally positioned single nucleus. They are attached to each other by intercalated discs to form a cardiac muscle fiber. The intercalated discs represent highly specialized cell- to cell- adhesion junctions. Resting sarcomere length in cardiac muscle (about 2.2 μm) is slightly shorter than in skeletal muscle. Cardiomyocytes are much smaller (about 80-100μm long and about 15 μm in diameter) than skeletal muscle fibers. Specialized cardiac conducting muscle cells exhibit a spontaneous rhythmic contraction. They generate and rapidly transmit action potentials to various parts of the myocardium Cardiac muscle cells can hypertrophy (grow larger) or hypotrophy (grow smaller) as a result of changing demands on the heart, but the cells are terminally differentiated and cannot divide. The heart does not appear to contain large numbers of “stem” cells similar to the satellite cells of skeletal muscle, and therefore only has a limited ability to regenerate when damaged. Heart muscle damaged by a heart attack heals by forming scar tissue. 4. Regeneration capacity of different types of muscle tissue 5. Composition of connective tissue layers that held muscle fibers together Connective tissue in skeletal muscle: - Endomysium- Surrounds individual fibers - Perimysium- Surrounds a group of fibers to form a fascicle - Epimysium- Surrounds the entire muscle and is dense connective tissue Connective tissue in tendon: - Epitendineum- Tendons are surrounded by a connective tissue capsule - Peritendineum- Divide fascicles by connective tissue - Endotendineum- Are groups of fibers surrounded by fibroblasts and very little connective tissue 6. Structure of red and white muscle fibers Red muscle fibers Type I “red” muscle, is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color Fibers specialized for aerobic metabolism develop a high myoglobin concentration. Slow twitch fibers contract for long periods of time but with little force. Have relatively more sarcoplasm. White muscle fibers Type II, “white” muscle, fast twitch that is least dense in mitochondria and myoglobin muscle. Fast twitch fibers contract quickly and powerfully but fatigue very rapidly sustains only short, anaerobic bursts of activity before muscle contraction becomes painful. In small animals this is a major fast muscle type, explaining the pale color of their flesh. 7. Histological structure of fascia A fascia is a layer of dense regular connective tissue containing closely packed bundles of collagen fibers oriented in a wavy pattern parallel to the direction of pull. A fascia is a structure of connective tissue that surrounds muscle, groups of muscle, blood vessels, and nerves, binding some structures together. Fasciae are flexible structures which make it able to resist great unidirectional tension forces. 8. Histological structure of tendon sheath Tendon is cord- like structures that attach muscle to bone. They consist of parallel bundles of collagen fibers and are made of dense regular connective tissue. Situated between these bundles are rows of fibroblasts called tendinocytes. It contains very few blood vessels 9. Histological structure of synovial bursa Synovial bursa- saclike cavity, lined with synovial membrane that secretes a viscous lubricating synovial (bursal) fluid, interposed between tendons and bony prominences or at other points of friction between moving structures. Physiology of muscles: 10. Types of muscles. Skeletal muscle: Voluntary, under conscious control, attaches to bones and enables movement Cardiac muscle: Involuntary regulated by autonomic nervous system and peacemaker cells. Smooth muscle: Involuntary, found in walls of hollow organs, controls content movement through lumen. 11. Functions and properties of muscles Functions: - Movement: Skeletal muscles move the body by contracting and pulling on tendons. - Posture: Maintain body posture against gravity - Support: Protect internal organs (abdominal muscles) - Control of openings: Sphincters regulate the openings of body orifices - Peristalsis: Smooth muscles propel content in tubular organs - Blood flow: Cardiac muscle pumps blood, smooth muscle in vessels regulates flow - Temperature regulation: Converts metabolic energy to heat Properties: - Excitability: Respond to stimuli - Contractility: Shorten and produce force - Extensibility: Stretch without damage - Elasticity: Return to original shape after stretching - Conductivity: Conduct electrical impulses 12. Structure of a skeletal muscle. Composed of muscle fibers (cells) bundled into fascicles - T-tubules: Conduct impulses into fibers - Sarcoplasmic reticulum (SR): Stores and releases calcium for contraction - Myofibrils: Composed of actin (thin) and myosin (thick) filaments 13. Sarcomere The basic contractile unit of a started muscle cell. - Z lines, contains I band, A bands, H zones and M lines  - Sliding filaments theory: Actin and myosin filaments slide past each other during contraction 14. Analysis of muscle contraction (Neuromuscular Junction, Sliding Filament Theory, Contraction of Motor Units, Contraction of Whole Muscle – lab work). 