9.5

Calcium ions diffuse from the sarcoplasmic reticulum into the sarcoplasm. An action potential is propagated to the presynaptic terminal of the motor neuron.

Occur during the lag phase of the muscle twitch

Passive tension is generated by ______.

The elastic components of muscle and surrounding connective tissue

An eccentric contraction is a form of ______ contraction.

Isotonic

The elasticity of muscle and its connective tissue contribute to _____ tension.

Passive

The total tension of a muscle is equal to the ______ of the active and passive tensions.

Sum

Term used to describe a single, brief contraction and relaxation cycle in a muscle fiber

Muscle twitch

Most muscle contractions are

A combination of isometric and isotonic contraction

When a maximal stimulus occurs, action potentials are generated in the axons of ______ of that muscle.

All motor units

Motor unit

All of the muscle fibers innervated by a single motor nerve fiber

Motor unit recruitment

An increase in the number of muscle fibers responding or contracting in order to increase the force produced by a muscle

Increasing recruitment in a muscle, causes the strength of the contraction to _____ by ______.

Increase, increasing the number of muscle fibers contracting

An isotonic contraction in which tension in the muscle increases enough to overcome the opposing resistance, while the muscle shortens is a(n) ______ contraction.

Concentric

A sub-threshold stimulus ______.

Does not cause a contraction

A muscular contraction in which tension is maintained in a muscle, but the opposing resistance is great enough to cause the muscle to increase in length is a(n) ______ contraction.

Eccentric

The muscle fibers lengthen passively. Calcium ions are actively transported back into the sarcoplasmic reticulum. The troponin-tropomyosin complexes move to inhibit cross-bridge formation.

Events that occur during the relaxation phase of the muscle twitch

What are smaller motor units used for?

Fine motor control

Which of the following is true of fine motor control?

Fine motor control requires small motor units

Whole muscles respond to stimuli in a _____ fashion.

Graded

Supra-maximal stimuli...

Have no additional effects on force production than a maximal stimuli.

Which of the following would increase twitch strength in a muscle fiber?

High stimulus frequency

In order to increase the strength of the contraction of a muscle fiber, the stimulus frequency should _______.

Increase

A single muscle fiber twitch

Is very short in duration and contains a contraction + relaxation phase

A supra-maximal stimulus has the same effect as a ______ stimulus.

Maximal

Conditions needed to cause treppe.

Maximal stimuli but at a low frequency

Recruitment occurs when ________ nerve fibers excite more motor units.

More

Which is true?

Most regular muscle contractions are not strictly isotonic or isometric.

All of the muscle fibers innervated by a single nerve fiber constitute a ______.

Motor unit

As a stimulus increases, an increasing number of motor neurons excite an increasing number of motor units. This is called ______.

Multiple motor unit summation

Cccurs when the frequency of action potentials sent to a skeletal muscle fiber increases thereby causing a corresponding increase in the duration of contraction until a period of sustained contraction is reached.

Multiple-wave summation

causes a sustained contraction in a muscle fiber can occur because the relaxation of a muscle fiber is not required before a second action potential can stimulate a second contraction occurs when the frequency of action potentials to a fiber increases causing a corresponding increase in fiber contraction

Occurs in Multiple-wave summation

increasing the number of muscle fibers contracting increasing the number of motor units stimulated

Recruitment increases the amount of force produced by

Stimuli which get progressively _____ and produce action potentials in axons of additional motor units are called sub-maximal stimuli.

Stronger

Name the type of stimuli that become progressively stronger and produce action potentials in axons of additional motor units.

Sub-maximal

A ______ is not strong enough to cause an action potential in any of the axons in a nerve and therefore it does not cause a contraction.

Sub-threshold stimulus

Active tension

The force applied to an object to be lifted when a muscle contracts

Which of the following demonstrates the graded response of whole muscle?

The force generated to lift a feather is much less than the force required to lift a 25-pound weight.

One of the consequences of treppe is the release of heat. Describe the effect that this has.

The heat released increases the activity of enzymes

What is threshold, as applied to muscle physiology?

The minimum voltage necessary to generate an action potential

What occurs when recruitment increases?

The number of fibers contracting increases. The amount of force produced during contraction increases

Events that occur during the lag phase of the muscle twitch

The troponin-tropomyosin complex changes its position and exposes active sites on the actin myofilaments. Sodium ions diffuse into the muscle fiber, causing a local depolarization that exceeds threshold and produces an action potential.

The sum of active and passive

Total tension

Residual calcium in the sarcoplasm can lead to ______.

Treppe

Frequent stimuli can lead to more tension with each stimulus, if all of the calcium has not been recovered by the sarcoplasmic reticulum. This step-like phenomenon is called ______.

Treppe (2)

True or false: A muscle fiber twitch does not last long enough or generate enough tension to perform any work.

True

Multiple-wave summation

can occur because the relaxation of a muscle fiber is not required before a second action potential can stimulate a second contraction causes a sustained contraction in a muscle fiber occurs when the frequency of action potentials to a fiber increases causing a corresponding increase in fiber contraction