Neurophysiology (Synapse, Action Potential, Tracts, Reflexes) MCQs

Physiology · 74 free questions with answers & explanations.

1. During the absolute refractory period of a nerve action potential, a second stimulus of any strength cannot generate another action potential. This is primarily because:
2. A patient suffers a hemisection of the spinal cord at T6 on the right side (Brown-Séquard syndrome). Which deficit is expected in the left lower limb?
3. The stretch reflex (myotatic reflex) is mediated by which receptor and pathway?
4. Spatial summation at a synapse refers to:
5. Cerebellar lesions produce ipsilateral ataxia because the cerebellum:
6. In a motor neuron receiving thousands of synaptic inputs, temporal summation is occurring. A single presynaptic neuron fires 3 action potentials in rapid succession (50 ms apart). Why does this cause greater depolarization than a single impulse?
7. A patient with a spinal cord injury at T10 shows absent voluntary movement and sensation below the lesion, but has exaggerated deep tendon reflexes in both legs one month after injury. Which mechanism explains the DTR hyperreflexia?
8. A researcher applies a depolarizing current to a node of Ranvier on a myelinated axon. The action potential jumps to the next node 1 mm away in 0.02 ms. Which property of myelin is most directly responsible for this saltatory conduction?
9. The spinothalamic tract (anterolateral system) carries pain and temperature. A patient reports loss of pain sensation in the left arm and right leg simultaneously. Where is the most likely lesion?
10. The NMDA receptor plays a critical role in long-term potentiation (LTP). Which property of the NMDA receptor channel is essential for its role as a 'coincidence detector' in LTP induction?
11. In the descending pain modulation system, periaqueductal grey (PAG) neurons activate raphe-spinal serotonergic and locus coeruleus noradrenergic neurons to inhibit dorsal horn nociception. At the spinal cord, the dominant inhibitory mechanism involves:
12. The Renshaw cell in the spinal cord provides which type of inhibition to alpha motor neurons, and what is its functional significance?
13. A patient with a complete cord lesion at T6 develops spastic paraplegia and exaggerated deep tendon reflexes below the lesion after the initial spinal shock phase. The return of hyperreflexia is best explained by:
14. Long-term potentiation (LTP) at hippocampal synapses requires initial AMPA receptor activation to relieve Mg2+ block from NMDA receptors. Which molecule acts as the 'coincidence detector' in LTP induction?
15. A patient has a Brown-Séquard syndrome at T6 on the right. Which combination of deficits is expected at the level T8 (two segments below the lesion)?
16. Renshaw cells in the spinal cord provide recurrent inhibition to alpha motor neurons via which neurotransmitter, and what is the clinical relevance of this circuit?
17. In the stretch reflex (myotatic reflex), Ia afferents from muscle spindles monosynaptically excite homonymous alpha motor neurons AND disynaptically inhibit antagonist motor neurons. The disynaptic inhibition is mediated by which interneuron?
18. A clinical examination reveals a patient cannot perceive vibration below the waist but has intact pain, temperature, and motor function. Which tract is primarily affected, and where does this tract first decussate?
19. Long-term potentiation (LTP) in the hippocampus requires initial activation of AMPA receptors followed by relief of Mg²⁺ block from which receptor, enabling Ca²⁺ influx as the key trigger for synaptic strengthening?
20. The stretch reflex arc (knee jerk) bypasses interneurons. Which unique anatomical arrangement within the ventral horn explains why the agonist contracts while the antagonist simultaneously relaxes?
21. Renshaw cells in the spinal cord provide recurrent collateral inhibition to α-motor neurons. What neurotransmitter do Renshaw cells use, and which receptor mediates their activation by motor neuron collaterals?
22. In pain transmission, the 'gate control theory' by Melzack and Wall proposes that activation of Aβ fibers inhibits pain. What is the synaptic mechanism in the dorsal horn?
23. The clasp-knife response in upper motor neuron lesions is characterized by initial hypertonicity followed by sudden release at peak stretch. What is the primary neural mechanism responsible for the sudden 'give'?
24. Long-term potentiation (LTP) at hippocampal CA3-CA1 synapses is critical for memory formation. The initial requirement for NMDA receptor activation during LTP induction depends on which co-requirement?
25. A patient with a complete spinal cord lesion at T10 develops autonomic dysreflexia after the period of spinal shock. This is characterized by sudden hypertension triggered by a noxious stimulus below the lesion. The mechanism involves:
26. Ia afferent fibers from muscle spindles make monosynaptic excitatory connections with alpha motor neurons of the same muscle. Simultaneously, they inhibit antagonist muscles through interneurons. What type of interneuron mediates this reciprocal inhibition?
