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Structure and histology of different types of muscles
- 1. PRESENTED BY: NAME: HITESH COURSE:B.Sc.(Hons.) ZOOLOGY COLLEGE ROLL.NO.: 5008 UNIVERSITY ROLL.NO: 19081569002 Submitted to : Dr. Smita Shukla DELHI UNIVERSITY SWAMI SHARDHANAND COLLEGE
- 2. Muscle isa specialized tissue of mesodermal origin. About 40-50 per cent of the body weight of a human adult is contributed by muscles. They have special properties like excitability, contractility, extensibility and elasticity. Muscles have been classified using different criteria, namely location, appearance and nature of regulation of their activities. Muscle have 4 characteristic properties i.e. Electrical excitability, Contractility , Extensibility and Elasticity.
- 3. 1. Mobility Themuscular system’s main function is to allow movement. When muscles contract, they contribute to gross and fine movement. 2. Stability Muscle tendons stretch over joints and contribute to joint stability. Muscle tendons in the knee joint and the shoulder joint are crucial in stabilization. The core muscles are those in the abdomen, back, and pelvis, and they also stabilize the body and assist in tasks, such as lifting weights.
- 4. 3. Temperatureregulation Maintaining normal body temperature is an important function of the muscular system. Almost 85 percent of the heat a person generates in their body comes from contracting muscles. 4. Organ protection Muscles in the torso protect the internal organs at the front, sides, and back of the body. The bones of the spine and the ribs provide further protection. Muscles also protect the bones and organs by absorbing shock and reducing friction in the joints.
- 5. OTHER PHYSIOLOGICALFUNCTIONS: BREATHING CIRCULATION DIGESTION URINATION. etc.
- 6. There are3 different types of muscles present in human body and they are 1. The Skeletal Muscles 2. The Cardiac muscles 3. The smooth muscles
- 7. Skeletal musclesare called so because they are closely associated with the skeletal system and involve in body movements and posture maintenance. These muscles are striated i.e. they have alternate dark and light bends present in them. These muscles can be voluntarily controlled. e.g. biceps brachii., triceps brachii.
- 8. The cardiacmuscles are present in the heart. The cardiac muscles are also striated in appearance. The movement i.e. rhythm of cardiac muscles can’t be voluntarily controlled but they can be altered by several hormones and neurotransmitters. The presence of intercalated disk is characteristic feature of the cardiac muscles.
- 9. The smoothmuscles are found in the visceral organs of the body like organs of GIT, in the skin etc. These muscles appear smooth under microscope as they don’t have any striatations present in them. The smooth muscles are involuntary in nature and controlled by ANS and several hormones and neurotransmitters can interfere in their functions.
- 11. The outermostlayer of a muscle is the epimysium which wraps together numerous fascicles wrapped with perimysium. Inside each fascicle are the individual muscle fibers wrapped around endomysium. Within the muscle fibers is where the functional unit of the fiber exists: the sarcomere. The sarcomere is the site where contraction occurs on the cellular level. In the sarcoplasm small thread like structures can be seen and they are known as myofibrils. These myofibrils runs throughout the length of the muscle fiber. These myofibrils contain myofilaments. These myofilaments are of two types the thin one is known as actin and the thick one is known as the myosin. Both of these filaments are protein.
- 12. These myofilamentsare confined and arranged in compartments known as sarcomere. This regular and repeated arrangement of actin and myosin forms the striations in the muscle. The actin and myosin are contractile protein and are involved in contraction of muscle along with them some structural protein are also there which provide strength, stability, extensibility to the myofibrils. E.g. titin, myomesin, neblin, dystrophin etc. Troponin and tropomyosin are regulatory proteins which are also present in the muscle fibres.
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- 15. The boundariesof sarcomere are denoted by z-lines or disk. Then I bands are present as we start moving from z –line towards the centre in this region only thin filaments i.e. actin is present. The I bands extend towards both side of z-lines. Dark bands are A bands and are located in the middle of sarcomere. A bands are formed by overlapping actin and myosin filaments. • M line in the middle of A bands represent linkage of myosin filaments and centre of sarcomere. • H bands on each side of M bands contain only myosin filaments. • When muscle contracts, I and H bands shorten, while A bands stay same.
- 16. The cardiacand skeletal muscles are very much similar in appearance and anatomy. The main difference is of functionality and locations. The cardiac muscles doesn’t get fatigued, they have a much greater no. of mitochondria for energy production. As described earlier cardiac muscles have presence of intercalated disk in the, these disk are very crucial for conduction of electrical impulse throughout the heart wall. These disks are irregular transverse thickenings of sarcolemma.
- 18. The smoothmuscle cells are thick at the centre and tapers towards the end. The smooth muscles also contain actin and myosin but they are not arranged in a repeated fashion that is why these muscles don’t look striated when observed. These muscles lack T-tubules also but instead they have caveolae, these are pouch like invaginations of plasma membrane and contain extracellular Ca ions.
- 19. The thinmyofilaments i.e. actin attaches to the dense bodies which are functionally similar to z-lines of sarcomere of skeletal muscles. Intermediate fibres are also present in these muscles which connect two adjacent dense bodies. The tension produced during in actin and myosin during contraction is transmitted to intermediate fibres, and these intermediate fibres under the influence pulls the two adjacent dense bodies. So the shortening of the muscle occur in a helix fashion.
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- 22. In theabove figure a section of skeletal muscle can be seen, this shows that the muscle fiber is multinucleated and the nucleus is present just below the sarcolemma. Cross striations with A and I bands can also be seen other sarcomere components like z-line, m-line are also observed. Endomysium with blood capillaries and fibroblast cells are also observed. Endomysium surrounding each muscle fiber and containing connective tissue cells called fibrocytes.
- 24. A transversesection of an skeletal muscle shows individual muscle fibers surrounded by connective tissue, the endomysium. The muscle fibers in turn are grouped into fascicles and surrounded by interfascicular connective tissue called perimysium. The muscle spindle can also be observed containing intrafusal fibres. Small nerve fibers associated with the muscle spindles are the myelinated and terminal unmyelinated nerve fibers (axons) surrounded by the supportive Schwann cells. s. Small blood vessels and an arteriole from the perimysium are also seen.
- 25. The TEMshows all the details of a myofibril it depicts all the components of a sarcomere i.e., the light and dark bands, the z-line, the m-line, h band etc.
- 27. The abovehigh-magnification photomicrograph illustrates the cardiac muscle fibers. This shows that cardiac muscles also show striations but are less pronounced. This also shows the branching in the cardiac muscle fibers . The figure shows a single central nucleus. The dark-staining intercalated disks are also present and connect individual cardiac muscle fibers. Small myofibrils can also be seen within each cardiac muscle fiber. Delicate strands of connective tissue fibers surround the individual cardiac muscle fibers. Endomysium with fibroblasts and capillaries are also seen here.
- 28. The transversesection of cardiac muscle are characterirised by the clear perinuclear sarcoplasm i.e., the sarcoplasm around the nucleus is clear and doesn’t seen to have any myofibrils.
- 30. The abovepicture shows both the longitudinal and transverse section of smooth muscles. The cells are elongated and tapered at the ends and have a single nuclei. The striations aren’t observed here because the arrangement of A and I bands are not regular. The nuclei is elongated or ovoid in shape. Smooth muscle also has a rich blood supply, that’s why numerous capillaries are observed between individual fibers. Connective tissues along with fibroblasts can also be observed.