Nerves and Muscle

Question 1

Extrafusal fibres

Answer 1

main fibres of muscles, respnsible for muslcular force porduction with skeletal muscles

Question 2

intrafusal fibres

Answer 2

muscle fibres contained within sensory organs called muscle spindles (inside) but not force producing

Question 3

three types of motor neurons that innervate different fibre types

Answer 3

Alpha motor neurons: innervate only extrafusal fibres
beta - extrafusal and intrafusal
gamma - only intrafusal

Question 4

single motor neuron innervation rule

Answer 4

in a mature animal, any given skeletal muscle fibre is innnervated by one and only one motor neuron

Question 5

motor unit - what is it?

2 characteristics

Answer 5

the whole alpha motor neuron together with all the extrafusal muscle fibres that it innervates

• smallest functional unit of the neuromotor system
• produces synchronized chontraction of innervated muscle fibres - to reduce computational load

Question 6

neuromuscular junction

Answer 6

synaptic connection between motor neuron axon terminal and muslce fibre (AP down axon to terminal - synchonized contraction of all the muscles that this alpha connects to)

Question 7

motor end plate

Answer 7

region of muslce fibre that receives neurotransmitter (ACh) from neuromuscular junction, produces EPSP at motor end plate that radiates along muscle fibre as motor unit action potential (MUAP)

Question 8

twitch contraction (2)

Answer 8

propagation of single AP along muscle fibre

muscle fibre generates contractile force for short time and then relaxes

Question 9

tetanic contraction (2)

Answer 9

propagation of train of APs along muscle fibr at relatively high frequency
force developed by muscle fibre is continuously above zero but may show variation due to individual twitches - no time to relax

Question 10

innervation ratio - what is it?

2 example

Answer 10

average number of fibres in a motor unit for a given muscle
fine control: small ratio - 5-100 fibres (extraocular, hand)
gross muscles: high ratio - 1000 fibres (back, thighs)

Question 11

Are all muscle fibres innervated are?

Answer 11

of the same fibre type

Question 12

ratio of action potential to motor unit action potential

Answer 12

1:1 - alpha motor neuron to muscle cell (all fibres)

Question 13

As age increases, what happens to your motor neurons?

Answer 13

innervate more muscle fibres which loses the accuracy

Question 14

physical differences in motor units (2) both are related to

Answer 14

size of the cell body
diameter of axon
alpha MN

Question 15

Muscle fibre types innervated are differentiated by (3)

Answer 15

physiological - vascularization, mitochondrial density etc.
contractile - capacity for force production
- fatigibility - low force/fatigue
mid force/fatigue (postural muscles)
high force/fatigue

Question 16

fast fatigue, fast twitch (3) - name 
- cell body 
- axon diameter 
- muscle fibres innervated (2) 
NCV

Answer 16

FF [MU1] 
largest cell body 
thickest axon diameter 
muscle fibres innervated: 
- highest force capacity 
- quickest fatigue 
nerve conduction velocity - ~100ms

Question 17

fast resistant, fast twitch (3) - name 
- cell body 
- axon diameter 
- muscle fibres innervated (2) 
NCV

Answer 17

FR[MU2]
mid-size cell body 
mid-size axon diameter 
muscle fibres innervated 
- mid-level force capacity 
- fatigue resistant 
nerve conduction velocity - less than FF [MU1], immediate properties

Question 18

fatigue-resistant, slow twitch (3) - name 
- cell body 
- axon diameter 
- muscle fibres innervated (2) 
NCV

Answer 18

S [MU3] 
smallest cell body 
thinnest axon diameter 
muscle fibres innervated 
- lowest force capacity 
- high fatigue - resistant 
nerve conduction velocity = ~40m/s

Question 19

Motor units and force production principle

Answer 19

muscle utilize neural input for purpose of creating muscle contraction which produces force

Question 20

How can forces be graded?

