3rd Lecture on Skeletal Muscle Physiology by Dr.roomi

7/29/2019 3rd Lecture on Skeletal Muscle Physiology by Dr.roomi

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Skeletal muscle Physiology

By

Dr. Mudassar Ali Roomi (MBBS, M. Phil)


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TETANIZATION:

Definition: Summation ofcontraction/twitchesSustained contraction withoutrelaxation.

Complete tetanus is producedwhen a muscle is stimulated at

a very rapid rate. Example: 60-70 stimuli/sec. Frequency of stimulation at

which complete tetanus isproduced is called tetanizingfrequency.

Muscle tension produced in

complete tetanization is greaterthan that in single muscletwitch.

Clostridium Tetani alphamotor neuron repeateddischarge and tetanus.


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INCOMPLETE & COMPLTE TETANUS

INCOMPLETE Repeated stimuli at a fast

raterelaxation of eachtwitch remainsincomplete incompletetetanus.

COMPLETE

Repeated stimuli at stillhigher raterelaxationphase disappearsaltogether sustained

contraction phase isobtained completetetanus.


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TETANY (increased excitability of motor

nerves)

CAUSES:

Parathyroidectomy (during thyroid surgery) lack of PTHplasma Ca+ level falls signs of neuromuscularhyperexcitability appear.

Alkalosis

plasma proteins behave as anions

bind cationsincluding Ca++decreased ionized calcium hypocalcemia less calcium available in ECF for membrane stabilizationno blocking of sodium channels by calcium cations (negativelycharged on inside) increased excitability of motor nerves tetany.

Hyperventilationhypocapnia (decreased CO2concentration) respiratory alkalosisplasma ionizedcalcium falls carpopedal spasm, a positive Chvostek sign &other signs of tetany).


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SIGNS OF TETANY:

CHVOSTEKS SIGN: Aquick contraction ofipsilateral facial muscles

elicited by tapping overthe facial nerve at theangle of the jaw.


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SIGNS OF TETANY:

TROUSSEAUS SIGN: Aspasm of muscles of theupper extremity thatcause flexion of the

wrist & thumb withextension of fingers. In individuals with mild

tetany with no obviousspasm, trousseaus sign

may be produced byoccluding circulation forfew minutes with a B.Pcuff.


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TREPPE / STAIRCASE PHENOMENON

Definition: When a muscle isstimulated by maximumstimuli at a frequency lessthan tetanizing frequencyprogressive increase in muscletension with repeated stimuli,

till it becomes constant. If threshold stimuli are applied

so that each stimulus reachesthe muscle when the muscletwitch due to previousstimulus has completedeach successive twitch shows

an increased amplitude till amaximum height is reachedthis is called as staircasephenomenon.


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Ca Gluconate IV Slowly over 20 minutes

Vitamin D


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Mechanism of Treppe

Greater availability of

calcium in sarcoplasm.

Accumulation of

metabolites. Rise in local

temperature.

All these exertbeneficial effect on

contraction.
http://www.google.com.pk/url?sa=i&rct=j&q=TREPPE+/+STAIRCASE+PHENOMENON&source=images&cd=&cad=rja&docid=6emJ-JJJWoOp2M&tbnid=i-czJm70HHDLRM:&ved=0CAUQjRw&url=http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/2010%20Exam%20Reviews/Exam%203%20Review/CH%2009%20Electromyography.htm&ei=m5gwUeD0OoeTtQbn8YDwCg&bvm=bv.43148975,d.Yms&psig=AFQjCNH7_FsF7BoRvAMLC6VmDm2wfqnSvA&ust=1362225637779153


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Muscle Atrophy

Definition of atrophy:decrease in the size of a tissuedue to decrease in size of itscells.

There is weakening andshrinking of a muscle

Mechanism: decrease in theactin, myosin filaments andthe diameter of myofiber.

May be caused by: Immobilization of muscles e.g.

in cases of bed ridden patient

Loss of neural stimulation e.g.in cases of nerve injury
http://www.google.com.pk/url?sa=i&rct=j&q=muscle+atrophy&source=images&cd=&cad=rja&docid=AqsofsIB0346qM&tbnid=pTJIY2s5A5-E9M:&ved=0CAUQjRw&url=http://www.healthcentral.com/diet-exercise/h/how-to-treat-muscle-atrophy.html&ei=_ZwwUf2ZJYjtswaI4oGICQ&bvm=bv.43148975,d.Yms&psig=AFQjCNExsMwmlPGEFFe3WzJBUXCFnrT0ow&ust=1362226807000025


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Muscle Hypertrophy

Definition of hypertrophy:

increase in the size of a

tissue due to increase in

size of its cells.

Enlargement of a muscle

More capillaries

More mitochondria

Caused by: Strenuous exercise

Anabolic Steroid hormones


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RIGOR MORTIS:

after deathmuscles of dead body become

rigid rigor mortis.

Its onset depends on:

Temperature: increased temperature rapid

onset.

Activity: Vigorous activity of muscle before

death rapid onset.


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Mechanism of Rigor Mortis

After death ATP is notavailable nodetachment of cross-bridges of myosin from

active site of actinfilaments rigor mortis.

After 16-24 hours rigormortis disappears due to

autolysis of muscleproteins (resulting fromhydrolytic enzymesreleased from lysosomes).


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SIGNIFICANCE of Rigor Mortis

Forensic significance: cangive us a clue about causeof death. In cases of

suicide, the gun or daggeris locked in the hand.

Time since death: it givesus some idea about timesince death. rigor mortis

remains for about 16hours after death. Itdisappears after 16-24 hrsof death.


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SLOW AND FAST MUSCLE FIBERS
http://www.google.com.pk/url?sa=i&rct=j&q=fast+and+slow+muscle+fibers&source=images&cd=&cad=rja&docid=qfnCo3lrwarSmM&tbnid=83bjHxsW5ezvkM:&ved=0CAUQjRw&url=http://www.stmary.ws/highschool/science/humanbio/quarter2/mp2Notes/MuscleTissueNotes.htm&ei=Gik4UZGROsjVsgbypoCoCA&bvm=bv.43287494,d.ZWU&psig=AFQjCNG8kr3imylbPShrh-sX-8_KG1BX1w&ust=1362721373110424


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SLOW AND FAST MUSCLE FIBERS


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SOURCES OF ENERGY DURING MUSCLE CONTRACTION


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3rd Lecture on Skeletal Muscle Physiology by Dr.roomi

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