Lab 10 - Muscle Physiology Flashcards
What was used to examine grip force
Hand dynamometer
What does skeleton provide
Support and articulation for body
What do bones act as
Support structures
What do joints function as
Pivot points
How to two or more muscles work
Antagonistically
What is skeletal muscle composed of
Long, multinucleate cells called fibers grouped into fascicles
What is motor unit
A single motor neuron, and all the muscle fibers that it innervates
What does an action potential in motor neuron induce and how
Action potential in the muscle fibers it innervates by releasing the neurotransmitter acetylcholine into the neuromuscular junction. This muscle action potential causes a brief increase in the intracellular concentration of calcium ions [Ca2+], and activates the contractile molecular machinery inside the fiber. This requires the use of intracellular supplies of adenosine triphosphate (ATP) as the energy source.
Summary if action potential in pre synaptic neuron to sliding of actin and myosin - excitation - contraction coupling
- Release of neurotransmitter at the motor end plate
- Binding of transmitter to postsynaptic acetylcholine receptors
- Opening of sodium channels
- Generation of end plate potential on surface of sarcolemma
- Surface propagation of action potential
- Passage of action potential down t-tubule system
- Depolarisation of sarcoplasmic reticulum
- Release of calcium from sarcoplasmic reticulum
- Calcium binding to troponin
- Conformational change in troponin ‘tugging’ tropomyosin from actin
- Uncovering of active sites on actin
- Myosin heads forming ‘cross bridges’ attaching to the actin
- Myosin heads ‘tilting’ pulling actin towards centre of sarcomere
- Cross bridges detach and reattach to the next active site
- Making and breaking of cross bridges repeats until muscle has shortened the required amount. This is known as the ratchet theory of muscle contraction.
- At the end of contraction calsequesterin pumps calcium back into the
sarcoplasmic reticulum.
What is a twitch
Brief contraction - result of sliding of actin and myosin
What is a whole muscle controlled by
Firing of up to hundreds of motor axons
What is spatial summation
Adjusting the number of active motor units , thus controlling the number of twitching muscle fibers - n.s controls muscle
What is spatial summation also known as
Motor unit recruitment
What is a motor unit
A single motor neuron and all the muscle fibres it innervates
What happens with muscles with fine degree of control
Muscles with a fine degree of motor control will have motor units composed of a small number of muscle fibres. Postural muscle, however, which require little fine control, will have motor units comprising many muscle fibres.
What is another way to control muscle contraction by n.s
Vary the frequency of action potentials in the motor axons
What happens at stimulation intervals greater than 200ms
Intracellular [Ca2+] is restored to baseline levels between action potentials and the contraction consists of separate twitches.
What happens at stimulation intervals between 200 ms (5Hz) and 75 ms (13.3Hz),
[Ca2+] in the muscle is still above baseline levels when the next action potential arrives
What is temporal summation
The muscle fibre has not completely relaxed and the next contraction is stronger than normal.
When do you see tetanus
Intervals of 50ms ( 20Hz )
What is tetanus
At even higher stimulation frequencies, the muscle has no time to relax between successive stimuli. The result is a big smooth contraction many times stronger than a single twitch due to series of closely spaced stimuli: a ‘tetanic’ contraction.
What happens at low frequency
the muscle will have time To relax between stimuli and the result will be a series of small individual twitches
What happens at high frequency
With increasing stimulus frequency the muscle will start to contract again before the contraction due to the previous stimulus is over. The resulting contraction will therefore be larger.
What happens when external nerve stimulation is applied
the volunteer will feel a brief ‘pinch’, a tingling sensation, with a twitching of the muscle. It may feel similar to the static discharge.
How is spatial summation investigated
The twitch response as the stimulus strength increases.
How is temporal summation investigated
Measure the effects of changing the interval between paired stimulus pulses.
What was stimulated
The ulnar nerve at the wrist
How long was each electric shock when stimulating nerve
0.5s
What is each wave
A separate thumb twitch response
What is the maximal response
Highest peak
This is at the end when all the peaks are stationary. Activated 100 percent of neuron innervated. As activated all motor units so it plateau as limiting factor
Did you get a twitch at 1mA stimulus? What does this tell you about the number of muscle fibres being stimulated - SPATIAL SUMMATION
No Because no muscle fibres are being stimulated/ being induced to contract = recruiting more motor neuron into response
What is the threshold current of response for your data - SPATIAL SUMMATION
All points before this is zero. The first increase after 0. 0 all the way across bottom up until certain point where you induce muscle contraction you can detect – 8 MAPS – the initial threshold – threshold of response. First stimulus current which is inducing muscle contraction
What proportion of the muscle fibres were contracting to produce the maximal response - SPATIAL SUMMATION
Graph plateau cannot induce anymore force max as no of neurons are stimulated
How does the force change with an increase in current of stimulation? Why does the force change like this-SPATIAL SUMMATION
More motor unit = muscle contraction. Keeps increasing until about 17mA Increase stimulus current = recruiting more motor units into response – action potential in more neurons – muscle contraction in more muscle fibres = increasing force of thumb twitch response = more stonger.
