16 Questions
What is the primary mechanism by which multiple fiber summation occurs?
Recruiting larger motor units as the strength of the signal increases
What is the term for the simultaneous contraction of multiple motor units?
Multiple fiber summation
What is the primary difference between small and large motor units?
Small motor units have less force, while large motor units have more force
What is the result of increasing the frequency of stimulation of a muscle?
Increased muscle contraction force
What is the term for the phenomenon where the strength of muscle contraction increases as the frequency of stimulation increases?
Frequency summation
What is the advantage of asynchronous contraction of motor units?
Smooth contraction, even at low frequencies of nerve signals
What is the primary reason why small motor units are driven first during muscle contraction?
They are driven by small motoneurons, which are more excitable
What is the term for the state of muscle contraction where the muscle contracts maximally, even at low frequencies of stimulation?
Tetanization
What is the term for when successive contractions become so rapid that they fuse together, and the whole muscle contraction appears to be completely smooth and continuous?
Tetanization
At what frequency does the strength of contraction reach its maximum?
At a slightly higher frequency than tetanization
What is the average maximum strength of tetanic contraction of a muscle operating at a normal muscle length?
3-4 kg/cm' of muscle
What is the primary cause of the staircase effect, according to the text?
Release of more and more calcium ions from the sarcoplasmic reticulum
What is the term for the phenomenon where the strength of contraction increases to a plateau after a long period of rest?
Staircase effect
What is the maximum amount of tension that can be applied to the patellar tendon by a quadriceps muscle?
800 pounds/inch²
Why is it possible for muscles to pull their tendons out of their insertions in bone?
Because of the maximum strength of contraction
What is the minimum amount of muscle strength at the onset of contraction after a long period of rest?
One-half of the maximum strength
Study Notes
Muscle Contraction and Strength
- Muscle contraction strength can be increased in two ways: multiple fiber summation and frequency summation
- Multiple fiber summation: increasing the number of motor units contracting simultaneously
- Larger motor units have up to 50 times the contractile force of smaller units
- The size principle: smaller motor units are driven by small motor nerve fibers and are more excitable
- Contraction alternates among motor units, providing smooth contraction even at low frequencies of nerve signals
Frequency Summation and Tetanization
- Frequency summation: increasing the frequency of contraction
- Individual twitch contractions occur one after another at low frequency of stimulation
- As frequency increases, successive contractions become more rapid, and total strength of contraction rises progressively
- At a critical frequency, successive contractions fuse together, appearing as a smooth and continuous contraction (tetanization)
- Maximum strength of contraction reached at a slightly higher frequency
Tetanization and Muscle Strength
- Tetany occurs due to maintained calcium ions in the muscle sarcoplasm between action potentials
- Maximum strength of tetanic contraction averages 3-4 kg/cm² of muscle (50 pounds/inch²)
- A quadriceps muscle can apply up to 800 pounds of tension to the patellar tendon
Changes in Muscle Strength
- The staircase effect (Treppe): strength of contraction increases to a plateau after a long period of rest
- Caused primarily by increasing calcium ions in the cytosol released from the sarcoplasmic reticulum with each successive muscle twitch
This quiz covers the concepts of muscle contraction, tetanization, frequency summation, and multiple fiber summation. It explains how increasing the number of motor units or the frequency of contraction affects overall muscle contraction.
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