15. Types of muscle contraction Isotonic: Muscle changes length under constant tension, for example lifting weights. Isometric: Muscle tension increases without changing length 16. Muscle tone and motor units Muscle tone: Baseline muscle tension maintaining posture and readiness Motor unit: A single motor neuron and the muscle fibers it contains, size varies depending on precision needed 17. Tetanus A sustained muscle contraction resulting from rapid and repeated stimulation 18. Muscular work Involves contraction and relaxation cycles powered by ATP. Prolonged work leads to fatigue and oxygen debt 19. Skeletal muscle fatigue Caused by depletion of energy reserves (ATP, glycogen), accumulation of lactic acid, or impaired calcium release. 20. Types of muscle fibers Type I: Slow- twitch, red, fatigue- resistant, efficient in prolonged, low- intensity activity Type II: Fast- twitch, white: - Ila: Fast oxidative, moderately resistant to fatigue - Ilb/Ilx: Fast glycolytic, powerful but fatigue quickly 21. Training Regular exercise improves muscle size, strength, endurance, and resistance to fatigue. It also enhances overall metabolism, circulation, and lung efficiency 22. The kinesthetic sense-proprioreceptors. Muscle spindles: Detect muscle length and changes in length Golgi tendon organs: Sense tension and protect muscles from excessive force Joint receptors: Provide information about joint angle and motion Biochemistry of muscles: 23. Proteins: Functions- Major components of structural tissue (muscle, skin, nails, hair) Primary structure - linear chain of amino acids. A peptide name is always ending with “yl” which is joint to the name of amino acid starting with the amino acids-end in sequence and the full amino acid name of the amino acids in the carboxyl- end. Non peptides are oxytocin and vasopressin. They have similar primary structures. Differ only in the amino acids at positions 3 and 8. Secondary structure- A 3D spatial conformation of the polypeptide backbone excluding the side chains. The two most common secondary structural elements are alpha helix and beta sheets. Proteins consist of long chains of amino acids, The structure of proteins are well defined shapes. These shapes are formed by hydrogen bonding. Hydrogen bonding forms intermolecular hydrogen bonds bw carbonyl group and the amino group. Alpha helix has a coiled shape held in place by hydrogen bonds bw the amine groups and the carbonyl groups of the amino acid along the chain. Beta sheets consists of polypeptide chains arranged side by side. Has hydrogen bonds bw chains, has R groups above and below the sheets. Is typical of fibrous proteins such as silk. Tertiary structure- 3D arrangement of its polypeptide chain in space. It is generally stabilized by outside polar hydrophilic hydrogen and ionic bond interactions, and internal hydrophobic interactions bw nonpolar amino acid side chains. Interacts and cross links bw different parts of the peptide chain. Quaternary structure- Combination of two or more tertiary units. It is stabilized by the same interactions found in tertiary structures. Hemoglobin consists of two alpha chains and two beta chains. The heme group in each subunit picks up oxygen for transport in the blood to the tissue. 24. Physico-chemical properties of proteins: Isoelectric point- Is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. Coagulation- Is the process of solidifying proteins, for example when you are bleeding, the blood will coagulate (solid). When proteins are heated at their isoelectric pH, a series of changes occur which is: - Dissociation of the protein subunits (disruption of quaternary structure) - Uncoiling of the polypeptide chains ( disruption of tertiary and secondary structure) - Matting together of the coiled polypeptide chains (coagulation) Denaturation- Is the process where it breaks down protein, for example when frying an egg, the proteins are breaking down to get that solid form. Denaturation of proteins involves the disruption and possible destruction of the secondary and tertiary