Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 701: Delta waves on EEG are seen in:

A. Fully relaxed deep sleep (Correct Answer)
B. Awake state with eyes closed
C. Awake state with eyes open
D. Transition from awakefulness to sleep

Explanation: ***Fully relaxed deep sleep*** - **Delta waves** (0.5-4 Hz) are characteristic of **Stage 3 and 4 NREM sleep**, which are considered deep sleep stages. - They reflect widespread **cortical synchronization** and reduced brain activity associated with restorative sleep. *Awake state with eyes closed* - This state is typically dominated by **alpha waves** (8-13 Hz), especially over the occipital lobe. - Alpha waves disappear when the eyes are opened or during mental exertion. *Awake state with eyes open* - An awake state with eyes open is characterized by low-amplitude, high-frequency **beta waves** (13-30 Hz) and sometimes **gamma waves** (>30 Hz), reflecting active cortical processing. - This pattern is associated with alertness and active thought. *Transition from awakefulness to sleep* - The transition from wakefulness to sleep (Stage 1 NREM sleep) is characterized by the appearance of **theta waves** (4-7 Hz) and a decrease in alpha activity. - This stage is often associated with slowing eye movements and drowsiness, not deep sleep delta waves.

Question 702: Which cells in the retina primarily depolarize in response to light stimulation?

A. Amacrine cells
B. Bipolar cells (Correct Answer)
C. Horizontal cells
D. Rods and cones

Explanation: ***Bipolar cells*** - **Bipolar cells** receive input from photoreceptors and are the first cells in the retinal pathway to depolarize in response to light stimulation. - Specifically, **ON-center bipolar cells** depolarize when light falls on the center of their receptive field, while OFF-center bipolar cells hyperpolarize. - The question refers to the **ON-center bipolar cells**, which show the characteristic depolarization response to light, transmitting excitatory signals to ganglion cells. *Amacrine cells* - **Amacrine cells** are interneurons that modulate signals between bipolar cells and ganglion cells. - They primarily process **temporal** and **spatial** aspects of visual information and provide lateral inhibition. - They do not primarily depolarize as a direct response to light stimulation. *Horizontal cells* - **Horizontal cells** provide **lateral inhibition** at the photoreceptor-bipolar cell synapse, enhancing contrast and spatial resolution. - They generally **hyperpolarize** in response to light and modulate photoreceptor output. - They do not serve as primary depolarizing cells in the light response pathway. *Rods and cones* - **Rods and cones** are photoreceptor cells that **hyperpolarize** (not depolarize) in response to light. - In darkness, they are depolarized and continuously release glutamate; light causes closure of cGMP-gated channels, leading to hyperpolarization. - This hyperpolarization is the initial transduction event that subsequently modulates bipolar cell activity.

Question 703: Which substance enhances the sensitivity of pain receptors but does not directly excite them?

A. Potassium ions
B. Prostaglandins (Correct Answer)
C. Bradykinin
D. Serotonin

Explanation: ***Prostaglandins*** - **Prostaglandins** are lipid compounds that do not directly activate pain receptors, but they enhance the sensitivity of nociceptors to other painful stimuli. - They are released during **inflammation** and contribute to the sensation of pain by lowering the threshold for neuronal activation. *Potassium ions* - **Potassium ions** directly depolarize nociceptors, thereby **exciting them** and causing pain. - Tissue damage and cell lysis release intracellular potassium, leading to direct pain perception. *Bradykinin* - **Bradykinin** directly excites pain receptors via its specific receptors (B1 and B2 receptors), leading to rapid depolarization and pain signals. - It also contributes to inflammation and vasodilation. *Serotonin* - **Serotonin** (5-HT) can directly activate certain types of nociceptors (e.g., 5-HT3 receptors), thereby **directly exciting them**. - It is released by platelets at injury sites and contributes to both pain and inflammation.

