What is muscle contraction?
It occurs when actin and myosin fibers slide across one another to shorten the sarcomere
What is required for efficient muscle tension?
The actin and myosin proteins must overlap but still have room for movement
What is the optimal length for maximum contraction force?
The optimal length of overlap (around 100% sarcomere length). At this length, myosin heads get a good grip on multiple actin active sites, and the sarcomere still has room to shorten
What happens if a muscle is overstretched (increased length)?
Contraction force is decreased because there is minimal overlap, preventing myosin heads from getting a good grip on actin sites. If it’s too stretched, no cross-bridges form, and tension is zero
What happens if a muscle is tightly compressed (decreased length)?
Contraction force is decreased because cross bridges can form, but the sarcomere has no further room to shorten
What is a myogram?
A recording of the force of a single muscle fiber twitch response over time
What is the Latent Period?
The time between the stimulus application and the onset of muscle contraction. The action potential sweeps the sarcolemma, and calcium ions are released from the sarcoplasmic reticulum
What is the Contraction Period?
The period when tension force increases.Calcium binds to troponin, altering tropomyosin position, exposing cross-bridge binding sites, and allowing cross-bridges to form and sarcomeres to shorten.
What is the Relaxation Period?
The period when tension force decreases.Calcium levels fall as it returns to the sarcoplasmic reticulum, covering the actin binding sites and preventing further cross bridges.
What two factors fine-tune the frequency and intensity of muscle contraction?
1.The number of motor units activated
2.The frequency of stimulation
What is a muscle twitch?
An individual contraction where a muscle fiber has time to fully relax between stimuli
What is Treppe?
A slight increase in force with each successive twitch, even when the muscle fiber is allowed to fully relax
What is Wave Summation?
An increase in force that occurs when a muscle fiber is allowed to partially, but not fully, relax before another stimulus is applied.This is because some calcium remains outside the sarcoplasmic reticulum.
What is Incomplete Tetanus?
The state achieved as stimulation frequency increases, causing force to increase to the maximum level allowed by the muscle’s structure
What is Complete Tetanus?
Occurs when the stimulation frequency is so rapid that the relaxation stage is completely eliminated, and the muscle sustains its maximum tension
Is Complete Tetanus the same as a muscle cramp? Why or why not?
No, Cramping is caused by dehydration, mineral deficiencies, or nerve/blood insufficiencies, not by frequency of stimulation
What is a motor unit?
One motor neuron and all of the muscle fibers it controls
How does motor unit size relate to movement type?
Small units are in muscles requiring precise movements (e.g., fingers, eyes).Large units are in muscles where power is needed (e.g., back, thighs)
What is the nature of a single motor unit’s contraction?
It is an all-or-nothing response; stimulation to threshold stimulates all associated fibers to contract completely
How is increased force generated in a whole muscle?
By recruitment of additional motor units. The overall force increases, but the maximum force of each individual motor unit does not change.
How is muscle tone maintained?
By the activation of alternating motor units in a muscle to maintain posture and body support without fatigue
Isotonic contraction
- muscle length
-tension vs. load
-description/ example
- shortens
- Contraction force is stronger than the load
- Shortening contraction where tension is consistent. ex. lifting a dumbbell
Isotonic Eccentric
- muscle length
-tension vs. load
-description/ example
-Elongates/Lengthens
- Load is greater than the maximum muscle tension
- May lead to overstretching and damage. ex. slowly lowering a dumbbell
Isometric
- muscle length
-tension vs. load
-description/ example
- does not change length
- Tension produced does not exceed the load
- Used to stabilize bones without moving them. Ex. holding a dumbbell steady .
