Cells To Systems Lecture 6- Muscle Tissue

Front 1

Specialization
Muscle cells or fibers are highly differentiated to allow

Back 1

contraction
Elongated form allows shortening along axis, elongation give rise to the use of fiber
Contain longitudinally oriented rod like contractile elements (myofibers)

Front 2

Classification of muscle fibers (cells)

Back 2

Muscle fibers are divided into two categories based on the presence or absence of light microscopically visible alternating light and dark banks running transversely across the muscle fiber

Front 3

Striated

Back 3

Skeletal
Associated with the skeleton and fascial tissues of the body
Is involved in gross body movement and tends to be under voluntary or conscious control
Cardiac
Confined to the heart
Is involved in pumping blood though the body and is under involuntary control

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Smooth

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No striations are visible under light microscope
Muscle usually occurs as an integral part of an organ where it makes up a major part of the organs wall
Under involuntary control

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Size and shape of skeletal muscle

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Long cylindrical cells with blunt/tapered ends
Fibers are multinucleated with nuclei located at the periphery of the cell just beneath the scacrolemma

Front 6

Nuclei of skeletal muscle

Back 6

Nuclei are oval
Pale
Basophilic
Peripherally located chromatin
1 or 2 nuclei

Front 7

Sarcoplasm of skeletal muscle

Back 7

Compromises organelles
Elongated sacrosomes
Poorly developed Golgi
Ribosomes
Glycogen granules

Front 8

Myofibrils of skeletal muscle

Back 8

Make up the bulk of the skeletal muscle fiber
Specific structure of these give rise to the striations visible
Stain Eosinophilic

Front 9

Striations of skeletal muscle

Back 9

Alternating transversely orientated light and dark bands
Striations due to the arrangement of the myofibrils relative to each other as well as their own special structure

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the A BAND
H ZONE
the I BAND
Z LINE

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Dark band-
Pale region at middle
Light band
Dark line in middle

Front 11

Sacromere of skeletal muscle

Back 11

The sacromere is the region of the muscle fiber between adjacent Z lines
It is the smallest regularly repeating unit and the basic contractile unit of the myofibril

Front 12

Myofibrils and myofilaments

Back 12

Myofibrils are long rod like structures arranged parallel to each other and run longitudinally within the cell
They are made up of regularly arranged groups of myofilaments which are two types:
Thick myosin myofilaments 15-16 nm diam
Thin actin myofilaments 5-6 nm diam

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A BAND-

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thick myosin filament span this region, resulting in dark staining

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I BAND-

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only thin actin filaments are present which results in pale staining

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Actin filaments extending into the A BAND give an outer darker region and the paler

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H ZONE (myosin only)

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Z LINE-

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this region is where actin filaments are anchored and kept in a particular array such that they lie between the myosin filaments within the A BAND

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M LINE-

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this is in the middle of the H ZONE where myosin filaments are anchored and kept in a particular spatial arrangement that accommodates the actin filaments

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Back 18

Front 19

muscle type?

Back 19

skeletal muscle

Front 20

The sarcoplasmic reticulum

Back 20

Extensive network of longitudinal tubules with transverse anastamoses and terminal dilations
Extends around and between the myofibrils forming interconnected sleeve like structures around these
They are connected transversely but separated into discrete units at the A/I junctions
These discrete units are either centered on the M line or Z line
All myofibrils in a given region o f a muscle fiber are surrounded by an interconnecting network of sarcoplasmic reticulum which contains a high concentration of calcium ions.

Front 21

The transverse tubule system (T-system)

Back 21

At the A/I junctions a system of slender transversely running tubules penetrate the muscle fibers and separate the terminal cisternae of adjacent sarcoplasmic reticulum units
These tubules also surround each myofibril in a given region
The T-system is formed by invagination of sarcolemma and therefore contains extracellular fluid
The region where the T-system tubules contact adjacent cisternae is called a TRIAD and is important in the initiation of muscle fiber contraction

Front 22

Contraction and innervations
Skeletal muscle fibers are innervated by

Back 22

motor nerves originating in the central nervous system
An action potential traveling down the nerve axon sets up an endplate potential which is propagated in an action potential in the sarcolemma
This action potential then travels down the T-system tubules into the depth of the muscle fiber.
At the triad this causes depolarization of the sacroplasmic reticulum with the result that Ca++ ins are released into the sarcoplasm surrounding the myofibrils
On exposure to Ca++ ions the myosin and actin filaments interact such that the actin filaments are drawn between the myosin filaments toward the M line causing shortening of the sacromere and the muscle fiber.
Relaxation occurs as Ca++ ions are withdrawn from the sacroplasm and returned to the sacrplasmic reticulum.

Front 23

Size and shape of cardiac muscle

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Cylindrical in shape
Fibers branch and anastomse with each other

Front 24

Nuclei of cardiac muscle

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Usually 1 but can be 2
Centrally located
Oval with blunt ends
Pale
Basophilic

Front 25

Sarcoplasm and myofibrils of cardiac muscle

Back 25

Eosinophilic

Front 26

Striations for cardiac muscle

Back 26

As for skeletal muscle but tissue possess intercalated discs

Front 27

Intercalated discs

Back 27

Distinct transverse dark bands scattered thought cardiac muscle tissue
Appear as straight or step like lines
In addition to striation
Regions of end to end contact between fibers and contain junctional complexes
GAP JUNCTIONS on lateral part of discs transmits contractile impulses between fibers, allows sequential contraction
DESMOSOMES AND FASCIA ADHERENS on transverse parts of discs anchor adjacent cells

Front 28

Control and innervations of cardiac muscle

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Contraction is initiated and synchronized by specialized regions within the heart-the sinoatrial and atroventricular nodes
The transmission of contractile impulses via purkinje fibers and the gab junctions between adjacent muscle fibers
Some modulation via autonomic nervous system

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Size and shape of smooth muscle

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An elongated spindle shaped cell with finely tapered ends

Front 30

Nuclei of smooth muscle

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Single, located in middle widest part of the cell
Cylindrical in shape, but often wrinkled, twist or helical
Basophilic with fine granular chromatin
1 or 2

Front 31

Sarcoplasm and myofibrils of smooth muscle

Back 31

Uniformly Eosinophilic

Front 32

Multi unit innervations of smooth muscle

Back 32

Each fiber has its own nerve ending which initiates contraction much like skeletal muscle
Allows small precise contraction

Front 33

Unitary innervations of smooth muscle

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Single nerve will innervate a muscle bundle or syncytium of many fibers
Tends to have inherent spontaneous contractility
Neural input tends to modify activity rather than initiate it
Fibers tend to be linked by junctional complexes allowing for sequential coherent contractions as occurs in peristalsis