MUSCLE TISSUEMUSCLE TISSUE

Types of muscle tissueTypes of muscle tissue

1.1. Skeletal musclesSkeletal muscles

2.2. Cardiac muscleCardiac muscle

3.3. Smooth muscleSmooth muscle

Skeletal muscleSkeletal muscle Consists of muscle fibres Consists of muscle fibres

(cylindrical, (cylindrical, multinucleated cells)multinucleated cells)

Muscle fiber=syncytiumMuscle fiber=syncytium Attention! A muscle fiber Attention! A muscle fiber

should not be confused should not be confused with a connective tissue with a connective tissue fiber. Muscle fibers are fiber. Muscle fibers are cellular elements , cellular elements , connective tissue fibers connective tissue fibers are extracellular products are extracellular products of connective tissue.of connective tissue.

Nuclei: oval, located Nuclei: oval, located peripherally under the peripherally under the cell membrane.cell membrane.

Multinucleation results Multinucleation results from the fusion of from the fusion of embryonic embryonic mononucleated mononucleated myoblasts( muscle cell myoblasts( muscle cell precursors) during precursors) during development.development.

Sarco…Sarco…

Sarco… - a prefix that means „muscular”. Sarco… - a prefix that means „muscular”. For example:For example:

Sarcolemma- the plasma membrane of the Sarcolemma- the plasma membrane of the muscle fibermuscle fiber

Sarcoplasm = cytoplasm of muscle fiberSarcoplasm = cytoplasm of muscle fiber

Sarcoplasmic reticulum = smooth Sarcoplasmic reticulum = smooth endoplasmic reticulum in muscle fibersendoplasmic reticulum in muscle fibers

SKELETAL MUSCLESKELETAL MUSCLE

The connective tissue associated with muscle is The connective tissue associated with muscle is given a specific set of names describing its given a specific set of names describing its relationship with the muscle fibers.relationship with the muscle fibers.

EndomysiumEndomysium- is the delicate layer of reticular - is the delicate layer of reticular fibers that immadietely surrounds individual fibers that immadietely surrounds individual muscle fibers. Blood and lymphatic vessels run muscle fibers. Blood and lymphatic vessels run between muscle fibres and parallel to them.between muscle fibres and parallel to them.

SKELETAL MUSCLESKELETAL MUSCLE

PerimysiumPerimysium- a thicker connective tissue layer that - a thicker connective tissue layer that surround a group of fibers to form a bundle or a surround a group of fibers to form a bundle or a fascicle.Larger blood vessels and nerves travel in fascicle.Larger blood vessels and nerves travel in the perimysium.the perimysium.

Epimysium-Epimysium- is a dense connective tissue that is a dense connective tissue that surrounds the collection of fascicles that surrounds the collection of fascicles that constitute the muscle.The major vascular and constitute the muscle.The major vascular and nerve supply of the muscle penetrates through nerve supply of the muscle penetrates through the epimysium.the epimysium.

MyofibrilsMyofibrils

The strucural and functional subunit of The strucural and functional subunit of the muscle fiber is the the muscle fiber is the myofibril.Muscle fibers are filled with myofibril.Muscle fibers are filled with these longitudinally arrayed these longitudinally arrayed subunits.subunits.

Myofibrils are composed of bundles of Myofibrils are composed of bundles of myofilaments.myofilaments.

MyofibrilsMyofibrils

Long, cylindrical filamentous bundles Long, cylindrical filamentous bundles Run parallel to the long axis of the Run parallel to the long axis of the

muscle fiber.muscle fiber. Consist of an end to end chainlike Consist of an end to end chainlike

arrangement of sarcomeres.arrangement of sarcomeres.

MyofilamentsMyofilaments

Myofilaments are the individual Myofilaments are the individual filamentous polymers of different filamentous polymers of different proteins.They form a myofibril and proteins.They form a myofibril and are the acurate contractile are the acurate contractile elements of striated muscle.elements of striated muscle.

Two kinds of filaments:Two kinds of filaments:

1.1. Thick filamentsThick filaments

2.2. Thin filamentsThin filaments

The arrangement of thick and thin The arrangement of thick and thin filaments gives rise to the filaments gives rise to the density differences that produce density differences that produce the cross-striations.the cross-striations.

