Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 361: Which of the following statements regarding memory is FALSE?

A. Structural changes occur in synapses during the development of long-term memory.
B. Short-term memory lasts as long as the person continues to think about it.
C. The primary site for the storage of long-term memory is the temporal lobe. (Correct Answer)
D. Bilateral loss of hippocampal function leads to the inability to encode recent events into long-term memory.

Explanation: **Explanation:** **1. Why Option C is the correct (False) statement:** While the temporal lobe (specifically the hippocampus and entorhinal cortex) is critical for the **processing and consolidation** of short-term memory into long-term memory, it is not the primary storage site. Long-term memories are widely distributed throughout the **cerebral cortex** (neocortex). For example, visual memories are stored in the occipital cortex, and language-related memories in the linguistic areas. Therefore, the statement that the temporal lobe is the "primary storage site" is physiologically incorrect. **2. Analysis of other options:** * **Option A (True):** Long-term memory involves **structural changes** (Long-Term Potentiation), including an increase in vesicle release sites, the number of transmitter vesicles, and the number of presynaptic terminals. * **Option B (True):** Short-term memory (working memory) is maintained by **reverberating neural circuits**. As long as the individual focuses on the information (rehearsal), the circuit remains active. * **Option D (True):** The hippocampus is essential for **anterograde consolidation**. Bilateral destruction results in the inability to form new long-term memories (Anterograde Amnesia), though remote past memories remain intact. **Clinical Pearls for NEET-PG:** * **Anterograde Amnesia:** Inability to form new memories (Hippocampal lesion). * **Retrograde Amnesia:** Inability to recall past memories (often seen in thalamic lesions or diffuse cortical trauma). * **Korsakoff’s Psychosis:** Characterized by anterograde amnesia and **confabulation** (filling memory gaps with fabrications), typically due to Thiamine (B1) deficiency affecting the mammillary bodies. * **Alzheimer’s Disease:** Early stages primarily affect the hippocampus, leading to loss of short-term memory first.

Question 362: Slow wave sleep is also known as which of the following?

A. REM sleep
B. NREM sleep (Correct Answer)
C. Both REM and NREM sleep
D. None of the above

Explanation: **Explanation:** Sleep is physiologically divided into two main stages: **Non-Rapid Eye Movement (NREM) sleep** and **Rapid Eye Movement (REM) sleep**. **Why NREM sleep is the correct answer:** NREM sleep is characterized by a progressive slowing of brain wave frequencies on an Electroencephalogram (EEG). It consists of three stages (N1, N2, and N3). Stage N3 is specifically characterized by high-amplitude, low-frequency **delta waves** (0.5–4 Hz). Because the overall brain activity is synchronized and slow compared to the waking state, the entire NREM phase is collectively referred to as **Slow Wave Sleep (SWS)**. During this phase, heart rate, blood pressure, and respiratory rate decrease, and the body undergoes restorative processes. **Why other options are incorrect:** * **REM sleep:** Also known as **Paradoxical Sleep** or **Desynchronized Sleep**. The EEG during REM shows high-frequency, low-voltage activity (beta-like waves) similar to an awake state, despite the person being in deep sleep with muscle atonia. * **Both REM and NREM:** These are distinct physiological states with opposing EEG patterns (synchronized vs. desynchronized); therefore, they cannot both be classified as slow wave sleep. **High-Yield Clinical Pearls for NEET-PG:** * **Growth Hormone:** Secretion peaks during Stage N3 (Slow Wave Sleep). * **Parasomnias:** Sleepwalking (somnambulism), sleep terrors, and bedwetting (enuresis) typically occur during **Stage N3 (NREM)**. * **Nightmares:** These occur during **REM sleep**, unlike night terrors. * **PGO Spikes:** (Pontine-Geniculate-Occipital) waves are the hallmark of the onset of REM sleep.

Question 363: All of the following are inhibitory neurotransmitters except one?

