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PSHL231 Neurophysiology > Labs 3/4 > Flashcards

Labs 3/4 Flashcards

1
Q

How does the twitch amplitude change when you increase stimulus voltage and why?

A

Increases because more muscle fibres are recruited meaning more tension produced.

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2
Q

In the skeletal muscle contraction lab how is the change in twitch amplitude different to what would occur in the body?

A

More voltage caused increased recruitment of motor units.

In the lab larger fibres were recruited first due to greater surface area meaning less resistance for voltage to enter.

Whereas, in the body the smaller motor units are recruited first.

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3
Q

What predominant fibre type is the soleus and what does that mean?

A

Soleus is a posture muscle.

Posture muscles are slow twitch - means it has more endurance / fatigue resistant.

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4
Q

What is the predominant fibre type of the EDL muscle?

A

Fast-twitch - means it has more power

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5
Q

Compare tetanic contraction between the soleus and the EDL?

A

Soleus reaches tetanus at a lower frequency than EDL

Tetanus in soleus is smoother than EDL

EDL fatigues quickly meaning it does not hold peak tension for long

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6
Q

What is time to peak measuring?

A

Beginning of response of twitch to its peak amplitude

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7
Q

Why do stimuli in unfused tetanus get closer together?

A

Due to the residual Ca2+

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8
Q

How does the activity of the RyR differ between slow and fast twitch fibres?

A

Less RyR in slow twitch fibres therefore has slower calcium release.

More RyR in fast twitch fibres therefore faster calcium release.

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9
Q

How does the myosin type differ between slow and fast twitch fibres?

A

In slow twitch fibres there is slow ATP hydrolysis meaning slow cross bridge cycling.

In fast twitch there is fast ATP hydrolysis meaning fast cross bridge cycling.

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10
Q

How does the activity of the SERCA pump differ between fast and slow twitch fibres?

A

In slow twitch the SERCA pumps calcium back into SR slowly meaning slower drop in tension (hence why more endurance).

In fast twitch SERCA pumps calcium rapidly back into SR meaning faster drop in tension (hence why has less endurance).

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11
Q

How does energy production differ between fast and slow twitch fibres?

A

Slow twitch fibres are oxidative meaning lots of ATP (32-36) generated but slower as requires oxygen.

Fast twitch are glycolytic meaning fewer ATP (2) generated but generated quickly but short term and create’s lactic acid.

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12
Q

Is there more mitochondria in slow or fast twitch fibres?

A

Slow - to support sustained energy production.

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13
Q

What does null hypothesis mean?

A

No difference

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14
Q

What is the difference between time to peak for soleus v EDL?

A

There is a significant difference between them - EDL has a faster time to peak than soleus due to predominately being fast-twitch fibres.

Meaning it is faster to peak but fatigues quickly.

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15
Q

Why is tetanic force greater than a twitch?

A

There is a frequent burst of AP causing a lot of calcium to be released.

The calcium reuptake still occurs but less than release allowing calcium to build up.

With max calcium all cross bridges can form.

Because the tissue is not relaxing elastic recoil does not need to be overcome with each twitch.

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16
Q

Describe optimal stretch:

A

Optimal stretch is when there is optimum alignment of action and myosin so that maximum cross bridge can be formed resulting in maximum tension.

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17
Q

Why is there less tension at excessive stretch?

A

because there is a decreased alignment of actin and myosin and less cross bridges can be formed.

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18
Q

What happens to tension if you continue to increase the length of the muscle?

A

tension will at first increase until optimum length of sarcomere has been reached and tension will start to decrease.

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19
Q

What is the effect of myasthenia gravis?

A

Makes antibodies that block, alter or destroy the acetylcholine receptors at NMJ preventing contraction from occurring.

20
Q

What would the effect of acetylcholinesterase be on someone with MG?

A

it breaks down antibodies that block, alter or destroy ACH receptors therefore it allows for Ach to remain and thus more likely to bind.

21
Q

What is minimum contraction tension?

A

The measure of tension developed when the stimulus voltage first occurs.

