HES 202- Week 1 Motor Units Flashcards
Week 1- Motor Units
What is a motor unit? What is it the functional unit of
An alpha motor neuron and all skeletal muscle fibres innervated by its axons. It is the functional unit of contraction
What are the two ways force is controlled by?
1) Altering the # of active MU’s (de/recruitment)
2) Changing frequency of activation (rate coding- MU discharge rate)
Describe saltatory conduction?
propagation of action potential down the axon
What is myelination?
insulates the axon and prevents movement of ions (Na and K) across the membrane
What is the purpose of Nodes of Ranvier
Ions move readily at gaps in the myelin sheath (Nodes of Ranvier) so an AP at one node brings the next node to threshold and initiates a new AP
2 benefits to saltatory conduction and myelination
1) Increases conduction velocity without a change in axon diameter
2) Reduces metabolic cost as only small segments of the axon require the Na K pump to restore the resting membrane potential
What does Curare prevent binding of? How long does it last for?
Prevents binding Ach to Ach receptors. Lasts 8-30 hours.
What does Botox prevent the release of? How long does it last?
Ach. Lasts 6-8 weeks.
What are two things Botox is used to treat?
Overactive muscles (cerebal palsy) and temporary cosmetic improvements.
What are the two MU classifications?
Type 1 and Type 2a and Type 2x
What can Type 1 be classified as and what do they innervate?
Slow MN that innervate oxidative muscle fibres, forming S MU’s
What can Type 2a be classified as and what do they innervate?
Fatigue resistant MN that innervate fast oxidative, glycolytic forming FR MU’s
What can Type 2x be classified as and what do they innervate?
Fast fatiguable MN that innervate glycolytic forming FF MUs
What is a twitch?
Physiological response of a MU to stimulation