Controlling muscle contraction

1. Controlling Muscle Controlling Muscle
Contraction Contraction
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Muscle ResponseMuscle Response
Chapter 8: Muscular SystemChapter 8: Muscular System
Unit 2: Support and MovementUnit 2: Support and Movement

2. Types of MuscleTypes of Muscle
Recall there are three types of muscleRecall there are three types of muscle
–Cardiac and Smooth muscle are Cardiac and Smooth muscle are
considered considered involuntaryinvoluntary
You cannot consciously control these musclesYou cannot consciously control these muscles
–Skeletal muscle is the only muscle tissue Skeletal muscle is the only muscle tissue
that is under that is under voluntary voluntary controlcontrol
You think to move your skeletal muscleYou think to move your skeletal muscle
You control your movements using your You control your movements using your
nervous system.nervous system.

3. Nervous SignalNervous Signal
When you want to move you big toe…When you want to move you big toe…
–You think about moving your big toeYou think about moving your big toe
–Your brain generates an electrical signalYour brain generates an electrical signal
–The signal is sent down your spineThe signal is sent down your spine
–The signal is sent down a nerve in your The signal is sent down a nerve in your
legleg
–The signal reaches the end of the nerve’s The signal reaches the end of the nerve’s
axon at the axon at the motor end platemotor end plate

4. Neuromuscular JunctionNeuromuscular Junction

5. AcetylcholineAcetylcholine
A nerve impulse will be sent to the end A nerve impulse will be sent to the end
of a motor neuron axon.of a motor neuron axon.
–This impulse will stimulate the release of This impulse will stimulate the release of
acetylcholine into the synaptic cleft.acetylcholine into the synaptic cleft.
Acetylcholine diffuses across synaptic cleft Acetylcholine diffuses across synaptic cleft
and react with receptors in motor plate of and react with receptors in motor plate of
muscle.muscle.
–Once acetylcholine in the muscle fiber membrane Once acetylcholine in the muscle fiber membrane
associates with a receptor, a associates with a receptor, a Muscle ImpulseMuscle Impulse is is
stimulated.stimulated.

6. Muscle ImpulseMuscle Impulse
Muscle Impulse AnimationMuscle Impulse Animation

7. Muscle ImpulseMuscle Impulse
The muscle impulse travels through The muscle impulse travels through
the transverse tubules, deep into the the transverse tubules, deep into the
muscle fibers, and reaches the muscle fibers, and reaches the
sarcoplasmic reticulum.sarcoplasmic reticulum.
–The sarcoplasmic reticulum contains a The sarcoplasmic reticulum contains a
high concentration of calcium ions.high concentration of calcium ions.
–Like a reservoir of calcium ready to burstLike a reservoir of calcium ready to burst

8. Role of Calcium IonsRole of Calcium Ions
In response to a muscle impulse, the In response to a muscle impulse, the
SR opens gates that allows Ca2+ to SR opens gates that allows Ca2+ to
move out.move out.
–Ca2+ ions bind with troponin, which Ca2+ ions bind with troponin, which
changes shape and moves tropomyosin changes shape and moves tropomyosin
off the actin binding sites.off the actin binding sites.
As a result, myosin is able to bind to actin As a result, myosin is able to bind to actin
and begin the contraction cycle described and begin the contraction cycle described
earlierearlier

10. Muscle RelaxationMuscle Relaxation
When nerve impulses cease, two When nerve impulses cease, two
events lead to muscle relaxation:events lead to muscle relaxation:
2.2.Acetylcholine is decomposed by Acetylcholine is decomposed by
AcetylcholinesteraseAcetylcholinesterase..
2. 2. Calcium ions are actively pumped back Calcium ions are actively pumped back
into the sarcoplasmic reticulum.into the sarcoplasmic reticulum.

11. Threshold StimulusThreshold Stimulus
When a muscle fiber is exposed to a series When a muscle fiber is exposed to a series
of nervous stimuli of increasing strength, of nervous stimuli of increasing strength,
the fiber remains unresponsive until certain the fiber remains unresponsive until certain
strength of stimulation is applied.strength of stimulation is applied.
–The minimum strength required to cause a The minimum strength required to cause a
contraction is called the contraction is called the Threshold StimulusThreshold Stimulus..

12. All-or-None ResponseAll-or-None Response
Muscle fiber exposed to a stimulus of Muscle fiber exposed to a stimulus of
threshold strength respond to its fullest threshold strength respond to its fullest
extent.extent.
–In other words, all the myosin heads react by In other words, all the myosin heads react by
binding and pulling on the actinbinding and pulling on the actin
–The extent of shortening depends on the The extent of shortening depends on the
resistance & the number of motor units that are resistance & the number of motor units that are
recruited for the liftrecruited for the lift
This phenomenon in which muscles always contracting This phenomenon in which muscles always contracting
fully is called the fully is called the All-or None ResponseAll-or None Response..

