Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 661: Activation of which of the following fibers results in first pain, which helps to localize the site and intensity of the noxious stimulus?

A. A delta fiber (Correct Answer)
B. A beta fiber
C. C fiber
D. B fiber

Explanation: ***A delta fiber*** - **A delta fibers** are **myelinated** and transmit signals rapidly, leading to the sharp, localized sensation known as **first pain**. - This rapid transmission allows for precise localization of the noxious stimulus and assessment of its initial intensity. *A beta fiber* - **A beta fibers** are primarily responsible for transmitting **light touch** and **vibration** sensations, not noxious stimuli. - While myelinated, their receptive fields and response characteristics do not align with the perception of first pain. *C fiber* - **C fibers** are **unmyelinated** and transmit signals slowly, resulting in a dull, aching, and poorly localized sensation known as **second pain**. - They are involved in the chronic and burning aspects of pain, not the initial, sharp localization. *B fiber* - **B fibers** are preganglionic autonomic fibers primarily involved in the **autonomic nervous system's** functions, not sensory perception of pain. - They are generally found in the autonomic ganglia and do not transmit somatic sensory information.

Question 662: During ocular surgery, when the eye surgeon touches the medial rectus, he asked the assistant to measure heart rate because of

A. Oculocardiac reflex (Correct Answer)
B. Occulocephalic reflex
C. Oculovagal reflex
D. None of the options

Explanation: ***Oculocardiac reflex*** - The **oculocardiac reflex** is a trigeminal-vagal reflex where pressure or traction on the **extraocular muscles** or globe can cause **bradycardia**, or other arrhythmias. - This reflex is mediated by the **trigeminal nerve (V1 ophthalmic branch)** carrying afferent signals to the **Gasserian ganglion**, then to the **main sensory nucleus of the trigeminal nerve** in the brainstem, which subsequently excites the **vagus nerve (efferent)** causing efferent parasympathetic stimulation to the heart leading to decreased heart rate. *Oculocephalic reflex* - The **oculocephalic reflex** (doll's eye maneuver) is used to assess brainstem function. - It involves turning the head and observing eye movements, which are generally conjugate in the opposite direction of head movement if the brainstem is intact. *Oculovagal reflex* - This term is essentially synonymous with the **oculocardiac reflex**, as the oculocardiac reflex involves the **vagus nerve** as its efferent pathway. - It specifically refers to the vagal (parasympathetic) response initiated by ocular stimulation leading to cardiac rate changes. *None of the options* - This option is incorrect because the oculocardiac reflex accurately describes the described phenomenon. - The surgeon is monitoring for a known physiological reflex where ocular manipulation affects cardiac rhythm.

Question 663: Structure of brain involved in emotion: a) Neocortex b) Limbic system c) Thalamus d) Hippocampus

A. Neocortex
B. Thalamus
C. Limbic system (Correct Answer)
D. Hippocampus

Explanation: ***Limbic system*** - The **limbic system** is a complex set of brain structures located on top of the brainstem and underneath the cortex that is primarily associated with **emotion**, motivation, memory, and behavior. - Key components include the **amygdala** (crucial for fear and emotional responses), **hippocampus** (memory formation with emotional context), **hypothalamus** (autonomic responses to emotion), and **cingulate gyrus** (emotional processing). - This is the **primary neuroanatomical system** responsible for emotional processing and regulation. *Neocortex* - The **neocortex** is the outermost layer of the brain involved in higher-level functions such as **conscious thought**, sensory perception, motor commands, and language. - While it modulates and interprets emotions, it is not the primary center for generating basic emotional responses. *Thalamus* - The **thalamus** acts as a **relay station** for sensory and motor signals to the cerebral cortex. - While it processes emotional stimuli, it does not initiate or primarily control emotional responses itself. *Hippocampus* - The **hippocampus** is a crucial part of the limbic system primarily involved in **memory formation**, particularly the consolidation of short-term to long-term memory, and **spatial navigation**. - While it plays a role in recalling emotionally charged memories, it is not the primary structure for the generation or direct experience of emotion itself.

