BIPN 100 Lecture Notes - Lecture 15: Muscle Fatigue, Motor Unit, Motor Neuron
13 Jun 2018
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BIPN 100 Lecture 15
5/7/2018
• Neurogenic muscle= a muscle that needs an input from the nervous system to contract
• In fused tetanus, fatigue causes muscle to lose tension despite continuing stimuli
• Motor unit
o Basic unit of contraction
o Consists of one a-alpha motor neuron and the muscle fibers it innervates
o Recruitments of additional motor units by the nervous system increases tension
o Once muscle may have many motor units of different fiber types
o Asynchronous recruitment of motor units helps avoid fatigue
▪ Different motor units take turns to maintain tension
▪ First to be recruited are those with the lowest threshold, followed by
those that have a higher threshold etc.
• Muscle mechanics
o Most are mixed between isotonic and isometric
▪ Isotonic contractions
• Length changes, tension stays the same
• Means same tension
• The tension is maintained at the same level, but the muscle
shortens
• Example: picking up purse, and then lifting it higher
▪ Isometric contraction
• Tension changes, length stays the same
• Means same length
• Series elastic elements
• Sarcomeres shorten while elastic elements stretch, resulting in
little changes in overall length
• Not moving
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