Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 801: What is the primary function of oligodendrocytes in the central nervous system?

A. Myelination of axons in the CNS (Correct Answer)
B. Form the blood-brain barrier
C. Act as immune cells in the CNS
D. Support and maintain neuronal health

Explanation: ***Myelinates the CNS*** - Oligodendrocytes are responsible for the **myelination of axons in the central nervous system (CNS)**, which enhances the speed of electrical signal transmission [1]. - They can myelinate multiple axons simultaneously, providing **support and insulation** to neuronal fibers [1]. *Nutrition of nervous tissue* - While oligodendrocytes contribute to the overall health of nervous tissue, their primary role is not **nutrition** but rather **myelination**. - Neurons and other glial cells, like astrocytes, are more involved in **metabolic support** and nutrition. *Behave like macrophages* - Oligodendrocytes do not function like macrophages; instead, their primary role is myelination, while **microglia** serve as the immune cells in the CNS. - Macrophages are involved in phagocytosis and immune defense, which is not characteristic of oligodendrocytes. *Lining the cavities of the CVS* - This description pertains more to the role of **endothelial cells** or **ependymal cells** rather than oligodendrocytes. - Oligodendrocytes are not involved in lining cavities, particularly in the cardiovascular system (CVS). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1255-1256.

Question 802: Which of the following is the scavenger cell in the CNS?

A. Astrocytes
B. Microglia (Correct Answer)
C. Oligodendrocyte
D. Schwann cell

Explanation: ***Microglia*** - **Microglia** are the primary immune cells of the CNS, functioning as **macrophages** that engulf cellular debris and pathogens. - They act as **scavenger cells** and play a crucial role in maintaining CNS homeostasis and responding to injury or infection. *Astrocytes* - **Astrocytes** provide **metabolic and structural support** to neurons, regulating the chemical environment of the CNS. - They are involved in the **blood-brain barrier** formation and neurotransmitter recycling but are not primarily scavenger cells. *Oligodendrocyte* - **Oligodendrocytes** are responsible for forming the **myelin sheath** around axons in the **central nervous system**, which aids in rapid nerve impulse conduction. - They do not possess phagocytic functions and are not scavenger cells. *Schwann cell* - **Schwann cells** form the **myelin sheath** around axons in the **peripheral nervous system**. - While they can assist in clearing debris after injury in the PNS, they are not the primary scavenger cells of the CNS.

Question 803: Which of the following cranial nerves has no role, direct or indirect, in olfaction?

A. Vagus nerve (CN X) - involved in autonomic and visceral functions.
B. Glossopharyngeal nerve (CN IX) - involved in taste and sensory functions.
C. Trigeminal nerve (CN V) - transmits sensory information from the face.
D. Hypoglossal nerve (CN XII) - controls tongue movements. (Correct Answer)

Explanation: ***Hypoglossal nerve (CN XII)*** - This nerve is solely responsible for **motor innervation of the intrinsic and extrinsic muscles of the tongue**, controlling tongue movements essential for speech and swallowing. - It has no known role, either direct or indirect, in the **sense of smell** or any related sensory processing. *Glossopharyngeal nerve (CN IX)* - The glossopharyngeal nerve is responsible for **taste perception from the posterior one-third of the tongue** and general sensation from the pharynx, but not directly involved in olfaction. - It indirectly influences the **perception of complex flavors**, which are a combination of taste and smell (retronasal olfaction), though it does not process odorants itself. *Vagus nerve (CN X)* - The vagus nerve provides **taste sensation from the epiglottis and base of the tongue**, and has extensive autonomic functions throughout the body. - Similar to CN IX, it indirectly contributes to **flavor perception** by integrating taste with olfactory input, creating the complete sensory experience of food, even though it has no direct role in processing **smell information**. *Trigeminal nerve (CN V)* - The trigeminal nerve transmits **general sensory information from the nasal cavity**, including touch, pain, and temperature, which can modulate the perception of smell (e.g., the "burn" of ammonia or cooling of menthol). - Its ophthalmic (V1) and maxillary (V2) divisions innervate the nasal mucosa, providing **chemesthetic somatosensory input** that combines with olfactory signals to create a complete sensory experience, even though it doesn't detect odors itself.

