Muscle Physiology Flashcards
What is the name of the motor unit used in this experiment?
The Gastrocnemius
What is the largest nerve in the body?
The sciatic nerve
What is the sciatic nerve a major nerve of in humans?
The sacral plexus
What is the sciatic nerve comprised of?
2 nerves: the common peroneal and the tibial nerves
Where do the nerve fibres arise from in the body?
From spinal roots L4-S2
How do you destroy the brain and spinal cord of the frog?
The frog is stunned and pithed
What are the final steps to removing the sciatic nerve and preparing the gastrocnemius muscle?
The in-situ length of the gastrocnemius muscle is measured and a ligature tied around the achilles tendon. This should be left long to facilitate attachment to the strain gauge.
The tendon is cut and the gastrocnemius muscle carefully dissected free up to the knee joint. The limb bones either side of the knee-joint are cut with coarse scissors allowing the muscle, nerve and knee-joint to be lifted free of the animal.
What does the trigger lead do?
The trigger lead co-ordinates delivery of the stimulus to the muscle with the start of the trace (beam) moving across the oscilloscope screen. Without this lead you would not be able to see the muscle contraction or the compound nerve action potential (CNAP).
What does the isolated stimulator do?
The stimulator can deliver electrical pulses via stimulating electrodes to either the sciatic nerve or the gastrocnemius muscle. Controls allow the stimulus parameters to be varied; voltage (V), duration (ms), frequency (Hz) and number (single or paired stimuli with a variable interval between them).
What do the stimulating electrodes 1 do?
These are used to electrically activate nerve fibres in the sciatic nerve to produce the CNAP.
What is the function of stimulating electrodes 2?
These are used to electrically activate the gastrocnemius muscle directly
What is the function of the recording electrodes?
These are used to record the CNAP of the sciatic nerve evoked by electrical stimulation.
Are the characteristics of the muscle twitch similar in all muscle?
No, the duration of the twitch varies according to the type of muscle in “slow fibres”, the twitch may last over 150ms, whereas in “fast fibres” it may be less than 10ms. Temperature also affects the duration of the twitch contraction.
What is the smallest functional unit of contraction in muscle?
A motor unit. A motor unit comprises a motor neurone and the muscle fibres it innervates. Each motor neurones branches and supplies several muscle fibres: thus activation of one motor neurone will activate several muscle fibres.
Are all motor units comprised of a motor neurone whose branches innervates 5-10 muscle fibres?
No, this may be typical of motor units of muscles concerned with fine graded movements but in large muscles of the leg and back, each motor neurone may innervate 120-170 muscle fibres