Cross- striationsCross- striations

Cross-striations are the principal histologic Cross-striations are the principal histologic feature of striated muscle.feature of striated muscle.

Longitudinally sectioned muscle fibres show Longitudinally sectioned muscle fibres show cross-striationscross-striations of alternating light and dark bands.of alternating light and dark bands.

Cross-striationsCross-striations

Cross-striations are evident in Cross-striations are evident in HE( hematoxylin-eosin) stained HE( hematoxylin-eosin) stained preparations of longitudinal sections preparations of longitudinal sections of muscle fibers.of muscle fibers.

The dark and light bands are termed: The dark and light bands are termed: the A band, the I band and the Z linethe A band, the I band and the Z line

Cross-striationsCross-striations

1.Dark stained bands = A bands= 1.Dark stained bands = A bands= anisotropicanisotropic(are birefringent in polarized light)(are birefringent in polarized light)

2.Light stained bands= I bands= 2.Light stained bands= I bands= isotropicisotropic(do not alter polarized light)(do not alter polarized light)

The Z line, H zone, M lineThe Z line, H zone, M line

The Z line= Z disc, is a dense zone The Z line= Z disc, is a dense zone that bisects the I bandthat bisects the I band

The H zone/band- is a light zone that The H zone/band- is a light zone that bisects the A bandbisects the A band

M line- is located in the middle of H M line- is located in the middle of H bandband

SarcomereSarcomere

- The functional unit of the myofibril.- The functional unit of the myofibril.- it`s a segment of the myofibril it`s a segment of the myofibril

between 2 Z lines.between 2 Z lines.- It measures 2-3 um in relaxed It measures 2-3 um in relaxed

muscle, may be stretched to more muscle, may be stretched to more than 4 um, and in extreme than 4 um, and in extreme contraction, may measure as little as contraction, may measure as little as 1 um.1 um.

SarcomereSarcomere Extends from Z line to Z lineExtends from Z line to Z line Sarcomere= (Z line +1/2 I band+A Sarcomere= (Z line +1/2 I band+A

band+1/2 I band+ Z line)band+1/2 I band+ Z line)

The structure of the sarcomereThe structure of the sarcomere1.1. Z line- a borderline of sarcomere.Thin filaments are Z line- a borderline of sarcomere.Thin filaments are

attached to it. Main protein- alfa actinin.attached to it. Main protein- alfa actinin.

2.2. Thin filaments- extend from the Z line to the H band. Thin filaments- extend from the Z line to the H band. The thin and thick filaments run between and parallel The thin and thick filaments run between and parallel to each other.to each other.

3.3. Thick filaments- occupy the A band, the central Thick filaments- occupy the A band, the central portion of the sarcomere.portion of the sarcomere.

4.4. I – band- contains thin filaments fixed to Z line.I – band- contains thin filaments fixed to Z line.

5.5. A -band- consist of two parts: 1. thin filaments A -band- consist of two parts: 1. thin filaments overlapping thick filaments 2. thick filaments (H overlapping thick filaments 2. thick filaments (H band)band)

6.6. M line- a region of a H band, at which lateral M line- a region of a H band, at which lateral connections are made between adjacent thick connections are made between adjacent thick filaments.filaments.

M lineM line

The major protein of the M line is The major protein of the M line is creatine kinase.Creatine kinase creatine kinase.Creatine kinase catalyzes the transfer of a phosphate catalyzes the transfer of a phosphate group from phosphocreatine to group from phosphocreatine to adenosine diphosphate(ADP) adenosine diphosphate(ADP) resulting adenosine triphosphate resulting adenosine triphosphate ( ATP). The energy from ATP is ( ATP). The energy from ATP is needed for the muscle contraction.needed for the muscle contraction.

ATP ADP + PiATP ADP + Pi

The structure of thin and thick The structure of thin and thick myofilamentsmyofilaments

Thin filaments are composed of 3 Thin filaments are composed of 3 different proteins:different proteins:

A)A) ActinActin

B)B) TropomyosinTropomyosin

C)C) TroponinTroponin

Thick filaments are composed of myosin.Thick filaments are composed of myosin.

