Nervous Control of Muscle Contraction

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Questions and Answers

What is a characteristic of the contraction of a single skeletal muscle fiber?

It can be graded in strength

It can be voluntarily altered in strength

It is a brief all-or-none twitch (correct)

It can be sustained for a long period of time

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 (correct)

By varying the type of muscle fibers stimulated

By stimulating all muscle fibers simultaneously

By stimulating different muscle groups

What determines the strength of contraction of a whole muscle?

The number of muscle fibers that contract (correct)

The speed at which muscle fibers contract

The type of muscle fibers stimulated

The frequency of muscle fiber stimulation

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 Signup and view all the answers

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 Signup and view all the answers

What happens when a motor neuron produces an action potential?

All the muscle fibers in its motor unit contract Signup and view all the answers

What is the result of recruiting more and more motor neurons?

The force developed by a muscle progressively increases Signup and view all the answers

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 Signup and view all the answers

What is a characteristic of muscles that hold up the body and maintain posture?

They are almost always partially contracted Signup and view all the answers

What is a motor unit composed of?

A single motor neuron and multiple muscle fibers Signup and view all the answers

What determines the strength of contraction of a motor unit?

The number of muscle fibers in a motor unit Signup and view all the answers

What is the result of a single action potential on muscle fiber?

A twitch lasting about 100 milliseconds or less Signup and view all the answers

What happens when the rate of muscle stimulation increases?

Further summation occurs, resulting in greater tension Signup and view all the answers

What is tetanus in the context of muscle physiology?

A smooth, sustained contraction Signup and view all the answers

What happens when a second action potential arrives before the muscle fiber has completely relaxed?

The two twitches add together, resulting in greater tension Signup and view all the answers

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 Signup and view all the answers

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.

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Description

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.