Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 561: Excitatory postsynaptic potential is due to?

A. Potassium influx
B. Sodium efflux
C. Sodium influx (Correct Answer)
D. Calcium influx

Explanation: **Explanation:** **1. Why Sodium Influx is Correct:** An Excitatory Postsynaptic Potential (EPSP) is a local, graded **depolarization** of the postsynaptic membrane. When an excitatory neurotransmitter (like Glutamate or Acetylcholine) binds to its receptor, it opens ligand-gated cation channels. Because the electrochemical gradient for **Sodium (Na⁺)** strongly favors its entry into the cell, there is a rapid **Sodium influx**. This addition of positive charge makes the resting membrane potential less negative (moving it toward the threshold), thus increasing the likelihood of an action potential. **2. Analysis of Incorrect Options:** * **Potassium Influx (A):** Potassium (K⁺) concentration is much higher inside the cell. Therefore, K⁺ typically moves *out* of the cell (efflux), not in. * **Sodium Efflux (B):** Moving Sodium out of the cell would require active transport (Na⁺/K⁺ ATPase) and would hyperpolarize the cell, which is the opposite of an EPSP. * **Calcium Influx (D):** While Calcium influx does occur in some neurons and is crucial for neurotransmitter release at the *presynaptic* terminal, the primary ion responsible for the rapid depolarization of the *postsynaptic* membrane in a standard EPSP is Sodium. **3. NEET-PG High-Yield Pearls:** * **IPSP (Inhibitory Postsynaptic Potential):** Usually caused by **Chloride (Cl⁻) influx** or **Potassium (K⁺) efflux**, leading to hyperpolarization. * **Spatial Summation:** Multiple presynaptic neurons firing simultaneously at different locations on the same postsynaptic neuron. * **Temporal Summation:** A single presynaptic neuron firing at a high frequency. * **Key Neurotransmitter:** **Glutamate** is the primary excitatory neurotransmitter in the CNS, acting mainly via AMPA and NMDA receptors to cause Na⁺/Ca²⁺ influx.

Question 562: Which sleep stage, as identified by EEG, is characterized by the presence of sleep spindles?

A. Stage 1
B. Stage 2 (Correct Answer)
C. Stage 3
D. Stage 4

Explanation: ### Explanation The correct answer is **Stage 2 (N2)** of Non-Rapid Eye Movement (NREM) sleep. **1. Why Stage 2 is Correct:** Stage 2 is the longest stage of the sleep cycle and is electrophysiologically defined by two hallmark features on the EEG: * **Sleep Spindles:** Brief bursts of high-frequency (12–14 Hz) activity originating from the interaction between the thalamus and the cortex. They are thought to play a role in memory consolidation and protecting sleep from external noise. * **K-complexes:** Large, high-amplitude waves that represent a brief period of cortical inhibition. **2. Why Other Options are Incorrect:** * **Stage 1 (N1):** This is the transition from wakefulness to sleep. The EEG shows low-voltage, mixed-frequency activity with a predominance of **Theta waves** (4–7 Hz). * **Stage 3 & 4 (N3):** These are collectively known as **Slow Wave Sleep (SWS)** or Deep Sleep. They are characterized by high-amplitude, low-frequency **Delta waves** (0.5–2 Hz). Stage 4 is distinguished by Delta waves occupying more than 50% of the EEG tracing. **3. High-Yield Clinical Pearls for NEET-PG:** * **Bruxism (Teeth Grinding):** Occurs primarily in Stage 2. * **Parasomnias:** Sleepwalking (Somnambulism), Night Terrors, and Bedwetting (Enuresis) typically occur during **Stage 3/4 (Deep Sleep)**. * **REM Sleep:** Characterized by **Sawtooth waves**, muscle atonia, and vivid dreaming. It is the stage where Nightmares occur. * **PGO Spikes:** (Ponto-Geniculo-Occipital) are the earliest signs of REM sleep. * **Ageing:** As age increases, the duration of REM sleep and Stage 4 sleep decreases.