Why does the scatter plot plateau? - SPATIAL SUMMATION
Activated 100 percent of neuron innervated. As activated all motor units and muscle fibres so it plateau as limiting factor. After 17 MAPS, plateu’s – reached flat line at top – cannot induce any more force even when applying more current, limiting factor is the number of neurons—no mater how much mores stimulus current we apply – cannot make muscle contract more – same if we took up to 1000 MAPS – not generate anymore – already activated 100%
What is the units of the stimulus current
mA
What happens to number of muscle fibres contracting as the stimulus current was increased
Increases
Why does varying the stimulus strength affect the thumb muscle twitch force?
Because more motor units/muscle fibres are being stimulated and more neurons being activated. At lower stimulus current – no response at all wasn’t sufficient to induce muscle contraction. At 10MAPS – waveform generated as you are inducing muscle twitch – force to thumb transducer – increase stimulus current – amplitude continue to increase –– more muscle contractions
What happens to the amplitude of the wave as the stimulus interval approaches 50ms? Why does this happen?
50ms isn’t enough time for muscles to contract or any muscle relaxation to occur before muscles induced to contract further from 2nd stimuli event - only 1 muscle contraction induced from 2 separate stimuli. Full force so 1st will be roughly double amplitude. Complete tetanus- continuous muscle contraction- longer so no time for muscle to relax at all = 1 peak – not 2 separate pekas. Incomplete tetanus- some time for muscle to relax before complete tetanus, muscle has some time to relax till so slight separation of peaks
What happens to amplitude of waveforms at 200mv
Same force and amplitude, 2 separate events though, closer together.
What happens to amplitude of waveforms at 150ms
Time for muscle to relax before 2nd one starts
Gap of 150ms gap – inbetween still time for muscle to fully relax after 1st muscle contraction before 2nd muscle contraction starts – same amplitude – same force
What happens to amplitude of waveforms at 100ms
Waveform different – 1st muscle contraction as expected BUT does not have time to fully relax before those muscle fibres are being induced to contract again due to 2nd stimulus.
What happens to amplitude of waveforms at 500ms
2 complete independent waveforms and muscle contractions – identical amplitude
Explain process of temporal summation
Increasing a muscle contraction force even though you keep same stimulus current but decrease the stimuli such that second stimuli induces a muscle contraction before muscle after first contraction has time to fully relax. You want to induce muscle to contract again even though its partially contracted. It is additive on top of the other contraction. One that gives just below maximal response – stimulate twice in a row and decrease the time inbetween
Larger amplitude = stronger forceful contraction
What is the phenomenon called that temporal summation results in
Tetanus
Is the stimulation interval (frequency) at which temporal summation occurs the same for fast and slow muscles?
They are not the same because:
• Fast muscles contract quicker.
• Slow muscles take longer period of time to contract
As the number of pulses increases, what happens to the force of the muscle contraction? and why?
The force increases because the amplitude and duration increase. The time period under wave increases hence more contractions
Inceases amplitude and duration increases- time period under waveform. Extending event for at least 50ms each time. Stimulate more time- increases amplitude f wave, time period under wave increases
Tetanus more info
- 2 consecutive stimuli together – 1 peak – single muscle contraction – amplitude double
- 3 consecutive stimuli each separate by 15ms – larger amplitude
- Artefact – uncomfortable – moved arm
- Prolonged muscle contraction – increase in amplitude for waves and longer duration of muscle contraction
- Tetanus – from infection you get overstimulation of muscle contraction – induced to go into tetanus
- Infection from bacteria – end up with muscle contraction – associated with lock jaw – affect muscles around jaw they are contracting – cant open mouth – fed through straw until clear infection so muscles relax or crack open jaw
- If infection into muscles with breathing e.g. diaphragm or ribcage -cant regulate breathing
- Tetani is in soil or rust
- Most of the time your body can fight it off – suppressed immune system or high levels
- Tetanus – endpoint of temporal summation – don’t see 2 separate musce contraction events – only see 1 – 1 wavefrom – increased amplitude – muscle contraction force greater
