Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 731: A 40-year-old woman is being evaluated for severe epilepsy. An MRI shows agenesis of the corpus callosum. What is the function of the corpus callosum?

A. Connects the two cerebral hemispheres (Correct Answer)
B. Regulates autonomic functions
C. Coordinates motor movements
D. Processes visual information

Explanation: **Connects the two cerebral hemispheres** - The **corpus callosum** is a large **commissural white matter tract** whose primary function is to transfer information and integrate functions between the right and left cerebral hemispheres. - Its agenesis can lead to neurological issues such as **epilepsy** due to impaired interhemispheric communication. *Regulates autonomic functions* - Autonomic functions like heart rate, digestion, and breathing are primarily regulated by the **autonomic nervous system** and structures like the **hypothalamus** and **brainstem**. - The corpus callosum has no direct role in regulating these involuntary bodily processes. *Coordinates motor movements* - **Motor coordination** is largely managed by the **cerebellum** and the **basal ganglia**, which help to refine and smooth movements. - While interhemispheric communication (via the corpus callosum) is important for complex motor tasks, it is not the primary structure for basic motor coordination. *Processes visual information* - **Visual information processing** mainly occurs in the **occipital lobes** of the cerebral cortex following input from the optic nerves and thalamus. - While the corpus callosum allows for cross-hemispheric integration of visual fields, it is not the primary center for initial visual processing.

Question 732: Which function is primarily associated with the corpus callosum in the brain?

A. Memory storage
B. Motor coordination
C. Interhemispheric communication (Correct Answer)
D. Sensory processing

Explanation: ***Interhemispheric communication*** - The **corpus callosum** is a large, C-shaped nerve fiber bundle found beneath the cerebral cortex. - It facilitates the **transfer of information and signals** between the two cerebral hemispheres, allowing them to communicate and coordinate functions. *Memory storage* - **Memory storage** is a complex function primarily associated with structures like the **hippocampus** and various cortical areas, not the corpus callosum itself. - While interhemispheric communication might indirectly support memory tasks, it is not the primary role of the corpus callosum. *Motor coordination* - **Motor coordination** involves several brain regions, including the **cerebellum**, motor cortex, and basal ganglia. - The corpus callosum contributes to the synchronization of motor actions between the two sides of the body but is not the primary center for coordination. *Sensory processing* - **Sensory processing** occurs primarily in specialized areas of the cerebral cortex, such as the **somatosensory cortex**, visual cortex, and auditory cortex. - While it helps integrate sensory information between hemispheres, the corpus callosum's main role is not processing sensory input itself.

Question 733: A patient with a lesion in the corpus callosum presents with disconnection syndrome. Which specific function is most likely to be impaired due to this condition?

A. Language processing
B. Motor skills
C. Visual perception
D. Interhemispheric communication (Correct Answer)

Explanation: ***Interhemispheric communication*** - A lesion in the **corpus callosum** directly disrupts the primary pathway for communication between the two cerebral hemispheres, leading to a **disconnection syndrome**. - This results in a lack of integration of sensory, motor, and cognitive information processed independently by each hemisphere, impacting various functions like transferring tactile information or recognizing objects held in one hand with the other. *Language processing* - While language processing can be affected in some disconnection syndromes (e.g., alexia without agraphia), it's not the most direct or generalized impairment. - Primary language centers are typically located unilaterally (e.g., **Broca's and Wernicke's areas** in the left hemisphere) and their direct damage causes aphasia, which is distinct from disconnection. *Motor skills* - Motor skills can be indirectly affected in complex tasks requiring bilateral coordination or cross-hemispheric planning (e.g., **sympathetic dyspraxia**). - However, direct motor deficits (paralysis or weakness) are usually due to lesions in the motor cortex or descending tracts, not primarily the corpus callosum. *Visual perception* - Visual perception can be disrupted in specific ways, such as **visual anomia** (inability to name objects seen in the left visual field) or **left hemialexia**. - However, the primary visual cortices are intact, and visual perception itself within each hemisphere is generally preserved, unlike the fundamental breakdown of communication between them.

Question 734: What is the role of myelin in the nervous system?

