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Suzanne D'Anna 2
Threshold Stimulus
any stimulus strong enough to initiate action potential
minimal strength of stimulation needed to cause a contraction
Suzanne D'Anna 3
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
Suzanne D'Anna 4
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
Suzanne D'Anna 6
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
Suzanne D'Anna 7
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
Suzanne D'Anna 9
Muscle Tone (tonus)
state of continuous partial contraction muscles are never totally relaxed important in maintaining posture loss of tone - body will collapse
Suzanne D'Anna 11
Isotonic Contractions
same as tone or tension myofilaments slide freely muscles shorten - movement occurs
Example:
- bending, rotating arms, smiling
Suzanne D'Anna 12
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
Suzanne D'Anna 14
Effect of Exercise on Muscles
amount of work done by a muscle is reflected in the muscle itself
inactivity leads to weakness of muscle
Suzanne D'Anna 15
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
Suzanne D'Anna 16
Aerobic or Endurance (cont.)
strengthens skeleton heart enlarges - more blood pumped gas exchange in lungs more efficient no increase in muscle size