Question 563: Which of the following is true about REM sleep?

A. Nightmares (Correct Answer)
B. Night terrors
C. Somniloquy
D. None of the above

Explanation: **Explanation:** The distinction between REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement) sleep is a high-yield topic in neurophysiology. **1. Why Nightmares are the Correct Answer:** Nightmares are defined as frightening dreams that occur during **REM sleep**. During REM sleep, brain activity is high (resembling an awake state on EEG), and dreaming is most vivid and elaborate. Because REM sleep occurs more frequently and for longer durations in the second half of the night, nightmares typically occur toward the morning. Upon waking, the individual is usually alert and can vividly recall the dream content. **2. Why the Other Options are Incorrect:** * **Night Terrors (Pavor Nocturnus):** These occur during **Stage N3 (Deep/Slow-wave sleep)** of NREM. Unlike nightmares, they involve intense autonomic arousal (tachycardia, sweating, screaming), and the individual usually has no memory of the event upon waking. * **Somniloquy (Sleep Talking):** This can occur in both REM and NREM sleep, but it is most commonly associated with **NREM sleep** stages. Since it is not exclusive to or a hallmark of REM in the way nightmares are, it is not the best fit. * **Somnambulism (Sleepwalking):** (Related concept) This also occurs during **Stage N3 NREM sleep**, not REM, because REM sleep is characterized by muscle atonia (paralysis). **Clinical Pearls for NEET-PG:** * **REM Sleep Characteristics:** Beta waves on EEG (desynchronized), muscle atonia, rapid eye movements, and fluctuating heart rate/respiration. * **N3 Stage:** Characterized by Delta waves; this is when night terrors, sleepwalking, and enuresis (bedwetting) typically occur. * **Pons:** The "REM-on" cells are located in the pontine reticular formation (Cholinergic neurons).

Question 564: A lesion in the medial lemniscus at the level of the pons causes which of the following clinical findings?

A. Loss of pain and temperature sensation on the same side of the body
B. Loss of pain and temperature sensation on the opposite side of the body
C. Loss of tactile sensation and proprioception on the same side of the body
D. Loss of tactile sensation and proprioception on the opposite side of the body (Correct Answer)

Explanation: **Explanation:** The **Medial Lemniscus** is the second-order neuron pathway of the **Dorsal Column-Medial Lemniscus (DCML) system**, which carries fine touch (tactile sensation), conscious proprioception, and vibration sense. **Why Option D is Correct:** The first-order neurons of the DCML system ascend ipsilaterally in the spinal cord and synapse in the *nucleus gracilis* and *cuneatus* in the lower medulla. At this level, the second-order neurons emerge as **internal arcuate fibers**, which **decussate (cross over)** to the opposite side to form the medial lemniscus. Therefore, by the time the medial lemniscus reaches the **pons**, it is carrying sensory information from the **contralateral (opposite)** side of the body. A lesion here results in a loss of these modalities on the opposite side. **Analysis of Incorrect Options:** * **Options A & B:** Pain and temperature are carried by the **Lateral Spinothalamic Tract**. While this tract also carries contralateral information at the level of the pons, it is anatomically distinct from the medial lemniscus. * **Option C:** This is incorrect because the DCML fibers cross in the **lower medulla**. Any lesion above the sensory decussation (pons, midbrain, or thalamus) will manifest as contralateral deficits, not ipsilateral. **High-Yield Clinical Pearls for NEET-PG:** * **Level of Decussation:** DCML decussates in the **lower medulla** (sensory decussation); Corticospinal tract decussates in the **lower medulla** (motor decussation); Spinothalamic tract decussates within **1-2 spinal segments** of entry. * **Blood Supply:** The medial lemniscus in the pons is primarily supplied by the paramedian branches of the **basilar artery**. * **Tabes Dorsalis:** Characterized by the destruction of dorsal columns (loss of proprioception/vibration), but the lesion is at the level of the spinal cord (ipsilateral).

Question 565: Which nerves comprise the parasympathetic nervous system?