A. Acetylcholine
B. Glutamate (Correct Answer)
C. Norepinephrine
D. Glycine

Explanation: **Explanation:** The primary classification of neurotransmitters is based on their effect on the post-synaptic membrane: **Excitatory** (causing depolarization via cation influx) or **Inhibitory** (causing hyperpolarization via anion influx or potassium efflux). **Why Glutamate is the Correct Answer:** **Glutamate** is the primary and most potent **excitatory neurotransmitter** in the mammalian Central Nervous System (CNS). It acts on receptors such as NMDA, AMPA, and Kainate, which open cation channels (Na⁺ and Ca²⁺), leading to an Excitatory Post-Synaptic Potential (EPSP). Therefore, it is not an inhibitory neurotransmitter. **Analysis of Other Options:** * **Glycine:** This is the major **inhibitory** neurotransmitter in the **spinal cord** and brainstem. It increases Cl⁻ conductance, leading to hyperpolarization. * **GABA (Gamma-Aminobutyric Acid):** Though not listed as an option, it is the major inhibitory neurotransmitter in the **brain**. * **Acetylcholine & Norepinephrine:** These are often "mixed" or "modulatory" neurotransmitters. However, in the context of standard NEET-PG questions, if a choice must be made against a purely excitatory molecule like Glutamate, these are categorized by their inhibitory roles in specific locations (e.g., Acetylcholine is inhibitory to the heart via M2 receptors; Norepinephrine can have inhibitory effects via alpha-2 receptors). **High-Yield Clinical Pearls for NEET-PG:** * **Strychnine:** Acts by competitively inhibiting Glycine receptors, leading to massive muscle spasms. * **Excitotoxicity:** Excessive Glutamate release is linked to neuronal death in stroke and ALS. * **Ketamine:** Acts as an antagonist at the NMDA (Glutamate) receptor. * **Riluzole:** A drug used in ALS that inhibits glutamate release.

Question 364: What is the earliest reflex to reappear after spinal shock?

A. Knee jerk
B. Ankle jerk
C. Bulbocavernous reflex (Correct Answer)
D. Abdominal reflex

Explanation: **Explanation:** **Spinal shock** is a clinical state following acute complete transection of the spinal cord, characterized by the temporary loss of all neurological activity (motor, sensory, and autonomic) below the level of the lesion. As the spinal cord recovers and becomes "hyper-irritable" due to denervation supersensitivity, reflexes return in a predictable chronological sequence. **Why Bulbocavernous Reflex is Correct:** The **Bulbocavernous reflex (S2-S4)** is consistently the **earliest reflex to reappear**, typically within 24 to 48 hours after the injury. It involves contraction of the anal sphincter in response to squeezing the glans penis or tugging on an indwelling Foley catheter. Its reappearance marks the **end of the spinal shock phase**. **Analysis of Incorrect Options:** * **Knee jerk (L2-L4) and Ankle jerk (S1-S2):** These are deep tendon reflexes (monosynaptic). While they were historically thought to return first, clinical studies confirm they reappear after the bulbocavernous reflex, often days to weeks later. * **Abdominal reflex (T7-T12):** This is a superficial polysynaptic reflex. Superficial reflexes are generally the last to return and may remain permanently absent in upper motor neuron lesions. **NEET-PG High-Yield Pearls:** 1. **Sequence of Return:** 1. Bulbocavernous reflex (Earliest) → 2. Polysynaptic reflexes (e.g., Flexor withdrawal) → 3. Monosynaptic reflexes (Deep tendon reflexes) → 4. Hyperreflexia/Spasticity (Latest). 2. **Clinical Significance:** The absence of the bulbocavernous reflex in a patient with paralysis suggests spinal shock; if the reflex is present but the patient is still paralyzed, it indicates a **complete spinal cord injury** rather than shock. 3. **First sign of recovery:** Often cited as the return of the **Flexor Withdrawal Reflex** (specifically the slight contraction of the hamstrings).

Question 365: Which EEG rhythm has the lowest frequency?

