Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells...

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Histology of Muscle Tissue .

Transcript of Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells...

Page 1: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Histology of Muscle Tissue

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Page 2: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Introduction

• Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one another to produce a contraction that changes both the length and the shape of the cell.

• Muscles function to produce force and cause motion.

Page 3: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Introduction cont…

• They are primarily responsible for maintenance of and changes in posture, locomotion, movement of internal organs, i.e. contraction of the heart and movement of food through the alimentary canal by peristalsis.

• Muscles form the flesh of the body and walls of hollow organs such as the gut, blood vessels.

Page 4: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Introduction cont…DEFINITION OF TERMS USED IN

MUSCLES.

Sarcolemma: the cell membrane

Sarcoplasm: the cytoplasm of the muscle

Sarcoplasmic reticulum: endoplasmic reticulum of the muscle

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Introduction cont…

Myocyte: a muscle cell Sarcosome: the mitochondria of a muscle cell Sarcomere: the contractile or functional unit

of muscle Striated muscle: is marked by transverse dark

and light bands, is made up of elongated usually multinucleated fibers, and includes skeletal and cardiac muscles of vertebrates.

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Functional characteristics of muscle Contractility:

-Unidirectional; generates pulling force

Excitability:

-Innervated; propagation of electrical impulses

Extensibility:

-Stretch with contraction of an opposing muscle

Elasticity:

-Recoils passively after being stretched

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Classification of Muscles

3 types of muscles, based on microscopic appearance of the muscle cells;

The skeletal Muscles

The Cardiac Muscles

The Smooth Muscles

Page 8: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

THE STRUCTURE OF THE MUSCLES

Page 9: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

The Skeletal Muscles

• Attached to skeletons by tendons.• Features of skeletal muscle cells; – Elongated, cylindrical in shape– Contain multiple peripheral nuclei

• Also they have specialized sER which stores Calcium

• Estimated; length 1-40mm, thickness 10-100µm

Page 10: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

CLASSIFICATION OF SKELETAL MUSCLES

Skeletal muscles are divided into two broad types: Type I, slow twitch fibers and Type II, fast twitch fibers

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Slow Twitch Fibers• Type I m. /Slow twitch m. / Red m.• Is dense with capillaries and is rich in

mitochondria and myoglobin, giving the muscle tissue its characteristic red color.

• It can carry more oxygen and sustain aerobic activity using fats or carbohydrates as fuel.

• Slow twitch fibers contract for long periods of time but with little force.

• Abundant in muscles responsible for maintenance of posture e.g. those in the legs, thigh, trunk, back and gluteal region.

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Fast twitch fibers

• Type II / Fast twitch m. / White m. • Anaerobic, glycolytic, "white" muscle with

few mitochondria and myoglobin. • Contract quickly and powerfully but easily

fatigue

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Comparison of Types of Skeletal Muscle Fibers

Characteristics Red Muscle Fibers White Muscle Fibers

Vascularization Rich vascular supply Poorer vascular supply

Innervation Smaller nerve fibers Larger nerve fibers

Fiber diameter Smaller Larger

Contraction Slow but repetitive; not easily fatigued; weaker contraction

Fast but easily fatigued; stronger contraction

Sarcoplasmic reticulum Not extensive Extensive

Mitochondria Numerous Few

Myoglobin Rich Poor

Enzymes Rich in oxidative enzymes; poor in adenosine triphosphatase

Poor in oxidative enzymes; rich in phosphorylases and adenosine triphosphatase

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Organization of Skeletal Muscle

• Epimysium: an external sheath of dense connective tissue surrounding the entire muscle

• Perimysium: thin septa of connective tissue around each bundle of muscle fibers

• Endomysium: a delicate layer of connective tissue surrounding each muscle fiber. It is composed mainly of a basal lamina and reticular fibers.