A. Cranial nerves III, VII, IX, X and sacral nerves S1, S2, S3, S4, S5
B. Cranial nerves III, VII, IX, X and sacral nerves S2, S3, S4 (Correct Answer)
C. Cranial nerves V, VII, IX, X and sacral nerves S2, S3, S4
D. Cranial nerves III, V, VII, X and sacral nerves S2, S3, S4

Explanation: **Explanation:** The Autonomic Nervous System (ANS) is divided into the Sympathetic (Thoracolumbar) and Parasympathetic (Craniosacral) divisions. The **Parasympathetic Nervous System (PSNS)** is termed "Craniosacral" because its preganglionic cell bodies are located in specific nuclei of the brainstem and the lateral gray horn of the sacral spinal cord. **1. Why Option B is Correct:** The outflow consists of: * **Cranial Component:** Four specific cranial nerves carry parasympathetic fibers: * **CN III (Oculomotor):** Ciliary ganglion (pupillary constriction/accommodation). * **CN VII (Facial):** Pterygopalatine and Submandibular ganglia (lacrimation/salivation). * **CN IX (Glossopharyngeal):** Otic ganglion (parotid salivation). * **CN X (Vagus):** Provides 75–80% of total parasympathetic outflow, supplying thoracic and abdominal viscera up to the splenic flexure. * **Sacral Component:** The **S2, S3, and S4** spinal segments (Pelvic Splanchnic Nerves) supply the distal colon, rectum, bladder, and reproductive organs. **2. Analysis of Incorrect Options:** * **Option A:** Incorrect because the sacral outflow is strictly limited to **S2–S4**. S1 and S5 do not contribute preganglionic parasympathetic fibers. * **Option C & D:** Incorrect because **CN V (Trigeminal)** is a purely sensory/motor nerve. While branches of CN V "hitchhike" or carry parasympathetic fibers to their targets, the nerve itself does not have a parasympathetic nucleus of origin. **High-Yield NEET-PG Pearls:** * **Mnemonic:** Remember **"1973"** (CN 10, 9, 7, 3) for the cranial outflow. * **Vagus Nerve:** It is the only cranial nerve that supplies structures outside the head and neck. * **Neurotransmitter:** Acetylcholine (ACh) is the neurotransmitter at **both** preganglionic and postganglionic synapses in the PSNS. * **Sacral Outflow:** Often referred to as the "Nervi Erigentes," essential for bladder contraction and penile erection.

Question 566: Which of the following parts of the brain contains dopaminergic neurons?

A. Locus ceruleus system
B. Cerebellum
C. Nigro striatal system (Correct Answer)
D. Midline raphe nucleus

Explanation: **Explanation:** The correct answer is **C. Nigro striatal system.** This system is one of the major dopaminergic pathways in the brain, where dopamine is synthesized by neurons in the **substantia nigra pars compacta (SNpc)** and projected to the striatum (caudate nucleus and putamen). This pathway is essential for the initiation and control of voluntary movement. **Analysis of Options:** * **A. Locus ceruleus system:** This is the primary site for **Norepinephrine** synthesis in the brain. It plays a key role in physiological responses to stress and panic. * **B. Cerebellum:** While the cerebellum is vital for motor coordination and balance, its primary neurotransmitters are **GABA** (Purkinje cells) and **Glutamate** (Granule cells), not dopamine. * **D. Midline raphe nucleus:** This is the principal site for **Serotonin (5-HT)** synthesis. It is involved in mood regulation, sleep-wake cycles, and pain modulation. **High-Yield Clinical Pearls for NEET-PG:** * **Dopaminergic Pathways:** There are four major pathways: 1. **Nigrostriatal:** Motor control (Deficit causes Parkinson’s disease). 2. **Mesolimbic:** Reward and addiction (Overactivity linked to positive symptoms of Schizophrenia). 3. **Mesocortical:** Cognitive function (Deficit linked to negative symptoms of Schizophrenia). 4. **Tuberoinfundibular:** Inhibits Prolactin secretion from the pituitary. * **Parkinson’s Disease:** Characterized by the progressive loss of dopaminergic neurons in the substantia nigra, leading to the classic triad of tremors, rigidity, and bradykinesia. * **Rate-limiting enzyme:** Tyrosine hydroxylase is the rate-limiting enzyme for dopamine synthesis.