A. Increase conduction velocity (Correct Answer)
B. Form synapses
C. Facilitate neurotransmitter release
D. Contribute to axonal integrity

Explanation: ***Increase conduction velocity*** - **Myelin** acts as an electrical insulator around the axon, preventing the leakage of ions across the membrane. - This **insulation** allows action potentials to "jump" between the **Nodes of Ranvier** (a process called **saltatory conduction**), significantly increasing the speed of nerve signal transmission. - This is the **primary and most important role** of myelin, increasing conduction velocity up to 100-fold. *Facilitate neurotransmitter release* - **Neurotransmitter release** occurs at the **axon terminal** in response to the arrival of an action potential and influx of calcium ions, a process not directly mediated by myelin. - **Myelin** primarily functions to speed up signal propagation along the axon, not to influence the final output at the synapse. *Form synapses* - **Synapses** are specialized junctions between neurons where information is transmitted, typically formed by the **axon terminal** of one neuron and the **dendrites** or cell body of another. - **Myelin** is located along the axon, not at the synaptic cleft, and does not directly participate in synapse formation. *Contribute to axonal integrity* - While myelin and myelinating cells (oligodendrocytes and Schwann cells) do provide **metabolic support** and **trophic factors** to axons, this is a **secondary function**. - The **primary role** of myelin is to increase conduction velocity through saltatory conduction, making it the best answer to this question.

Question 735: Which neurotransmitter is primarily responsible for mediating the 'fight or flight' response of the sympathetic nervous system?

A. Acetylcholine
B. Serotonin
C. Norepinephrine (Correct Answer)
D. Dopamine

Explanation: ***Norepinephrine*** - **Norepinephrine** is the primary neurotransmitter released by most **postganglionic sympathetic neurons**, acting on adrenergic receptors to mediate the diverse effects of the 'fight or flight' response. - Its effects include increased heart rate, vasoconstriction, bronchodilation, and glucose release, all crucial for preparing the body for perceived threats. *Acetylcholine* - While acetylcholine is used by **preganglionic sympathetic neurons** and in the sympathetic innervation of **sweat glands**, it is generally associated with the **parasympathetic nervous system's** 'rest and digest' functions. - It also plays a role in the somatic nervous system at the **neuromuscular junction**. *Serotonin* - **Serotonin** is a neurotransmitter primarily involved in regulating mood, sleep, appetite, and learning, and is largely found in the central nervous system and the gastrointestinal tract. - It does not directly mediate the acute 'fight or flight' response of the autonomic nervous system. *Dopamine* - **Dopamine** is involved in reward, motivation, motor control, and pleasure, and is a precursor to norepinephrine and epinephrine. - While it has significant roles in the brain and can influence sympathetic activity, it is not the primary neurotransmitter directly mediating the widespread 'fight or flight' response in the periphery.

Question 736: Withdrawal reflex is an example of which of the following?

A. Monosynaptic reflex
B. Polysynaptic reflex (Correct Answer)
C. Both A and B of the above
D. None of the options

Explanation: ***Polysynaptic reflex*** - The **withdrawal reflex** involves multiple synapses between sensory neurons, interneurons, and motor neurons. - This complex pathway allows for coordinated muscle contractions (e.g., flexion of a limb) and inhibition of antagonistic muscles to quickly move away from a painful stimulus. *Monosynaptic reflex* - A **monosynaptic reflex** involves only one synapse between a sensory neuron and a motor neuron, such as the **stretch reflex** (e.g., patellar reflex). - It does not involve interneurons, making it a simpler and faster reflex arc. *Both A and B of the above* - The withdrawal reflex is specifically **polysynaptic**, not monosynaptic, because it requires interneurons to integrate the sensory input and coordinate the motor response. - Combining both would imply it can be both at the same time, which is incorrect for this specific reflex. *None of the options* - This option is incorrect because the withdrawal reflex clearly fits the definition and characteristics of a **polysynaptic reflex**. - There is a definitive correct answer provided among the choices.

Question 737: What is the rate of CSF formation in children?

A. 0.3 ml/min (Correct Answer)
B. 1 ml/min
C. 3 ml/min
D. 20 ml/min

Explanation: ***0.3 ml/min*** - The rate of **cerebrospinal fluid (CSF) formation** is approximately **0.3-0.4 ml/min** in both children and adults. - This rate is relatively **constant across age groups**, although total CSF volume varies (50-60 ml in infants, ~150 ml in adults). - This production rate supports a total CSF volume turnover about **3-4 times per day**. - CSF is primarily produced by the **choroid plexus** in the brain ventricles. *1 ml/min* - This rate is **3 times higher** than the normal physiological CSF production rate. - Such an elevated rate would lead to rapid accumulation of CSF and could result in **hydrocephalus**. - Overproduction of CSF is a rare cause of hydrocephalus (e.g., choroid plexus papilloma). *3 ml/min* - A CSF formation rate of 3 ml/min is **10 times higher** than normal and would be pathologically extreme. - This would result in severe and rapid **hydrocephalus** with significant intracranial pressure elevation. - No normal physiological state is associated with such a high CSF production rate. *20 ml/min* - This rate is **extremely and unrealistically high** (>60 times normal). - Would be incompatible with normal brain function, causing extreme and potentially fatal **hydrocephalus**. - Does not reflect any known physiological or pathological condition of CSF production.

Question 738: Intracranial pressure is not raised during

A. Status epilepticus
B. Hyperventilation (Correct Answer)
C. Head injury
D. Subdural hematoma

Explanation: ***Hyperventilation*** - **Hyperventilation** reduces **PaCO2**, leading to cerebral vasoconstriction and decreased cerebral blood flow, thereby lowering **intracranial pressure (ICP)**. - This is a common maneuver used to temporarily reduce acutely elevated ICP in emergency settings. *Status epilepticus* - **Status epilepticus** significantly increases **cerebral metabolic demand**, leading to increased cerebral blood flow and volume, which can raise **ICP**. - Prolonged seizures can also cause **cerebral edema** due to metabolic disturbances, further contributing to elevated ICP. *Head injury* - **Head injury** frequently causes **brain swelling** (cerebral edema), hematoma formation (extradural, subdural, intraparenchymal), or hydrocephalus, all of which expand intracranial contents and increase **ICP**. - The direct trauma can disrupt the **blood-brain barrier**, leading to vasogenic edema and increased brain volume. *Subdural hematoma* - A **subdural hematoma** is a collection of blood between the dura mater and the arachnoid mater, which acts as a mass lesion within the rigid cranial vault. - This added volume directly increases **intracranial pressure** by occupying space and compressing brain tissue.

Question 739: 'C' fibers carry sensations through which pathway?

A. Posterior column
B. Anterior spinothalamic tract
C. Lateral spinothalamic tract (Correct Answer)
D. All of the options

Explanation: ***Lateral spinothalamic tract*** - **C fibers** are unmyelinated nerve fibers that transmit **slow, dull, burning, or aching pain**, as well as **temperature** sensations. - The **lateral spinothalamic tract** is the primary ascending pathway responsible for conveying these **pain and temperature** sensations from the spinal cord to the brain. *Posterior column* - The **posterior column-medial lemniscus pathway** is primarily responsible for transmitting **fine touch, vibration, conscious proprioception, and two-point discrimination**. - It consists of thickly myelinated A-beta fibers, which are distinct from the unmyelinated C fibers involved in pain transmission. *Anterior spinothalamic tract* - The **anterior spinothalamic tract** mainly carries crude touch and pressure sensations. - While it is a part of the anterolateral system, it does not primarily transmit the pain and temperature signals carried by C fibers. *All of the options* - This option is incorrect because C fibers specifically transmit sensations through the **lateral spinothalamic tract**, not all the listed pathways. - Each pathway has distinct roles in sensory transmission, and C fibers are not associated with the posterior column or exclusively with the anterior spinothalamic tract for their primary functions.

Question 740: Which type of fibers carry warmth sensation?

A. Aα fibers
B. C fibers (Correct Answer)
C. Aβ fibers
D. Aδ fibers

Explanation: ***C fibers*** - **C fibers** are **unmyelinated**, slow-conducting nerve fibers responsible for transmitting **dull, aching pain** and **warmth sensations**. - They are also involved in conveying **itching** and some types of **light touch**. *Aα fibers* - **Aα fibers** are **large**, **myelinated** and are primarily involved in transmitting **proprioception** (sense of body position) and **motor information** to skeletal muscles. - They have the **fastest conduction velocity** among peripheral nerve fibers. *Aβ fibers* - **Aβ fibers** are **medium-sized**, **myelinated** fibers that primarily transmit **light touch**, **pressure**, and **vibration** sensations. - They are responsible for discriminative touch and tactile sensations. *Aδ fibers* - **Aδ fibers** (not Aγ) are **small**, **myelinated** fibers that transmit **fast, sharp pain** and **cold** sensations. - They conduct more rapidly than C fibers due to myelination.

Practice by Chapter

Neurons and Glial Cells

Practice Questions

Synaptic Transmission

Practice Questions

Sensory Processing

Practice Questions

Motor Control Systems

Practice Questions

Autonomic Nervous System

Practice Questions

Hypothalamus and Limbic System

Practice Questions

Cerebral Cortex Functions

Practice Questions

Electroencephalography

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Neuroplasticity

Practice Questions

Sleep and Wakefulness

Practice Questions

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