Page 15: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Organization of Skeletal Muscle

Page 16: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.
Page 17: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Skeletal Muscle Cells

Page 18: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Organization of Skeletal Muscle Fibers

• Has light and dark bands as seen under light microscope

• A bands: darker bands• I bands: lighter bands• Z line: a dark transverse line that bisects each

I band• Sarcomere: the smallest repetitive subunit of

the contractile apparatus, extends from Z line to Z line.

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Organization cont..

Myofibrils:• Long cylindrical filamentous bundles filling

the sarcoplasm• They run parallel to the long axis of the

muscle fiber• Consist of an end – to end chainlike

arrangement of sarcomeres• Sarcomeres in myofibrils causes the entire

muscle fiber to exhibit a characteristic pattern of transverse striations.

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Organization cont..

• The pattern of sarcomere is mainly due to the presence of two types of filaments:

• Thick filaments–1.6 m long and 15 nm wide;

• Thin filaments–1.0 m long and 8 nm wide.

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Organization cont..

• Thick filaments: occupy the A bands, the central portion of the sarcomere.

• Thin filaments: run between and parallel to the thick filaments and have one end attached to the Z line.

• I bands consist of the portions of the thin filaments that do not overlap the thick filaments.

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Organization cont..

• H band: lighter zone on the center of the A band. Corresponds to a region consisting only of the rodlike portions of the myosin molecule• M line: bisects the H band. It is a region at which

lateral connections are made between adjacent thick filaments.• The major protein of the M line is Creatine kinase which

catalyzes the transfer of a phosphate group from phosphocreatine ( a storage form of high – energy phosphate groups) to ADP, thus supplying ATP for muscle contraction.

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Sarcomere

S = Sarcomere, unit of muscle functionA = A-band, region of myosinI = I-band, region of actinH = H-zone, region of just myosinZ = Z-line, sarcomere boundaryM = M-line, sarcomere center

• Portion of a myofibril, showing sarcomere structure

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• The four main proteins found in striated muscle filaments include:–Actin–Tropomyosin–Troponin–Myosin

• Myosin and actin together represent 55% of the total protein of striated muscle

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• Thin filaments are composed of actin, tropomyosin and troponin

• Thick filaments are composed of myosin• Actin is present as long filamentous (F-actin)

polymers consisting of two strands of globular (G-actin) monomers,

• Each G-actin monomer contains a binding site for myosin

• Actinin and desmin (an intermediate filament protein) are believed to tie adjacent sarcomeres together, thus keeping the myofibrils in register.

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• Tropomyosin, a long, thin molecule about 40 nm in length, contains two polypeptide chains.

• Troponin is a complex of three subunits: –TnT, which strongly attaches to

tropomyosin; –TnC, which binds calcium ions; –TnI, which inhibits the actin and myosin

interaction.

A troponin complex is attached at one specific site on each tropomyosin molecule

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• Myosin, • Is a much larger complex (molecular mass 500

kDa), • Small globular projections at one end of each

heavy chain form the heads, which have ATP-binding sites as well as the enzymatic capacity to hydrolyze ATP (ATPase activity) and the ability to bind to actin.

• The myosin molecules are composed of a rod-like portion (light meromyosin) and twin rounded heads (heavy meromyosin).

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• Sarcoplasmic Reticulum & Transverse Tubule System• To provide for a uniform contraction, skeletal

muscle possesses a system of transverse (T) tubules• Adjacent to opposite sides of each T tubule are

expanded terminal cisternae of the sarcoplasmic reticulum.

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• This specialized complex, consisting of a T tubule with two lateral portions of sarcoplasmic reticulum, is known as the triad• At the triad, depolarization of the sarcolemma-

derived T tubules is transmitted to the sarcoplasmic reticulum membrane.

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Cardiac Muscles

• Cardiac muscles are involuntary muscles found in the heart and in some walls of large blood vessels associated with the heart.

