LAB EXAM LAB 1: MU recruitment Flashcards
where does an AP travel when a motor neuron is deplozariz
down axon to neuromuscular junction
what NT is released at the NMJ and where
acetylcholine in synaptic cleft
what does the relased of scetyl choline due
actiavtes acetyl choline receptors which allow the muscle membrane adjucatent to the end plate to reach its threshold
what is the result of a muscle end plate reaching threshold
generation of Ap in muscle fiber and the contraction of the fiber
what is another name for contraction
tweitch
what is a motor unit
a motor neuron, its aox and all the muscle fibers taht the axon innervates
true or false: the MU is the largest functional unit in the neuromuscular systyem
false
it is the smallest therefore the smallest part of the ystem that can be controlled independatnylu
true or false: msucles fibers cannot be activatied independatnly
true
a single otor neuron innervates 1 or several muscel fibers
several
each muscle fiber is innervated by 1 or more motor neuron nervre ending
only 1 motor neurons nerve ending
what are some different chracterties of muscle fibers and MU
speed of contraction, max force production
resistance to fatigue
different motor units have the same or different innervation ration
varying innervation ration
muscles used for fine dexterous movement (hand, eye) have low or high innervation
low innervation ration
what dose it mean to have a low innervation ration
one motor neuron only innervaties a few muscle fibers
muscles used for foreceful and ballistic movements (like quads) have a low or high innervation ration
high innervation radio
what does it mean to have a high innervation ration
one motor neuron innrvations many muscle fibers
how are wide reanges of movements acheived
by varying the number of active motor units which then cahnges the amount of force produced
what are the 3 factors that determine degress of skeletal muscle contraction
1) degree of muscle strength (length tension relation)
2) the acvation of desrired number of motor units (intensity of activation)
3) the frequency of motor neuron impulses in each motor unit (frequency of activation)
the sequential activation of motor units to perform a designmated task is called …
motor unit recruitment
explain length tension relationship
the degree of tension developped is determined by the overlap between actin/myosin
too much overlap or not enough overlap does not allow enough force to be generalted
=THERE IS AN OPTIMAL OVERLAP LENGTH
what are muscles recruited according to
size princicple: hennemans sixe principle
explain intensity (hennemans size principle)
motor units are recruited according to size (smallest motor units actviated first)
what is the activtion freq for maintaening posture
20 pulses/sec
activation freq for walking
Walking
• 30 pulses/sec
activation freew for full out sprint
Full-out sprint (measured in quad)
• 75 pulses/sec
rtue or false: the electical impulse generated and conducted by each fiber is very strong
false, very weak (100 microvolts)
explain how this small impulse can be detected by a pair of electrons
many fibers conduction simultaneously indice voltage differences in overlying skin that are large enough to be detected by a pair of surfrace electrodes
what is the def of electromyography
the detection, amplicafication and recording of these changes in skin voltage produced by activation of underlying msucle contracttion
what is the recording of electromyography called
electromyogram (EMG)
true or faale: EMG is a direct measure of muscle force
(and whyP
false it is not a direct measure of force
since depolarization triggers contraction, the AP precede tje contraction
(ie. EMG is recorded priot to any force generation mecanism)
what is the force measured with and in what units in the lab
kg by handgrip dynamotor
what is the def of sksetlal muscle fatigue
decrease in muscles ability to generate force
what is muscle fatigue caused by
revversible depeletion of the msucle energy/field supply (ie. glycogen)
when does fatigue occur
when muscle uses energy sources faster than they can be generated
what is the onjective of the demo
show how increases intensity andfrequency of msucel stim effects force of muscle contraction produced
what is the nerve used for the demo
median nerve at the wrist
what are the single signal pulses appkied to the thenar muscle
50-70 v or more, 1 ms
when is the demo ended
when the thenar muscle fully contacts (ie./ thumb flexion)
what is the force of the demo of the thumb recorded by
transducer
what is the actual procedure for demo
electrons placed on swabbed skin
place in transfucer
1) deliver single stimulat at 5 second intervales (causing a twitch)
voltage is increased until maximal stimulatm is verified (when there is no firther rise is twitch torque)
=shows how indivadual motor units are recruited by increase intensity of stim
2) muscle is stim with bursts of impulses (increasing freqnuencies= 3, 7,10,15
=showing how frequency of activation effects muscle force and how fluid locaomots actions are acheived via summation
what does it indicatied when there is no fruther rise in twitch torque deteted
all motor units have neen actvated for that muscle (shows how indivadual motor units are recruited by increase intensity of stim)
what is incomplete tentanus
muscle exhibits shorter and shorter contraction-relaxation cycles resulting in the summation of contractions. In this case, there is still time for partial muscle relaxation before the next stimulus.
