Muscular Tissue M1 2024.pptx

Muscular Tissue Dr. Moustafa Al Sawy 10/4/23 Special names of muscular cells 1) It is formed of muscle cell = muscle fiber = myofiber 2) Their cytoplasm is called Sarcoplasm. 3) Sarcoplasm contains {myofibril-sERmitochondria- myoglobin} to serve its contractile function. 4) Their SER is called Sa...

Muscular Tissue Dr. Moustafa Al Sawy 10/4/23 Special names of muscular cells 1) It is formed of muscle cell = muscle fiber = myofiber 2) Their cytoplasm is called Sarcoplasm. 3) Sarcoplasm contains {myofibril-sERmitochondria- myoglobin} to serve its contractile function. 4) Their SER is called Sarcoplasmic reticulum. 5) Their plasma membrane is called Sarcolemma. There are three types of muscle fibers: 1- Skeletal (striated and voluntary) 2- Cardiac (striated and unvoluntary) 3- Smooth (non striated and unvoluntary) 10/4/23 Organization of a Skeletal Muscle Thin layers of connective tissue surround and organize the contractile fibers: The epimysium, an external sheath of dense irregular connective tissue, surrounds the entire muscle. They are carrying the larger nerves, blood vessels, and lymphatics of the muscle. The perimysium is a thin connective tissue layer that immediately surrounds each bundle of muscle fibers termed a fascicle. Nerves, blood vessels, and lymphatics penetrate the perimysium to supply each fascicle. The endomysium, within fascicles a very thin, delicate layer of reticular fibers and scattered fibroblasts. It surrounds the external lamina of individual 10/4/23 Microscopic structure of striated muscle  Striated muscle cells (fibers) form the structural basis of skeletal muscles.  Each striated muscle cell (fiber) is a long thin cylindrical structure, typically 50–60 μm in diameter and up to 10 cm long, depending on its location.  It has multiple peripheral nuclei  Its acidophilic cytoplasm contains all cell organelles with prominent cytoskeleton’s myofibrils and cell inclusions (glycogen and myoglobin).  Myoglobin is a globular protein like hemoglobin, it contains iron atoms allows it for O2 storage. 10/4/23 Myofibrils  Myofibrils are the contractile elements of skeletal muscle cell. They are thin cylindrical structure with 1-2um diameter. They are composed of overlapping of thick (myosin) and thin (actin) myofilaments.  According to the arrangements of myofilaments, the myofibril shows: 1-Dark band (mainly myosin) {anisotropic =A band }. In the center of each A-band, there is a pale area called H-band which is bisected a thin M-line. 2- Light band (mainly actin){isotropic =I band}. Each I-band is bisected by a thin dark line, the Z-line. 10/4/23 Sarcomere -Sarcomere is the functional contractile unit of striated muscles. -It lies between 2 successive Z line. Sarcomere consists of: One dark band in the middle and two halves of light band on either side. -The A bands are composed mainly of thick filaments in addition to portions of overlapping thin filaments. The center of A band shows the presence of a lighter zone , the H zone, that corresponds to a region consisting only of the myosin molecule. -A cross section in the region of filament overlap shows each thick filament surrounded by six thin filaments in the form of a hexagon 10/4/23 10/4/23 Myofilaments 1.Thin filament {actin}:  It is 5nm diameter. It is formed of F-actin which is double helical polymer of G-actin protein Troponin and tropomyosin are two proteins associated with actin. Tropomyosin, a 40-nm-long coil of two polypeptide chains located in the groove between the two twisted actin strands Troponin, a complex of three subunits: TnT, which attaches to tropomyosin; TnC, which binds Ca2+; and TnI, which regulates the actinmyosin interaction 10/4/23 Myofilaments 2. Thick filament {myosin}  It is 15nm in diameter. Each myosin filament consists of 300 myosin molecules, each molecule resembles two golf clubs. Myosin is a large complex with two identical heavy chains and two pairs of light chains. Myosin heavy chains are thin, rodlike motor proteins twisted together as myosin tails. Globular projections containing the four myosin light chains form a head at one end of each heavy chain. The myosin heads bind to: 1- Actin, forming transient crossbridge between the thick and thin filaments 2- ATP, catalyzing energy release (actomyosin ATPase activity). 