Question 704: Function of preoptic nucleus of hypothalamus:

A. Sexual behaviors
B. Temperature regulation
C. Thirst
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - The **preoptic nucleus** of the hypothalamus is a multifunctional region involved in **sexual behaviors**, **temperature regulation**, and **thirst** regulation. - Its diverse roles stem from its extensive neural connections and specialized neuronal populations that respond to thermal, osmotic, and hormonal stimuli. **Sexual behaviors** - The **medial preoptic area (MPOA)** within the preoptic nucleus plays a critical role in **male sexual behavior**, mating, and parental care. - Lesions in this area impair copulatory behavior in males across multiple species. - It integrates hormonal signals (testosterone, estrogen) with sensory inputs to regulate reproductive behaviors. **Temperature regulation** - The **anterior hypothalamic-preoptic area** is the primary thermoregulatory center of the brain. - Contains **warm-sensitive neurons** that detect increases in blood/brain temperature and trigger heat loss mechanisms (vasodilation, sweating). - Damage to this area impairs the ability to respond to heat stress. **Thirst regulation** - The preoptic nucleus, particularly through connections with the **organum vasculosum of the lamina terminalis (OVLT)**, monitors **plasma osmolality**. - Osmoreceptive neurons in this region detect dehydration and trigger thirst and **ADH release**. - Essential for maintaining fluid-electrolyte homeostasis.

Question 705: Cerebral perfusion pressure is

A. mean arterial pressure - intracranial pressure (Correct Answer)
B. cerebral blood flow / brain surface area in m^2
C. cerebral blood flow * brain surface area in m^2
D. mean arterial pressure + intracranial pressure

Explanation: ***mean arterial pressure - intracranial pressure*** - **Cerebral perfusion pressure (CPP)** is defined as the net pressure gradient causing blood flow to the brain, calculated by subtracting the **intracranial pressure (ICP)** from the **mean arterial pressure (MAP)**. - A healthy CPP is crucial for maintaining adequate **cerebral blood flow** and preventing **brain ischemia** or injury. *cerebral blood flow / brain surface area in m^2* - This formula represents **cerebral blood flow density** or intensity across a surface area, not the actual perfusion pressure. - While relating to brain perfusion, it does not account for the **pressure gradient** that drives blood into the brain. *cerebral blood flow * brain surface area in m^2* - This calculation yields a value that is a product of flow and area, not a measure of the effective **perfusion pressure**. - It does not incorporate the **intracranial pressure**, which is a critical opposing force to cerebral blood flow. *mean arterial pressure + intracranial pressure* - Adding **mean arterial pressure (MAP)** and **intracranial pressure (ICP)** would result in a value that does not reflect the *net driving pressure* for blood into the brain. - **ICP** acts as a resistance against arterial flow, so it must be subtracted, not added, to determine the effective perfusion pressure.

Question 706: Which of the following sensations is transmitted by the Dorsal Tract/Posterior column?

A. All of the options
B. Pain
C. Fine touch (Correct Answer)
D. Temperature

Explanation: ***Fine touch*** - The **dorsal column-medial lemniscus pathway** is primarily responsible for transmitting discriminative touch, vibration, and **proprioception**. - **Fine touch** (also known as discriminative touch) is a key sensation within this pathway, allowing for precise localization and discrimination of tactile stimuli. *All of the options* - This is incorrect because the dorsal column-medial lemniscus pathway does not transmit all sensory modalities listed in the options. - Specifically, **pain** and **temperature** are transmitted via the spinothalamic tracts. *Pain* - **Pain** sensation is primarily transmitted by the **spinothalamic tracts** (specifically the lateral spinothalamic tract) which is distinct from the dorsal column. - Damage to the dorsal column pathway would generally not impair pain sensation. *Temperature* - **Temperature** sensation is also primarily transmitted by the **spinothalamic tracts** (lateral spinothalamic tract), not the dorsal column. - The dorsal column pathway is specialized for mechanosensory information.

Question 707: Fine touch is lost in lesion of

A. Lateral spinothalamic tract
B. Pyramidal tract
C. Dorsal column pathway (Correct Answer)
D. Anterior spinothalamic tract

Explanation: ***Dorsal column pathway*** - The **dorsal column-medial lemniscus pathway** is responsible for transmitting **fine touch**, **vibration**, and **proprioception** from the periphery to the cerebral cortex. - A lesion in this pathway would result in the loss of these specific sensory modalities, including fine touch. *Lateral spinothalamic tract* - This tract is primarily responsible for transmitting **pain** and **temperature** sensations. - A lesion in the lateral spinothalamic tract would lead to a loss of pain and temperature sensation, not fine touch. *Pyramidal tract* - The **pyramidal tract** (corticospinal tract) is primarily involved in **voluntary motor control**. - A lesion in this tract would result in **motor deficits** such as weakness or paralysis, rather than sensory loss, including fine touch. *Anterior spinothalamic tract* - The anterior spinothalamic tract transmits **crude touch** and **pressure** sensations. - While it carries touch information, it specifically handles non-discriminative, **crude touch**, not the highly localized, discriminative **fine touch** mediated by the dorsal columns.