ActinActin

- Is present as long filamentous (F-actin) polymers Is present as long filamentous (F-actin) polymers consisting of 2 strands of globular( G- actin ) consisting of 2 strands of globular( G- actin ) monomers.monomers.

- The polymers are twisted around each other in a The polymers are twisted around each other in a double helical formation.double helical formation.

- Each G-actin monomer contains a binding site for Each G-actin monomer contains a binding site for myosinmyosin

- Actin filaments are fixed to the Z line by a protein Actin filaments are fixed to the Z line by a protein called alfa-actinin.called alfa-actinin.

TropomyosinTropomyosin

- long, thin molecule, built up of 2 polypeptide long, thin molecule, built up of 2 polypeptide chainschains

- Molecules are bound head to tail, forming Molecules are bound head to tail, forming filamentsfilaments

- Tropomyosin filaments lie along the two twisted Tropomyosin filaments lie along the two twisted actin strandsactin strands

- Each tropomyosin molecule covers 7 G-actin Each tropomyosin molecule covers 7 G-actin molecules and has one troponin- binding place.molecules and has one troponin- binding place.

TroponinTroponin

A complex of 3 subunits:A complex of 3 subunits:

1.1. Troponin T ( TnT)- attached to Troponin T ( TnT)- attached to tropomyosintropomyosin

2.2. Troponin C ( TnC)- binds calcium Troponin C ( TnC)- binds calcium ionsions

3.3. Troponin I ( TnI)- inhibits the actin-Troponin I ( TnI)- inhibits the actin-myosin interactionmyosin interaction

MyosinMyosin Composed of 2 heavy Composed of 2 heavy

chains and 4 light chains.chains and 4 light chains. Heavy chains are twisted Heavy chains are twisted

togethertogether At one end of each heavy At one end of each heavy

chain- „heads”chain- „heads” The heads have ATP-The heads have ATP-

binding sites and the binding sites and the enzymatic capacity to enzymatic capacity to hydrolyze ATP.They have hydrolyze ATP.They have also ability to bind to actin.also ability to bind to actin.

The primary proteins ( actin , myosin, The primary proteins ( actin , myosin, trpomyosin, troponin) constitute trpomyosin, troponin) constitute more than 75% of the total protein of more than 75% of the total protein of the muscle fiber and are visible as the muscle fiber and are visible as the thick and thin filaments.The the thick and thin filaments.The remaining structural proteins include:remaining structural proteins include:

- TitinTitin- NebulinNebulin- Alfa-actininAlfa-actinin- MyomesinMyomesin- C proteinC protein

Contractile mechanism-sliding Contractile mechanism-sliding filament modelfilament model

When a muscle contracts, each When a muscle contracts, each sarcomere shortens and becomes sarcomere shortens and becomes thicker , but the myofilaments thicker , but the myofilaments remain the same length. It means remain the same length. It means that the shortening of the sarcomere that the shortening of the sarcomere must be due to an increase in the must be due to an increase in the overlap of thick and thin filaments.overlap of thick and thin filaments.

Sarcoplasmic reticulumSarcoplasmic reticulum- Is arranged in networks around or between Is arranged in networks around or between

a group of myofilamentsa group of myofilaments- One network of sarcoplasmic reticulum One network of sarcoplasmic reticulum

surrounds the A band, and another surrounds the A band, and another network surrounds the I bandnetwork surrounds the I band

- Where the two networks meet, at the Where the two networks meet, at the junction between A and I bands, the junction between A and I bands, the sarcoplasmic reticulum forms a ringlike sarcoplasmic reticulum forms a ringlike channel- terminal sac (cisterna) around channel- terminal sac (cisterna) around the filaments of the myofibril.the filaments of the myofibril.

- Main function: magazine and regulator of Main function: magazine and regulator of calcium ions!calcium ions!

TRIADSTRIADS

- Invaginations of the plasma Invaginations of the plasma membrane of the muscle cell form membrane of the muscle cell form the T system. The T tubules are the T system. The T tubules are located between the adjacent ER`s located between the adjacent ER`s terminal cisternae.terminal cisternae.

- The complex of T tubule and two The complex of T tubule and two terminal cisternae is called TRIAD.terminal cisternae is called TRIAD.