Question 567: Pavlov's experiment on dogs demonstrates which type of learning?

A. Conditional response (Correct Answer)
B. Unconditional response
C. Procedural memory
D. Familiarity

Explanation: **Explanation:** The correct answer is **Conditional response** (also known as Classical Conditioning). This form of learning, pioneered by Ivan Pavlov, involves pairing a neutral stimulus with a stimulus that naturally evokes a response. **Why Option A is correct:** In Pavlov’s experiment, a dog was presented with food (Unconditioned Stimulus), which naturally caused salivation (Unconditioned Response). Pavlov then introduced a bell (Neutral Stimulus) just before feeding. After repeated pairings, the dog began to salivate at the sound of the bell alone. This learned behavior is termed a **Conditional Response**. It represents a type of **associative learning** where an organism learns the relationship between two stimuli. **Why other options are incorrect:** * **B. Unconditional response:** This is an innate, reflexive reaction to a stimulus (e.g., salivating when food touches the tongue) that does not require prior learning. * **C. Procedural memory:** This refers to "how-to" learning (e.g., riding a bike or playing an instrument). It involves the cerebellum and basal ganglia rather than simple stimulus-response association. * **D. Familiarity:** This is a component of recognition memory (non-associative) where one feels a sense of prior encounter without necessarily recalling specific details. **High-Yield Clinical Pearls for NEET-PG:** * **Brain Areas:** Classical conditioning of motor responses (like the eye-blink reflex) primarily involves the **cerebellum**, while emotional conditioning (like fear) involves the **amygdala**. * **Non-Associative Learning:** Includes **Habituation** (decreased response to a repeated benign stimulus) and **Sensitization** (increased response to a stimulus after a noxious one). * **Operant Conditioning:** Unlike Pavlovian conditioning, this involves learning the consequences of behavior (rewards/punishments), famously studied by B.F. Skinner.

Question 568: What is the primary function of the basal ganglia?

A. Preprogramming of voluntary activity (Correct Answer)
B. Control of equilibrium
C. Sensory integration
D. Short-term memory

Explanation: ### Explanation **1. Why Option A is Correct:** The basal ganglia (comprising the striatum, globus pallidus, substantia nigra, and subthalamic nucleus) act as a critical processing link between the cerebral cortex and the thalamus. Their primary role is the **planning and preprogramming of complex voluntary movements**. They do not initiate movement directly; instead, they convert an abstract "thought" of movement into a specific motor strategy. This involves selecting desired motor patterns while inhibiting competing, involuntary movements, ensuring that voluntary activity is smooth and coordinated. **2. Why the Other Options are Incorrect:** * **Option B (Control of equilibrium):** This is primarily the function of the **vestibulocerebellum** (flocculonodular lobe) and the vestibular apparatus. * **Option C (Sensory integration):** The **thalamus** is the major relay station and integrator for sensory information (except olfaction) before it reaches the cortex. * **Option D (Short-term memory):** This is associated with the **prefrontal cortex** and the **hippocampus** (for consolidation into long-term memory), not the basal ganglia. **3. High-Yield Clinical Pearls for NEET-PG:** * **The Direct Pathway (D1 receptors):** Stimulates movement ("Pro-kinetic"). * **The Indirect Pathway (D2 receptors):** Inhibits movement ("Anti-kinetic"). * **Parkinson’s Disease:** Results from the destruction of dopaminergic neurons in the **Substantia Nigra pars compacta**, leading to a "poverty of movement" (bradykinesia and rigidity). * **Huntington’s Chorea:** Involves the degeneration of GABAergic neurons in the **Striatum (Caudate nucleus)**, leading to hyperkinetic, jerky movements. * **Hemiballismus:** Caused by a lesion in the **Subthalamic Nucleus**, resulting in wild, flailing limb movements.