structures. Proteins lose their biological activity. It involves: - Heat and organic compounds that break the hydrogen (H) bonds and disrupts hydrophobic interactions - Acids and bases that break hydrogen (H) bonds bw polar R groups and disrupt ionic bonds. - Heavy metal ions that react with S-S bonds to form solids - Agitation such as whipping that stretches peptide chains until bonds break 25. Simple proteins (albumins, globulins, protamine, histones, prolamins, glutelin, scleroproteins)- Only contain amino acids Complex proteins (nucleoproteins, chromoproteins, glycoproteins, phosphoproteins, lipoproteins)- Attached with a carbohydrates 26. Classification and function of proteins Catalytic proteins: Enzymes Structural proteins: Collagen, elastin Contractile proteins: Myosin, actin Transport proteins: Hemoglobin, myoglobin, albumin, transferrin  Regulatory proteins or hormones: Insulin, growth hormone Genetic proteins: Histones Protective proteins: Immunoglobulins, interferons, clotting, clotting factors 27. Complete proteins- Contain all the essential amino acids in the required proportion: casein of milk, egg white Incomplete proteins- They lack one essential amino acid.They cannot promote body growth in children, but may be able to sustain the body weight in adults. Proteins from pulses are deficient in methionine. 28. Precipitations and qualitative reactions of proteins (based on laboratory works). 29. Hydrolysis of proteins- The peptide bonds split to give smaller peptides and amino acids. Occurs in the digestion of proteins, occurs in cells when amino acids are needed to synthesize new protein and repair tissue. Hydrolysis of a dipeptide- In lab for a peptide to occur hydrolysis we needed acid or base, water and heat. In our bodies enzymes catalyse the hydrolysis of proteins. 30. Proteins of muscles- Muscle proteins are the most important for muscle contraction. Muscle proteins are divided into Sacroplasma proteins (water soluble)- Myoglobin, the amount depends on the activity of the respective muscle group. Its function is to accumulate oxygen in the muscles, the color of the muscle depends on it too. Calcezvestrine, an acidic protein that contains more than 40 Ca2+ ion- binding units in the molecule, its function is to stimulate the onset of muscle contraction. Fibrillar myofibril proteins (insoluble in water) Myofibrils proteins- Myofibrils are a complex of contractile (contractile) proteins. Myofibrils consist of 2 types of longitudinal filaments of protein origin filaments: The first type is thick filaments (ø 16 nm) consisting of 200-400 molecules of protein myosin The second type - thin filaments (ø 9 nm), consisting of a complex of proteins actin, tropomyosin and troponin Myosin, actin, and tropomyosin account for about 90 percent. of all proteins involved in the muscle contraction process Myosin- Its molecule is made up of a fibrillar part, a "tail" made up of two identical twisted α-helices that form a supercoil and end up with globular "heads" at the other end. Function of myosin:  1. Myosin molecules spontaneously bind to filaments under physiological conditions. About 400 tails of myosin molecules interlock to form a myosin filament. 2. Myosin has ATPase activity - It hydrolyzes ATP: ATP + H2O ADP + Pi + H + - The free energy of this reaction is used to contract the muscles 3. The myosin "heads" and part of the tail connect to the actin transverse bridges. Myosin can be thought of as a mechanoenzyme that catalyzes the conversion of energy from chemical bonds into mechanical energy. Actin (G-actin) The major component of skeletal muscle thin filaments is monomeric, globular protein, composed of a single polypeptide chain of 374 amino acids Actin filaments Actin filaments consist of actin, tropomyosin (Tm), and three troponin proteins. The actin core consists of two twisted F-actin (fibrillar actin) chains Actin Two chains of tropomyosin molecules are attached to the F-actin filaments by flexible joints. They are located in a depression formed by two action chains. Tropomyosin is periodically bound to a complex of three troponin proteins consisting of troponin C (Ca2 + binding), troponin I (inhibitory), and troponin T (tropomyosin binding) Myosin and actin complex When the heads of the myosin molecule bind to the actin threads, actomyosin is formed. This interaction creates the force applied to the thick (myosin) and thin (actin) the filaments move (slip) one in another respect. 