TRIAD= 1 T TUBULE+ 2 TERMINAL TRIAD= 1 T TUBULE+ 2 TERMINAL CISTERNAECISTERNAE

Mechanism of contractionMechanism of contraction

1.1. Depolarization of the sarcoplasmDepolarization of the sarcoplasm2.2. The depolarization signal is transmitted through The depolarization signal is transmitted through

the T tubule to the sarcoplasmic reticulum the T tubule to the sarcoplasmic reticulum membrane.membrane.

3.3. Calcium ions are released into the vicinity of the Calcium ions are released into the vicinity of the overlapping thick and thin filaments.overlapping thick and thin filaments.

4.4. Calcium ions are bined to the TnC subunit of Calcium ions are bined to the TnC subunit of troponin.troponin.

5.5. The comlex of troponins changes its structure The comlex of troponins changes its structure and drives the tropomyosin deeper into the and drives the tropomyosin deeper into the groove of the actin helix. Consequence: groove of the actin helix. Consequence: exposition the myosin –binding sites on the exposition the myosin –binding sites on the actinactin

Mechanism of contractionMechanism of contraction

6. Interaction=bridgening between the myosin head 6. Interaction=bridgening between the myosin head and actin. Result: and actin. Result:

ATP ADP + PiATP ADP + Pi

7.Deformation=bending of the myosin head7.Deformation=bending of the myosin head

8. Movement of the myosin heads pulls the actin 8. Movement of the myosin heads pulls the actin past the myosin filament.past the myosin filament.

SEQUENCE OF EVENTS IN CONTRACTION

1. Nerve impulse travels down axon2. Acetylcholine released into synaptic cleft, depolarizing the

sarcolemma3. Voltage gated Na+ channels open, Na+ enters muscle cell4. Depolarization spreads including traveling down t-tubule5. Voltage sensor proteins in t-tubules change conformation6. Ca2+ rapidly released from sarcoplasmic reticulum (via Ca2+

release channels) 7. Ca2+ binds to the TnC subunit of troponin a) Troponin shifts tropomyosin deeper into groove, b) ADP-

Pi-myosin complex binds to active site on actin c) Pi is released d) myosin has conformational change pulling actin is pulled toward m-line releasing ADP e) ATP binds to Myosin releasing it from actin f) ATP hydrolyzed into ADP and Pi

8. Ca2+ is sequestered into the sarcoplasmic reticulum

Relaxed Contracted

DIAGRAM OF ACTIN-MYOSIN INTERACTION

1au1au1au

THE CONTRACTION CYCLE

THE CONTRACTION CYCLE

THE MOTOR UNITEach muscle is served by at leastone motor nerve containinghundreds of motor axons.

A motor neuron and all the fibersit supplies is called a MOTOR UNIT. These fibers may be spreadthroughout the muscle.

When a motor neuron transmits anelectrical impulse all the fibers itinnervates contract.

Muscles that exert fine control havesmall motor units (e.g. eyes, fingers).

Large muscles have large motor unitsand have less precise control (e.g. muscles of weight bearing, locomotion).

Motor innervationMotor innervation

Skeletal muscle fibers are richly innervated Skeletal muscle fibers are richly innervated by motor neurons that originate in the by motor neurons that originate in the spinal cord or brain stem.spinal cord or brain stem.

The axons of the neurons branch as they The axons of the neurons branch as they near the muscle, giving rise to twigs that near the muscle, giving rise to twigs that end on individual muscle fibers.end on individual muscle fibers.

The Motor End Plate is the contact made by The Motor End Plate is the contact made by the terminal branches of the axon with the the terminal branches of the axon with the muscle.muscle.

Types of muscle fibresTypes of muscle fibres

Type I (slow)Type I (slow) Type II ( quick)Type II ( quick)

Rich in sarcoplasm-Rich in sarcoplasm-myoglobin- dark red myoglobin- dark red colourcolour

Contain less Contain less myoglobin-light red myoglobin-light red colourcolour

Related to continous Related to continous contractioncontraction

Related to rapid Related to rapid contractioncontraction

Types: IIA, IIB(fastest), Types: IIA, IIB(fastest), IIC IIC

THE MOTOR UNITEach muscle is served by at leastone motor nerve containinghundreds of motor axons.