Question 708: Increased intracranial pressure (ICP) is characterised by:

A. Hypotension and tachycardia
B. Bradypnea and hypotension
C. Hypertension and tachycardia
D. Bradycardia and irregular respiration (Correct Answer)

Explanation: ***Bradycardia and irregular respiration*** - Increased intracranial pressure (ICP) classically manifests with **bradycardia** (slow heart rate) and **irregular respiration**, often accompanied by **hypertension** (**Cushing's triad**). - These are compensatory mechanisms aimed at maintaining cerebral perfusion in the face of rising ICP. - The bradycardia is a **reflex response** to hypertension (baroreceptor reflex) as the body attempts to reduce cardiac output. *Hypotension and tachycardia* - **Hypotension** and **tachycardia** are more indicative of **hypovolemic shock** or **sepsis**, where the body attempts to compensate for reduced blood volume or systemic inflammation. - They are generally not associated with the primary features of elevated ICP, which typically causes a reflex increase in blood pressure. *Hypertension and tachycardia* - While **hypertension** is a component of Cushing's triad in elevated ICP, **tachycardia** is not. - The classic response to increased ICP involves reflex **bradycardia** to decrease cardiac output and maintain cerebral perfusion pressure. *Bradypnea and hypotension* - **Bradypnea** (slow breathing) can occur with increased ICP, but **hypotension** is generally not a primary compensatory response. - Instead, the body tries to increase cerebral perfusion pressure through **hypertension** as part of the Cushing response.

Question 709: All are true about Decerebrate posture except:-

A. Exaggerated gamma motor neuron discharge
B. Flexion of upper extremity and extension of lower extremity (Correct Answer)
C. Extension of both upper and lower extremity
D. Reticulo spinal tract is also involved

Explanation: ***Flexion of upper extremity and extension of lower extremity*** - This description corresponds to **decorticate rigidity**, not decerebrate rigidity. - In decorticate rigidity, there is **flexion** of the **upper extremities** and **extension** of the **lower extremities**, indicating a lesion above the red nucleus. *Exaggerated gamma motor neuron discharge* - Decerebrate rigidity is characterized by an **increase in muscle tone** due to disinhibition of extensor muscles, which is mediated by increased **gamma motor neuron activity**. - This increased discharge leads to potentiation of the **stretch reflex**, contributing to the rigidity. *Extension of both upper and lower extremity* - **Decerebrate posture** is defined by **extension of all four limbs** (both upper and lower extremities). - This posture results from a lesion in the brainstem **below the red nucleus** but above the vestibular nuclei, causing disinhibition of the pontine reticular formation and vestibular nuclei, which primarily excite extensor muscles. *Reticulo spinal tract is also involved* - The **reticulospinal tracts** (both pontine and medullary) play a crucial role in regulating muscle tone and posture. - In decerebrate rigidity, the **pontine reticulospinal tract** is overactive due to loss of cortical inhibition, leading to **increased extensor tone**.

Question 710: Maximum area in homunculus signifies?

A. Increased precision of movements (Correct Answer)
B. More muscle fibers are present
C. Low control and unskilled movements
D. Larger size of the body part

Explanation: ***Increased precision of movements*** - A larger area on the homunculus represents a greater density of **sensory receptors** or motor neurons dedicated to that body part, allowing for more **fine-tuned control** and sensation. - This increased representation enables body parts like the hands and face to perform **complex and precise movements** such as writing or speaking. - The cortical area is proportional to the **functional importance** and precision required, not the physical size of the body part. *More muscle fibers are present* - While there may be more muscle fibers in some areas, the size on the homunculus primarily reflects the **neural innervation density** and the precision of control, not merely the bulk of muscle. - A large muscle group with relatively simple movements might have fewer cortical neurons dedicated to it than a smaller, more dexterous body part. *Low control and unskilled movements* - A maximum area in the homunculus signifies **high control** and highly skilled movements, as more cortical processing power is dedicated to these regions. - Areas with less cortical representation typically have **cruder, less precise movements** and sensory discrimination. *Larger size of the body part* - The homunculus does **not** represent the actual physical size of body parts. - Small body parts like fingers and lips have **disproportionately large** cortical representation due to their need for precision, while larger parts like the trunk have minimal representation.

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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