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Muscle Tissue -...

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Muscle Tissue 1.Muscle tissue organization, histogenesis and functions 2.Classification of muscle tissue 3.Smooth muscle tissue 4.Striated (skeletal) muscle tissue 5.Cardiac (heart) muscle tissue 6.Regeneration of muscle tissue
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Page 1: Muscle Tissue - nikolai.lazarov.pronikolai.lazarov.pro/.../2014/medicine/histology/05_Muscle_Tissue.pdf · 3.Smooth muscle tissue 4.Striated(skeletal) ... Smooth muscle types visceral

Muscle Tissue

1.Muscle tissue – organization,

histogenesis and functions

2.Classification of muscle tissue

3.Smooth muscle tissue

4.Striated (skeletal) muscle tissue

5.Cardiac (heart) muscle tissue

6.Regeneration of muscle tissue

Page 2: Muscle Tissue - nikolai.lazarov.pronikolai.lazarov.pro/.../2014/medicine/histology/05_Muscle_Tissue.pdf · 3.Smooth muscle tissue 4.Striated(skeletal) ... Smooth muscle types visceral

Prof. Dr. Nikolai Lazarov 2

Muscle tissue

� body movements

� digestion

� blood circulation

� respiratory movements

� other movement activities,

incl. cellular contraction

� succession of relax and contraction:

� transformation of chemical into mechanical energy

� Textus muscularis:� cells – myocytes� extracellular matrix

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Prof. Dr. Nikolai Lazarov 3

Muscle fibers – myofibers

� muscle cells = myocytes (leiomyocytes, rhabdomyocytes, cardiomyocytes):� elongated, cylindrical or fusiform = myofibers� sarcolemma = plasmalemma� sarcoplasm = cytoplasm� sarcoplasmic reticulum =

smooth endoplasmic reticulum� sarcosomes = mitochondria� myoglobin: oxygen-binding protein� connective tissue components:

� endomysium (Gr. endon, within + mys, muscle)� perimysium (Gr. peri, around, near + mys)� epimysium (Gr. epi, upon + mys)

Gr. sarkos, flesh

�myoepithelial cells�pericytes�myofibroblasts in healing wounds�myoid cells of the testis

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Prof. Dr. Nikolai Lazarov 4

Myofibrils and myofilaments

� myofibrils: fill the muscle fibers

� separated by sarcoplasmic reticulum

� myofilaments:� thick and thin filaments

(contractile proteins)

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Prof. Dr. Nikolai Lazarov 5

Histogenesis

� skeletal muscle – mesoderm� somites – skeletal muscles

of the trunk

� general mesoderm – muscles of the head and limbs

� embryonic origin:� smooth muscle –

mesenchyme

� striated – mesoblast

� myoepithelial cells –skin ectoblast

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Prof. Dr. Nikolai Lazarov 6

Functions

� movements of the body

as a whole

� body posture stabilization

� volume regulation of the

internal organs: sphincters

� movement of substances

within living organisms:

blood, lymph, air, food and

fluids, urine, sperm

� heat production: involuntary

contractions of the skeletal

muscles (trembling)

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Prof. Dr. Nikolai Lazarov 7

Properties of muscle tissue

� irritability� the ability of a muscle to respond

to a stimulus

� conductivity� the ability of a muscle to conduct

electrical impulses across the membrane

� contractility� the ability of a muscle to shorten

and to produce energy

� extensibility� the ability of a muscle to lengthen

beyond its resting length

� elasticity� the ability of a muscle to return to

its original length without damage

NB:NB:NB:NB:muscles can only pull or contract, not pushmuscles can only pull or contract, not pushmuscles can only pull or contract, not pushmuscles can only pull or contract, not push!!!!

