Lab 2 – Skeletal Muscle
1. Describe basic setup
a. What was manipulated? Intensity, frequency
b. What was measured? Twitch tensions
c. What concepts were investigated?
i. Frog, sciatic nerve, gastroc,
d. What was investigated?
i. Effects of stimulus frequency and intensity on contraction-the more intensity, the higher the twitch tension. The more freq- the more twitch tension (By ~4.0pps we start to see summation of the twitches and by ~15pps we see no single twitches because the muscle has reached tetanic contraction) ii. Effects of Ach blocker- tubocurare- twitch tension declines. Blocks Ach and no muscle contraction. It is necessary for acetylcholine to bind to receptors in order for sodium ion channels to open and allow an action potential to occur in the muscle which is known as an end plate potential iii. Effects of direct muscle stimulation
2. Expected results
a. Increasing amplitude- increase in twitch tension
b. Increasing frequency- increase in twitch tension
c. Tubocurare- decrease in twitch tension
d. Direct stimulation- The nerve fiber innervates all the muscle fibers, while direct stimulation only connects to several muscle fibers and therefore it needs time to spread out to other muscle fibers.
Also, muscle has a much larger capacitance than nerves, therefore, it takes much higher voltage to get the same muscle tension. Therefore, we can say that, under the same stimulus voltage, muscle tension of direct stimulation is less than that of stimulation of nerve, or conversely, for eliciting same muscle tension, it requires higher voltage for direct stimulation than nerve stimulation.
3. Physiology and general concepts
a. Action potentials- electrode sends electrical signals to the gastrocnemius and causes an action potential to occur
b. Cross-bridge formation- Acetylcholine is a neurotransmitter that binds to its receptors on the motorend plate of the muscle. By binding to the receptor, it causes another action potential in