what is fused tetanus
there is no time for relaxation between stimuli, resulting in the fusion of individual contractions
into a single, smooth, total muscle contraction. This leads to fluidity of movement.
unfused tetanus causes fluidity or movement
false, fused tetnus
what does wave summation mean
there is no time to relax before next stitm is applied so force is :summated”
ie;: added to the previous one for increase in force
what is the main difference between incomplete and completet teatnus
abundance of intra-cellular Ca++.
explain CA and contraction for complete tetanus
With the decreased time between stimuli in complete tetanus, the Ca++ has less time to clear from the sarcoplasm.
=The resulting build-up of Ca++ leads to the sustained contraction and fluid
movement.
when does treppe occur
muscle is repeatedly activated following a rest period, which leads to an
increase in tension with no wave summation
=The strength ofcontraction increases to a plateau.
what is another name for treppe and what is the reason behind it
This phenomenon is also known as the “staircase effect” and
is thought to be due to increasing Ca++ in the cytosol.
what is task 1 of the MU lab and its resultant objective
increasing clench force
Determine the relationship between the force
of muscle contraction and the intensity of EMG
activity (in dom and non dom)
what is task 2 and its corresponding objectivw
continued clench at max force
Determine time to fatigue at 50% of maximum
clench force
true or false: you can have jewelylry aand watches for experiement
false
where are the 3 electrodes placed
over the belly of the felxor muscles (first distal to anticubilta fossa on medial side, 2) 10cm distal to sceond)
3) unlar styloi process (medial wrist, on bone)
what is the function of the elcecttron placed on the ulnar styloid process
ground electode
explain calibration
Zero the dynamometer and EMG, Provide max grip strength = 100%
=the system then determines an interval for
the tests
explain task 1 (increasing clench force)
every ttwo seconds you are going to increase clench force to a certain level
test ends when max grip force is reached (nom and dom)
explain task 2 (fatigue)
clench dyna for as long as you can and test stops when force level falls below 50% of maximal achieved
what values to you get for task 1
force at peak (max foce)
what values do you get for fatigue test
time to fagtigue
what are 4 reasons to epxlain decline in strenght as one fatigues
A depletion of muscle glycogen (ATP) in prolonged intense activity leads to the inability of the contractile and metabolic processes of the muscle fibre to continue supplying the same work output.
- Transmission of the nerve signal through the neuromuscular junction can diminish
slightly after intense prolonged muscle activity, leading to muscular fatigue. - Interruption of blood flow leads to loss of nutrient supply and loss of oxygen, resulting in muscular fatigue within 1 to 2 minutes.
- An increased level of blood and muscle lactate can impair the function of contractile proteins.
what is NADH
NADH is short for Nicotinamide Adenine Dinucleotide. It is a derivative of vitamin B
(niacinamide) combined with a ribose (5 carbon sugar), a phosphate group and an adenine
=coenzyme (found in cytosol and mito)
what is the role of NADH
The role of NADH in cellular metabolism is directly linked to the role of NAD+. These
compounds are the most important carriers of the H+ atoms that are released during the breakdown of energetic substrates. This breakdown occurs in order to produce ATP,
which subsequently transports the H+ to the respiratory chain of electrons located in the inner membranes of the mitochondrion. There, the H+ are relinquished to the electron acceptors of the respiratory chain. This process is a major component of aerobic metabolism
what is the difference between FAD and NAD
NAD and FAD are both electron (hydrogen) carriers.
is that FAD is able to accept and carry 2 hydrogen ions, whereas NAD can only accept 1 hydrogen ion.
FAD cannot produce more ATP than NAD since NAD enters the ETC earlier
the more ATP can be produced.
every NADH molecule, 3 ATP
every FADH2 molecule, 2 (ATP
what is the relationship between IMEG and force
as the transmission of the electrical nerve signals sent to the
muscle increases,
the force of the contraction produced by the muscles also increases
indicates that the subject’s muscles are responding well to the signals sent by the motor neurons.
why is it possible the dom arm has a lower peak
The fact that the dominant arm is more efficient at sending out the signals and having the muscles contract at the corresponding force is most likely due to the fact that the dominant arm carries out all the very fine motor skills
non dom=better for ballistic
