AP 151 Lab: Skeletal Muscle Physiology

Flashcards about skeletal muscle physiology.

Where does the motor neuron release acetylcholine (Ach)?

Neuromuscular junction

What is the role of calcium in muscle contraction?

It is an activating signal for the sliding of actin filaments.

From what structure is calcium released to initiate muscle contraction?

Sarcoplasmic reticulum (SR)

What happens to a muscle when calcium is pumped back into the SR?

The muscle relaxes.

Is calcium moving out of the SR into the sarcoplasm an example of passive or active transport?

Passive

Is calcium moving from the sarcoplasm back into the SR an example of passive or active transport?

Active

What is required for skeletal muscle to be stimulated?

An electrical signal from a motor neuron or electric shock

What serves as the signal for muscle contraction?

Calcium released from the sarcoplasmic reticulum (SR)

Who conducted the frog leg experiment in 1780?

Luigi Galvani

What is a muscle twitch?

When a muscle quickly contracts and relaxes after a single electrical shock of sufficient voltage.

What happens to the strength of a muscle twitch as voltage increases?

The strength of the twitch increases up to a maximum.

What are the three phases of a muscle twitch?

Lag (latent) phase, contraction phase, and relaxation phase

What occurs during the lag (latent) phase of a muscle twitch?

Time between the stimulus and the contraction

What occurs during the contraction phase of a muscle twitch?

Calcium (Ca2+) is released from the SR

What occurs during the relaxation phase of a muscle twitch?

Calcium (Ca2+) is pumped back into the SR

What is a motor unit?

A motor neuron and all the muscle fibers it controls

What happens when a motor unit is stimulated?

All the muscle fibers under control of that motor neuron contract together.

What is the result of stimulation of a motor unit?

Weak contraction of the entire muscle

How are muscle fibers arranged within a muscle in relation to motor units?

The muscle fibers in a single motor unit are spread out within the muscle.

What is the purpose of small motor units?

Allow for precise control of force output

What is the purpose of large motor units?

Allow for production of large amounts of force (but not precise control)

What is motor unit recruitment?

A measure of how many motor neurons are activated in a particular muscle.

How does motor unit recruitment affect contraction strength?

The higher the recruitment, the stronger the muscle contraction will be.

How are motor units recruited based on size?

Small motor units are recruited first, and large motor units are recruited last.

What is threshold stimulus?

The minimum voltage that results in a contraction

What does a threshold stimulus stimulate?

The smallest motor unit

What is maximal stimulus?

The minimum voltage that triggers the maximal contraction

What happens when a muscle receives maximal stimulus?

All motor units of a muscle have been recruited.

What is wave summation?

Muscle fibers that are developing tension are stimulated again before the fibers have relaxed.

What is the rationale behind wave summation?

More Ca2+ is released from SR (as opposed to being pumped back to SR), resulting in stronger contraction.

What are two ways to cause a stronger muscle contraction?

Motor unit recruitment and wave summation

What is incomplete tetanus?

Increasing the frequency of electrical shocks decreases the relaxation time between twitches.

What is complete tetanus?

At a certain frequency, there will be no relaxation, resulting in a smooth, sustained contraction.

How does an increase in stimulus frequency affect contraction strength?

Increases contraction strength due to wave summation (increase in quality of muscle fibers).

How does an increase in stimulus intensity affect contraction strength?

Increases contraction strength due to motor unit recruitment (increase in quantity of muscle fibers).

Which two mechanisms do we use when lifting a heavy object?

Motor unit recruitment and wave summation

What is the role of the alpha motor neuron?

It is considered a lower motor neuron that innervates skeletal muscle fibers.

What is the function of the myelin sheath around the alpha motor neuron?

Insulation for faster transmission of electrical signals.

What is the location and function of the dorsal root?

Posterior, sensory

What is the location and function of the ventral root?

Anterior, motor