Endocrine System: Overview s1

Control of Muscle Tension

To complete this worksheet, select: Module: Support and Movement Activity: Animations Title: Control of Muscle Tension

Introduction

1. Name four factors that determine muscle tension: Sarcomere length, frequency of stimulation, motor unit size and recruitment of motor units.

Sarcomere Length

2. How does the degree of myosin and actin filament overlap affect muscle tension? The degree of overlap between actin and myosin filaments influences muscle tension. Insufficient or excessive overlap of the filaments will result in decreased tension.

3. What is the optimal sarcomere length for skeletal muscle? The greatest tension is developed when there is an optimal amount of overlap.

4. How do overstretched or under-stretched sarcomeres affect contraction force?

Overstretched or understretched sarcomeres develop less contraction force.

5. Overstretched: Explain why muscle contraction weakens if sarcomeres are overstretched. When overstretched the overlap between the myosin and actin myofilaments is reduced. Smaller numbers of crossbridges results in lower muscle tension and weaker contraction.

6. Understretched: Explain why muscle contraction weakens if sarcomeres are understretched. In an understetched sarcomere the ends of the actin myofilaments begin to overlap and hinder one another. The crossbridge formation decreases, muscle tension declines and the contraction force weakens. Twitch and Motor Unit Size

7. a. Define a motor unit.

a group of muscle cells controlled by a single neuron.

b. Define a muscle twitch. a single contraction brought about by a single action potential.

8. What occurs during each of the following stages of a muscle twitch (myogram):

a. Latent Period: a brief period immediately following stimulation where there is no contraction. Here calcium ions are flowing out of the sarcoplasmic reticulum, crossbridges are forming and the elastic components of muscle are being stretched.

b. Contraction Period: Muscle contracts and the fibers shorten.

c. Relaxation Period: Muscle relaxes and the fibers lengthen.

9. a. Describe the motor unit differences between muscles with fine control, like the hands, and muscles like the quadriceps. Muscles involved with fine control have small motor units while those moving large body parts such as the quadriceps have large motor units.

b. Describe how motor unit size affects contraction force.

Twitch contraction force depends on motor unit size. Large motor units produce more tension and greater contraction force than small motor units.

Frequency of Stimulation 10. Define the difference between each of the following:

a. single twitch this represents the muscle response to a single stimulus.

b. wave summation when a muscle responds to a second stimulus before it has completely relaxed from the initial stimulus will result in a stronger contraction.

c. unfused tetanus Successive stimulations of the same intensity at a frequency that does not allow the muscle to completely relax from previous contractions will result in contractions with increasing tension.

d. fused tetanus Rapid, successive stimulations of the same intensity at a frequency that does not allow any degree of muscle relaxation from previous contractions produce a smooth sustained contraction.

Recruitment of Motor Units

11. As the number of motor units increases, so does the force of the muscular contraction. Describe each of the following: a. Threshold stimulus The minimum stimulus intensity necessary to produce a weak muscle tension resulting from the activity of a single motor unit.

b. Submaximal stimulus The intensity of a stimulus necessary to produce a stronger muscle tension resulting from the activity of multiple motor units..

c. Maximum stimulus The intensity of a stimulus necessary to produce the maximum force of the muscle resulting from the activity of all of the muscle’s motor units.

12. How long can a muscle undergo a maximum stimulus? A muscle can contract maximally for a few seconds.

13. Define asynchronous recruitment. Asynchronous recruitment is alternating the contraction of motor units to allow the muscle to sustain contraction for longer periods of time. 14. a. Explain how muscle tone is achieved. This is a firmness in muscles sustained by small groups of alternating contracting motor units. The contractions are not strong enough to produce movement.

b. Why is muscle tone important? What happens if neural damage eliminates muscle tone? Muscle tone maintains muscle strength and keeps the muscle in a state of readiness. If neural damage eliminates muscle tone, then muscle wasting will take place.