10/4/23 View of Myofilament Structure 10/4/23 The transverse tubule T-tubule -The sarcolemma sends transverse invagination into sarcoplasm - T-tubules present at A-I bands junction -It conducts the impulse from outer to deeper parts of skeletal muscle  There are 2 triads in each sarcomere  Importance of T- tubules & SR: nerve impulse wave of depolarization sweeps along sarcolemma into T- tubules Depolarization of T- tubules release of Ca from sER interaction of actin & myosin muscle contraction 10/4/23 Sarcoplasmic Reticulum  It is sER  It forms transverse wider cisternae (tubules) on each sides of Ttubules  Two terminal cisternae of sER+T-tubules triad at A-I junctions.  Function: regulation of muscle contraction by releasing or sequestering Ca { it regulates Ca concentration within the myofibril } 10/4/23 Contraction of the Muscle  Nerve impulse + energy from ATP in mitochondria sliding of actin over myosin pushing two Z lines inward shorting the distance bet. them H zone disappears as it will contain both actin & myosin.  The sarcomere & whole myofibril are shortened. 10/4/23 Accessory proteins of myofilaments - Titin: connects the Z line to the M band, to prevent overstretch of the sarcomere. Titin contains elastic elements that act as molecular springs and contribute to the passive elasticity of muscle. - α actinin: At Z bands, Actin, Nebulin, and Titin are attached to it. - Nebulin: another giant protein, spans the length of thin actin filaments and attaches them to the Z lines. - Trobomodulin: attach to the free end of actin to regulate its length. 10/4/23 Types of Muscle Fibers Type Myoglob Number in of Content Mitochon Enzyme Content Contract ATP ion Generation Major sites Red (slow; type 1) Intermedi ate (type 2A) High Many High in oxidative enzymes; low in ATPase Slow but repetitive; not easily fatigued Oxidative Postural phosphorylatio muscles of n back Intermediat e Intermediat e Intermediate in oxidative enzymes and ATPase Fast but not easily fatigued Oxidative Major phosphorylatio muscles of n legs and anaerobic glycolysis White (fast; type 2B) Low Few Low in oxidative enzymes; high in ATPase and phosphorylas es Fast and easily fatigued Anaerobic glycolysis dria 10/4/23 Extraocula r muscles Most muscles contain a mixture of all types, with one type predominant. Fiber typing is determined the functional properties of a particular muscle with some genetic differences. Marathon runners have more type 2A fibers than power lifters, who have a higher percentage of type 2B fibers. Training can change the percentage of fiber types, mostly in one direction; training for marathons, for example, produces more type 2A fibers. 10/4/23 CLINICAL POINT Myotonia is a neuromuscular condition characterized by slow or delayed relaxation of a muscle after voluntary contraction. It may arise in any muscle group by sudden exposure to cold temperature but usually improves after the muscles have been warmed up with brief exercise. Myotonia congenita (or myotonic muscular dystrophy) is a genetic disorder that usually begins in infancy or early childhood. It is caused by mutations in the gene that controls voltage-gated chloride ion (Cl-) in the sarcolemma of skeletal muscle fibers. Subsequent interruption in Cl- flow triggers prolonged muscle contractions and stiffness. Although the disease severity differs among individuals, physical therapy and other rehabilitative procedures may improve the muscle function. 10/4/23 Delayed onset muscle soreness It is caused by a single, unaccustomed, intensive exercise event leading to sensation of skeletal muscle soreness, stiffness, and pain. Symptoms typically begin at the muscle-tendon junction and then spread throughout the affected muscle. Underlying mechanisms are loss of muscle fiber integrity (sarcolemmal tearing, myofilament disruption, cytoskeletal disarray, Z-band streaming) accompanied by acute inflammation in the endomysium, which sensitizes surrounding nociceptors (pain receptors). Muscle fibers undergo repair and remodeling via an increase in protein synthesis and activation of satellite cells. 10/4/23 An investigator is studying the microstructure of skeletal muscle fibers to identify new targets for skeletal muscle relaxation. He obtains a biopsy from the brachioradialis of a test subject and observes it under a transmission electron microscope. A photomicrograph of the structures seen during microscopy is shown. Which of the following parts contains the greatest proportion A of actin filaments? B C D E 10/4/23