Lab - Content Week 8 - Muscle Flashcards
The electromyogram (______), is a…?
Recording of the electrical activity in skeletal muscles as they contract.
The EMG can be conveniently recorded from ____________ muscles by two surface ___________ placed on the _______.
These are then connected to a __________ that measures the…?
Superficial
electrodes
skin
voltmeter
potential difference between the two electrodes.
In an EMG how is the output read? Wouldn’t the resulting frequency be too small from such small muscle contractions in positions like the resting state?
The output is amplified so it can be read.
It is also filtered to remove electrical noise and then displayed on a computer-based data analysis system that plots the changes in the potential difference against time.
What is the set up for electromyography?
1 Thoroughly clean the skin overlaying the TRICEPS BRACHII on your supjects dominant arm using the alcoholic wipes provided.
- Once the skin has dried, apply one of the gel-filled electrode pads over the proximal belly of the muscle. This point is easier to find if the subject contracts the muscle as you apple the pad. Make sure the pad is applied firmly and then apply a second pad to the distal belly of the muscle.
- Repeat steps 1 & 2 to apply a pair of electrode pads over the belly of the biceps brachii muscle on the same arm.
- Place the earth strap around the wrist of the same arm as the other electrodes and then wait a few minutes to allow the electrode pads to adhere to the skin.
- Now connect the electrode pads on the biceps brachii muscle to the leads connected to channel 1 (CH1) of the data analysis system and the triceps brachii muscle electrodes to channel 2 (CH2) as shown in the diagram below. Finally connect the fifth electrode on the earth lead.
- Adjust the subjects seat height so that they can sit comfortably with their forearm resting on the bench
- Arrange the cables so that they are out of the way and won’t interfere with movements of the forearm
List the process of forearm flexion
- With your subject sitting comfortably and their forearm and elbow resting on the bench (palm facing up) start the data analysis system and record the RMG from both muscles for 10-15 seconds.
- Now ask your subject to SLOWLY raise their forearm (leaving their elbow in contact with the bench) until it is vertical and then lower it back to the starting position. It should take around 5 seconds for the subject to raise their arm and then another 5 seconds to lower it again.
- Repeat this cycle twice more (so that you have a total of three cycles) and then stop the data analysis system.
- Use the auto scale feature to optimise the amplitude of the EMG recording from both muscles and adjust the horizontal scaling so that only the three cycles of movement are visible in the screen and then answer the following questions.
What do you observe in the EMG recording from the biceps brachii during forearm flexion?
Recently, we demonstrated that there are unique phase differences between the biceps and triceps brachii during arm cycling. While the biceps brachii exhibits cyclical muscle activity, with large bursts in the EMG signal during the flexion phase and almost no activity in the extension phase, the triceps brachii demonstrates bursts of muscle activity in both phases
What physiological events are being recorded in an EMG?
The EMG signal is a biomedical signal that measures electrical currents generated in muscles during its contraction representing neuromuscular activities. The nervous system always controls the muscle activity (contraction/relaxation).
Why do you think the amplitude of the EMG is so small?
What could you do to improve the signal to noise ratio for the EMG?
Increase the sensitivity of the recorder?
What is the function of the low level of electrical activity observed in biceps brachii and triceps brachii even when the arm is not moving?
This low level electrical activity is the result of the brain maintaining posture during rest
Skeletal muscles that act of the same joint are sometimes arranged in ___________ _______
Functional pairs
Functional pairs: for any particular movement, one of these muscle has to ___________ while the other muscle _________ to enable the movement occur
Contracts
Relaxes
The muscle that causes the movement by contracting is known as the ________ and the muscle that relaxes is known as the __________
agonist
antagonist
In the agonist and antagonist experiment what did we do?
We used EMG to work out the agonist and antagonist for different types of forearm movement
List the steps to agonist and antagonist EMG experiment
- With your subject sitting comfortably get them to place their hand (palm facing up) on their upper leg and adjust their position (or seat height) so that their palm is just touching the underside of the bench. Start the data analysis system and record the EMG from both muscles for 10-15 seconds.
- Now ask the subject to try and lift the bench off the ground using only their dominant hand. After 5 second get them to relax for 10-15 seconds and then try again. Repeat this once more (so you have three contraction phases) and then stop the data analysis system.
- Now get your subject to rest their hand on the top edge of the bench (again with their palm facing up) and start the data analysis system and record the EMG from both muscles for 10-15 seconds. This time get the subject to try push the bench down in to the floor for 5 seconds before relaxing again. Get them to repeat this sequence twice more (again so you end up with three contraction cycles) before stopping the data analysis system.
- Optimise the data analysis system so you can see all the data from this experiment and then answer the following questions.