Bone and Muscles.pdf

Bone and Muscles Bone  Bone is a connective tissue in which the cells and fibers are embedded in a matrix (ground substance), that contains crystals of complex calcium salt, hydroxyapatite  It has supportive and protective role  Periosteum-covers the outer surface of bones  Endosteum-th...

Bone and Muscles Bone  Bone is a connective tissue in which the cells and fibers are embedded in a matrix (ground substance), that contains crystals of complex calcium salt, hydroxyapatite  It has supportive and protective role  Periosteum-covers the outer surface of bones  Endosteum-thinner layer, lines the interior of the bones Covering of Bone Macroscopic Structure of the Bone  Shaft or diaphysis(longitudinal section)- a)Substantia compacta or compact bone- dense bone surrounding voluminous central medullary cavity or marrow cavity  b)Substancia spongiosa or cancellous bone- this is what happens to the compact bone as it approaches the end of the diaphysis. They become thinner and the medullary cavity contains a three- dimensional network of branching bone spicules(trabeculae) Macroscopic Structure of the Bone  Articular cartilage- thin hyaline cartilage that covers the end of long bones when it forms a joint with another bone  Epiphyseal plate- thin zone of hyaline cartilage, separates the diaphysis from a short segment of long bones of growing children, at either end called epiphysis  In flat bones of skull , compact bone forms outer and inner layer , referred to as outer table and inner table of the bone  Corresponding to medullary cavity of long bone is the diploe Microscopic Structure  Osteoprogenitor cells- fusiform shaped cell found in the periosteum and endosteum. Cells are inactive precursors of the osteoblasts, the bone forming cells of growing bone  Osteoblasts- cuboidal, or low columnar cell aligned on bone surfaces. They synthesize type I collagen, glycoproteins, and proteoglycans of the ground substance, and several minor proteins (osteocalcin, osteonectin, osteopontin, and osteoproteregin) Different Bone Cells Microscopic Structure  Osteocytes- residing in lacunae within the calcified matrix. They are the principal cells of adult bone. A number of slender tapering cell processes radiate from the cell body which occupy canaliculi coming from lacuna  Osteoclast- very large cell up to 15 micrometer in diameter and contains 4 to 40 nuclei. They are involved in internal remodeling and renewal of bone.  Beneath each osteoclast there is a shallow depression on the surface of the bone and it is called Howship’s lacuna Different Bone Cells Organization of lamellar bone  The compact bone of adults is made up of cylindrical subunit called Haversian system or osteons  Osteons- made up of 5-15 lamellae of calcified matrix arranged around a central canal  Volkmann’s canals- oblique channels that pass through lamellae that connects the central canal of the osteons or to the marrow cavity Haversian System Lamellar bone  Interstitial lamellae- parallel lamellae that occupies the angular areas between the osteons  Cement line- thin refractile layer that lines the outer boundary of each Haversian system or osteon  Outer circumferential lamellae – just beneath the periosteum.They go around the entire circumference of the shaft without interruption. Comparable lamellae beneath the endosteum are called inner Histogenesis of bone  2 Different types of Osteogenensis  Intramembranous Ossification- when bone is formed by replacing the primitive connective tissue (mesenchyme). Occurs in flat bone of the skull  Endochondral Ossification- bone formation takes place in pre–existing cartilage. Occurs in long bones of the appendicular skeleton Muscles Functions of Muscle Tissue  Producing movement  Maintaining posture  Stabilizing joints  Generating heat Types of Muscles Type Voluntary/ Striations Movement of Location Involuntary Muscles Skeletal Voluntary + Rapid but tires Skeletal muscles easily which attach to (“muscle and cover the fibers”) bony skeleton Cardiac Involuntary + Usually steady Heart rate Smooth Involuntary - Slow and Walls of hollow sustained visceral organs (“muscle (e.g. stomach, fibers”) urinary bladder, etc.) Skeletal Muscle Microscopic View Microscopic Anatomy: Skeletal Muscle Fiber  Long, cylindrical cell, multiple oval nuclei arranged beneath the sarcolemma  Diameter: 