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Quiz: Movement: Muscles, Reflexes, and Motor Control

Test your understanding of Chapter 7. Choose the best answer, then click Show Answer to check.

Question 1

What is a motor unit?

  1. A whole muscle together with all of the nerves that reach it
  2. One motor neuron together with all of the muscle fibers it controls
  3. A single muscle fiber together with its actin and myosin filaments
  4. A sensory neuron and a motor neuron that form a reflex loop
Show Answer

The correct answer is B. A motor unit is one motor neuron plus every muscle fiber it connects to; when the neuron fires, all of those fibers contract together. Option A describes a whole muscle, which contains many motor units, not one.

Concept Tested: Motor Unit Bloom's Level: Remember

Question 2

Where is the primary motor cortex?

  1. On the postcentral gyrus of the parietal lobe
  2. In the occipital lobe at the back of the brain
  3. In the cerebellum, under the back of the brain
  4. On the precentral gyrus of the frontal lobe
Show Answer

The correct answer is D. The primary motor cortex is a strip of the frontal lobe on the precentral gyrus, just in front of the central sulcus. The postcentral gyrus (option A) sits just behind the central sulcus and holds the somatosensory cortex, which is why the two are easy to mix up.

Concept Tested: Primary Motor Cortex Bloom's Level: Remember

Question 3

In Parkinson's disease, which neurons are mainly lost?

  1. Dopamine-making neurons in the substantia nigra pars compacta
  2. Acetylcholine-releasing motor neurons in the spinal cord
  3. Neurons of the cerebellum that correct movement errors
  4. Upper motor neurons in the primary motor cortex
Show Answer

The correct answer is A. Parkinson's disease mainly results from the loss of dopamine-making neurons in the substantia nigra pars compacta, which send dopamine to the striatum. Option B describes lower motor neurons, whose loss causes floppy weakness and wasting, not the slowness and rigidity of Parkinson's.

Concept Tested: Substantia Nigra Bloom's Level: Remember

Question 4

During skeletal muscle contraction, what is the main job of calcium released inside the muscle fiber?

  1. It supplies the energy that powers each myosin power stroke
  2. It carries the nerve signal across the neuromuscular junction
  3. It moves tropomyosin aside so myosin can grab actin
  4. It makes each myosin head let go of actin and reset
Show Answer

The correct answer is C. Calcium acts as the "on switch": it shifts the blocking protein tropomyosin and uncovers grip sites on actin so myosin heads can bind and pull. Options A and D describe jobs of ATP, and option B describes acetylcholine.

Concept Tested: Skeletal Muscle Contraction Bloom's Level: Understand

Question 5

Why does activity in the direct pathway of the basal ganglia lead to more movement?

  1. It sends commands straight to the muscles through the spinal cord
  2. It inhibits GPi/SNr, which releases the thalamus from inhibition
  3. It excites the subthalamic nucleus, which then excites the cortex
  4. It releases extra dopamine directly onto the motor cortex
Show Answer

The correct answer is B. GPi/SNr normally act as a brake on the thalamus. The direct pathway inhibits that brake, so the thalamus is released and can excite the motor cortex. This "double negative" is called disinhibition. Option C is wrong because exciting the subthalamic nucleus is part of the indirect pathway, which presses the brake harder.

Concept Tested: Direct and Indirect Pathways Bloom's Level: Understand

Question 6

Why is the knee-jerk (patellar) reflex so fast?

  1. The signal crosses only one synapse in the spinal cord and never has to reach the brain first
  2. The signal travels to the motor cortex at nearly the speed of light
  3. The quadriceps senses the tap and contracts without any nerves involved
  4. The cerebellum predicts the tap and starts the kick ahead of time
Show Answer

The correct answer is A. The stretch reflex is monosynaptic: muscle spindle sensory neurons synapse directly on quadriceps motor neurons in the spinal cord, so the loop is very short. Option C reflects the misconception that muscles act on their own; the muscle contracts only because its motor neuron fires.

Concept Tested: Stretch Reflex Bloom's Level: Understand

Question 7

A 45-year-old man injured a nerve in his right leg. His right thigh muscle is now weak, floppy, and visibly thinner, with small twitches under the skin. His right knee-jerk reflex is absent, and his toes curl down when the sole is stroked. Where is the damage most likely?

  1. Upper motor neurons in the left primary motor cortex
  2. The right side of the cerebellum
  3. The basal ganglia on the left side
  4. Lower motor neurons supplying the right thigh
Show Answer

The correct answer is D. Floppy weakness, muscle wasting, fasciculations, an absent reflex, and no Babinski sign are classic lower motor neuron signs. Damage in the left motor cortex (option A) would also weaken the right leg, but it would cause spasticity, brisk reflexes, and an upgoing toe instead.

Concept Tested: Upper vs Lower Motor Neuron Bloom's Level: Apply

Question 8

A woman with early Parkinson's disease begins taking carbidopa-levodopa, and her movements improve. According to the basal ganglia model in this chapter, what most likely changed in her brain?

  1. GPi/SNr became more active, putting a stronger brake on the thalamus
  2. Dopamine from the medicine crossed into the brain directly from the blood
  3. Her brain made more dopamine, strengthening the direct pathway and weakening the indirect pathway
  4. Her lost substantia nigra neurons grew back and began firing again
Show Answer

The correct answer is C. The brain converts levodopa into dopamine, which excites the direct (GO) pathway and inhibits the indirect (NO-GO) pathway, weakening the brake on the thalamus. Option B is wrong because dopamine itself can't easily cross the blood-brain barrier, which is why levodopa is used. Option D is wrong because levodopa does not replace lost neurons.

Concept Tested: Levodopa Bloom's Level: Apply

Question 9

A 58-year-old woman has trouble buttoning her shirt with her left hand. When she reaches for her nose, her left hand overshoots and shakes more as it gets close. She walks with a wide, unsteady gait. Her strength and reflexes are normal. Where is the problem most likely?

  1. The left side of the cerebellum
  2. The right side of the cerebellum
  3. The basal ganglia on the left side
  4. The right primary motor cortex
Show Answer

The correct answer is A. Overshooting (dysmetria), a tremor that worsens near the target (intention tremor), and a wide unsteady gait point to the cerebellum, and cerebellar damage affects the same side of the body. Option B is the common mistake of applying the motor cortex's opposite-side rule to the cerebellum.

Concept Tested: Cerebellar Coordination Bloom's Level: Analyze

Question 10

For Parkinson's disease, deep brain stimulation electrodes are placed in the subthalamic nucleus (STN) or the internal globus pallidus (GPi). Which reasoning best explains why these targets make sense?

  1. The STN and GPi are where dopamine is made, so stimulating them refills dopamine
  2. In the classic model, the STN and GPi help create the too-strong brake on the thalamus, so changing their activity can ease it
  3. The STN and GPi are in the spinal cord, where they connect directly to leg muscles
  4. The STN and GPi are where the corticospinal tract crosses to the other side
Show Answer

The correct answer is B. With too little dopamine, the indirect pathway releases the STN, which excites GPi, and the GPi/SNr brake on the thalamus becomes too strong. DBS at these nodes changes that abnormal activity. Option A is wrong because dopamine is made in the substantia nigra pars compacta, not the STN or GPi.

Concept Tested: Deep Brain Stimulation Bloom's Level: Analyze