27. A patient presents with loss of pain and temperature sensation in the right upper and lower extremities, with preservation of vibration sense and proprioception on the same side. The lesion is most likely in the:
28. Gamma motor neurons regulate the sensitivity of muscle spindle stretch receptors during active muscle contraction. Which functional consequence results from gamma motor neuron activation concurrent with alpha motor neuron discharge (alpha-gamma coactivation)?
29. NMDA receptors are considered 'coincidence detectors.' Which two simultaneous conditions are required to relieve the Mg²⁺ block and allow ionic current through the NMDA receptor channel?
30. The dorsal column–medial lemniscal pathway carries fine touch and proprioception. Neurons in the nucleus gracilis and nucleus cuneatus (second-order neurons) project to the ventral posterolateral (VPL) nucleus of the thalamus. At which level do these fibers cross the midline?
31. Renshaw cells in the spinal cord provide recurrent inhibition of alpha motor neurons. They are activated by collaterals from the same alpha motor neuron axon and release which inhibitory neurotransmitter, and this circuit serves which functional purpose?
32. A patient with a medullary lesion develops the following deficits: ipsilateral facial numbness (pain and temperature) with contralateral body numbness (pain and temperature), ipsilateral Horner syndrome, hoarseness, and dysphagia. This is Wallenberg (lateral medullary) syndrome. The ipsilateral facial numbness is due to damage to which structure?
33. Long-term potentiation (LTP) at hippocampal Schaffer collateral–CA1 synapses requires NMDA receptor activation and subsequent CaMKII autophosphorylation. CaMKII phosphorylates AMPA receptor subunit GluA1 at Ser831 and drives AMPA receptor insertion. Which aspect of this mechanism is responsible for 'silent synapses' becoming active during LTP?
34. Long-term potentiation (LTP) in hippocampal CA1 neurons requires NMDA receptor activation. The NMDA receptor is considered a 'coincidence detector' because it requires which two simultaneous events for Ca²⁺ entry?
35. The spinocerebellar tracts convey unconscious proprioceptive information to the cerebellum. Which statement correctly distinguishes the dorsal spinocerebellar tract (DSCT) from the ventral spinocerebellar tract (VSCT)?
36. A patient has damage to the lateral corticospinal tract at C5 on the right side. Which pattern of deficits would be expected?
37. Renshaw cell inhibition in the spinal cord is an example of which type of inhibitory circuit, and its major functional purpose is:
38. Long-term potentiation (LTP) in hippocampal CA1 neurons requires coincident pre- and postsynaptic activity. The molecular detector of this coincidence is the NMDA receptor acting as a 'coincidence detector' because:
39. In myasthenia gravis, the fatigable weakness is due to antibody-mediated destruction of nicotinic ACh receptors (nAChRs) at the neuromuscular junction. The electrophysiological finding on repetitive nerve stimulation (RNS) is a decremental response because:
40. The spinocerebellar tracts transmit proprioceptive information to the cerebellum. Regarding the dorsal (posterior) spinocerebellar tract (DSCT) of Clarke's column:
41. Gamma motor neurons regulate muscle spindle sensitivity independently of alpha motor neuron activity. During a voluntary contraction (alpha-gamma coactivation), the role of gamma motor neurons is:
42. A 65-year-old woman with Parkinson's disease has markedly reduced striatal dopamine. The basal ganglia indirect pathway becomes overactive. Tracing the indirect pathway, the sequential consequences of reduced dopamine on the D2-receptor expressing striatal neurons are:
43. Long-term potentiation (LTP) at hippocampal Schaffer collateral synapses requires NMDA receptor activation. The molecular 'coincidence detector' function of the NMDA receptor requires:
44. The stretch reflex (myotatic reflex) is a monosynaptic reflex arc. A patient with an upper motor neuron lesion at T8 shows hyperreflexia of knee and ankle jerks. The mechanism of hyperreflexia after UMN lesion is:
45. Inhibitory post-synaptic potentials (IPSPs) are generated by which mechanism?
46. A patient with a spinal cord lesion at T10 has loss of pain and temperature sensation on the contralateral side beginning 2 segments below the lesion, with preserved ipsilateral proprioception. Which tract is damaged?
47. In the stretch reflex (myotatic reflex), Ib afferents from Golgi tendon organs produce which effect when the muscle is overloaded?