Question 664: A 30-year-old male regained consciousness 36 hours after an accident. It was then discovered that the patient is unable to create new memories. The probable site of lesion for this symptom is:

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

Explanation: ***Hippocampus*** - The **hippocampus** is a critical brain structure for the formation of **new declarative memories** (episodic and semantic memory). Damage to this area, often seen after trauma or anoxia, typically leads to **anterograde amnesia**. - The inability to create new memories (anterograde amnesia) is a classic symptom of **hippocampal damage**, as this region plays a vital role in memory consolidation from short-term to long-term memory. *Amygdala* - The **amygdala** is primarily involved in processing **emotions**, particularly fear, and plays a role in the formation and retrieval of **emotional memories**. - Damage to the amygdala would more likely result in deficits in emotional processing or the emotional component of memories, rather than a general inability to form new declarative memories. *Neocortex* - The **neocortex** is responsible for higher-level cognitive functions, including **long-term storage of memories**, language, perception, and voluntary movement. - While memories are ultimately stored in the neocortex, damage to this area would typically manifest as deficits in specific cognitive functions (e.g., aphasia, agnosia) or affect previously stored memories, rather than the initial formation of new memories. *Hypothalamus* - The **hypothalamus** is a key brain structure for regulating various **autonomic functions** and **hormone release**, including body temperature, hunger, thirst, and circadian rhythms. - While it has indirect connections to memory circuits, damage to the hypothalamus would primarily lead to disruptions in homeostatic processes, not specifically the inability to form new memories.

Question 665: In cold caloric stimulation test, the cold water induces the slow phase of nystagmus (movement of the eyeball) in the following direction

A. Upwards
B. Downwards
C. Towards the opposite side
D. Towards the same side (Correct Answer)

Explanation: ***Towards the same side*** - In a **normal cold caloric test**, cold water stimulates the ear, causing the **slow phase of nystagmus** to drift towards the **irrigated ear (same side)**. - This response is due to decreased firing rate of the vestibular nerve on the cooled side, causing the eyes to deviate towards the irrigated ear. - The slow phase represents the vestibular-driven component of the response. *Upwards* - Upward eye movement is not the primary response to cold caloric stimulation of the horizontal semicircular canal. - Vertical eye movements would suggest involvement of vertical canals or brainstem pathology, not a normal horizontal canal response. *Downwards* - Downward eye movement is not the typical response to cold caloric stimulation. - This does not align with the physiological response of the horizontal semicircular canal being stimulated by cold water. *Towards the opposite side* - The **fast phase** (corrective saccade) beats towards the opposite side, which is why the mnemonic "COWS" (Cold Opposite, Warm Same) exists. - However, the question specifically asks about the **slow phase**, which moves towards the same (irrigated) side. - Clinically, nystagmus is named by its fast phase direction, but the slow phase is the vestibular-driven component.

Question 666: In a posterior column lesion, which of the following is NOT affected? a) Vibration b) Temperature c) Fine touch d) Position sense

A. Vibration
B. Temperature (Correct Answer)
C. Fine touch
D. Position sense

Explanation: ***Temperature*** - The **spinothalamic tract** carries temperature sensation. This tract is located in the **anterolateral column** of the spinal cord, not the posterior column. - A posterior column lesion would therefore **not affect temperature sensation**, as these pathways are distinct. *Vibration* - **Vibration sense** is transmitted via the **dorsal (posterior) columns** of the spinal cord. - Damage to this pathway, as in a posterior column lesion, would **impair vibration perception**. *Fine touch* - **Fine touch** (discriminative touch) is conveyed by the **dorsal (posterior) columns** through the **dorsal column-medial lemniscus pathway**. - A lesion in the posterior column would therefore **disrupt fine touch discrimination**. *Position sense* - **Proprioception**, or position sense, is primarily carried by the **dorsal (posterior) columns**. - A posterior column lesion would lead to **ataxia** and an inability to perceive the position of limbs without visual input.