• The cells are mononucleated with centrally located nucleus

• The cells have small amount of cytoplasm containing many mitochondria with closely parked cisternae, golgi apparatus and lipid droplets, with large amount of glycogen

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Cardiac muscle cont…

• The cells have less prominent connective tissue, but extensive cappillary and lymphatic network

• A unique and distinguishing characteristic of cardiac muscle is the presence of intercalated disks represent junctional complexes found at the interface between adjacent cardiac muscle cells

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Page 36: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.
Page 37: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

INTERCALATED DISCo There are three main junctional

specializations within the Intercalated disk:o Fasciae adherentes, serve as anchoring

sites for actin filaments of the terminal sarcomeres.

o Essentially, they represent hemi-Z bands.o Maculae adherentes (desmosomes) present

in the transverse portion and bind the cardiac cells together, preventing them from pulling apart under constant contractile activity.

o On the lateral portions of the disk, gap junctions provide ionic continuity between adjacent cells.

o The significance of ionic coupling is that chains of individual cells act as a syncytium, allowing the signal to contract to pass in a wave from cell to cell.

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• Lengths of individual cardiac muscle cells vary, on average they are 15 μm in diameter and 80 μm in length

• Muscle cells of the atria are somewhat smaller than those of the ventricles.

• These cells also house granules (especially in the right atrium) containing atrial natriuretic peptide, a substance that functions to lower blood pressure

• This peptide acts by decreasing the capabilities of renal tubules to resorb (conserve) sodium and water.

Page 39: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

• Organelles• The extracellular fluid is the primary calcium

source for cardiac muscle contraction.• The sarcoplasmic reticulum of cardiac muscle

does not form terminal cisternae and is not nearly as extensive as in skeletal muscle; instead, they form a diad. (one T tubule and one sarcoplasmic reticulum cisterna)

• The diads in cardiac muscle cells are located in the vicinity of the Z line.

Page 40: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Smooth Muscles• Type of muscle which exhibit no striations• Have cells that are elongated, spindle shaped, with

a single elongated(CORK SCREW SHAPED) centrally located nucleus• Myosin and actin are longitudinally placed and

anchored by desmin• They are found in the walls of hollow viscera (e.g

GIT, some of the reproductive tract, and the urinary tract), walls of blood vessels, larger ducts of compound glands, respiratory passages, and small bundles within the dermis of skin.• Are involuntary muscles

Page 41: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Smooth Muscles

• Regulated by the autonomic nervous system, hormones , and local physiological conditions.

• Smooth muscle cells contains numerous invaginations of the plasma membrane called caveolae which allows calcium ions from extracellullar space into cells.

-They are capable of regeneration (contains undifferentiated mesenchymal cells)

-Specialized for slow but prolonged contraction and are resistant to fatigue.

Page 42: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Functions of Smooth Muscles

• Contractile functions• Exogenous protein synthesis. –Among the substances manufactured by

smooth muscle cells for extracellular utilization are collagen, elastin, glycosaminoglycans, proteoglycans, and growth factors

Page 43: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Light Microscopy View of Smooth Muscle Fibers

• Light microscopy reveals that smooth muscle fibers are short, spindle-shaped cells with a centrally placed nucleus.

• Smooth muscle fibers are fusiform, elongated cells

• Each smooth muscle cell is surrounded by an external lamina, which invariably separates the sarcolemma of contiguous muscle cells

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Page 46: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Fine Structure of Smooth Muscle

• The perinuclear cytoplasm of smooth muscle cells, especially the regions adjacent to the two poles of the nucleus, contains numerous mitochondria, Golgi apparatus, rough endoplasmic reticulum (RER), smooth endoplasmic reticulum (SER), and inclusions such as glycogen• An extensive array of interweaving thin

filaments (7 nm) and thick filaments (15 nm) is present.

Page 47: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Fine Structure of Smooth Muscle

• The thin filaments are composed of actin (with its associated caldesmon), and tropomyosin, with the notable absence of troponin).

• The thick filaments are composed of the same myosin II that is present in skeletal muscle.