A motor neuron and all the fibersit supplies is called a MOTOR UNIT. These fibers may be spreadthroughout the muscle.

When a motor neuron transmits anelectrical impulse all the fibers itinnervates contract.

Muscles that exert fine control havesmall motor units (e.g. eyes, fingers).

Large muscles have large motor unitsand have less precise control (e.g. muscles of weight bearing, locomotion).

THE MOTOR END PLATE

ACh, released from the axon terminal, binds to receptors on the junctional folds of the sarcolemma which then depolarizes. This depolarization is passed via the t-tubules and triad to the sarcoplasmic reticulum and results in the release of calcium which initiates the contraction cycle.

CARDIAC MUSCLECARDIAC MUSCLE

Cardiac muscleCardiac muscle

- cross-striated( like skeletal muscle)cross-striated( like skeletal muscle)- Each cardiac muscle cell posesses 1-2 Each cardiac muscle cell posesses 1-2

nuclei( centrally located).nuclei( centrally located).- Muscle cells are surrounded by endomysium Muscle cells are surrounded by endomysium

( connective tissue) and blood capillaries.( connective tissue) and blood capillaries.- Intercalated disks-junctional complexes between Intercalated disks-junctional complexes between

adjacent cardiac muscle cells.(transverse portion, adjacent cardiac muscle cells.(transverse portion, lateral portion).lateral portion).

- Sructure and mechanism of contractile proteins-- Sructure and mechanism of contractile proteins-similar to skeletal muscle.similar to skeletal muscle.

Intercalated disksIntercalated disks Intercalated disks Intercalated disks

contain 3 kinds of contain 3 kinds of junctional junctional specializations:specializations:

1.1. Fasciae adherentesFasciae adherentes2.2. Maculae Maculae

adherentes(desmosoadherentes(desmosomes)mes)

3.3. Gap junctionsGap junctions

Cardiac muscleCardiac muscle

TYPE OF TYPE OF MUSCLEMUSCLE

T tubulesT tubules Sarcoplasmic Sarcoplasmic reticulumreticulum

SKELETALSKELETAL -more numerous -more numerous and larger and larger

- found at the - found at the level of A-I level of A-I junction junction

- well developed- well developed

CARDIACCARDIAC -less number -less number and smallerand smaller

-found at the -found at the level of the Z level of the Z lineline

- Well developed - Well developed but not as well but not as well as in skeletal as in skeletal musclemuscle

CARDIAC CARDIAC MUSCLEMUSCLE

1 T tubule+1 sarcoplasmic 1 T tubule+1 sarcoplasmic reticulum cisterna=DIADreticulum cisterna=DIAD

SKELETAL SKELETAL MUSCLEMUSCLE

1 T tubule+2 sarcoplasmic 1 T tubule+2 sarcoplasmic reticulum cisternae=TRIADreticulum cisternae=TRIAD

TYPE OF MUSCLETYPE OF MUSCLE MITOCHONDRIAMITOCHONDRIA

SKELETALSKELETAL -only 2% of the -only 2% of the cytoplasmic volume cytoplasmic volume occupied by occupied by mitochondriamitochondria

CARDIACCARDIAC -numerous, occupy -numerous, occupy over 40% of the over 40% of the cytoplasmic volumecytoplasmic volume

PURKINJE FIBERS

Large fiber diameterClear central region

(Glycogen)

SMOOTH MUSCLESMOOTH MUSCLE

Smooth muscleSmooth muscle

Where??Where??- Alimentary canalAlimentary canal- Genitourinary tractGenitourinary tract- Blood vesselsBlood vessels- Respiratory tractRespiratory tract- Other localisations: iris, ciliary body Other localisations: iris, ciliary body

of the eye, arrector pili muscles of the eye, arrector pili muscles (skin)(skin)

Smooth muscleSmooth muscle

-composed of elongated, nonstriated cells-composed of elongated, nonstriated cells

-each cell is enclosed by basal lamina and a -each cell is enclosed by basal lamina and a network of reticular fibres.network of reticular fibres.

-the cells are larger at their midpoints and taper -the cells are larger at their midpoints and taper toward the ends.toward the ends.