Question 569: Fine voluntary movements are transmitted by which neural pathway?

A. Lateral corticospinal tract (Correct Answer)
B. Dorsal column
C. Anterior horn
D. Spinothalamic tract

Explanation: ### Explanation **Correct Answer: A. Lateral corticospinal tract** The **Lateral Corticospinal Tract (LCST)** is the primary pathway for fine, skilled, and voluntary movements, particularly of the distal limbs (fingers and toes). Approximately 80-90% of the corticospinal fibers decussate (cross over) at the lower medulla to form the LCST. These fibers synapse directly or indirectly on lower motor neurons in the spinal cord. The ability to perform "fractionated" movements—such as playing a piano or buttoning a shirt—is a hallmark function of this tract. **Why the other options are incorrect:** * **B. Dorsal Column:** This is a **sensory** pathway responsible for fine touch, vibration, and conscious proprioception. It does not transmit motor commands. * **C. Anterior Horn:** This is a location (anatomical site) in the spinal cord gray matter where motor neuron cell bodies reside. While it is the "final common pathway" for motor output, it is not a neural tract itself. * **D. Spinothalamic Tract:** This is an **ascending sensory** pathway that carries pain, temperature, and crude touch information to the thalamus. ### NEET-PG High-Yield Pearls: * **Origin:** Most fibers originate from the Primary Motor Cortex (Brodmann area 4), Premotor Cortex (Area 6), and Supplementary Motor Area. * **Decussation:** Occurs at the **Pyramids** of the medulla. Lesions above the decussation cause contralateral deficits; lesions below cause ipsilateral deficits. * **Clinical Sign:** Damage to the LCST results in **Upper Motor Neuron (UMN)** signs: spasticity, hyperreflexia, and a positive Babinski sign. * **Anterior Corticospinal Tract:** Unlike the lateral tract, the anterior tract (10-20% of fibers) does not decussate in the medulla and primarily controls **proximal/axial muscles** for posture.

Question 570: All of the following are excitatory neurotransmitters except?

A. Gamma-aminobutyric acid (Correct Answer)
B. Acetylcholine
C. Dopamine
D. Serotonin

Explanation: ### Explanation **Neurotransmitters** are chemical messengers classified based on their effect on the post-synaptic membrane: **Excitatory** (causing depolarization) or **Inhibitory** (causing hyperpolarization). **Why Gamma-aminobutyric acid (GABA) is the correct answer:** GABA is the **primary inhibitory neurotransmitter** in the adult mammalian Central Nervous System (CNS). When GABA binds to its receptors (GABA-A), it opens chloride channels, leading to an influx of negatively charged chloride ions. This results in **hyperpolarization** of the post-synaptic neuron, making it less likely to fire an action potential. **Analysis of Incorrect Options:** * **Acetylcholine (ACh):** Primarily excitatory, especially at the neuromuscular junction (nicotinic receptors) and in the autonomic ganglia. It can be inhibitory in specific locations (e.g., the heart via M2 receptors), but it is classically categorized as excitatory. * **Dopamine:** A catecholamine that can be both excitatory or inhibitory depending on the receptor (D1 is generally excitatory, D2 is inhibitory). However, in the context of general classification, it is grouped with excitatory biogenic amines. * **Serotonin (5-HT):** Generally acts as an excitatory neurotransmitter in pathways involving mood, sleep, and appetite regulation, though it has complex modulatory roles. **High-Yield Clinical Pearls for NEET-PG:** * **Glycine:** The major inhibitory neurotransmitter in the **spinal cord**. * **Glutamate:** The primary and most potent **excitatory** neurotransmitter in the CNS. * **GABA-A vs. GABA-B:** GABA-A is ionotropic (fast, chloride channel), while GABA-B is metabotropic (slow, G-protein coupled, potassium channel). * **Clinical Correlation:** Benzodiazepines and Barbiturates work by potentiating the effects of GABA at the GABA-A receptor, used clinically for sedation and seizure control.

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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