Twitch, Summation and Tetanus of Skeletal Muscle - Easy and Fun explanations!

the frequency of motor neuron

stimulation a single action potential

from a motor neuron will produce a

single contraction in muscle fibers of

its motor unit this isolated contraction

is called a twitch the tension produced

by a single twitch can be measured by a

Maia Graham which is an instrument that

measures the amount of tension produced

over time each twitch undergoes three

phases a latent period a contraction

phase and a relaxation phase during the

latent period the action potential is

being propagated along the sarcolemma

and calcium ions are released from the

sarcoplasmic reticulum

however contraction has not yet occurred

in the contraction phase calcium ions in

the sarcoplasm have bound to troponin

tropomyosin has shifted away from active

binding sites and crossbridges have

formed here the circum years are

actively shortening to the point of peak

tension in the relaxation phase tension

decreases as contraction stops calcium

ions are pumped out of the sarcoplasm

back into the sarcoplasmic reticulum and

crossbridge cycling stops this returns

the muscle fiber to its resting state

although a person can experience a

muscle twitch a single twitch does not

produce any significant muscle activity

in a living body a series of action

potentials to the muscle fibers is

necessary to produce a muscle

contraction that can produce work normal

muscle contraction is more sustained and

it can be modified by input from the

nervous system to produce varying

amounts of force this is called a graded

muscle response the frequency of action

potentials or nerve impulses from a

motor neuron as well as the number of

motor neurons transmitting action

potentials both affect the tension

produced in skeletal muscle

if the fibers are stimulated while a

previous twitch is still occurring the

second twitch will be stronger this

response is called wave summation we

have summation occurs because the

excitation contraction coupling effects

of successive motor neuron signaling is

summed or added together at the

molecular level summation occurs because

the second stimulus triggers the release

of more calcium ions which become

available to activate additional Cir

commuters while the muscle is still

contracting from the first stimuli

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summation results in greater contraction

of the motor unit if the frequency of

motor neuron signaling increases

summation and subsequent muscle tension

in the motor unit continues to rise

until it reaches a peak point the

tension at this point is about three to

four times greater than the tension of a

single twitch this state is referred to

as incomplete tetanus during incomplete

tetanus the muscle goes through quick

cycles of contraction with a short

relaxation phase for each if the

stimulus frequency is so high that the

relaxation phase disappears completely

the contractions become continuous in a

process called complete tetanus during

complete tetanus the concentration of

calcium ions in the sarcoplasm allows

virtually all of the sarcomeres to form

cross bridges and to shorten this allows

the contraction to continue

uninterrupted tetanus is the fusion of

contractions to produce a continuous

contraction