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Prof. Dr. Nikolai Lazarov 8

Types of muscle tissue

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Prof. Dr. Nikolai Lazarov 9

Smooth muscle tissue

� origin: mesenchyme

� involuntary: ANS innervation

� tonus

� peristalsis

� nonstriated

� in the walls of hollow and tubular organs:� blood vessels

(with exception of capillaries)

� alimentary canal

� respiratory tract

� urogenital system

� associated with hair follicles in the skin (arrector pili muscles)

� Characteristics:Textus muscularis nonstriatus (glaber)

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Prof. Dr. Nikolai Lazarov 10

Smooth muscle tissue

� leiomyocyte (Gr. leios, smooth)

�shape: fusiform or “spindle shaped"

�length: 30-500 µm

�thickness: 5-10 µm

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Prof. Dr. Nikolai Lazarov 11

Ultrastructure

� actin filaments (4.5 µm/7 nm):

� actin, tropomyosin, calmodulin – Ca2+

� myosin (2.2 µm/17 nm):

� myosin II

� dense bodies, corpora densa

(contain α-actinin = similar to the Z line)

� caveolae (analogous to Т-tubule system)

� intermediate filaments (10 nm):

� desmin (skeletin), vimentin = non-contractile proteins

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Prof. Dr. Nikolai Lazarov 12

Smooth muscle types

� visceral (single-unit) smooth muscles� in the walls of hollow organs� small blood vessels

• relatively poor nerve supply• abundant gap junctions �

function in syncytial fashion

� multi-unit smooth muscles� large arteries� upper respiratory tract� muscles of hair follicles� iris and ciliary body of the eye

• rich nerve supply

• innervate individual cells

• allow for fine control

• provide very precise and graded contractions

� two types of smooth muscle:

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Prof. Dr. Nikolai Lazarov 13

Regulation of contraction and relaxation

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Prof. Dr. Nikolai Lazarov 14

Skeletal muscle tissue

� the most abundant tissue in the vertebrate body– 40% of the body mass

� origin: mesoblast (myotomes)

� voluntary: CNS innervation� strong, quick voluntary control

of contraction/relaxation

� cross-striated

� skeletal muscles

� initial and end parts of the digestive tract

� muscles of the head(incl. eye, ear)

� muscles of respiration

Textus muscularis striatus (skeletalis)

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Prof. Dr. Nikolai Lazarov 15

Skeletal muscle development

� 100 myoblasts (mononucleated) – 1 mature musclecell (multinucleated): syncytium (symplast)

� satellite (myosatellite) cells: retain their potential for theformation of new cells (stem cells)

� does not divide postnatally

� muscle growth –

augmentation of cell

volume (hypertrophy)

Gr. syn, together + kytos, cell

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Prof. Dr. Nikolai Lazarov 16

Skeletal muscle tissue

� rhabdomyocyte (Gr. rhabdo, striped)

�shape: elongated, cylindrical

�length: 1-40 cm

�diameter: 10-100 µm

�numerous nuclei: 10-100/cell, located right up under the plasma membrane

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Prof. Dr. Nikolai Lazarov 17

Organization of skeletal muscle

�Skeletal muscle

�Muscle fasciculus

�Muscle fiber

�Myofibril

�Myofilaments

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Prof. Dr. Nikolai Lazarov 18

Myofibril

� 85-90% of the myofiber volume

� 2500-3500/rhabdomyofiber

� long cylindrical filamentous structure

with a diameter of 0.5-2 µm

� system of transverse (T-) tubules –

encircle the boundaries of the А-I bands

� “triad” = Т-tubule + 2 terminal cisternae:

depot of Ca2+

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Prof. Dr. Nikolai Lazarov 19

Ultrastructure

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Prof. Dr. Nikolai Lazarov 20

Sarcomere

� А band (anisotropic, i.e., birefringent in polarized light)

� H zone (from the German “Hell”, bright)

� М line (mesophragm, "Mittel", middle of the sarcomere): creatine kinase

� I band (isotropic, does not alter polarized light, monorefrigent)

� Z disk (“Zwischenscheibe”, the band in between the I bands)= telophragm: α-actinin

� Sarcomere (Gr. sarkos + meros, part):