A. Alpha
B. Beta
C. Delta (Correct Answer)
D. Theta

Explanation: **Explanation:** Electroencephalogram (EEG) rhythms are classified based on their frequency (measured in Hertz, Hz) and amplitude. The frequency of these waves is inversely proportional to the level of cortical activity and alertness. **1. Why Delta is the Correct Answer:** **Delta waves** have the **lowest frequency (0.5 – 4 Hz)** and the highest amplitude. They represent the most synchronized brain activity. In adults, they are the hallmark of **Stage 3 Non-REM (Deep/Slow-wave) sleep**. Their presence in an awake adult is always pathological, indicating generalized encephalopathy or deep midline lesions. **2. Analysis of Incorrect Options:** * **Theta (4 – 7 Hz):** These are the second slowest waves. They are normal in children and in adults during drowsiness or Stage 1 sleep. * **Alpha (8 – 13 Hz):** These are moderate-frequency waves seen in a relaxed, awake state with **eyes closed**. They are most prominent in the occipital region and disappear (alpha block) upon opening the eyes or mental concentration. * **Beta (13 – 30 Hz):** These have the **highest frequency** and lowest amplitude. They are seen during active thinking, mental concentration, or states of high alertness (desynchronized rhythm). **3. NEET-PG High-Yield Clinical Pearls:** * **Mnemonic for Frequency (Highest to Lowest):** **B**eta > **A**lpha > **T**heta > **D**elta (**B**at **A**nd **T**he **D**og). * **Alpha Block (Berger Effect):** The replacement of alpha rhythm by beta rhythm when eyes are opened. * **Sleep Spindles & K-complexes:** Characteristic features of **Stage 2 NREM sleep**. * **Sawtooth waves:** Characteristic of **REM sleep**. * **Drug Effect:** Benzodiazepines and Barbiturates typically increase Beta activity.

Question 366: Which of the following is an inhibitory amino acid?

A. Glutamate
B. Aspartate
C. Glycine (Correct Answer)
D. Somatostatin

Explanation: ### Explanation **Correct Answer: C. Glycine** **Reasoning:** Neurotransmitters in the central nervous system (CNS) are broadly categorized as excitatory or inhibitory. **Glycine** is the primary **inhibitory amino acid neurotransmitter** in the **spinal cord** and brainstem. It acts by binding to ionotropic receptors that open chloride ($Cl^-$) channels. The influx of negatively charged chloride ions causes hyperpolarization of the postsynaptic membrane, resulting in an Inhibitory Postsynaptic Potential (IPSP), which makes the neuron less likely to fire. **Analysis of Incorrect Options:** * **A & B. Glutamate and Aspartate:** These are the primary **excitatory** amino acid neurotransmitters in the CNS. Glutamate is the most abundant excitatory neurotransmitter in the brain, acting on NMDA, AMPA, and Kainate receptors to cause depolarization. * **D. Somatostatin:** While somatostatin has inhibitory functions (such as inhibiting growth hormone and insulin release), it is a **neuropeptide**, not an amino acid. **High-Yield Clinical Pearls for NEET-PG:** * **GABA vs. Glycine:** GABA is the major inhibitory neurotransmitter in the **brain**, whereas Glycine is the major inhibitory neurotransmitter in the **spinal cord**. * **Strychnine Poisoning:** Strychnine is a lethal alkaloid that acts as a competitive **antagonist of glycine receptors**. By blocking inhibition, it leads to unchecked excitatory activity, resulting in severe convulsions and "opisthotonus" (spinal arching). * **Renshaw Cells:** These are inhibitory interneurons in the spinal cord that utilize **Glycine** to provide negative feedback to alpha motor neurons (recurrent inhibition). * **Dual Role:** Interestingly, Glycine also acts as an obligatory **co-agonist** with Glutamate at the excitatory **NMDA receptor** in the brain.

Question 367: During a typical 7-hour sleep duration, which stage of sleep do adults spend the maximum amount of time in?