Answer 20

Magnitude of force generated depends on

• number of active motor units
• firing/discharge rates of active units

Question 21

same force output can be achieved by

Answer 21

more MUs firing at lower frequency OR fewer MUs firing at higher frequency

Question 22

how to maximize force output

Answer 22

More MUs and high frequency

Question 23

Henneman size principle

Answer 23

the order in which the motor units of a muslce are recruited into force production is determined by the size of associated motor neuron - smaller MU to larger MU
- [S]->[FR]->[FF]

Question 24

low grade contractions achieved by

Answer 24

fatigue resistant, slow twitch [s] - can last over an hour

Question 25

Larger MUs are recruited as

Answer 25

contraction force increases, but [s] does not decrease

Question 26

increases in muscle tension (force) achieved by

Answer 26

orderly recruitment of MU

Question 27

derecruitment

Answer 27

as force output declines - derecruitment follows inverse order FF, FR, S

Question 28

Reasons for force decline? (2)

Answer 28

``` voluntary decline (muscle relaxation) Fatigue (sustained contraction) - MU drop out ```

Question 29

How to record MU activity in a muscle

Answer 29

electromyography

Question 30

EMG: what is it and ow does it work?

Answer 30

electromyography - algebraic sum of MUAP train - MUAP firing over time graphical rep of the electrical acivity of a skeletal muscle "electrode" records MUAPs as they pass beneath the site of recording

Question 31

How does MUAP get detected by the recording electrodes?

Answer 31

AP crosses neuromuscular junction to depolorize all muscle fibres within a MU - release of Ach then postsynaptic neurons receive the signals

Question 32

In what direction do MUAPs propagate?

Answer 32

both directions along the muscle fibre

Question 33

what are the 2 types of electrodes?

Answer 33

intramuscular (fine wire) EMG | Surface (inferential) EMG

Question 34

Intramuscular (fine-wire) EMG (3)

Answer 34

Records MUAP within targeted muscle only small, muscle specific receptive zone precise and accurate recording from receptive zone

Question 35

suface/inferential EMG (3)

Answer 35

extramuscular records MUAP of all MU in proximity to electrodes - multiple MU within/across muscle precision requires knowledgeable application

Question 36

2 principles of recording MUAP

Answer 36

1. distance from recording site affects amplitude of recorded MUAP - alpha motor neuron synapses with muscle fibre(s) which get detected by the electrodes on the muscle fibre - as we get further away the amplitude gets smaller 2. recorded sighal h(t) represents the sum of all MUAP occurring within the vicinity of recording electrodes at that point in time

Question 37

what do we do to raw EMG data?

Answer 37

we rectify it - half way rectified is to turn all the negative ones into positives, after rectifying both - full way - we can use it to infer force

Question 38

appearance of EMG signal depends on 3

Answer 38

anatomy, neurophysiology, instrumentation

Question 39

how does anatomy construct EMG signal? 1-3

Answer 39

MU - alpha MN and associated muslce fibres - # of muscle fibres innervated - contractile properties of innervated fibres

Question 40

how does neurophysiology construct EMG signals? 1-2

Answer 40

MUAPs - #MU recruited - depends of force - firing frequency of MUs - depends on force

Question 41

3 ways to use EMG

Answer 41

Clinical, sport, industrial

Question 42

clinical applications of EMG - 3

Answer 42

diagnosis - duration and amplitude surgical intervention - effects intended rehab - muscle activity - after a stroke

Question 43

purpose of ground electrode | factors affecting signal quality

Answer 43

take out background activity/system noise by taking out the common activity between it and the electrodes cable sway, light, electrical appliances

Question 44

sport application of EMG

Answer 44

performance - pro vs amateur

Question 45

industrial application of EMG

Answer 45

fatigue - of different muscle groups - ergonomics/work injuries

Question 46

Semmler - EMG activity for elbow flexor groups before and after 4 weeks of casting - 2 -3

Answer 46

no change in force production, however, neural strategy is altered - conpensatory recruitment of synergistic muslces at onset - brachialis dropout (MU fatigue) - intermittent firing in synergistic muscles following dropout CNS strategy to compensate for fatigue