Transcript 5-3 Responses

Muscular Responses
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Threshold Stimulus
any stimulus strong enough to initiate
action potential
 minimal strength of stimulation needed
to cause a contraction

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All-Or-None Response
individual muscle cells contract to their
fullest extent when exposed to stimulus
of threshold strength
 muscle fibers do not partially contract
 if stimulus is strong enough to initiate an
action potential, a nerve impulse is
transmitted along entire neuron at a
constant strength
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Twitch Contraction
brief contraction of all the muscle fibers
in a motor unit
 lasts only a fraction of a second
 response to a single action potential in
its motor unit
 myogram is a record of a muscle
contraction

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Myogram
(single muscle twitch)
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Myogram
latent period
- delay between the time that the
stimulus was applied and the time that
the muscle responded
 period of contraction
- muscle pulls at its attachments
 period of relaxation
- muscle returns to its former length
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Tetanus or Tetanic Contraction
state of smooth sustained muscle
contraction
 muscle is stimulated very rapidly
 no evidence of relaxation
 point at which the muscle is unable to
relax before next stimulus
 results from the addition of Ca+2 released
from sarcoplasmic reticulum
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Twitch

brief muscular contraction followed by
relaxation
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Muscle Tone
(tonus)
state of continuous partial contraction
 muscles are never totally relaxed
 important in maintaining posture
 loss of tone - body will collapse
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Types of Muscle Contractions
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Isotonic Contractions
same as tone or tension
 myofilaments slide freely
 muscles shorten - movement occurs

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Example:
- bending, rotating arms, smiling
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Isometric Contractions
muscles do not shorten
 myofilaments do not move freely
“skidding their wheels”
 muscles are unable to slide because
they are trying to move something more
or less immovable
 Example:
- pushing against a wall
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Types of Exercise
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Effect of Exercise on Muscles
amount of work done by a muscle is
reflected in the muscle itself
 inactivity leads to weakness of muscle
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Aerobic or Endurance
results in stronger, more flexible
muscles
 greater resistance to fatigue due to
increased blood supply to muscles
 benefits body metabolism
 improves digestion, elimination
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Aerobic or Endurance
(cont.)
strengthens skeleton
 heart enlarges - more blood pumped
 gas exchange in lungs more efficient
 no increase in muscle size
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Weight Resistance Exercises
increase muscle mass
 the use of immovable or slightly movable
objects
 requires little time, every other day
 increase muscle size - increase strength
 weight lifting will not increase endurance
 will increase muscle definition
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