Question 804: Hypotension in acute spinal injury is due to:

A. Loss of sympathetic tone (Correct Answer)
B. Loss of parasympathetic tone
C. Orthostatic hypotension
D. Vasovagal attack

Explanation: ***Loss of sympathetic tone*** - **Acute spinal cord injury** above T6 can interrupt the sympathetic outflow from the central nervous system. - This leads to unopposed **parasympathetic activity**, causing **vasodilation**, **bradycardia**, and resultant **hypotension**. *Loss of parasympathetic tone* - Loss of parasympathetic tone would typically result in **tachycardia** and potentially **hypertension**, as sympathetic activity would be unopposed. - This is not the primary mechanism for hypotension observed in acute spinal injury. *Orthostatic hypotension* - While patients with spinal cord injury can experience orthostatic hypotension, the initial acute hypotension is due to the fundamental physiological disruption of **autonomic control**. - **Orthostatic hypotension** specifically refers to a drop in blood pressure upon standing, which is a symptom that can persist, but not the direct cause of acute neurogenic shock. *Vasovagal attack* - A **vasovagal attack** is typically triggered by emotional stress or pain, leading to temporary reflex-mediated bradycardia and vasodilation. - It is not the underlying cause of sustained hypotension in the setting of acute spinal cord injury.

Question 805: Appreciation of shape and size of an object placed in the hand is lost in the lesion of which tract?

A. Tractus gracilis
B. Tractus cuneatus (Correct Answer)
C. Lateral spinothalamic tract
D. Spinoreticular tract

Explanation: ***Tractus cuneatus*** - The **tractus cuneatus** (fasciculus cuneatus) carries **fine touch**, **vibration**, and **proprioception** from the upper limb and upper trunk. - Loss of the ability to appreciate the **shape and size of an object** placed in the hand (**astereognosis**) is a classic symptom of damage to this pathway, as it integrates sensory information for object recognition. *Tractus gracilis* - The **tractus gracilis** (fasciculus gracilis) carries similar sensory information (fine touch, vibration, proprioception) but from the **lower limb** and lower trunk. - A lesion here would affect sensation in the legs and lower body, not directly in the hands. *Lateral spinothalamic tract* - The **lateral spinothalamic tract** primarily transmits **pain** and **temperature** sensations. - Damage to this tract would result in deficits in pain and temperature perception, not the ability to recognize object shape or size. *Spinoreticular tract* - The **spinoreticular tract** conveys poorly localized **pain** and **emotional aspects of pain** to the reticular formation. - Its dysfunction would lead to alterations in pain perception and emotional responses to pain, not astereognosis.

Question 806: Which characteristic is most indicative of the human brain's responsiveness?

A. Every cell of brain has a specific function
B. It is a closed system and so not influenced by changes occurring outside
C. Its functions are profoundly affected by changes in external environment (Correct Answer)
D. It has control centers for all motor actions and sensory inputs

Explanation: ***Its functions are profoundly affected by changes in external environment*** - The brain constantly processes and reacts to **sensory information** from the external world, demonstrating its high responsiveness. - Changes in the environment, such as light, sound, temperature, or social interactions, can significantly alter brain activity and behavior, showcasing its dynamic nature. *Every cell of brain has a specific function* - While different brain regions are specialized, individual neurons can be involved in various functions and often work in complex networks rather than having a single, exclusive role. - The concept of every single cell having a unique, specific function oversimplifies the intricate and **plasticity** of neuronal interactions. *It is a closed system and so not influenced by changes occurring outside* - This statement is incorrect; the brain is an **open system** that continuously interacts with and is influenced by the internal and external environments. - Sensory inputs, emotional stimuli, and physiological needs from outside the brain directly impact its functioning and decision-making processes. *It has control centers for all motor actions and sensory inputs* - While the brain does contain sophisticated control centers for motor actions and processes sensory inputs, this particular characteristic defines its comprehensive control rather than its *responsiveness*. - Responsiveness emphasizes the brain's ability to **adapt** and react to environmental changes, which is a broader concept than simply having control centers.

Question 807: Which of the following is known as Berger's rhythm in EEG?