10-100 um, Length: up to 30 cm  Sarcoplasm contains large amounts of glycosomes and myoglobin  Each muscle fiber contains hundreds to thousands of myofibrils Rodlike structures, 1-2 um, account for 80 % of cellular volume Contain the contractile elements of skeletal muscle fibers Microscopic Anatomy: Skeletal Muscle Fiber  Striations: repeating series of dark bands and light bands that are nearly perfectly aligned with one another  A band: dark band  I band: light band  H zone: light zone in midsection of A band  M line: bisects the H zone  Z disc (or Z line): bisects the I band Microscopic Anatomy: Skeletal Muscle Fiber Sarcomere: Region of a myofibril between two successive Z discs Contains an A band flanked by half an I band at each end Smallest contractile unit of a muscle fiber (ave. 2 um long) Microscopic Anatomy: Muscle Fiber  Myofilaments Thick filaments – composed of myosin Thin filaments – composed of actin Thick Filaments  Each myosin molecule has: Rodlike tail consisting of two interwoven helical polypeptide chains Two globular heads which contain ATPase enzymes – split ATP to generate energy during contraction Thin Filaments  Polypeptide subunits of actin called G actin (globular actin) contain the active sites to which myosin heads attach during contraction Thin Filaments Tropomyosin – rod-shaped protein which spirals about the actin core  Helps stiffen actin  Blocks myosin binding sites on actin so that the myosin heads cannot bind to the thin filaments Troponin  Binds tropomyosin and helps position it on actin  Binds calcium ions Sarcoplasmic Reticulum and T- Tubules  Two sets of intracellular tubules that participate in regulation of muscle contraction  Sarcoplasmic reticulum  T Tubules Sarcoplasmic Reticulum Composed of interconnecting tubules that surround each myofibril Form large, perpendicular cross channels at the A band-I band junctions called terminal cisternae (occur in pairs) Regulates intracellular Ca+ (stores Ca+ and releases it on demand when the muscle fiber is stimulated to contract) T- Tubules  Elongated tubes located at each A band-I band junction, formed by the sarcolemma penetrating into the cell interior  Lumen is continuous with the extracellular space  Conduct impulses to the deepest regions of the muscle cell and to every sarcomere  Triad: terminal cisterna + T tubule +sarcoplasmic ret Triad  As each T tubule protrudes deep into the cell it runs between the paired terminal cisternae of the SR  Terminal cisterna + T tubule + SR Sliding Filament Model Contraction During contraction, the thin filaments slide past the thick filaments so that the actin and myosin filaments overlap to a greater degree Sliding Filament Theory Definition of Terms  Synaptic cleft Space that separates the axon terminal and the muscle fiber Filled with gel-like extracellular substance rich in glycoproteins and collagen fibers  Acetylcholine (ACh) Neurotransmitter released from the presynaptic vesicles  Acetylcholinesterase Enzyme located in the synaptic cleft which breaks down Ach  Motor endplate Trough-like part of the muscle fiber’s sarcolemma Highly-excitable region, responsible for initiation of action potentials across the muscle's surface Neuromuscular Junction Cardiac Muscle Structure of Cardiac Myocytes  Cardiac myocytes- separate cellular unit of cardiac muscle  80 micrometer in length, 15 micrometer in diameter  Joined end to end at junctional complexes called intercalated disks which is comparable to zonula adherens of epithelial junction Cardiac muscle  Principal identifying features of cardiac muscle are:  1. Centrally placed single nucleus of the myocytes  2.Presence of transverse intercalated disks at intervals along the length of the myofibers Smooth Muscle Microscopic Structure  Smooth muscle is made up long fusiform cells with an elongated nucleus located centrally  Ratio of actin to myosin filament is 12 to 1  Gap junction – provides the cell-cell communication necessary for integrated contraction Histophysiology  Smooth muscle contraction is initiated by influx of calcium that binds to calcium binding protein called calmodulin.  The calcium-calmodulin complex binds to myosin light chain-kinase that activates and catalyzes the phosphorylation of myosin light chains, enabling to interact with actin filaments and cause contraction Thank you for listening !