Neurology, MBBS Second Year. This chapter is split into 4 topics and has
151 practice questions. The topics covered are listed below, followed by
10 free sample questions from the chapter.
Sample questions: NN 34. Stretch Reflex – Muscle Spindle
10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.
Q1. Which statement best contrasts extrafusal and intrafusal fibers regarding attachment?
A. Neither fiber type is associated with bone
B. Intrafusal fibers attach to tendons while extrafusal fibers are free
C. Both fiber types attach directly to tendons
D. Extrafusal fibers attach to tendons, whereas intrafusal fibers do not connect to tendons and instead have proprioceptors(correct answer)
Answer: D.Extrafusal fibers are attached to the tendon, which is attached to bone, so that contraction produces movement. Intrafusal fibers do not connect to tendons but instead contain proprioceptors and are encapsulated as muscle spindles.
Q2. Because muscle spindles run parallel to the extrafusal fibers, stretching the whole muscle:
A. Also stretches the spindle and its sensory endings(correct answer)
B. Bypasses the spindle entirely
C. Shortens the spindle
D. Has no effect on the intrafusal fibers
Answer: A.Intrafusal fibers are encapsulated in sheaths forming muscle spindles that run parallel to the extrafusal fibers, so a stretch applied to the muscle also stretches the intrafusal fibers and their sensory endings.
Q3. If intrafusal fibers could no longer sense stretch, the muscle would lose the ability to:
A. Receive alpha motor innervation
B. Detect the degree of stretch and the velocity of the muscle(correct answer)
C. Attach to the tendon
D. Generate any force at all
Answer: B.Intrafusal proprioceptors are the structures that pick up length and velocity; without them the muscle loses this sensory information, though force generation by extrafusal fibers (alpha innervated) is unaffected.
Q4. The very large diameter of group 1a fibers is physiologically important because it:
A. Makes them efferent fibers
B. Prevents action potential generation
C. Allows the fastest possible conduction of stretch information toward the spinal cord(correct answer)
D. Reduces the sensitivity of the muscle spindle
Answer: C.Group 1a fibers are among the largest nerves in the body and thus have among the fastest conduction velocities, which is important because they carry information about a rapidly changing stimulus such as stretch.
Q5. After gamma motor neuron firing, which ion enters the neuron?
A. Potassium
B. Calcium
C. Chloride
D. Sodium(correct answer)
Answer: D.The sequence is: acetylcholine release, sodium ions enter the neuron, an action potential is generated, the sarcoplasmic reticulum is activated, calcium is pushed out and binds to the cross bridge, inducing stretching.
Q6. Which is the correct order of events after a gamma motor neuron is stimulated?
Answer: D.The note gives the sequence as: acetylcholine release, sodium ions enter the neuron, action potential is generated, the sarcoplasmic reticulum is activated, calcium is pushed out and binds to the cross bridge, inducing stretching.
Q7. Why does the gamma motor neuron cascade culminate in stretching rather than contraction of the extrafusal muscle?
A. Because gamma motor neurons do not innervate extrafusal fibers; they act on intrafusal fibers and set their length(correct answer)
B. Because sodium does not enter the neuron
C. Because calcium is never released
D. Because acetylcholine is inhibitory at this site
Answer: A.Gamma motor neurons innervate the intrafusal fibers only; alpha motor neurons are the ones that act on extrafusal fibers. Gamma activity therefore stretches the spindle machinery rather than producing movement directly.
Q8. Place the following sensory events in the correct order: 1) threshold potential is reached, 2) mechanically gated channels open, 3) an action potential is generated, 4) sodium enters the cell.
A. 2, 1, 4, 3
B. 2, 4, 1, 3(correct answer)
C. 4, 2, 1, 3
D. 1, 2, 4, 3
Answer: B.Mechanically gated channels open, sodium enters, the membrane becomes more positive and moves from resting membrane potential to threshold potential, and only then do voltage-gated channels open to generate the action potential.
Q9. In the intrafusal monosynaptic reflex, the sensory fibers from the stretched spindle synapse with:
A. The tendon itself
B. Type 1b fibers of the tendon
C. Only the dorsal root ganglion
D. The gamma motor neuron of the quadriceps or an inhibitory interneuron that inhibits the hamstring intrafusal fibers(correct answer)
Answer: D.In the intrafusal reflex the afferents synapse with either the gamma motor neuron, which stimulates the intrafusal fibers of the quadriceps, or with an inhibitory interneuron that inhibits the intrafusal fibers of the hamstrings.
Q10. Gamma motor neuron firing is increased during a precise task such as threading a needle. Which spindle property changes?
A. Spindle sensitivity to stretch decreases
B. The spindle stops sending information
C. Spindle sensitivity to stretch increases(correct answer)
D. The spindle changes to detecting tension
Answer: C.Gamma drive tightens the intrafusal fibres, which raises spindle sensitivity (the fusimotor set-point). Standard knowledge (beyond the note): fusimotor control of spindle sensitivity, as noted in the UMN/LMN note.