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Lecture 5

ANA300Y1 Lecture Notes - Lecture 5: Myocyte, Skeletal Muscle, Muscle Tone

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Jeffrey Kopstein

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Motor units and muscle control
Motor unit = single motor neurons and all muscle fibres that it innervates
Fibres of muscles units are intermingled; no anatomical subdivisions; more
uniform tension throughout
Muscle Tone
When not contracting, muscle still has some activated motor units; some
tension generated but not enough to overcome resistance = resting tension
Rotating recruitment of different motor units, which maintains muscle tone
Muscle tone especially important in antigravity muscles (which are involved
in balance and posture)
Muscular Contraction + Energy
1 ATP consumed/cycle of myosin head
5 cycles/second
1000s of ATP molecules consumed per cell
Aaerobic Metabolism:
oRequires O2 and organic molecules
oProduces ATP and CO2
oRequires glycogen,
oProduces ATP, lactic acid
Some skeletal muscles use aerobic, some use anaerobic
Distribution of Muscle Fibre Types
Fast twich use anaerobic
Slow twitch use aerobic
Some skeletal muscle very vascularized = slow twitch fibres
Haemoglobin binds to oxygen
Myoglobin is a storage depot for oxygen within skeletal muscles; slow twitch
muscles need lots of myoglobin
Slow twitch fibres are red; fast twitch muscles are white ish
Slow twitch fibres have more mitochondria
Fast twitch have lots of glycolytic enzymes in cytoplasm
Cross sectional diameter of slow twitch muscle is smaller; fast twitch larger,
more uniform throughout
More cross-bridge binding = more tension, so fast twitch muscles have more
tension (also due to larger diameter)
No ATP = no crossbridge binding; so fast twitch fibres are fatigue resistant
b/c don’t require O2; but slow twitch are more resistant bc constant flow of
oxygen through blood
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