Page 48: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

Feature Skeletal Muscle Cardiac Muscle Smooth Muscle

Sarcomeres and myofibrils Yes Yes No

Nuclei Multinucleated; peripherally located

One (or two); centrally located One; centrally located

Sarcoplasmic reticulum Well-developed with terminal cisterns

Poorly defined; some small terminals

Some smooth endoplasmic reticulum

T tubules Yes; small, involved in triad formation

Yes; large, involved in dyad formation

No

Cell junctions No Intercalated disks Nexus (gap junctions)

Contraction Voluntary; "all or none" Involuntary; rhythmic and spontaneous

Involuntary; slow and forceful; not "all or none"

Calcium control Calsequestrin in terminal cisternae Calcium from extracellular sources and the sarcoplasmic reticulum

Calcium from extracellular sources (via caveolae) and the sarcoplasmic/endoplasmic reticulum

Calcium binding Troponin C Troponin C Calmodulin

Regeneration Yes, via satellite cells No Yes

Mitosis No No Yes

Nerve fibers Somatic motor Autonomic Autonomic

Connective tissue Epimysium, perimysium, and endomysium

Connective tissue sheaths and endomysium

Connective tissue sheaths and endomysium

Distinctive features Long; cylinder-shaped; many peripheral nuclei

Branched cells; intercalated disks; one or two nuclei

Fusiform cells with no striations; single nucleus

Page 49: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

REGENERATION OF MUSCLE

• Although skeletal muscle cells do not have the capability of mitotic activity, the tissue can regenerate because of the presence of satellite cells.

• These cells may undergo mitotic activity, resulting in hyperplasia, subsequent to muscle injury.

• Under certain other conditions, such as "muscle building," satellite cells may fuse with existing muscle cells, thus increasing muscle mass during skeletal muscle hypertrophy.

• Skeletal muscle cells regulate their number and their size by the secretion of a member of the transforming growth factor-β (TGF-β) superfamily of extracellular signaling molecules, myostatin.

Page 50: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

REGENERATION OF MUSCLE

• Cardiac muscle is incapable of regeneration. Following damage, such as a myocardial infarct, fibroblasts invade the damaged region, undergo cell division, and form fibrous connective tissue (scar tissue) to repair the damage.

Page 51: Histology of Muscle Tissue.. Introduction Muscle is a soft tissue of animals made up of muscle cells containing protein filaments that slide past one.

REGENERATION OF MUSCLE • Smooth muscle cells retain their mitotic capability to

form more smooth muscle cells. • This ability is especially evident in the pregnant

uterus, where the muscular wall becomes thicker both by hypertrophy and hyperplasia

• Small defects, subsequent to injury, may result in formation of new smooth muscle cells.

• These new cells may be derived via mitotic activity of existing smooth muscle cells, as in the gastrointestinal and urinary tracts, or from differentiation of relatively undifferentiated pericytes accompanying some blood vessels

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Referrences

1. K.L. Moore (2008). The Developing Human; Clinically Oriented Embryology 8th Edition

2. Richard Snell, Clinical Neuroanatomy, 6th Edition3. Alfred Carey Carpenter (2007). "Muscle“, natomy Words.

http://anatomyalmanac.blogspot.com/2008/01/from-archive-muscle-comes-from-latin.html. Retrieved October 3, 2012.

4. Douglas Harper (2012). "Muscle“, Online Etymology Dictionary. http://www.etymonline.com/index.php?allowed_in_frame=0&search=muscle&searchmode=none. Retrieved October 3, 2012.

5. Marieb, EN; Hoehn, Katja (2010). Human Anatomy & Physiology (8th ed.). San Francisco: Benjamin Cummings. p. 312. ISBN 978-0-8053-9569-3

6. McCloud, Aaron (30 November 2011). "Build Fast Twitch Muscle Fibers“. Complete Strength

7. Janqueira, Caneiro – Basic histology – Text and Atlas 11e8. Color Textbook of Histology9. Past presentations10. www.google.com ( diferrent search words related to histology of muscle tissue)