Neurophysiology Practice Questions

Q: Which of the following substances cannot cross the blood-brain barrier?

Large protein molecule. ***Large protein molecule*** - The **blood-brain barrier (BBB)** is formed by tight junctions between endothelial cells, which restrict the passage of large molecules. - Large protein molecules **cannot easily diffuse** across these tight junctions and active transport mechanisms for such molecules are limited. *Glucose* - Glucose is essential for the brain's metabolism and actively crosses the BBB via **glucose transporters (GLUT1)** found on endothelial cells. - This active transport ensures a continuous supply of energy to the brain. *Oxygen* - Oxygen is a **small, lipid-soluble gas** that readily diffuses across the cell membranes of the BBB endothelial cells. - Its passage is crucial for **neuronal aerobic respiration**. *Lipophilic drug* - **Lipid-soluble (lipophilic) drugs** can easily dissolve in the lipid bilayer of the BBB endothelial cells and passively diffuse across the barrier. - This property is often exploited in drug design to target the central nervous system.

Q: Which one of the following phenomena is closely associated with slow-wave sleep?

Sleepwalking. ***Sleepwalking*** - **Sleepwalking** (somnambulism) is a **parasomnia** that typically occurs during **slow-wave sleep (SWS)**, particularly in stages N3. - During SWS, the brain waves are slow, and the body's motor systems can still be active, leading to complex behaviors like walking while asleep. *Dreaming* - While dreams can occur in all sleep stages, **vivid and elaborate dreams** are most strongly associated with **REM (rapid eye movement) sleep**. - Dreams in **SWS** tend to be less vivid, more fragmented, and less emotionally charged. *Atonia* - **Atonia**, or muscle paralysis, is a hallmark feature of **REM sleep**, which prevents individuals from acting out their dreams. - In contrast, **muscle tone is typically maintained** during slow-wave sleep. *Irregular heart rate* - An **irregular heart rate** can be a feature of **REM sleep**, where autonomic nervous system activity is highly variable alongside rapid eye movements. - During **slow-wave sleep**, physiological functions such as heart rate tend to be **slowed and regular**, reflecting deep relaxation.

Q: A 72-year-old woman with insomnia participates in a sleep study. As part of the study protocol, she has EEG leads attached, then goes to sleep. At one point during the evening, 12-16 Hz sleep spindles and K-complexes are observed. Which stage of sleep is associated with this pattern?

Stage 2. ***Stage 2*** - **Sleep spindles** (12-16 Hz bursts) and **K-complexes** (high-amplitude negative deflection followed by a positive component) are the definitive EEG markers of **Stage 2 non-REM sleep**. - This stage represents a deeper level of sleep than Stage 1, where the body begins to relax more, and eye movements cease. *REM* - **REM sleep** is characterized by low-voltage, mixed-frequency EEG activity resembling wakefulness, along with **rapid eye movements** and muscle atonia. - While dreaming is prevalent during REM, **sleep spindles** and **K-complexes** are notably absent. *Stage 1* - **Stage 1 (N1 non-REM sleep)** is the transition from wakefulness to sleep, marked by the disappearance of alpha waves and the appearance of **theta waves** (3-7 Hz). - It does not contain **sleep spindles** or **K-complexes**, which are characteristic of deeper sleep stages. *Stage 3* - **Stage 3 (N3 non-REM sleep)**, commonly known as **deep sleep** or **slow-wave sleep**, is defined by the presence of **delta waves** (0.5-2 Hz) accounting for 20% or more of the EEG. - Although it is a deeper stage of sleep, **sleep spindles** and **K-complexes** are not the primary defining features; **delta wave activity** predominates.

Q: Renshaw cell inhibition is a typical example of inhibition:

Recurrent. ***Recurrent*** - **Renshaw cells** are inhibitory interneurons in the spinal cord that receive excitatory input from **alpha motor neurons** and then in turn inhibit those same alpha motor neurons. - This forms a **negative feedback loop** that is characteristic of recurrent inhibition, helping to regulate motor neuron firing. *Direct* - This typically refers to inhibition where a neuron directly inhibits another neuron without an intermediary, which is not the case for Renshaw cells. - In direct inhibition, the inhibitory neuron forms a synapse directly onto the target cell's dendrites or soma to reduce its excitability. *Indirect* - Indirect inhibition generally involves an excitatory neuron activating an inhibitory interneuron, which then inhibits the target neuron. - While Renshaw cells are interneurons, the key characteristic here is the feedback *to the originating neuron*, which makes it specifically recurrent rather than just generally indirect. *Presynaptic* - **Presynaptic inhibition** occurs when an inhibitory neuron (or another neuron) reduces the amount of neurotransmitter released from the presynaptic terminal of another neuron. - Renshaw cells exert their inhibitory effect postsynaptically on the motor neurons, not by modulating neurotransmitter release from their presynaptic terminals.

Question 1

Which of the following substances cannot cross the blood-brain barrier?

Accepted Answer

Large protein molecule

Answer

Glucose

Answer

Oxygen

Answer

Lipophilic drug

Question 2

Which one of the following phenomena is closely associated with slow-wave sleep?

Accepted Answer

Sleepwalking

Answer

Dreaming

Answer

Atonia

Answer

Irregular heart rate

Question 3

A 72-year-old woman with insomnia participates in a sleep study. As part of the study protocol, she has EEG leads attached, then goes to sleep. At one point during the evening, 12-16 Hz sleep spindles and K-complexes are observed. Which stage of sleep is associated with this pattern?

Accepted Answer

Stage 2

Answer

REM

Answer

Stage 1

Answer

Stage 3

Question 4

Renshaw cell inhibition is a typical example of inhibition:

Accepted Answer

Recurrent

Answer

Presynaptic

Answer

Indirect

Answer

Direct

Neurophysiology — MCQs

Neurophysiology — MCQs

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