SLE2/MODULE 6- Motor Units TYPING

Question 1

MUs can be compared with one another based on what 3 physiological properties

Answer 1

-speed of contraction
-magnitude of twitch force
-resistance to fatigue

Question 2

2 common methodologies to compare MUs

Answer 2

-direct (physiological measurements)
-indirect (estimated from histochemical, biochemical, + molecular measures)

Question 3

evoked contractions

Answer 3

artificially stimulated by an external resource outside of the human body

Question 4

what protocol uses evoked contractions

Answer 4

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)

Question 5

voluntary contractions

Answer 5

individual is able to produce by sending a signal down from brain to the muscles of interest

Question 6

voluntary contractions (2)

Answer 6

-recruitment threshold
-discharge rate

Question 7

discharge rate

Answer 7

how quickly APs + spikes are produced + what the variability is between them

Question 8

who created the Burke protocol

Answer 8

Dr. Robert Burke

Question 9

Burke protocol is direct/indirect

Answer 9

direct

Question 10

what was used in the Burke protocol

Answer 10

S-transducer
-stimulated muscle through an artificial/evoked stimulus

Question 11

contractile properties of MUs

Answer 11

force (mechanical event) exerted by a motor unit varies with activation rate (electrical events)

Question 12

twitch

Answer 12

force evoked in response to a single action potential

Question 13

tetanus

Answer 13

summation of twitch forces in response to multiple action potentials

Question 14

unfused tetanus

Answer 14

APs not firing quick enough

Question 15

the Burke protocol entails measuring what

Answer 15

measuring twitch and tetanic forces in single MUs by evoking contractions (ARTIFICIAL) with brief electrical stimuli to motor neurons or axons

Question 16

Twitch characteristics for MUs range from ____ to ____

Answer 16

-weak, slow-contracting
-strong, fast-contracting

Question 17

motor unit typing- type FF

Answer 17

fatigue SENSITIVE with FAST twitch contraction time

Question 18

motor unit typing- type FR

Answer 18

fatigue RESISTANT with FAST twitch contraction time

Question 19

motor unit typing- type S

Answer 19

fatigue RESISTANT with SLOW twitch contraction time

Question 20

if we see a dip in the profile of tetanus…

Answer 20

we say that the twitch has sag

Question 21

motor unit typing- presence of sag

Answer 21

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

Question 22

motor unit typing- fatigability

Answer 22

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

Question 23

greater summation of twitch forces at lower stimulation rates for slow/fast tiwtch

Answer 23

slow

Question 24

rewatch slide 10

Question 25

what did data show when comparing max tetanic force vs twitch contraction time for an artificial stimulus

Answer 25

-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

Question 26

how would the data be distributed if there were fast + slow twitch motor units

Answer 26

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

Question 27

Bottinelli et al.

Answer 27

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.

Question 28

what does MHC determine

Answer 28

the amount of myosin ATPase, an enzyme for progressing the ability of the cross-bridge cycle.

Question 29

myosine ATPase enzyme

Answer 29

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

Question 30

2 techniques that classify muscle fibers

Answer 30

-histochemical assays for characterizing MYOSIN ATPase
-molecular measurement to look at (gel electrophoresis) of MYOSIN HEAVY CHAIN ISOFORMS

Question 31

types of myosin ATPase characterized in histochemical assays

Answer 31

type I
type IIa
type IIb (IIx)

Question 32

types of myosin heavy chain isoforms characterized in molecular measurement

Answer 32

MHC-I
MHC-IIa
MHC-IIx

Question 33

there is low/high correspondance between these classification systems (histochemical assays + molecular measurement)

Answer 33

high
-but they provide no info about contractile properties

Question 34

histochemical assays + molecular measurement are direct/indirect

Answer 34

INDIRECT

Question 35

biochemical fiber typing is direct/indirect

Answer 35

INDIRECT

Question 36

the properties of human motor units are best characterized by measuring what 2 things

Answer 36

-recruitment threshold
-twitch force

Question 37

arbitrary where cut offs are for all these