Physiology Lab Quiz 3

What does electromyography (EMG) do?

It measures the electrical activity produced by skeletal muscle fibers during activation.

What does an EMG record?

• Motor neuron firing

• Action potentials in muscle fibers

• Motor unit recruitment

• Voltage changes (mV)

• RMS amplitude (mV·s)

❗ Important:

• EMG measures electrical activity, NOT direct muscle force.

• More EMG amplitude = more motor units recruited

What did the shocking lab measure?

• Twitch Response

• Summation & Tetanus

What happens when a stimulus is increased for a twitch response?

• More motor units were recruited

• Twitch amplitude increased

• Response eventually plateaued

What is temporal summation?

• Stimuli delivered closer together

• Muscle doesn’t fully relax

• Force increases

What is an incomplete tetanus?

Partial relaxation between stimuli

What is a complete tetanus?

• No relaxation

• Smooth, sustained contraction

Higher frequency = stronger contraction.

What did the shocking lab measure?

• Twitch Amplitude

• Recruitment

• Summation

• Tetanus

What did the sensory lab measure?

Receptor Function & Sensory Thresholds

Why does twitch amplitude increase with stimulus intensity?

More motor units are recruited.

Who had the fastest nerve response?

Sarah (28)

Highest Conduction Velocity =

Fastest Nerve Response

Who showed the greatest muscle activation?

Ryu (highest RMS) 440-500

What causes tetanus?

High-frequency stimulation preventing relaxation.