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

Explanation: ***Alpha waves*** - **Alpha waves**, with a frequency of **8-13 Hz**, are characteristic of a relaxed, awake state with eyes closed. - They are also known as **Berger's rhythm** because Hans Berger, the father of EEG, first described them. *Beta waves* - **Beta waves** have a higher frequency (**13-30 Hz**) and are associated with active thinking, problem-solving, and alertness. - They tend to be low amplitude and are not referred to as Berger's rhythm. *Theta waves* - **Theta waves** have a frequency of **4-7 Hz** and are typically seen during sleep or deep relaxation. - They are not associated with Berger's rhythm. *Delta waves* - **Delta waves** are the slowest waves, with a frequency of **0.5-4 Hz**, and are characteristic of deep sleep. - They are not referred to as Berger's rhythm.

Question 808: Which of the following is an example of explicit memory?

A. Procedural
B. Nondeclarative
C. Working
D. Semantic (Correct Answer)

Explanation: ***Semantic*** - **Semantic memory** is a type of **explicit memory** that stores general knowledge and facts about the world, such as the capital of France or the meaning of words. - It is a form of **declarative memory** because it involves conscious recall of information. *Procedural* - **Procedural memory** is a type of **implicit memory** involving the recall of how to do things, like riding a bike or tying a shoelace. - This type of memory is often acquired through repetition and is not consciously recalled in the same way as explicit memories. *Nondeclarative* - **Nondeclarative memory** is another term for **implicit memory**, which includes procedural memory, classical conditioning, and priming. - It is characterized by unconscious recall and influences behavior without conscious awareness. *Working* - **Working memory** is a system for temporarily holding and manipulating information needed for cognitive tasks. - While it involves conscious processing, it is distinct from long-term explicit memories that are *stored* and *retrieved*; it's more about active maintenance than long-term recall.

Question 809: Alpha block on EEG is typically observed during which of the following activities?

A. Seizures
B. Concentrating (Correct Answer)
C. Sleep
D. None of the options

Explanation: ***Concentrating*** - **Alpha rhythm** (8-13 Hz) is strongest in the **posterior regions** of the brain during quiet wakefulness with closed eyes. - When a person opens their eyes or engages in mental activity like concentrating, the alpha rhythm **attenuates or disappears**, a phenomenon known as alpha blocking or **alpha desynchronization**. *Sleep* - During sleep, the EEG activity changes from alpha to slower rhythms like **theta** (4-7 Hz) and **delta** (0.5-3 Hz), along with the appearance of sleep spindles and K-complexes. - **Alpha waves diminish** significantly or are entirely absent, substituted by these other waveforms. *Seizures* - Seizures are characterized by **abnormal, hypersynchronous neuronal activity**, which manifests on EEG as abrupt changes in frequency, amplitude, and morphology, such as **spikes and sharp waves**, or generalized spike-and-wave discharges. - While alpha rhythms might be present in the interictal period, the ictal phase shows distinct, abnormal activity, not normal alpha blocking. *None of the options* - This option is incorrect because alpha block is a well-described phenomenon associated with specific mental states. - **Concentrating** directly causes the attenuation of alpha rhythms.

Question 810: Bilateral ablation of which of the following structures results in the inability to form long-term memories?

A. Amygdala
B. Cingulate gyrus
C. Hippocampus (Correct Answer)
D. Hypothalamus

Explanation: ***Hippocampus*** - The **hippocampus** is a crucial brain structure involved in the consolidation of short-term memories into **long-term memories**, particularly declarative (facts and events) memory. - Bilateral ablation of the hippocampus results in **anterograde amnesia**, the inability to form new long-term memories after the injury, while remote memories may remain intact. *Amygdala* - The **amygdala** is primarily involved in processing and regulating **emotions**, especially fear and aggression, and in emotional memory. - While it contributes to emotionally charged memories, its bilateral damage does not typically cause the inability to form new general long-term memories. *Cingulate gyrus* - The **cingulate gyrus** plays a role in various functions including emotion, learning, and memory, but it's more involved in the emotional component of memory and **attention**. - Its bilateral ablation would not primarily result in a complete inability to form new long-term memories, but rather could affect emotional responses and learning. *Hypothalamus* - The **hypothalamus** is essential for maintaining **homeostasis**, regulating functions like body temperature, hunger, thirst, and hormone release. - While it influences motivated behaviors that can impact memory, its direct ablation does not primarily lead to a deficit in long-term memory formation.

Practice by Chapter

Neurons and Glial Cells

Practice Questions

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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