Question 667: Pruning is:

A. Programmed elimination during development (Correct Answer)
B. Programmed elimination during irradiation
C. Programmed elimination during cancer
D. Programmed elimination during senility

Explanation: ***Programmed elimination during development*** - **Pruning** refers to the **programmed elimination** of excess **synapses** and **neurons** in the developing brain. - This process sculpts neural circuits, making them more efficient and specialized for cognitive functions. *Programmed elimination during irradiation* - **Irradiation** typically causes **cell damage** and death through mechanisms like **DNA damage**, which is not considered pruning. - While it can lead to programmed cell death (apoptosis), it is an exogenous injury, not a physiological developmental process. *Programmed elimination during cancer* - **Cancer** involves uncontrolled cell growth and often resistance to programmed cell death, rather than programmed elimination. - While some cancer treatments aim to induce cell death (e.g., apoptosis), this is a therapeutic intervention, not pruning. *Programmed elimination during senility* - **Senility** (aging) is associated with **neurodegeneration** and neuronal loss, but this is generally considered pathology or age-related decline, not pruning. - Pruning is a precisely timed and regulated developmental process, distinct from the stochastic and generally deleterious processes of aging.

Question 668: What is the normal intracranial pressure in a child (in mmH2O)?

A. 30-70 mm of H2O
B. 50-80 mm of H2O (Correct Answer)
C. 50-150 mm of H2O
D. 100-150 mm of H2O

Explanation: ***50-80 mm of H2O*** - This range represents the normal **intracranial pressure (ICP)** values for children. - While exact reference ranges can vary slightly between sources, this option falls within the generally accepted normal limits for a child. *30-70 mm of H2O* - This range is typically considered normal for **infants**, who have more compliant skulls and lower baseline ICP. - It is often too low for an older child, especially once the **fontanelles** have closed. *50-150 mm of H2O* - The upper end of this range (above 80 mmH2O) would indicate **elevated ICP** in children. - While the lower end is normal, the broadness makes it less precise for normal physiologic ICP. *100-150 mm of H2O* - This range clearly indicates **elevated intracranial pressure** in a child, necessitating immediate clinical evaluation and intervention. - Normal ICP in children is significantly lower than these values.

Question 669: Spinothalamic tract carries ?

A. Two point discrimination
B. Kinesthesia
C. Pain and temperature (Correct Answer)
D. Proprioception

Explanation: ***Pain and temperature*** - The **spinothalamic tract** is primarily responsible for transmitting **pain** and **temperature** sensations to the brain. - This pathway decusates (crosses over) at the level of the spinal cord, meaning sensory information from one side of the body is processed by the contralateral brain. *Two-point discrimination* - This sensory modality is primarily carried by the **dorsal column-medial lemniscus pathway**, not the spinothalamic tract. - It involves the ability to distinguish two separate points of touch on the skin. *Kinesthesia* - **Kinesthesia**, the sense of movement, is also a function of the **dorsal column-medial lemniscus pathway**. - It allows awareness of body and limb position without visual input. *Proprioception* - **Proprioception**, the sense of joint position and limb orientation in space, is mediated by the **dorsal column-medial lemniscus pathway**. - This pathway is crucial for coordinated movement and balance.

Question 670: Wave II in BERA originates from ?

A. Cochlear nucleus
B. Distal eighth nerve
C. Lateral lemniscus
D. Proximal eighth nerve (Correct Answer)

Explanation: ***Proximal eighth nerve*** - **Wave II** of the **Brainstem Auditory Evoked Response (BAER)**, or BERA, is generated by the **proximal portion of the auditory (eighth cranial) nerve** as it enters the brainstem. - This wave reflects the electrical activity of the auditory nerve fibers just before they synapse in the cochlear nucleus. *Cochlear nucleus* - The **cochlear nucleus** is primarily associated with the generation of **Wave III** of the BERA, following the auditory nerve activity. - It's the first synapse in the central auditory pathway, processing signals from the auditory nerve. *Distal eighth nerve* - The **distal portion of the eighth cranial nerve** is where **Wave I** of the BERA originates, representing the initial compound action potential from the auditory nerve as it exits the cochlea. - This wave reflects the activity closest to the cochlea, preceding the more central brainstem responses. *Lateral lemniscus* - The **lateral lemniscus** is a major ascending auditory pathway in the brainstem, and its activity contributes to later waves, specifically **Wave V or VI**, which are generated from the more rostral brainstem structures. - It plays a role in transmitting auditory information from the cochlear nuclei and superior olivary complex to the inferior colliculus.

Practice by Chapter

Neurons and Glial Cells

Practice Questions

Synaptic Transmission

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Sensory Processing

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Motor Control Systems

Practice Questions

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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