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Unformatted text preview: muscle fiber is
correlated with axonal conduction speed. 47 KNES 462 ©FK ‘08 the froce your muscele create during motor activities--its not a binary signal
off or on- you cant tune the force over a very whide range The Motor Unit: Force Grading I
• Two ways to grade force of muscle contraction:
– recruitment of muscle cells is ranked (size principle): 2 mechanisms • slow units first, respond to weak synaptic input
• fast fatigue-resistant next size principal--- the slow twitch activate ﬁrst.then int--then fast twitch • fast fatigable last modulation--at 100 hz the muscel goes into fused tetonous-- aka
muscel cramp. – modulation of firing rate of motor neurons:
• lowest firing rates for steady contraction: ~ 8 Hz
• higher rates for more intense contractions: ~ 25-80 Hz
48 KNES 462 ©FK ‘08 The Motor Unit: Force Grading II
• Other scenario: constant low force needed over
long period of time
– Approx. half of muscle fibers are active;
– With ongoing contraction, some fatigue, and some
‘rested’ ones jump in and assist;
– Fast fatigue resistant fibers are additionally recruited ;
– Large units (fast fatigue) kick in;
– This scenario is only valid for fairly low contraction only works if blood ﬂow is not affected
forces (<25% maximum voluntary muscle contraction [MVA])
49 KNES 462 ©FK ‘08 KNES 462 The Motor Unit: Size Principle 50 KNES 462 ©FK ‘08 recpetor-records the state of something Sensors / Receptors 53 KNES 462 ©FK ‘08 Muscle Receptors they are called proprioceptors--...
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This document was uploaded on 03/19/2014 for the course KNES 462 at Maryland.
- Winter '13