Motor System and Electromyography Flashcards
Lecture 7/8/9
Equivalent name for neuromuscular junctions
motor end plates
Why does Acetylcholine depolarize the muscle?
Both K+ and Na+ can flow through ACh receptor however, more Na+ enters than K+ leaves
Thin muscle filament
actin
Thick muscle filament
myosin
sliding filament theory
shortening (overlap) causing contraction
Inward Ca2+ flow causes…
the release of ACh at the neuromuscular junction
ACh diffuses to the motor end plates, binds to the receptors and…
opens the Na+ channels leading to an action potential
The action potential in the sarcolemma (exterior) travels inward via…
the T-tubules to the triads
Once the action potential has reached the interior (triads) where is Ca2+ released from?
terminal cisternae (of sarcoplasmic reticulum)
Once Ca2+ is released for a second time what happens?
Ca2+ binds with troponin, and moves tropomyosin, exposing actin/myosin binding site, and triggering power strokes (muscle shortening)
What must be moved aside to expose the actin/myosin binding site?
Tropomyosin
What is the first step in excitation contraction coupling?
Ca2+ binds with troponin
Describe the power stroke?
Hinging of myosin head causing actin to slide across myosin (uses ATP)
What are some attributes of Type 1: slow, oxidative fibres
1) less force
2) less energy
3) slow fatigue
4) fast recovery
ie. walking
What are some attributes of Type 2: fast, glycolytic fibres
1) more force
2) more energy
3) fast fatigue
4) slow recovery
ie. sprinting
In a myoglobin stain are the slower, more oxidative/aerobic fibres darker or lighter?
Darker
Def: motor unit
single motorneuron and all of the muscle fibres it innervates
Def: motor pool
all the motor units innervating a given muscle
Why might the distribution of lower motor neurons (spanning multiple spinal segments) be beneficial?
In case of a minor injury, if one level is injured you will still have use of the muscle
The summation of successive isometric twitches will result in…
a build up of force
Unfused tetanus (contraction/relaxation) will result in…
sub-maximal force output (not perfect summation)
Fused tetanus will result in…
maximum force output (smooth curve)
Which muscle fibres produce more force output?
Fast twitch (more glycolytic)
Sarcomere
contractile unit btwn two
“z” discs
Muscle fibres consist of many…
myofibrils
Myofibrils contain…
thin filament (actin), and thick filament (myosin)
Given the same synaptic input, which motor units are more excitable- smaller/larger?
Smaller, b/c larger are leakier
Where are alpha motor neurons located?
Ventral horn of spinal cord
What does is mean for larger motor units to be less excitable/leakier?
Na+ leaks out making depolarization (positive inside) more difficult
Do motor units begin firing action potentials (“get recruited”) at the same time?
No, they get recruited at different levels of force output (and de-recruit in the opposite order)
Smaller (slow twitch) motor units get recruited…
first (and de-recruit last)
Larger (fast twitch) motor units get recruited…
later because they require more force to fire
Surface electromyography uses…
standard EMG placements across the body that measure muscle fibre action potentials as they pass below the electrode
How do you correctly place electrodes in surface electromyography?
-placed over the thickest part of muscle (belly)
-aligned with the direction of muscle fibres (pennation angle)
What are some characteristics of larger motor units (MU)?
-fast conduction velocity
-more force
-fatigable
What are some characteristics of smaller motor units?
-least amount of muscle fibres
-slower
Rectification
make all negative values (EMG) positive… like taking the absolute value
Smoothing
filtering/averaging the rectified EMG data
Muscle force output
Rectified and smooth EMG trace that corresponds to the approximate amount of force produced by the muscle
EMG signal is approximately ________ in relation to muscle force output
linear
Maximal Voluntary Contraction
Highest amplitude measured on EMG
Indwelling electromyography (“fine-wire” EMG)
Needle inserted into target muscle and wire remains in muscle, hooked to muscle fibres
What are some benefits of indwelling EMG
-can measure smaller amounts of motor units
-can measure deeper fibres clearer
-“less noise”
-eliminates “cross talk” (signal contamination)
Can we increase the amplitude of EMG during maximum voluntary contraction
Yes, with strength training
In what ways can training make you faster, stronger, better?
-increase # of fast muscle fibres
-neurons can also grow in size (increasing conduction velocty)
Immobilization of motor neurons
-decrease in EMG amplitude
-bedrest, casting, exposure to long periods of microgravity