-single nucleus located in the central part of cell-single nucleus located in the central part of cell

-cytoplasmic organelles are concentrated at each -cytoplasmic organelles are concentrated at each end of the nucleus.end of the nucleus.

-ER well developed-ER well developed

- Absence of T tubules- Absence of T tubules

Smooth musclesSmooth muscles

-the narrow part of one cell lies -the narrow part of one cell lies adjacent to the broad parts of adjacent to the broad parts of neighboring cells.neighboring cells.

- Not striated! No sarcomers.Not striated! No sarcomers.

Smooth muscleSmooth muscle

DIAGRAM OF A SMOOTH MUSCLE CELL

Dense body

Actinfilament

Myosinfilament

Mechanism of contractionMechanism of contraction

In smooth muscles bundles of In smooth muscles bundles of myofilaments crisscross obliquely myofilaments crisscross obliquely through the cell, forming a through the cell, forming a latticelike network.latticelike network.

Three kinds of filaments:Three kinds of filaments:1.1. Thin filaments ( actin, tropomyosin)Thin filaments ( actin, tropomyosin)2.2. Thick filaments( myosin)Thick filaments( myosin)3.3. Intermediate filaments(desmin, Intermediate filaments(desmin,

wimentin)wimentin)

The dense bodiesThe dense bodies

Two kinds: Two kinds:

1.1. Membrane associatedMembrane associated

2.2. CytoplasmicCytoplasmic

Content: alfa-actininContent: alfa-actinin

Function: transmition of contractile force to Function: transmition of contractile force to adjacent smooth muscle cellsadjacent smooth muscle cells

Smooth muscleSmooth muscle

Mechanism of contractionMechanism of contraction

Calcium ions in the cytosolCalcium ions in the cytosol

Calcium ions+calmodulin(protein)Calcium ions+calmodulin(protein)

(Ca++ - calmodulin) complex(Ca++ - calmodulin) complex

Activation of myosin light-chain kinase(the enzyme responsible for Activation of myosin light-chain kinase(the enzyme responsible for the phosphorylation of myosin)the phosphorylation of myosin)

Mechanism of contractionMechanism of contraction

Activation of myosin light-chain kinase(the enzyme responsible for Activation of myosin light-chain kinase(the enzyme responsible for the phosphorylation of myosin)the phosphorylation of myosin)

Phosphorylation of myosinPhosphorylation of myosin

Reaction between the myosin`s head and actinReaction between the myosin`s head and actin

contractioncontraction

CONTRACTION OF SMOOTH MUSCLE CELLS

Smooth muscle-longitudinal and Smooth muscle-longitudinal and cross sectioncross section

Innervation of smooth muscleInnervation of smooth muscle

Autonomic system( sympathetic and Autonomic system( sympathetic and parasympathetic)parasympathetic)

Spontaneus activity of the muscle Spontaneus activity of the muscle even without the nervous stimulieven without the nervous stimuli

Regeneration of muscle tissueRegeneration of muscle tissue

CARDIAC- no CARDIAC- no regeneration regeneration capacity. capacity. Damage( infarct) is Damage( infarct) is replaced by the replaced by the proliferation of proliferation of connective tissue.connective tissue.

Regeneration of muscle tissueRegeneration of muscle tissue

SKELETAL-limited regeneration.SKELETAL-limited regeneration.

Satellite cells= regenerating cellsSatellite cells= regenerating cells

-population of mononucleated cells, that lies -population of mononucleated cells, that lies within the basal lamina surrounding each within the basal lamina surrounding each mature muscle fiber.After injury become mature muscle fiber.After injury become activated, proliferate and fuse to form a activated, proliferate and fuse to form a new skeletal muscle fibers.new skeletal muscle fibers.

Regeneration of muscle cellsRegeneration of muscle cells

Similar activity of Similar activity of satellite cells may satellite cells may cause a muscle cause a muscle hypertrophy- for hypertrophy- for example after example after extensive exercise.extensive exercise.

Regeneration of muscle tissueRegeneration of muscle tissue

SMOOTH MUSLE- a very good SMOOTH MUSLE- a very good regenerative capacityregenerative capacity