31. Muscles protein functions. Body moving Respiration (diaphragm and intecostal contractions) Digestion Vascular tone and blood circulation Excretion In muscles, chemical energy is converted into kinetic (mechanical work) 32. Muscles nitrogenous compounds (non-protein) and their functions. Muscles contain low molecular weight organic compounds that contain nitrogen in their structure. These are: - Nucleotides (ATP, ADP, AMP). - Creatine (arginine and glycine) and phosphocreatine - In muscle, phosphocreatine can transfer the phosphate group attached by a macroergic bond to ADP and regenerate an ATP molecule that is important for muscle contraction. - Carnosine and anserine- Dipeptides reduce muscle fatigue and increase the amplitude of muscle contraction. - Carnitine- is a specific muscle compound (carrier) that transports fatty acid residues from the cytoplasm across the inner mitochondrial membrane. - Amino acids- Muscles primarily assimilate branched-chain amino acids: isoleucine, valine, and leucine. They make up about 50 percent. of all amino acids entering the muscle. These amino acids are the major donors and energy sources of the amino groups used to aminate pyruvate to alanine. More than 50 percent. The α-amino acid nitrogen produced in muscle consists of alanine and glutamine nitrogen. 33. Muscles non-nitrogenous compounds and their functions. Glycogen The main non-nitrogenous organic matter in the muscles, the reserve polysaccharide (a form of glucose storage). Glycogen accumulations are present in almost all tissues except blood cells and bone tissue. Most glycogen is stored in the liver up to 10%. The amount in the muscle varies from 0.3 to 2 percent. The amount of glycogen in the muscles depends on the work of the muscles and their mass. In resting muscles, it accumulates the most, but in active muscles, its stores almost disappear. Lactate, pyruvate and other carboxylic acids are formed during the process of glucose and amino acid metabolism. Lipids- In muscle, it performs two functions: phospholopids and sterols are structural elements of cell membranes, and triglycerides are a reserve source of energy. Inorganic salts- It contains mainly potassium and sodium cations. K+ is mainly present in muscle fibers and Na+ in the intercellular medium. Smaller amounts: Mg, Ca and Fe. Ca2+ ions are important for muscle contraction, they stimulate this process. 34. Mechanism of muscle contraction. Muscle contraction is the process by which muscle tissue shortens and tension occurs. The signal to contract is transmitted by an electrical impulse that propagates through the motor nerves and reaches the muscles through the junction of the nerve and muscle in the sarcolemma (a thin film covering the muscle fibers). 35. Stages of the biochemical cycle of muscle contraction. 1. The muscle rests before contraction. When the muscle is relaxed, the myosin head is between the thick and thin filaments. It itself hydrolyzes ATP to ADP and inorganic phosphate, but the hydrolysis products are not released (hydrolysis of ATP occurs faster than removal of catalytic products). In stage 1, the muscle is irritated, tropomyosin changes its position, calcium ions clump together with troponin. The myosin head, which contains ADP and Pi, can rotate at a sufficiently large angle and join the F-actin to form an angle of 90 ° with its axis (actin-myosin complex). A transverse bridge is formed. 2. Fusion occurs, the actin-myosin-ADP interaction releases Pi. Myosin changes the angle of the transverse bridge with the axis of the actin thread from 90 ° to 45 ° (the conformation requiring the least energy) by pulling the actin towards the center of the sarcomere (10– 15 nm). A shrinkage force is created, which attracts actin. The release of ADP from myosin completes the push of force. 3. The energy supply takes place. The new ATP molecule binds to the myosin-F-actin complex. The myosin-ATP complex is little related to actin, so the myosin "head" relaxes from the actin in the sarcomere center using the energy of the degradation of adenosine triphosphate (ATP). 4. The newly bound ATP is hydrolyzed by the free myosin "head", and a new interaction with the thin filament occurs without relaxing Pi and ADP. The cycle repeats. ATP separates the myosin head from the thin filament (F-actin) and is the driving force behind muscle contraction. Under this scheme, all the muscles contract. The main factor regulating muscle contraction is Ca2 + ions. The highest muscle contraction activity is when the concentration of Ca2 + ions is about 10-6-10-5 mol / l. If the ion concentration drops to 10-7 mol / l the muscle loses its contractile properties even in the presence of ATP.