Practice Section 3: Motor Units And Muscle Contraction (4.4) - Chapter 4: Movement Analysis
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Section 3: Motor Units and Muscle Contraction

Practice - Section 3: Motor Units and Muscle Contraction

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Practice Questions

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Question 1 Easy

What makes up a motor unit?

  • Answer: A motor neuron and all the muscle fibers it innervates/controls.
  • Hint: Consider the two main biological components that bridge the nervous and muscular systems.

💡 Hint: Consider the two main biological components that bridge the nervous and muscular systems.

Question 2 Easy

What is the primary function of a motor neuron within this unit?

  • Answer: To transmit electrical impulses (action potentials) from the central nervous system to the muscle fibers to trigger contraction.
  • Hint: Think about the neuron's role as a "messenger" or "trigger."

💡 Hint: Think about the neuron's role as a "messenger" or "trigger."

4 more questions available

Interactive Quizzes

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Question 1

What comprises a motor unit?

  • Type: mcq
  • Options: Only a muscle fiber, A motor neuron and its innervated muscle fibers, Only a motor neuron, A sensory neuron and muscle fibers
  • Correct Answer: A motor neuron and its innervated muscle fibers
  • Explanation: A motor unit is the functional unit of skeletal muscle, including the single neuron and every fiber it stimulates.
  • Hint: It must include both the "controller" and the "performers."
Only a muscle fiber
A motor neuron and its innervated muscle fibers
Only a motor neuron
A sensory neuron and muscle fibers * **Correct Answer**: A motor neuron and its innervated muscle fibers * **Explanation**: A motor unit is the functional unit of skeletal muscle
including the single neuron and every fiber it stimulates. * **Hint**: It must include both the "controller" and the "performers."

💡 Hint: It must include both the "controller" and the "performers."

Question 2

True or False: Larger motor units are primarily involved in fine motor control and high-precision tasks.

  • Type: boolean
  • Options: True, False
  • Correct Answer: False
  • Explanation: Larger motor units are activated for power and strength; small motor units are required for fine control.
  • Hint: Think about whether you use your thigh muscles or your finger muscles to thread a needle.
True
False * **Correct Answer**: False * **Explanation**: Larger motor units are activated for power and strength; small motor units are required for fine control. * **Hint**: Think about whether you use your thigh muscles or your finger muscles to thread a needle.

💡 Hint: Think about whether you use your thigh muscles or your finger muscles to thread a needle.

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Challenge Problems

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Challenge 1 Hard

Analyze the "All-or-None" Law in the context of motor units. If a motor neuron reaches its threshold and fires, but the muscle needs to lift a very light weight, can the neuron signal only half of its muscle fibers to contract?

  • Solution: No. According to the All-or-None Law, once the motor neuron fires, all muscle fibers in that specific motor unit will contract at 100% capacity. To lift a lighter weight, the body does not reduce the force of a single unit; instead, it recruits fewer total motor units.
  • Hint: Think of a light switch—it is either on or off for every bulb connected to that circuit.

💡 Hint: Think of a light switch—it is either on or off for every bulb connected to that circuit.

Challenge 2 Hard

Discuss how a neuromuscular disease like ALS (which causes motor neuron death) would affect the "recruitment" process.

  • Solution: As motor neurons die, the muscle fibers they once controlled are left "orphaned." If neighboring neurons try to compensate by adopting these fibers, the motor units become larger and less precise. This leads to a loss of fine motor control and, eventually, as recruitment fails, significant muscle weakness and atrophy.
  • Hint: Consider what happens when the "coach" is missing—the "players" cannot receive the signal to play.

💡 Hint: Consider what happens when the "coach" is missing—the "players" cannot receive the signal to play.

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Reference links

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