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Nerve and Muscle Physiology

Motor Units and Muscle Contraction Practice Questions

20 free Motor Units and Muscle Contraction practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 20 Medium

A motor unit is best defined as:

  1. A All of the skeletal muscles within a single human limb
  2. B A single isolated skeletal muscle fiber
  3. C A motor neuron and the muscle fibers it innervates
  4. D A group of tendons that connect muscles to bones

Correct answer: A motor neuron and the muscle fibers it innervates

A motor unit consists of a single motor neuron and all the muscle fibers it controls. It is the functional unit of muscle contraction.

Question 2 of 20 Medium

Which type of motor unit is specialized for fine, precise movements?

  1. A Large motor units
  2. B Fast glycolytic units
  3. C Small motor units
  4. D Intermediate units

Correct answer: Small motor units

Small motor units innervate fewer muscle fibers, allowing precise control of movement, such as in the fingers or eyes.

Question 3 of 20 Medium

Which process increases muscle force by activating additional motor units?

  1. A Recruitment
  2. B Temporal summation
  3. C Tetany
  4. D Muscle fatigue

Correct answer: Recruitment

Recruitment increases muscle force by activating more motor units. Larger forces require activation of more units.

Question 4 of 20 Medium

Which principle states that smaller motor units are recruited before larger ones?

  1. A Size principle
  2. B All-or-none principle
  3. C Summation principle
  4. D Muscle fatigue

Correct answer: Size principle

The size principle ensures that smaller motor units are recruited first, providing smooth and controlled increases in muscle force.

Question 5 of 20 Medium

What is temporal summation in muscle contraction?

  1. A Increase in contraction frequency
  2. B Increase in motor units recruited
  3. C Decrease in resting muscle length
  4. D Increase in ATP production

Correct answer: Increase in contraction frequency

Temporal summation occurs when stimuli are delivered in rapid succession, increasing contraction strength by preventing full relaxation.

Question 6 of 20 Medium

Which condition results from sustained, high-frequency stimulation of muscle fibers?

  1. A Twitch
  2. B Fatigue
  3. C Tetany
  4. D Relaxation

Correct answer: Tetany

Tetany is a sustained contraction that occurs when stimuli are frequent enough to prevent relaxation between contractions.

Question 7 of 20 Medium

Which type of muscle fiber is most commonly found in large motor units?

  1. A Fast glycolytic fibers
  2. B Slow oxidative fibers
  3. C Intermediate fibers
  4. D Fast oxidative-glycolytic fibers

Correct answer: Fast glycolytic fibers

Large motor units often consist of fast glycolytic fibers, which generate strong contractions but fatigue quickly.

Question 8 of 20 Medium

Which phase of a muscle twitch involves calcium release?

  1. A Latent period
  2. B Contraction phase
  3. C Relaxation phase
  4. D Rest period

Correct answer: Latent period

The latent period is the time between stimulus and contraction, during which calcium is released from the sarcoplasmic reticulum.

Question 9 of 20 Medium

Which factor determines the strength of a single muscle twitch?

  1. A Total number of motor units activated
  2. B Overall size of the muscle fiber
  3. C Frequency of repeated stimulation
  4. D Intensity of stimulus above threshold

Correct answer: Intensity of stimulus above threshold

In a whole-muscle nerve stimulation experiment, motor axons have varying activation thresholds, so raising the stimulus intensity above threshold recruits progressively more motor units, producing a graded increase in twitch strength up to a maximal stimulus. This is distinct from the all-or-none law, which governs only a single fiber's response to one action potential.

Question 10 of 20 Medium

Which phenomenon occurs when a second stimulus is applied before full relaxation of a muscle?

  1. A Fatigue
  2. B Recruitment
  3. C Inhibition
  4. D Summation

Correct answer: Summation

Summation occurs when a second stimulus increases force because the muscle has not fully relaxed from the first contraction.

Question 11 of 20 Medium

Which property ensures that a muscle fiber either contracts fully or not at all?

  1. A Summation
  2. B Motor unit recruitment
  3. C Muscle fatigue
  4. D All-or-none law

Correct answer: All-or-none law

The all-or-none law states that a muscle fiber responds completely once the threshold is reached.

Question 12 of 20 Medium

Which type of contraction occurs when muscle tension increases but length does not change?

  1. A Isotonic
  2. B Isometric
  3. C Concentric
  4. D Eccentric

Correct answer: Isometric

Isometric contraction generates tension without changing muscle length, such as holding a weight steady.

Question 13 of 20 Medium

Which type of contraction involves muscle shortening while producing force?

  1. A Isometric
  2. B Eccentric
  3. C Concentric
  4. D Isokinetic

Correct answer: Concentric

Concentric contraction occurs when muscle shortens during force production, such as lifting an object.

Question 14 of 20 Medium

Which type of contraction involves muscle lengthening while under tension?

  1. A Isometric
  2. B Concentric
  3. C Eccentric
  4. D Passive

Correct answer: Eccentric

Eccentric contraction occurs when a muscle lengthens while resisting a force, such as lowering a weight.

Question 15 of 20 Medium

Which factor increases muscle force during contraction?

  1. A Reduced motor unit recruitment
  2. B Decreased stimulation frequency
  3. C Increased motor unit recruitment
  4. D Lower intracellular calcium ion levels

Correct answer: Increased motor unit recruitment

Increasing motor unit recruitment activates more muscle fibers, increasing total force production.

Question 16 of 20 Medium

Which mechanism allows graded muscle contractions?

  1. A All-or-none response
  2. B Motor unit recruitment
  3. C Single fiber contraction
  4. D Constant stimulation

Correct answer: Motor unit recruitment

Graded contractions occur by varying the number of motor units recruited and the frequency of stimulation.

Question 17 of 20 Medium

Which type of motor unit is activated last during increasing force demands?

  1. A Small motor units
  2. B Intermediate units
  3. C Large motor units
  4. D All simultaneously

Correct answer: Large motor units

Large motor units are recruited last according to the size principle, contributing to greater force production.

Question 18 of 20 Medium

Muscle fatigue is primarily caused by:

  1. A Increased oxygen supply
  2. B Buildup of metabolic byproducts
  3. C Decreased neurotransmitter release
  4. D Increased mitochondrial density

Correct answer: Buildup of metabolic byproducts

Fatigue results from accumulation of lactic acid, inorganic phosphate, and depletion of energy stores.

Question 19 of 20 Medium

Which event marks the beginning of muscle contraction at the neuromuscular junction?

  1. A Calcium ion release
  2. B Acetylcholine binding
  3. C ATP hydrolysis
  4. D Myosin cross-bridge formation

Correct answer: Acetylcholine binding

Acetylcholine binds to receptors on the muscle membrane, initiating depolarization and contraction.

Question 20 of 20 Medium

Which term describes a single contraction and relaxation cycle of a muscle fiber?

  1. A Tetany
  2. B Twitch
  3. C Summation
  4. D Recruitment

Correct answer: Twitch

A twitch is a single contraction-relaxation cycle in response to a single stimulus.

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