SLE2/MODULE 6- Motor Units TYPING Flashcards
MUs can be compared with one another based on what 3 physiological properties
-speed of contraction
-magnitude of twitch force
-resistance to fatigue
2 common methodologies to compare MUs
-direct (physiological measurements)
-indirect (estimated from histochemical, biochemical, + molecular measures)
evoked contractions
artificially stimulated by an external resource outside of the human body
what protocol uses evoked contractions
Burke protocol
-looks at the profile of twitch (submaximal tetanus) + whether sag exists or not + whether or not that profile is resistant to fatigue or fatigable (aka prone or susceptible to influence of fatigue)
voluntary contractions
individual is able to produce by sending a signal down from brain to the muscles of interest
voluntary contractions (2)
-recruitment threshold
-discharge rate
discharge rate
how quickly APs + spikes are produced + what the variability is between them
who created the Burke protocol
Dr. Robert Burke
Burke protocol is direct/indirect
direct
what was used in the Burke protocol
S-transducer
-stimulated muscle through an artificial/evoked stimulus
contractile properties of MUs
force (mechanical event) exerted by a motor unit varies with activation rate (electrical events)
twitch
force evoked in response to a single action potential
tetanus
summation of twitch forces in response to multiple action potentials
unfused tetanus
APs not firing quick enough
the Burke protocol entails measuring what
measuring twitch and tetanic forces in single MUs by evoking contractions (ARTIFICIAL) with brief electrical stimuli to motor neurons or axons
Twitch characteristics for MUs range from ____ to ____
-weak, slow-contracting
-strong, fast-contracting
motor unit typing- type FF
fatigue SENSITIVE with FAST twitch contraction time
motor unit typing- type FR
fatigue RESISTANT with FAST twitch contraction time
motor unit typing- type S
fatigue RESISTANT with SLOW twitch contraction time
if we see a dip in the profile of tetanus…
we say that the twitch has sag
motor unit typing- presence of sag
reduction in evoked force during an unfused tetanus when electrical stimuli (25) were elicited at an inter-stimulus interval 1.25 times the contraction time
motor unit typing- fatigability
how much the peak force declined in response to a train of electrical stimuli (13) delivered at 40 Hz once each second for a few minutes
greater summation of twitch forces at lower stimulation rates for slow/fast tiwtch
slow
rewatch slide 10
what did data show when comparing max tetanic force vs twitch contraction time for an artificial stimulus
-this data shows that there is no distinct group type; there is intermingling between some of these groups, no clear distinction
-continuous distribution between peak tetanic force and twitch contraction time
-so its not really appropriate to characterize motor units based on the protocol Burke has outlined
how would the data be distributed if there were fast + slow twitch motor units
see slide 14
-circles indicate where we would see ALL fast vs slow motor units because it would ideally be very distinct but this is not hwat happens in reality
Bottinelli et al.
by means of a muscle biopsy, Bottinelli et al. compared the contractile properties of fiber segments that differed in myosin heavy chain (MHC) isoform composition.
what does MHC determine
the amount of myosin ATPase, an enzyme for progressing the ability of the cross-bridge cycle.
myosine ATPase enzyme
there is some sort of catalyzation for the hydrolysis of myosin ATP energy store
-this reaction of the myosin heavy chains isoforms is the immediate resource that our system uses to get energy to drive muscle contractions
2 techniques that classify muscle fibers
-histochemical assays for characterizing MYOSIN ATPase
-molecular measurement to look at (gel electrophoresis) of MYOSIN HEAVY CHAIN ISOFORMS
types of myosin ATPase characterized in histochemical assays
type I
type IIa
type IIb (IIx)
types of myosin heavy chain isoforms characterized in molecular measurement
MHC-I
MHC-IIa
MHC-IIx
there is low/high correspondance between these classification systems (histochemical assays + molecular measurement)
high
-but they provide no info about contractile properties
histochemical assays + molecular measurement are direct/indirect
INDIRECT
biochemical fiber typing is direct/indirect
INDIRECT
the properties of human motor units are best characterized by measuring what 2 things
-recruitment threshold
-twitch force
arbitrary where cut offs are for all these