A. Stage 1 NREM
B. Stage 2 NREM (Correct Answer)
C. Stage 3 NREM
D. REM sleep

Explanation: **Explanation:** Sleep is divided into two main types: **Non-Rapid Eye Movement (NREM)** and **Rapid Eye Movement (REM)** sleep. In a healthy adult, NREM sleep accounts for approximately 75–80% of the total sleep cycle, while REM accounts for the remaining 20–25%. **Why Stage 2 NREM is Correct:** Stage 2 NREM (Light Sleep) is the longest phase of the sleep cycle. In a typical 7-hour sleep duration, an adult spends approximately **45–55%** of their total sleep time in this stage. It is characterized electroencephalographically (EEG) by the presence of **Sleep Spindles** and **K-complexes**. **Analysis of Incorrect Options:** * **Stage 1 NREM:** This is the transition phase between wakefulness and sleep. it is the shortest NREM stage, accounting for only **5%** of total sleep. * **Stage 3 NREM:** Also known as Slow Wave Sleep (SWS) or Deep Sleep, characterized by Delta waves. It accounts for about **15–20%** of sleep time and predominates in the first third of the night. * **REM Sleep:** Characterized by "paradoxical" EEG activity (beta-like waves) and muscle atonia. It accounts for **20–25%** of sleep. While REM periods lengthen as the night progresses, the cumulative time remains significantly less than Stage 2. **High-Yield Clinical Pearls for NEET-PG:** * **EEG Landmarks:** Stage 2 is defined by Sleep Spindles (12-14 Hz) and K-complexes. * **Bruxism (Teeth Grinding):** Occurs predominantly in Stage 2 NREM. * **Deep Sleep Disorders:** Sleepwalking (Somnambulism) and Night Terrors occur during **Stage 3 NREM**. * **Nightmares:** Occur during **REM sleep**. * **Ponto-Geniculo-Occipital (PGO) spikes:** These are the earliest signals of the transition from NREM to REM sleep.

Question 368: In the brain, which cells are responsible for converting glutamate to glutamine?

A. Oligodendrocytes
B. Astrocytes (Correct Answer)
C. Ependymal cells
D. Microglia

Explanation: ### Explanation The correct answer is **Astrocytes**. This process is a critical component of the **Glutamate-Glutamine Cycle**, which prevents excitotoxicity in the central nervous system (CNS). **Why Astrocytes are correct:** Glutamate is the primary excitatory neurotransmitter in the brain. After its release into the synaptic cleft, it must be rapidly removed to prevent overstimulation of neurons. Astrocytes take up excess glutamate via excitatory amino acid transporters (EAATs). Inside the astrocyte, the enzyme **Glutamine Synthetase** converts glutamate into **glutamine**, a non-toxic, electrochemically neutral amino acid. This glutamine is then transported back to neurons, where it is converted back into glutamate by the enzyme *glutaminase*, completing the cycle. **Why the other options are incorrect:** * **Oligodendrocytes:** These cells are responsible for the myelination of axons in the CNS. They do not play a primary role in the metabolic recycling of glutamate. * **Ependymal cells:** These ciliated epithelial cells line the ventricles of the brain and the central canal of the spinal cord, primarily aiding in the production and circulation of Cerebrospinal Fluid (CSF). * **Microglia:** These are the resident macrophages of the CNS. Their primary role is immune surveillance and phagocytosis, not neurotransmitter metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperammonemia:** In liver failure (Hepatic Encephalopathy), excess ammonia crosses the blood-brain barrier. Astrocytes use this ammonia to convert glutamate to glutamine. The resulting accumulation of glutamine causes osmotic swelling of astrocytes, leading to **cerebral edema**. * **Marker:** Glial Fibrillary Acidic Protein (GFAP) is a specific intermediate filament used as a marker for astrocytes. * **Blood-Brain Barrier (BBB):** Astrocytes contribute to the integrity of the BBB via their "foot processes."

Question 369: What is the root value of the supinator jerk?

