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

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: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!!!!


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 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


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

� 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


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


Mechanism of contraction

rigor mortis

Sliding Filament Hypothesis: Huxley


Motor end plate

� myoneural junction – cholinergic (ACh)

Myasthenia gravis


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


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


� 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


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

� “diad” = Т-tubule + one SR cistern


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