16 Questions
What is a characteristic of the contraction of a single skeletal muscle fiber?
It is a brief all-or-none twitch
How does the nervous system produce graded contractions of whole muscles?
By varying the number of muscle fibers that contract and the rate at which muscle fibers are stimulated
What determines the strength of contraction of a whole muscle?
The number of muscle fibers that contract
Why can you voluntarily alter the extent and strength of a muscle's contraction?
Because the nervous system can vary the number of muscle fibers that contract
What is the difference between the contraction of a single skeletal muscle fiber and a whole muscle?
A single muscle fiber contracts all-or-none, while a whole muscle contracts in a graded manner
What happens when a motor neuron produces an action potential?
All the muscle fibers in its motor unit contract
What is the result of recruiting more and more motor neurons?
The force developed by a muscle progressively increases
What is the purpose of alternating activation among motor units in some muscles?
To reduce the length of time any one set of fibers is contracted
What is a characteristic of muscles that hold up the body and maintain posture?
They are almost always partially contracted
What is a motor unit composed of?
A single motor neuron and multiple muscle fibers
What determines the strength of contraction of a motor unit?
The number of muscle fibers in a motor unit
What is the result of a single action potential on muscle fiber?
A twitch lasting about 100 milliseconds or less
What happens when the rate of muscle stimulation increases?
Further summation occurs, resulting in greater tension
What is tetanus in the context of muscle physiology?
A smooth, sustained contraction
What happens when a second action potential arrives before the muscle fiber has completely relaxed?
The two twitches add together, resulting in greater tension
What is the outcome when the rate of stimulation is so high that the muscle fiber cannot relax at all between stimuli?
The muscle enters a state of tetanus
Study Notes
Nervous Control of Muscle Tension
- Contraction of a whole muscle (e.g., biceps) is graded, allowing for varying levels of strength and extent of contraction.
- Graded contractions are achieved by varying the number of muscle fibers that contract and the rate of muscle fiber stimulation.
Motor Units and Recruitment
- A motor unit consists of a single motor neuron and all the muscle fibers it controls.
- When a motor neuron produces an action potential, all muscle fibers in its motor unit contract as a group.
- The strength of the resulting contraction depends on the number of muscle fibers the motor neuron controls.
- Recruitment, or the activation of more motor neurons, increases the force developed by a muscle.
- The number of motor neurons recruited and the size of their motor units determine the level of muscle contraction.
Muscle Contraction and Relaxation
- A single action potential produces a twitch lasting about 100 milliseconds or less.
- Summation occurs when subsequent action potentials arrive before the muscle fiber has completely relaxed, resulting in greater tension.
- As the rate of stimulation increases, further summation occurs.
- At high rates of stimulation, muscle fibers cannot relax between stimuli, resulting in a smooth, sustained contraction called tetanus.
Learn how the nervous system controls muscle tension and contraction. Discover how the number of muscle fibers and stimulation rate affect the strength of muscle contractions.
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