Written by : Heba abu hazeem

Corrected by : Shady soghayr

The 1st lecture in muscles : skeletal

muscle

Chapter 10. Muscle Tissue

Muscle Tissue: Introduction

• Muscle tissue is composed of cells differentiated for optimal use of

the universal cell property termed contractility.

•

• Microfilaments and associated proteins together generate the forces

necessary for cellular contraction.

• Nearly all muscle cells are of mesodermal origin and they

differentiate mainly by a gradual process of cell lengthening with

simultaneous synthesis of myofibrillar proteins.

• Three types of muscle tissue can be distinguished on the basis of

morphologic and functional characteristics and the structure of

each type is adapted to its physiologic role.

• Skeletal muscle.

• Cardiac muscle.

• Smooth muscle

What is the specific thing of muscular tissue?

Has the ability to contract

*microfilaments (polymer of amino acid )

*skeletal muscle is voluntary

Types of muscle tissue

Skeletal Muscle

• Skeletal muscle consists of muscle fibers, which are long,

cylindrical multinucleated cells with diameters of 10–100 m.

• Multinucleation results from the fusion of embryonic mesenchymal

cells called myoblasts.

• The long oval nuclei are usually found at the periphery of the cell

under the cell membrane.

This characteristic nuclear location is helpful in discriminating skeletal

muscle from cardiac and smooth muscle, both of which have centrally

located nuclei

*cardiac , skeletal are striated.

Skeletal fiber =skeletal cell

*mioblast the origin of the mesoderm make fusion together to form a

single skeletal muscle fiber

single fiber of skeletal muscle

*stalite cells :

Cell membrane is single layer fiber and external lamina

*muscle fiber contain basal lamina & reticular fiber

*skeletal muscle( miou lemma) lemma = thick\

Thick cell membrane

It is not dense but it looks like this because the :

\1- cell membrane

2- reticular fibers

3- external lamina

Development of skeletal muscle.

Organization

• The masses of fibers that make up the various types of muscle are

: an the Epimysiumarranged in regular bundles surrounded by

external sheath of dense connective tissue surrounding the entire

muscle.

The connective tissue (thin septa of connective tissue from the

epimysium) surrounding each fascicle (bundles of fibers within a muscle)

. Perimysiumis called the

• Each muscle fiber is itself surrounded by a more delicate

: composed of a basal lamina the Endomysiumconnective tissue,

synthesized by the multinucleated fibers themselves as well as

reticular fibers and fibroblasts.

• Within each fiber the nuclei are displaced peripherally against the

sarcolemma.

*when damage reaches deeper than the lemma it will not be closed by

epithelium but by a scare tissue and the myofibrils that where damaged

will not regenerate (replacing the original tissue by connective tissue )but

if the injury was not deep enough it will be replaced normally by

fibroblasts to epithelium as it was before

*muscles have capsules (connective tissue)to cover it

*biceps: (dense irregular connective tissue)

*epimysium : connective tissue surrounded muscle

*perimysium :connective tissue reducing separate small portion /large

*functional unit of muscle organ (bundle)fascicle

*each muscle fiber enclosed be endomysium

*endomysium : 1-reticular fiber

2- cell membrane

3- external lamina

*each group of muscle fiber close by perimysium the functional unit of

the organ .

Each bundle consists of muscle cell

Each muscle cell enclosed by endomysium

Organization of skeletal muscle

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SKELETAL MUSCLE

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The Role of The Connective Tissue

1- Is to transmit the mechanical forces generated by the contracting

muscle cell/fibers because individual muscle cells seldom extend from

one end of a muscle to the other.

2- Blood vessels penetrate the muscle within the connective tissue

septa and form a rich capillary network in the endomysium.

Capillaries of skeletal muscle

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Myotendinous junction.

- Tendons develop together with skeletal muscles and join muscles to the periosteum of bones. The collagen fibers of tendons are continuous with those in the connective tissue layers in the muscle, forming a strong unit that allows muscle contraction to move the skeleton.

- The longitudinal section shows part of a tendon (T) inserted into the endomysium and perimysium of a muscle.

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*myotendinous tendon between

muscle fiber & dense irregular connective tissue .

Muscle Fibers

• Under the light microscope, longitudinally sectioned skeletal

alternating light and dark of ( onsstriati-crossmuscle fibers show

bands. • A bands.are called darker bands The

• I bands .are called lighter bands The

• by a dark transverse bisectedis seen to be I bandIn the TEM each

Z line .line, the

The repetitive functional subunit of the contractile apparatus, the

from Z line to Z line, extends Sarcomere

*under light microscope we can see cross-striation (a-band/i-band)

*each cell consist of multiple functional unit (sacromere)

*under electron microscope :

I band seen to be bisected (dark)

Z band

*H band (very dark)

Cross- striations

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Cross- striations

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Muscle Fibers

• The sarcoplasm has little RER or free ribosomes.

• It is filled primarily with long cylindrical filamentous bundles

running parallel to the long axis of the fiber. myofibrils called

• The myofibrils have a diameter of 1–2 m and consist of an end-to-

end repetitive arrangement of sarcomeres. The lateral registration

of sarcomeres in adjacent myofibrils causes the entire muscle fiber

to exhibit a characteristic pattern of transverse striations.

• The A and I banding pattern in sarcomeres is due mainly to the

.thin & Thickregular arrangement of two types of myofilaments:

*mainly thick fiber :myosin

*mainly thin fiber : 1- actin

2- troponin

3- tropomyosin

The presence of the Troponin is used to distinguish the skeletal muscle

from the smooth because the smooth contains another type

H zone the only thick area in A band *

*Z line the connection of the thin fiber

The Thick & Thin filaments • The Think filaments (1.6 m long and 15 nm wide), they occupy the

A band, the central portion of the sarcomere. The thin filaments run

between and parallel to the thick filaments and have one end

attached to the Z line.

• Thin filaments are (1.0 m long and 8 nm wide).

• consist of the portions of the thin filaments that do not I bands The

overlap the thick filaments (which is why they are lighter staining).

• are composed mainly of thick filaments in addition to The A bands

overlapping portions of thin filaments.

• , the a lighter zone in its centerband shows the presence of The A

like -, that corresponds to a region consisting only of the rodH zone

portions of the myosin molecule with no thin filaments present.

• , a region where lateral M line is the Bisecting the H zone

connections are made between adjacent thick filaments. Major

myomesin.proteins present in the M line region are

*maximum contraction :

H zone zero

A band

Totally over lapping of myosin and actin

The Thick & Thin filaments • , which tropomyosin, the actin-Fof are composedThin filaments

.troponinalso and

• . myosinconsist primarily of Thick filaments

• of the total protein of 55% together represent actinand Myosin

striated muscle.

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Sarcoplasmic Reticulum & Transverse Tubule System

• In muscle the smooth endoplasmic reticulum (SER) is specialized

for Ca2+ ion sequestration.

• To provide for a uniform contraction, skeletal muscle fibers have a

system of transverse (T) tubules. These fingerlike invaginations of

the sarcolemma form a complex network of tubules that encircles

every myofibril near the A-I band boundaries of each sarcomere.

• Adjacent to opposite sides of each T tubule are expanded terminal

cisternae of the sarcoplasmic reticulum. This specialized complex,

ly two small cisternae of consisting of a T tubule and usual

a Triad., is known as sarcoplasmic reticulum

At the triad, depolarization of the sarcolemma-derived T tubules is

transmitted to the sarcoplasmic reticulum membrane

Sarcoplasmic Reticulum & Transverse Tubule System

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