9808 Lecture Notes - Lecture 6: Extraocular Muscles, Skeletal Muscle, Muscle Fatigue
19 Jun 2018
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Muscle lecture 2
Comparing muscles twitches – different muscle have different muscle twitches , contraction and
relaxation will vary
Blue – extraocular muscle – control eye movement,
doesn’t need long sustained movement therefore
has short contraction relaxation period
Green – gastro calf - used for bigger movements
contracts more slowly for a longer period of time,
Orange – Soleus- sits under calf, used for bigger
movements contracts more slowly for a longer
period of time,
Factors that increase the force of skeletal muscle contraction
Recruit more muscle fibres ,
Can activate larger muscle fibre ,
increase in frequency of
stimulation ( wave summation ,
tetanus ) , how much muscle has
been used (fatigue causes
decrease in force ) , thickness of
muscle fibres
All factors that increase contraction force
Muscle Contraction
• Graded muscle responses are:
– Variations in the degree of muscle contraction ( are required for proper and controlled movement
of skeletal movement )
• Responses are graded by:
– Changing the frequency of stimulation
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– Changing the strength of the stimulus
Wave Summation – if want to change the frequency of stimulation
• If stimulus is delivered to a muscle in close succession the second twitch will be stronger
- More action potential more movement
- Because muscle has already contracted it can respond further
Stimulus Intensity and
Muscle Tension
•Threshold stimulus – the
stimulus strength at which the first observable muscle
contraction occurs . need a sufficient number of
muscle fibres firing for a response in muscle to move
•Recruitment – get more muscle fibres , bring more
and more fibres
Tetanus – don’t get confused with disease
- Sufficient delivery of stimuli can result in
complete or incomplete tetanus .
• Complete tetanus - a smooth sustained contraction of maximal strength , relaxation time between
twitches become shorter ,calcium concentration increases
• Incomplete tetanus – progression to a sustained but quivering contraction, before you reach
complete tetanus
Muscle Contractions
• Muscle tone – constant slight contraction of muscles, even when relaxed, doesn’t produce active
movements, helps to keep muscle firm , healthy and ready to respond to stimuli , contributes to
joint stability and helps maintain posture . it responds to activation of stretch receptors in muscles
and tendons .
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find more resources at oneclass.com
• Agonist – prime mover , eg bicep curl the agonist is bicep
• Antagonist– opposes the prime mover eg in bicep curl antagonist is tricep
• Synergist – assists the prime mover by stabilising joints or aiding the prime mover ( same
movement )
Contraction of Skeletal Muscle
• Contraction – refers to activation of the myosin cross bridges, force
generating action . Contraction ends when atp is there and myosin
detaches.
• Isometric contraction - Muscle shortens but does not change angle. No
shortening or lengthening during contraction. Sarcomeres shorten but not
in its entire length
• Isotonic
– concentric contraction = decreasing muscle length
– Eccentric contraction = working muscle lengthens during exercise
Muscle Metabolism – energy to cause muscle to contract
• ATP = adenosine triphosphate = provides energy for contraction , also important to undo cross
bridges and used for calcium pump to get calcium back into sarcoplasmic reticulum , must be
regenerated as fats as it is used.
• ADP = adenosine diphosphate , is used ATP loses a phosphate.
• ATP provides energy for muscle contraction – Only energy source used directly for contraction
Energy for contraction- way to reproduce ATP
Atp is only source used for contractile activity o must be regenerated as fast as it is used.
Explains atp , anaerobic and aerobic energy systems
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Comparing muscles twitches different muscle have different muscle twitches , contraction and relaxation will vary. Blue extraocular muscle control eye movement, doesn"t need long sustained movement therefore has short contraction relaxation period. Green gastro calf - used for bigger movements contracts more slowly for a longer period of time, Orange soleus- sits under calf, used for bigger movements contracts more slowly for a longer period of time, Factors that increase the force of skeletal muscle contraction. Can activate larger muscle fibre , increase in frequency of stimulation ( wave summation , tetanus ) , how much muscle has been used (fatigue causes decrease in force ) , thickness of muscle fibres. Variations in the degree of muscle contraction ( are required for proper and controlled movement of skeletal movement : responses are graded by: Wave summation if want to change the frequency of stimulation: if stimulus is delivered to a muscle in close succession the second twitch will be stronger.
