Zzzzzzzzzzzz MUSCLE 2011

8/3/2019 Zzzzzzzzzzzz MUSCLE 2011

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MUSCLEassignaltarget

OPS


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MUSCLE CELL

STRIATED

- Skeletal

- Cardiac

SMOOTH


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For SKM and CDM the termcell isusually replaced by fiber

Note:

sarcolemma, sarcoplasm, sarcoplasmic-

reticulum (SR),sarcomere.


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SKELETAL

Axon termini, secreting Ach synapse with SKM(paracrine)*

SKM transmembrane receptor uptakes Ach

Adequate AP is required to overcome thresholdpotential of the hillock (known as: all-or-nothing law)

RMP about 95 mV. Threshold about 50 mV

*Synapse = neuromuscular-junction, =endplate


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NEURO-MUSCULAR SYNAPSE


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SKM fiber is multinucleated, cylindrical-shaped and composed of ultrastuctures.Several protein arrange in distinguished

pattern Mitochondria and nuclei located beneath the

sarcolemma

Fibres are covered with connective tissuecontaining nerves, blood vessels


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Mitosis is supressed by

myostatin factor.

Bigger muscle is

obtained by enlargement

of fibers and connective

tissues.


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One fibre has several fibrils,surrounded by SR.

Each fibril is made up of array of parallel filaments

Filament : 1. thick (myosin)2. thin (actin)

Others: Troponins (TN) (TN-C, TN-I, TN-N)

Tropomyosin (TM)Nebulin, tropomodulin, konektin.etc.


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tropomyosin actin troponin


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Sarcolemma has branches ie. transversustubuli that approach two cysternae of SR (andso the AP too !!!)


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SR in blue


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The AP depolarizes the SR cysternae (RyRc)causing a Ca-ion efflux to sarcoplasm. Itstarget is TN-C.

Increase of Ca-ion eventually contracts thefibers.

Ca ions pump back to SR fibers relaxe

AP of fibers contract-relax resembles axon

For detail see Lodish et al.,


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Energy for contraction : creatinP,glycogen, mitochondrial respiration


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CARDIAC MUSCLE

Y-shaped fiber (branching cells) usually withsingle nucleus, but mitochondria >>> SKM

Fibers are intercalated

by adherent-junction

(intercalated disc)

which have gap junction


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Gap junction enables AP passes from fiber to fiber socontraction occurs in a synchronous wave


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CDM

Gap-junction enables AP to pass from fiber to fiber socontraction occurs in a synchronous wave

Molecular mechanism of contract-relax similar to SKMBUT AP that triggers heart beat is generated within the

heart itself !! (pace-maker).

Autonomic nerves simply modulate (increasing ordecreasing the AP )

Energy : obligatory oxygen !


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SMOOTH MUSCLE


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Smooth Muscle

Cells are not striated; spindle-shaped withsingle central nucleus

Fibers smaller than those in skeletal muscle

No sarcomeres

- not arranged as symmetrically as in skeletalmuscle, not as organized striationsMore actin than myosin

Caveolae: indentations in sarcolemma;

- may act like T tubules

Dense bodies (instead of Z disk), insarcoplasm

- connect intermediate filaments, and


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JUNCTIONS in SMOTH MUSCLES


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Other proteins in smooth muscle

- desmin, vimentin, caldesmon- calponin (inhibits myosin activity)

located along actin

- calmodulin (inhibited by drug)- myosin light chain kinase (MLCK)

for contraction

- myosin light chain phosphatase

(MLCP) for relaxation


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SM i h i


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SM contraction mechanism

SM l i h i


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SM relaxation mechanism


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Stimulation does not depend on neuron (butautonomic motor neuron reach SM and canstimulate or relax depending on whichneurotransmitter. Norepinephrine? NO?

Histamin? Oxytocin ?) In brief, like CDM, SM has pace maker.

Contraction is slower than striated muscle buttakes longer time


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Nerve stimulation activates the Ca ion

receptors, so Ca influx occurs

Certain drug and hormone

can activate special receptor

so that the internal Ca ions

efflux from the SR (agonist)

The next slides show molecules

in cell signaling pathway lecture.


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C i f 3 l t


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Comparison of 3 muscle types


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Disorders of muscle tissue

Muscular dystrophy

a group of inherited muscle

destroying disease

Muscles enlarge with fat and connective tissue

Muscles degenerate

Ex./Duchenne muscular dystrophy

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Zzzzzzzzzzzz MUSCLE 2011

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