1. By: Rebecca Dgien and Alivia Heivly
7-5
By: Rebecca Dgien and Alivia Heivly

2. Sarcomere shortening and muscle fiber stimulation produce tension
Individual muscle cells surrounded and tied together by connective tissue
Tension when muscle cells contract, they pull on collagen fibers, producing an active force
Before Movement can occur:
Applied tension must overcome resistance
Compression a push applied to an object
Muscle cells can only contract
Amount of tension produced by an individual muscle depends on the number of pivoting cross bridges it contains
A passive force that opposes movement

3. Frequency of Muscle Fiber Stimulation
Twitch- single stimulus-contraction-relaxation sequence in a muscle fiber
Duration can be 7.5 msec or 100 msec
Myogram- graph of tension development in muscle fibers during a twitch
Latent Period- starts during stimulation and usually last about 2 sec
Contraction Phase- Tension rises to a peak

4. Summation and Incomplete Tetanus
Summation- addition of one twitch to another
Incomplete Tetanus- Muscle producing almost peak tension during rapid cycles of contraction and relaxation

5. Complete Tetanus
Occurs when the rate of stimulation is increased until the relaxation phase is completely eliminated, producing maximum tension
Action potentials are arriving so fast that the sarcoplasmic reticulum does not have time to reclaim calcium ions

6. Number of Muscle Fibers Activated
Motor Unit- single motor neuron and all the muscle fibers it innervates
Recruitment- activation of more and more motor units
Peak tension production occurs when all motor units in the muscle are contracting in complete tetanus

7. Muscle Tone Motor units within particular muscle are always active
Their contractions tense and firm the muscle
Resting tension in Skeletal muscle
A skeletal muscle that is not regularly stimulated by a motor neuron will atrophy

8. Isotonic and Isometric Contractions
Isotonic Contraction- tension rises and skeletal muscle length changes
Isometric Contraction- muscle as a whole does not change length and tension produced doesn’t ever exceed load

9. Muscle Elongation Following Contraction
Contraction is active, but elongation is passive
After contraction a muscle fiber usually returns to its original length through a combination of elastic forces, the movements of opposing muscles, and gravity
Generated when a muscle fiber contracts and tugs on the flexible extracellular fibers of the endomysium

10. Checkpoint Questions
10. The frequency of motor unit stimulation and number of motor units involved
11. Gross, the greater number of fibers the more powerful contraction
12. Yes, during isometric contraction