Chapter 4 Flashcards
Factors that influence Actomyosin binding states
(actomyosin is a complex of the contractile protein filament of muscle tissues are composed of)
Interference of transition state of actomyosin cross bridges.
From weakly bound with low-force state to strong with high-force state
This occurs during contraction, may develop products like calcium, hydrogen, inorganic phosphate, reactive oxygen, reactive nitrogen species. These changes would slow down contractile speed, influence the # of cross bridges in high force config or influence force-generating capability.
Changes in force generating capability/shape of force (velocity) results in decreased power.
metabolic changes that influence steps of transition causes decreased force production.
Neuromuscular Transmission Failure
This is failure of a nervous impulse to be translated into an impulse on the sarcolemma.
Hard to determine.
Three main possiblities behind neuromuscular transmission failure
Neurotransmitter Depletion
Postsynaptic Membrane Failure
Failure of Axon Branches to pass on action potential
(see notebook for descriptions of each)
Muscle Wisdom
The gradual decline in muscle activation during fatigue exemplified by the decrease in the firing frequency of motor units during rhythmic or sustained effort.
Does this over time because the contractile speed is slowing down thus require low frequencies to maintain MVC force.
Fatigue Reflex
There is a reflex by which information is transmitted via smaller afferents from the fatigued muscles to the spinal cord and that has an inhibitory effect on motoneuron excitability.
This is how the motoneuron cell body knows what is happening at the metabolic level of muscle.
(muscle telling motoneurons to chillout because they are tired so stop exciting the nerve)
What roles to muscle spindles and golgi tendon play on fatigue response?
Spindle: Increase gain (afferent firing rates didn’t decrease as much as force) No response to firing rate/stretch
Ia & II: increased sensetivity
Glogi tendon organ: decreased sensetivity
Spinal cord inhibition role on fatigue.
?
Influence subsided bery quickly with continued stimulation because of the gradually reduced efficacy of transmission of inhibitory inputs to motoneurons.
Filtered information during contraction maintained optimal excitation of motor pool.
Group III v.s Group IV afferents
more?
Group III afferents: respond to mechanical stimuli, increased mechanical sensitivity to some substances thus more sesitive during fatigue.
Group IV afferents: primary nocieptors. Increase firing rates in presence of certain substances.
Gamma-Motoneuron Response (fusimotor Neuron)
Fusimotor drives also became more similar (less discriminative) after fatigue. Normal variability of responses to stretch among cells was reduced. Info on muscle length was lost, affects on neuromuscular coordination.
Fatigue related changes in intrinsic motoneuron properties
(Very little known about fatigue related changes)
-Stimulation of Group III and IV afferents results in changes in intrinsic motoneuron membrane properties that change firing behavior during excitation.
These indicate a general change in parametes significant in cell excitability and rhythmic firing properties.
