PHYS20008 Lecture Notes - Lecture 10: Reuptake, Motor Neuron, Troponin
10 May 2018
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Lecture 10
- Skeletal muscle: one of the main efferent pathways that enables us to regulate
external environment
- Skeletal muscles cells are excitable cells → can fire APs (causes contraction)
- Motor unit refers to a single alpha motor neuron and all the muscle fibres it
innervates, single alpha motor neuron going down into muscle ⇒ branching out and
innervating a collection of muscle fibres
- More than one motor unit in a single muscle
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- Each motor unit has all or none response - stimulation of a motor neuron activates all
of its component muscle fibres
- All muscle fibres in a single motor unit have similar metabolic and contractile
properties
- Alpha motor neurons recruited according to their size: smallest ones recruited first,
largest ones recruited last
- Increase force of muscle contraction by recruiting additional motor units (not by
getting individual muscle fibres to contract harder)
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find more resources at oneclass.com
- Low force contraction: only recruit the red ones (a proportion of muscle fibres are
actually contracting)
- More motor units → can lift heavier object
- Muscle fibres are in parallel → when just red ones contract/actively contracting, the
others are going to squish up and contract effectively along for the ride (not putting
energy in but because in parallel, can contract a small proportion of those and the
other ones will move along with them)
- One motor unit will only have one fibre type in it
- Muscles have different proportions of fast twitch and slow twitch
- Fast twitch muscle fibre: 15 types, more powerful and faster, less fatigue resistant,
muscles that move hands (quick, fatigue quickly, use tool for a while hand gets sore)
- Slow twitch muscle fibre: much more fatigue resistant, core muscles (not doing
anything fancy but need to be working all the time to keep upright)
- Heart - cardiac muscle (involuntary like smooth muscle)
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- Bundles of muscle fibres in muscles
- Muscle fibre = muscle cell, multi-nucleated
- Contract a few or collection of muscle fibres and the whole muscle will shorten
(muscle contraction to shorten that muscle)
- All human skeletal muscles are a mixed collection of more than one fibre type (in
contrast to other vertebrate species)
- These fibre types differ in rate of myofibrillar ATPase, identity of contractile and
regulatory proteins as well as proteins of the SR and T-tubules
- The most basic division of fibre types is made on twitch and fatigue characteristics
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find more resources at oneclass.com
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- Type I → slow twitch fibres, are aerobic, high density of capillaries, higher oxidative
capacity, lots of blood coming in, recruited first (for low strength contraction), fatigue
resistant
- Type II → fast twitch fibres, sparse density of capillaries, fatigue easily, low oxidative
capacity, single unit has more fibres (greater force of contraction)
- Twitch = single unit of contraction for muscle fibre, fire one AP on skeletal muscle
fibre → it has one quick contraction in response to that AP (one unit)
- Normally, fire a train of APs that create much longer sustained contraction called
tetanus
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find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Skeletal muscle: one of the main efferent pathways that enables us to regulate external environment. Skeletal muscles cells are excitable cells can fire aps (causes contraction) Motor unit refers to a single alpha motor neuron and all the muscle fibres it innervates, single alpha motor neuron going down into muscle branching out and innervating a collection of muscle fibres. More than one motor unit in a single muscle. Each motor unit has all or none response - stimulation of a motor neuron activates all of its component muscle fibres. All muscle fibres in a single motor unit have similar metabolic and contractile properties. Alpha motor neurons recruited according to their size: smallest ones recruited first, largest ones recruited last. Increase force of muscle contraction by recruiting additional motor units (not by getting individual muscle fibres to contract harder) Low force contraction: only recruit the red ones (a proportion of muscle fibres are actually contracting)