22
Q

What is fusion frequency?

A

Frequency where individual twitches can no longer be seen in response to the stimuli (tetanus or tectonic contraction) because they are become fused at the particular frequency.

23
Q

Does soleus or EDL reach tetanaus at lower frequency?

A

Soleus

24
Q

What does EMG stand for?

A

Electromyogram = meaning electricity in the muscle in graph form

25
Q

What is being represented as EMG amplitude increases?

A

Increase electricity in the muscle due to brain recruiting more motor units.

26
Q

What are the physiological processes that generate the EMG waves?

A

AP process

27
Q

What factors determine conduction velocity in axons?

A

Diameter = larger diameter = faster conduction

Myelination = more myelination = fast conduction

28
Q

Why were two stimulation sites used when determining nerve conduction velocity of ulnar nerve?

A

Because we only wanted to see how fast the AP was conducting along the axon of ulnar nerve - by having two stimulation sites we can eliminate other events close to the muscle that slow the conduction.

29
Q

Why is the conduction velocity slowed down at the muscle around ulnar nerve?

A

The process is slow at the muscle because the axons branch and get smaller, NMJ transmission and generation of the end-plate potential on the sarcolemma

30
Q

What is a monosynaptic reflex?

A

Single synapse occurring in the SC

31
Q

What are the two features of monosynaptic reflexes?

A

Reproducible and quick

32
Q

What do reflexes prevent?

A

Stretching and tearing

33
Q

What factors determine the latency of the T-reflex in the soleus muscle?

A

Path length (height)
Axon myelination
Axon diameter

34
Q

What is the M wave?

A

The electrical response shown on a EMG as a result of the direct stimulation of motor neuron’s - appears when just a few motor axons are stimulated between knee to soleus.

35
Q

What is the H wave?

A

The electrical reflex response shown on EMG as a response to the stimulation of sensory neuron’s which then activate motor neurons in the SC (indirect activation of motor neuron’s).

(Knee to spinal cord to soleus)

36
Q

What is threshold voltage?

A

The lowest voltage needed to activate motor or sensory axons resulting in an electrical response (EMG) in the muscle.

37
Q

Does the M or H wave come first?

A

M

(direct stimulation/shorter length means shorter latency).

38
Q

Why does the H wave disappear when M wave is at max?

A

Because all motor neuron’s have already been directly activated and now in refractory period they cannot be activated again. Therefore when sensory neuron’s activated they have no motor neuron’s to stimulate.

39
Q

What is hyperglycemias?

A

High blood glucose

40
Q

What is T-reflex?

A

A T-reflex, also known as the Tonic Stretch Reflex, is a reflex response elicited by stretching a muscle. It involves the activation of muscle spindles, which are sensory receptors embedded within the muscle fibers. When a muscle is stretched, these spindles are stimulated, sending sensory signals to the spinal cord.

For example by tapping its tendon with a reflex hammer, the muscle spindle is stretched, which activates sensory neurons. These neurons then send signals to the spinal cord, where they synapse with motor neurons. This, in turn, triggers a reflexive contraction of the muscle, which is the T-reflex.

The T-reflex is a protective mechanism that helps to prevent overstretching or damage to muscles by causing a rapid contraction in response to sudden stretching. It’s one component of the overall reflex arc involved in maintaining muscle tone and posture.

41
Q

Do sensory axons from muscle spindles synapse directly on motor neuron’s?

A

Yes

42
Q

How is the T-reflex stimulated?

A

Stretching of a muscle activating muscle spindles which are sensory receptors inside muscle fibres.

43
Q

What is the primary reason for the EMG increases in amplitude with increased force of contraction?

A

Additional motor units being recruited.

44
Q

What results in the amplitude of the M wave being inversely related to the amplitude of the H wave?

A

The refractory period of action potentials in motor axons.

45
Q

Can a single stimulus to the knee activate more than one response?

A

Yes - the soleus muscle can be activated twice (M wave and H wave) in response to a single stimulus.

PSHL231 Neurophysiology (10 decks)

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