13. Recording a Muscle Recording a Muscle
ContractionContraction
A muscle can be stimulated A muscle can be stimulated
electrically, and when it contracts, its electrically, and when it contracts, its
movement can be recorded.movement can be recorded.
–The resulting muscle contraction pattern The resulting muscle contraction pattern
is called a is called a MyogramMyogram..

14. Recording ContractionsRecording Contractions
If a muscle is exposed to a single If a muscle is exposed to a single
stimulus to activate some of its motor stimulus to activate some of its motor
units, the muscle will contract and units, the muscle will contract and
then relax.then relax.
–A single contraction that lasts only a A single contraction that lasts only a
fraction of a second is called a fraction of a second is called a TwitchTwitch..
The delay between the time the stimulus was The delay between the time the stimulus was
applied and the time the muscle responded is applied and the time the muscle responded is
the the Latent PeriodLatent Period..

16. Recording Contractions Recording Contractions
ContinuedContinued
The latent period lasts less than 0.001 The latent period lasts less than 0.001
seconds.seconds.
–This period is followed by a This period is followed by a Period of Period of
ContractionContraction when the muscle pulls at its when the muscle pulls at its
attachments.attachments.
A A Period of RelaxationPeriod of Relaxation when it retunes to when it retunes to
its former length.its former length.

18. SummationSummation
A muscle fiber exposed to a series of A muscle fiber exposed to a series of
stimuli of increasing frequency reaches stimuli of increasing frequency reaches
a point when it is unable to completely a point when it is unable to completely
relax before the next stimulus in the relax before the next stimulus in the
series arrives.series arrives.
–The force of individual twitches combines The force of individual twitches combines
by the process of by the process of SummationSummation..

19. Series of TwitchesSeries of Twitches

20. SummationSummation

21. Tetanic ContractionTetanic Contraction
When the resulting forceful, sustained contraction When the resulting forceful, sustained contraction
lacks even partial relaxation, it is called a lacks even partial relaxation, it is called a Tetanic Tetanic
ContractionContraction..

22. Use and Disuse of Use and Disuse of
Skeletal MuscleSkeletal Muscle
Skeletal muscles are very responsive Skeletal muscles are very responsive
to use and disuse.to use and disuse.
–Forcefully exercising muscles causes them Forcefully exercising muscles causes them
to enlarge (to enlarge (Muscular HypertrophyMuscular Hypertrophy))
–Unused muscle undergoes Unused muscle undergoes AtrophyAtrophy
decreasing their size and strength.decreasing their size and strength.

23. Muscle FibersMuscle Fibers
There are two types of muscle fibers:There are two types of muscle fibers:
Slow Twitch FibersSlow Twitch Fibers
Fast Twitch FibersFast Twitch Fibers
These fiber types respond differently to These fiber types respond differently to
exercise/stress.exercise/stress.

24. Slow FibersSlow Fibers
A muscle contracting weakly activates A muscle contracting weakly activates
a specialized group of muscle fibers a specialized group of muscle fibers
called called Slow FibersSlow Fibers..
–When stimulated, slow fibers produce When stimulated, slow fibers produce
more mitochondria, and a more extensive more mitochondria, and a more extensive
capillary networkcapillary network
Mitochondria for extra ATP productionMitochondria for extra ATP production
Capillaries to deliver more oxygenCapillaries to deliver more oxygen
*Their overall size does not change*Their overall size does not change

25. Fast FibersFast Fibers
Forceful exercise, in which a muscle Forceful exercise, in which a muscle
exerts more than 75% of its maximum exerts more than 75% of its maximum
force, utilizes specialized muscle fibers force, utilizes specialized muscle fibers
called called Fast FibersFast Fibers..
–In response to strenuous exercise, these In response to strenuous exercise, these
fibers produce new filaments of actin and fibers produce new filaments of actin and
myosin.myosin.
The diameter of the muscle fibers increase, The diameter of the muscle fibers increase,
and the entire muscle enlarges.and the entire muscle enlarges.
The extra myosin and actin fibers give the The extra myosin and actin fibers give the
muscle more strengthmuscle more strength

26. DisuseDisuse
If regular exercise stops:If regular exercise stops:
–Capillary network shrinkCapillary network shrink
–Number of mitochondria within the Number of mitochondria within the
muscle fibers dropsmuscle fibers drops
–Number of actin and myosin filaments Number of actin and myosin filaments
decreasedecrease
Unused muscle may decrease to less than Unused muscle may decrease to less than
half its usual size within a few months.half its usual size within a few months.