Topic 10: Skeletal Muscle Physiology - Muscle Tension Flashcards
1
Q
What is muscle tension?
A
- force exerted by a muscle or muscle fiber
in lecture, more globular heads tagging on to myofilaments means more tension
2
Q
What is muscle tension determined by?
A
- number of cross bridges formed
3
Q
In a muscle fiber, what is muscle tension affected by? (4)
A
- Frequency of Stimulation
- Fiber length
- Size of Fiber
- Fatigue
4
Q
What are the factors of frequency of stimulation? (4)
A
- Single Stimulus
- Second stimulus arrives before complete relaxation from first
- Rapid sequence of stimuli
4.High frequency of stimuli
5
Q
What happens when you have a single stimulus? (5)
A
- Produces a twitch (a weak contraction and relaxation not normally occurring in skeletal muscles)
- Causes an AP (lasts 1-2 msec)
- Latent period (2 msec) where excitation-contraction coupling occurring
- Contraction period (10-100 msec) increased tension
- Relaxation that decreases tension
6
Q
What happens during the contraction period of a single stimulus? (4)
A
- increased tension
1. Cross bridge attachment and sliding filaments
2. a lot of calcium released from SR on stimulation, but taken back rapidly by SR Ca2+-ATPase so not all myosin heads attach
3. Does not reach maximum possible tension
7
Q
What happens in relaxation of a single stimulus? (2)
A
- calcium pumped into SR
- ATP releases myosin, etc
8
Q
What happens if a 2nd stimulus arrives before complete relaxation from first stimulus? (5)
A
- muscle AP always completed (refractory period) but uptake of calcium by SR is not yet complete (fiber relaxing)
- second stimulus causes release of more calcium, adding to that already in the cytosol
- more myosin heads then attach
- produces second contraction with increased tension, aka wave summation
- this contraction has no refractory period
9
Q
What happens during rapid sequence of stimuli? (2)
A
- tension increases further (increased calcium availability to wave summation)
- partial relaxation between contractions produces quivering, called INCOMPLETE TETANUS
10
Q
What happens during high frequency of stimuli? (2)
A
- no relaxation between contraction (ie. sustained contraction) called COMPLETE TETANUS
- all troponin saturated with calcium and fiber warm (ATP synthesis makes heat) so it works faster
11
Q
Which of the following occurs normally in the body, rapid sequence of stimuli or high frequency of stimuli?
A
high frequency