48. Long-term potentiation (LTP) at glutamatergic synapses in the hippocampus requires coincident activity in both pre- and postsynaptic neurons. The molecular 'coincidence detector' that enables this is:
49. A patient sustains a lesion at the level of the right internal capsule posterior limb. The expected combination of deficits on examination is:
50. The Hoffman reflex (H-reflex) is the electrophysiological analog of the monosynaptic stretch reflex. It is elicited by:
51. A 45-year-old presents with ptosis, ophthalmoplegia, and proximal muscle weakness that worsens with repetitive use. EMG shows decremental response at 3 Hz stimulation. Which physiological mechanism explains the EMG finding?
52. The axon hillock has the lowest threshold for action potential generation in a neuron. Which biophysical property accounts for this?
53. A 35-year-old woman presents with unilateral loss of pain and temperature sensation from her right arm, with contralateral (left) loss of proprioception and vibration. MRI shows a lesion in the right side of the cervical spinal cord at C5 level. Which syndrome does this represent, and which tract is ipsilaterally affected for proprioception?
54. During a compound nerve action potential study, a myelinated nerve fiber conducts at 60 m/s. What is the approximate axon diameter of this fiber, and which Erlanger-Gasser classification does it belong to?
55. Synaptic long-term potentiation (LTP) in the hippocampus requires co-activation of AMPA and NMDA receptors. Which of the following correctly explains the 'coincidence detector' function of the NMDA receptor?
56. Long-term potentiation (LTP) in the hippocampus is the cellular basis for learning and memory. The NMDA receptor acts as a 'coincidence detector.' This means:
57. A 70-year-old man develops progressive gait instability described as wide-based with inability to tandem walk, past-pointing on finger-nose test, and scanning dysarthria. Imaging shows atrophy of the vermis and anterior cerebellar lobe. Which specific cerebellar circuit abnormality explains the gait ataxia?
58. Which of the following correctly distinguishes the DIRECT and INDIRECT pathways of the basal ganglia and their roles in movement?
59. During a stretch reflex, muscle spindle Ia afferents synapse monosynaptically on homonymous motor neurons and simultaneously activate Ia inhibitory interneurons that inhibit antagonist motor neurons. This simultaneous facilitation of agonist and inhibition of antagonist is termed reciprocal inhibition. Which is the inhibitory neurotransmitter released by the Ia inhibitory interneuron onto the antagonist motor neuron?
60. Long-term potentiation (LTP) in hippocampal CA1 neurons requires NMDA receptor activation. Which molecular event is the essential gate for NMDA receptor opening that makes LTP coincidence-dependent (Hebbian)?
61. In a neuromuscular junction, the vesicular acetylcholine transporter (VAChT) moves ACh from the cytoplasm into synaptic vesicles. The energy for this transport comes from:
62. The Renshaw cell in the spinal cord provides recurrent inhibition to motor neurons. Which of the following accurately describes this circuit?
63. Long-term potentiation (LTP) at hippocampal CA3-CA1 synapses requires coincident presynaptic and postsynaptic activity. The molecular switch that detects this coincidence is:
64. Long-term potentiation (LTP) in the hippocampus requires activation of NMDA receptors. The NMDA receptor's unique 'coincidence detector' property means it requires both:
65. A patient with a spinal cord injury at C5 is examined 6 months later. The injury is complete (no motor or sensory function below C5). Which reflex would you EXPECT to be PRESENT below the level of the lesion?
66. A patient suffers a complete lesion at the C5 spinal cord level. Which pattern of sensory and motor loss would be expected immediately below the level of injury?
67. The Ia afferent fiber from the muscle spindle synapses on which type of neuron to produce the stretch reflex?
68. Long-term potentiation (LTP) in the hippocampus is the cellular substrate of declarative memory formation. Which molecular sequence is correct for the induction of LTP?
69. Long-term potentiation (LTP) in the hippocampus requires NMDA receptor activation. Which molecular event is the essential gate that allows NMDA receptors to conduct current?
70. A 55-year-old man suffers a stroke affecting the right internal capsule. He develops contralateral (left) upper motor neuron signs including spastic hemiplegia and hyperreflexia. Which specific part of the internal capsule carries the corticospinal (pyramidal) fibres?
71. Ia afferents from muscle spindles terminate monosynaptically on alpha motor neurons to produce the stretch reflex. Which inhibitory interneuron ensures that the antagonist muscle relaxes during this reflex?
72. The absolute refractory period of a neuron corresponds to which phase of the action potential?
73. Inhibition of the Ia afferent synapse onto antagonist motor neurons during a muscle stretch reflex is termed:
74. Long-term potentiation (LTP) at hippocampal synapses requires NMDA receptor activation. The 'Hebbian' property of NMDA receptors that makes them ideal for coincidence detection is: