Muscle PhysiologyZZZ

7/31/2019 Muscle PhysiologyZZZ

1/27

MUSCLEPHYSIOLOGY


2/27

INTRODUCTION

Muscle contraction

shortening/tensing of a muscle

when tension develops Like most excitable cells, muscle

fibers respond to the excitation signal

with a rapid depolarization which iscoupled with its physiological

response: contraction.


3/27

Contraction is regulated by calcium ion

concentration. In the resting state, a fiber keeps

most of its intracellular calcium carefullysequestered in an extensive system of vessicles

known as the sarcoplasmic reticulum. There are

at least two receptors in the chain between

depolarization and calcium release. Oncereleased, calcium binds to troponin, opening the

myosin binding sites on filamentous actin, and

force is produced.
http://muscle.ucsd.edu/musintro/fibril.shtmlhttp://muscle.ucsd.edu/musintro/fibril.shtml


4/27

Muscle Contraction

Action potentialgenerated is propagatedalong the sarcolemma

and down the T tubules

Action potential triggers Ca2+

release from SarcoplasmicReticulum

Ca2+ binds to troponin;troponin changes shape,

removing the blockingaction of tropomyosin;

actin active sites exposed

Contraction; myosincross bridges alternately

attach to actin and detach,pulling actin filaments

toward the center of thesarcomere

Removal of Ca2+ by activetransport into the SR afterthe action potential ends

Tropomyosin blockagerestored blocking actinactive site; contractionends and muscle fiber

relaxes


5/27

OBJECTIVE

This experiment aimed to observe the

different responses of the gastrocnemius

muscle to different frequencies and

intensities of stimulation through shock.


6/27

HYPOTHESIS

The more the frequent the stimulation, the

higher tension involved. #WWWYKI


7/27

MATERIALS & METHODS

Kymograph apparatuswas set up.

The drum (coveredwith white paper) was

smoked untilcompletely covered

with soot.

Picture 1. Kymograph Apparatus

Picture 3. Kymograph Apparatus with

drum covered with soot


8/27

MATERIALS & METHODS

gastrocnemiusmuscle of an

unconscious frog

was cut off

Drops of Ringersreagent were appliedto the muscle so as

to keep it from drying

up

Unconscious Frog Cutting off the leg Ringers Reagent


9/27

muscle-femurpreparation wasattached to the

kymograph apparatusby a thread

The thigh with thegastrocnemius musclewas put in place in the

kymograph

thread

Gastrocnemius

muscle

electrode

Ringers

reagent

beingapplied

muscle


10/27

Single Shock

Two succeeding stimuli (not longerthan half a second from each

other)

Stimulation for at least 5 times

(with increasing speed at whichstimuli are applied)

Stimulation with steadily increasingrate and intensity until muscle no

longer responded to stimulation

electrode

Ringers

reagent

being

appliedmuscle

Application of stimuli to themuscle-femur preparation:


11/27

RESULTSPicture 1. A Simple Muscle Twitch


12/27

Simple Muscle Twitch

Occurred when a singlestimulus in the form of a

single shock was

applied

Represented by a single

wave on kymograph

tracings

Latent period,

contraction period,

relaxation period


13/27

RESULTS

Picture 2. A Summation

M

uscleStrength

(

Tension)

Time (ms)


14/27

Summation

Occurs after the applicationof two successive stimuli

Kymograph tracings

showed two twitcheswherein the second twitch

was greater than the first

an increase in thefrequency with which a

muscle is stimulated

increases the strength of

contraction

MuscleStrength

(Tension)

Time (ms)


15/27

Summation

With rapid stimulation (so rapid that a muscle does not

completely relax between successive stimulations), a

muscle fiber is re-stimulated while there is still some

contractile activity. As a result, there is a 'summation' of

the contractile force.


16/27

Summation

With rapid stimulation there isn't enough time between

successive stimulations to remove all the calcium from

the sarcoplasm. So, with several stimulations in rapid

succession, calcium levels in the sarcoplasm increase.

More calcium means more active cross-bridges and,therefore, a stronger contraction.


17/27

RESULTS

Picture 3. The Treppe or Staircase Effect

MuscleStr

ength

(Tension)

Time (ms)


18/27

Staircase (Treppe) Effect

happens when a skeletalmuscle is stimulated

immediately after the

relaxation phase has ended;

the contraction that occurswill develop a slightly higher

maximum tension than the

first stimulation. The increase

in peak tension will continue

over the next stimulationsuntil stimulation is stopped.

MuscleStr

ength

(Tension)

Time (ms)


19/27

Staircase (Treppe) Effect

The rise is a result of a gradual increase in the

concentration of calcium ions in the sarcoplasm, in part

because the ion pumps in the sarcoplasmic reticulum are

unable to recapture them in the time between

stimulations.

It is possible that metabolic products that form during the

activity accumulate and the slight increase in

temperature of muscle act created more favourableconditions for excitation-contraction coupling to work

(Hallare, n.d.).


20/27

Tetanus

Tetanus is a result of

sustained contraction

wherein a muscle fiber

is stimulated so rapidly

that it does not relax atall between stimuli.

Muscle

Strength

(Tension)

Time (ms)


21/27

RESULTS

Picture 4. Incomplete Tetanus

MuscleStrength

(Tension)

Time (ms)


22/27

Incomplete Tetanus

The graph starts like a wave summation until itrose to a peak. It was a plateau with a line not as

constant as the other plateau (shaky tracings)

This happens when the stimulation of the muscle

is continued and the muscle is never allowed to

relax completely.

A muscle producing peak tension during rapid

cycles of contraction and relaxation is

in incomplete tetanus.


23/27

RESULTS

Picture 5. Complete Tetanus

MuscleStre

ngth

(Tension)

Time (ms)


24/27

Complete Tetanus

obtained by increasing the stimulation rate until

the relaxation phase is eliminated. During

complete tetanus, action potentials arrive so

rapidly that the sarcoplasmic reticulum does nothave time to reclaim the calcium ions. The high

Ca2+ concentration in the cytoplasm prolongs the

contraction state, making it continuous.


25/27

Muscle Contraction


26/27

Conclusion

The hypothesis is acceptable based on

results of the simple muscle twitch,

summation, staircase effect, and tetanus.


27/27

Recommendation

Avoid smudging the soot on the drum.

Documents

Muscle PhysiologyZZZ