�length: 2-3 µm (~2.5 µm) – extends from Z line to Z line

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Prof. Dr. Nikolai Lazarov 21

Sarcomere

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Prof. Dr. Nikolai Lazarov 22

Myofilaments� thin (actin) filaments – 1 µm long/8 nm wide:

� actin – long filamentous polymers of F-actin;• 2 twisted strands of G-actin – globular monomer, 5.6 nm in diameter

� tropomyosin – 40 nm in length extending over 7 G-actin molecules• 2 polypeptide chains

� troponin – ТnT, TnI, TnC at intervals of 40 nm, attached to tropomyosin

� thick (myosin) filaments – 1.6 µm long/15 nm wide:� head (ATPase activity) + proximal 60 nm of tail = heavy meromyosin� distal 90 nm of the tail = light meromyosin� 2 identical heavy chains and 2 pairs of light chains

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Prof. Dr. Nikolai Lazarov 23

Mechanism of contraction

rigor mortis

Sliding Filament Hypothesis: Huxley

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Prof. Dr. Nikolai Lazarov 24

Motor end plate

� myoneural junction – cholinergic (ACh)

Myasthenia gravis

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Prof. Dr. Nikolai Lazarov 25

Neuromotor unit

� motor unit = an individualsomatic motoneuron and all the skeletal muscle fibers(cells) it innervates

� a single nerve fiber (axon) can innervate up to 160 muscle fibers (cells), that all contract at the same time

� the number of motor units and the variable size of each unit can control the intensity (force) of a muscle contraction

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Prof. Dr. Nikolai Lazarov 26

Types of muscle fibers

� Red fibers (slow oxydative) – type I

� White fibers (fast glycolytic) – type IIb

� Intermediate (slow oxydative) – type IIa

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Prof. Dr. Nikolai Lazarov 27

Cardiac muscle tissue

� origin: mesenchyme� involuntary: ANS

� quick continuous automatic contraction:

conduction system

� striated� in the wall of the

� heart (myocardium)� some large vessels

Textus muscularis striatus cardiacus

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Prof. Dr. Nikolai Lazarov 28

� cardiomyocyte (Gr. cardia, heart)

�three types of cardiac myocytes: contractile, conductive, secretory

�shape: cylindrical, bifurcated

�length: 85-100 µm

�diameter: 15-20 µm

�only 1 (or 2) centrally located pale-staining nuclei

�delicate sheath of endomysial connective tissue containing a rich capillary network

Cardiac muscle tissue

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Prof. Dr. Nikolai Lazarov 29

Cardiomyocyte� Т-tubules: at the level of Z band

� “diad” = Т-tubule + one SR cistern

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Prof. Dr. Nikolai Lazarov 30

Ultrastructure� mitochondria: 40% of the cytoplasmic volume� atrial granules (ANF and BNF): 300-400 nm

� lipid droplets and lipofuscin� glycogen granules� intercalated discs:

� fascia adhaerens – in the transverse portion� macula adhaerens (desmosomes) – in the vicinity,

bind the cardiac cells together � gap junction (nexus) – in the lateral portion,

provides ionic continuity between cells

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Prof. Dr. Nikolai Lazarov 31

Myoepithelial cells

�basket cells:

�sweat gland

�mammary gland

�lacrimal gland

�salivary glands

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Prof. Dr. Nikolai Lazarov 32

Regeneration of muscle tissue

� Cardiac muscle has almost no regenerative capacity beyond early childhood:

� mature cardiac muscle cells do not divide

� proliferation of connective tissue �

myocardial scars

� Skeletal muscle can undergo limited

regeneration

� source of regenerating cells is believed

to be the satellite cell (stem cell)

� Smooth muscle is still capable of an active

regenerative response (division)

� viable mononucleated smooth muscle cells

and pericytes from blood vessels provide

for the replacement of the damaged tissue

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Prof. Dr. Nikolai Lazarov 33

Thank youThank youThank youThank you ............


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