Muscle Tissue - Lazarov · Cardiac muscle tissue cardiomyocyte (Gr. cardia, heart) three types of...

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

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


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


Myofibrils and myofilaments

myofibrils: fill the muscle fibers

separated by sarcoplasmic reticulum

myofilaments: thick and thin filaments

(contractile proteins)


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


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)


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: muscles can only pull or contract, not push!


Types of muscle tissue


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)


Smooth muscle tissue

leiomyocyte (Gr. leios, smooth)

shape: fusiform or “spindle shaped”

length: 30-500 µm

thickness: 5-10 µm


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


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:


Regulation of contraction and relaxation


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)


Skeletal muscle development

100 myoblasts (mononucleated) – 1 mature

muscle cell (multinucleated): syncytium (symplast)

satellite (myosatellite) cells: retain their potential for the formation of new cells (stem cells)

does not divide postnatally

muscle growth –

augmentation of

cell volume (hypertrophy)

Gr. syn, together + kytos, cell


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


Organization of skeletal muscle

Skeletal muscle

Muscle fasciculus

Muscle fiber

Myofibril

Myofilaments


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+


Ultrastructure


Sarcomere

Sarcomere (Gr. sarkos + meros, part):

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

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

titin (3700 kDa) – connects thick filaments to the Z disc nebulin (600 kDa) – helps anchor thin filaments to α-actinin

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

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Sarcomere

Prof. Dr. Nikolai Lazarov


Sarcomere


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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Mechanism of contraction

Prof. Dr. Nikolai Lazarov


Mechanism of contraction

rigor mortis

Sliding Filament Hypothesis: Huxley

Sliding Filament Hypothesis: Sir Andrew F. Huxley (1917-2012)

26 Prof. Dr. Nikolai Lazarov

65-Year Anniversary of Sliding Filament

Huxley, A.F., and R. Niedergerke. 1954. Structural changes in muscle during contraction; interference microscopy of living muscle fibers. Nature. 173:971–973. Huxley, H., and J. Hanson. 1954. Changes in the cross-striations of muscle during contraction and stretch and their structural interpretation. Nature 173:973–976.

The improver of natural knowledge absolutely refuses to acknowledge authority, as such.

For him, skepticism is the highest of duties, blind faith the one unpardonable sin.

Thomas H. Huxley

On the Advisableness of Improving Natural Knowledge, 1866


Motor end plate

Myasthenia gravis

myoneural junction – cholinergic (ACh)


Neuromotor unit

motor unit = an individual somatic 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


Types of muscle fibers

Red fibers (slow oxydative) – type I

White fibers (fast glycolytic) – type IIb

Intermediate (slow oxydative) – type IIa


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


Cardiac muscle tissue

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


Cardiomyocyte Т-tubules: at the level of Z band

“diad” = Т-tubule + one SR cistern

33 Prof. Dr. Nikolai Lazarov

Cardiomyocyte


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


Myoepithelial cells

basket cells:

sweat gland

mammary gland

lacrimal gland

salivary glands


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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Muscle Tissue - Lazarov · Cardiac muscle tissue cardiomyocyte (Gr. cardia, heart) three types of...

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