A. C3C4
B. C4C5
C. C5C6 (Correct Answer)
D. C8T1

Explanation: **Explanation:** The **supinator jerk** (also known as the brachioradialis reflex) is a deep tendon reflex elicited by tapping the distal end of the radius. This stretch reflex primarily tests the **C5 and C6 nerve roots** via the radial nerve. **Why C5C6 is Correct:** The brachioradialis muscle is innervated by the radial nerve. The primary spinal segments responsible for this motor output are C5 and C6. When the tendon is struck, the sensory impulse travels to these spinal levels, and the resulting motor response causes flexion and slight supination of the forearm. **Analysis of Incorrect Options:** * **C3C4:** These roots primarily contribute to the **phrenic nerve** (diaphragm) and sensory innervation of the neck and upper shoulder. They do not mediate any major limb reflexes. * **C4C5:** While C5 is involved in the supinator and biceps jerks, C4 is not a primary component of these distal limb reflexes. * **C8T1:** These roots form the lower trunk of the brachial plexus and mediate the **finger jerk** (C8) and the intrinsic muscles of the hand. **High-Yield Clinical Pearls for NEET-PG:** * **Inverted Supinator Jerk:** A crucial clinical sign where tapping the radius results in finger flexion instead of elbow flexion. This indicates a **C5-C6 cord lesion** (lower motor neuron lesion at C5-C6) with an associated upper motor neuron lesion affecting levels below (hyperreflexia of C8-innervated finger flexors). * **Reflex Quick-Reference:** * Biceps Jerk: C5, C6 (Musculocutaneous nerve) * Supinator Jerk: C5, C6 (Radial nerve) * Triceps Jerk: C7, C8 (Radial nerve) * Knee Jerk: L2, L3, L4 (Femoral nerve) * Ankle Jerk: S1, S2 (Tibial nerve)

Question 370: Which of the following statements about the blood-brain barrier is false?

A. There are gaps between tight junctions at the active sites. (Correct Answer)
B. There are no gaps between active sites.
C. There is less activity in the membrane.
D. Fibronectin provides a barrier for diffusion.

Explanation: **Explanation:** The **Blood-Brain Barrier (BBB)** is a highly selective semipermeable border that separates the circulating blood from the brain extracellular fluid. **Why Option A is the Correct (False) Statement:** The hallmark of the BBB is the presence of **continuous tight junctions (zonula occludens)** between the endothelial cells of the brain capillaries. Unlike peripheral capillaries, there are **no gaps or fenestrations** between these cells. These tight junctions create a high electrical resistance barrier that prevents the paracellular movement of polar molecules and macromolecules. Therefore, stating there are "gaps" is physiologically incorrect. **Analysis of Other Options:** * **Option B:** This is a true statement. The absence of gaps ensures that substances must pass *through* the cell membranes (transcellular) rather than between them, allowing for strict metabolic control. * **Option C:** This is true. Endothelial cells in the BBB exhibit **low pinocytotic activity** (less vesicular transport/membrane activity) compared to peripheral vessels, further limiting the non-specific transport of solutes. * **Option D:** This is true. The **basal lamina**, which contains proteins like **fibronectin**, laminin, and type IV collagen, provides structural integrity and acts as a secondary physical and chemical filter against diffusing molecules. **NEET-PG High-Yield Pearls:** * **Components of BBB:** Endothelial cells (tight junctions), Basal lamina, and **Astrocyte foot processes** (which induce the formation of tight junctions). * **Circumventricular Organs (CVOs):** These are specific areas where the **BBB is absent**, allowing the brain to monitor systemic changes (e.g., Area Postrema for vomiting, Posterior Pituitary for hormone release, OVLT for osmolarity). * **Permeability:** The BBB is highly permeable to **CO2, O2, and lipid-soluble substances** (e.g., alcohol, steroid hormones) but impermeable to plasma proteins and large organic molecules.

Practice by Chapter

Neurons and Glial Cells

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Synaptic Transmission

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Sensory Processing

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Motor Control Systems

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Autonomic Nervous System

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Hypothalamus and Limbic System

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Cerebral Cortex Functions

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Electroencephalography

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Neuroplasticity

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Sleep and Wakefulness

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