EMG practical Flashcards
What are the four different properties of a muscle cell and what do they mean?
Contractile - shorten in response to electrical stimuli
Elastic - recoil to resting length after being stretched
Excitable - can recieve and respond to stimuli
Extensible: can stretch when not contracted
What is a motor unit?
A single motor neuron and all the muscle fibres that is innervates.
What makes up a neuromuscular junction?
An axon terminal, synaptic cleft and the motor endplate of the muscle fibre.
What is meant by recruiment in muscle?
The combined effect of multipe muscle fibres reaching action potential and contracting.
Smaller motor units will contracted at lower stimuli than larger motor units
The force of twitch increases as more motor units are activated until maximal force when all motor units are activated is reached.
Why is the freqeuncy of action potential generation important in muscle fibres?
There is a time delay between action potential generation and contraction.
When action potentials have a higher frequency so are in closer proximity not all calcium ions have been transported back into the SR.
This can result in stronger and larger duration contraction
Note multiple action potentials can occur during one contraction.
What is meant by a muscle twitch?
One complete cycle of contraction and relaxation in a muscle.
Why can you have multiple action potentials during one muscle contraction?
Action potential is only a few milliseconds in duration.
Ca2+ remains in the sarcoplasm and muscle tension persists for longer, hence muscle still contracting when the next action potential arrives.
What is meant by muscle summation?
In one motor unit, related action potential in high frequency that the muscle does not have time to relax between contraction, creates a smooth movement
What is meant by tetanic contraction or a state of tetanus in muscle?
When action potential generation is in high frequency, meaning muscle fibres are unable to relax between action potential generation
Results in a continous contraction that is stronger than a single twitch.
What is mean by incomplete tetanus in muscles?
When stimulation frequency is high but at a rate that still allows partial relaxation of muscle between twitches.
What is meant by contraction?
The generation of tension within muscle fibres that results from excitation of motor neurons.
What are the different types of isotonic muscle contraction?
Concentric - muscle shortens
Eccentric - muscle lengthens.
What is tetanus?
A state of sustained anf involuntary muscle contraction.
An infectious disease caused by the neurotoxin tentanospasmin causing widespread tetanic contraction.
Treated by muscle relaxants
Over 10 to 20% of people with tetanus die.
What are the different names for a muscle cell?
Myocyte
Muscle fiber
Muscle Cell.
What is the relationship between muscle properties and the size of motor units within the muscle?
Smaller motor units are associated with muscles with smaller forces but greater fine control or dexterity, activated by smaller stimuli
Larger motor units generate more force but with less dexterity, require greater stimuli.
What channels found on the sarcoplasmic reticulum are related to the movement of calcium ion?
Ryanodine receptors are is close association with L-type Ca2+ channels on the T tubule, action potential in the T-tubule results in activation of ryanodine channels to release calcium ions.
SERCA channels actively transport calcium ions back into the SR to aid muscle relaxation.
What is excitation-contraction coupling?
The conversion of an electrical stimulus into a mechanical response, the release of Ca2+ provides the link between electrical excitation and contraction. Excitation preceeds contraction.
How is muscle contraction tension and smoothness maintained during the cross-bridge cycle?
Crossbridges form independently of each other, so at any one time there are some crossbridges bound and others that are not.
Compare the durations of action potentials, calcium release and muscle contraction?
Action potential lasts about 1ms
Calcium release starts immediatly after, peaks at about 20ms and continues till 90ms
Twitch force peaks at about 60ms and continues until 180ms
When does muscle contraction stop?
When the SR runs out of Ca2+.
At what frequency of action potential dose muscle contraction generally occur?
Below 200ms
During tetanus how many motor units are involved.
All the motor units
What is an EMG?
In basic terms what is it used for?
An electromyography
Measures the electrical potential in a muscle, used to diagnose myopathy conditions and neurogenic conditions.
Measures the time taken for an electrical impulse to travel between the electrodes, average speed is 50/60m/s
What is CMAP?
Compound motor/muscle action potential
The summation of action potentials of all action potentials at all activated motor units.
