Muscle Contraction Lab Flashcards
What is (i) passive tension (ii) peak tension (iii) active tension?
(i) baseline tension before the muscle is stimulated to contract; this is the resting tension at that particular muscle length
(ii) the total or peak tension measured at the peak of contraction
(iii) peak tension - active tension
The active tension is the tension generated by the contractile apparatus; (the force generated by cross bridge cycling)
What is responsible for passive resting tension?
Generated from the stretch of the series elastic & the muscle itself due to the length that the muscle is held at
Explain what is meant by ‘active tension’. How is it calculated?
Active tension = the force generated by the interaction of actin and myosin in that ATP-dependent
manner
e.g. the actual generation of force due to the contraction of the sarcomere and not the recoil caused by the material properties of the muscle.
It is calculated from subtracting the passive force
from the total force generated by the muscle
(peak tension - active tension).
Why is it essential to use a muscle such as sartorius to obtain a laser diffraction pattern?
Think about how thick a more defined muscle would be, and whether thicker muscles would generate too
much noise to give a clear picture.
• Why are the spectra obtained from a real muscle different from those obtained with the grating?
Think of the other components of muscle that aren’t the sarcomeres – Nuclei, mitochondria, sarcoplasmic
reticulum, connective tissue etc – All of these factors can scatter light and produce a noisier image than
you’d get with a very uniform glass grating.
How do the mechanical /elastic properties of the muscle influence the contractile response during a
twitch, summation and tetanic contraction?
This relates to the series elastic component of muscle – that elastic, connective tissue that sheaths
every aspect of the muscle and becomes continuous with the tendons.
As the muscle can only exert force on the bone by going through the tendon, it’s considered to be in “series”. For that force to be transmitted to the bone, we have to first stretch the series elastic component.
Does a single twitch do this efficiently?
A tetanic contraction will stretch that series elastic and allow a more efficient transference of force.
What would happen if muscle attached directly to bone?
How much extra tension can be produced during a tetanic contraction as opposed to a single twitch
6/7 times greater
What pattern/frequency of stimulation produces a tetanic contraction?
The frequency of depolarisation means that mycoplasmic calcium levels don’t dip below that “threshold”, so the actin/myosin interaction generates tension in a continual, smooth force.
What pattern/frequency of stimulation produces summation?
Remember that this is due to the muscle being stimulated to contract again before it’s completely relaxed from the previous contraction.
The key thing is to think about the mycoplasmic calcium concentrations and how they oscillate above and below that “threshold” required for contraction.
What is the difference between a concentric isotonic contraction and an eccentric isotonic
contraction?
Concentric means the muscle shortens, eccentric means the muscle lengthens – both whilst generating
force.
What is the difference between an isometric and an isotonic contraction?
ISOTONIC contractions involve a change in the muscle length, maintain the same force as it changes in length. ISOMETRIC contractions involve no change in length with changing force.
If you blocked acetylcholine receptors at the neuromuscular junction, how would normal
contraction (stimulated through nerve activity) be affected? Would a muscle being electrically
stimulated directly be affected?
Muscle contraction caused by electrically stimulating the nerve would be blocked, but if the muscle itself
was electrically stimulated directly it would contract.
