Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 741: Dull visceral pain is carried by which type of neurons?

A. A delta
B. Aa
C. C fibres (Correct Answer)
D. B

Explanation: ***C fibres*** - **C fibres** are unmyelinated, small-diameter nerve fibres that conduct impulses slowly (0.5-2 m/s). - They are primarily responsible for transmitting **dull, aching, burning, and chronic pain**, including the diffuse, visceral pain often associated with internal organs. - Visceral pain is typically poorly localized and carried predominantly by C fibers. *A delta* - **A-delta (Aδ) fibres** are thinly myelinated, small-diameter nerve fibres that conduct impulses at moderate speeds (5-30 m/s). - They transmit **sharp, localized, and acute pain** (fast pain or "first pain"), which is different from the dull visceral pain described. - These fibers are responsible for the initial sharp sensation of pain. *Aa* - **Aα (alpha) fibres** are large-diameter, heavily myelinated nerve fibres that conduct impulses very rapidly (70-120 m/s). - They are primarily involved in transmitting **proprioception** (sense of body position) and **motor information to skeletal muscles**, not pain. *B* - **B fibres** are lightly myelinated, small-diameter nerve fibres (3-15 m/s), predominantly found in the autonomic nervous system. - They typically transmit **preganglionic autonomic signals** and are not directly involved in the sensation of somatic or visceral pain.

Question 742: What is the total volume of cerebrospinal fluid (CSF) in an adult human?

A. 150 ml (Correct Answer)
B. 500 ml
C. 50 ml
D. 800 ml

Explanation: ***150 ml*** - The total volume of **cerebrospinal fluid (CSF)** in an adult human is approximately 150 ml, distributed within the brain's ventricles, subarachnoid space, and spinal canal. - This volume is constantly replenished; about 500 ml of CSF are produced daily, meaning the entire volume is replaced several times a day. *500 ml* - While 500 ml is the approximate **daily production rate** of CSF, it is not the total static volume present in the central nervous system at any given time. - The CSF is continually produced and reabsorbed, maintaining a circulating volume of about 150 ml. *50 ml* - 50 ml is significantly **lower** than the actual total volume of CSF found in an adult human. - Such a low volume would likely be insufficient to provide adequate **cushioning** and metabolic support for the brain and spinal cord. *800 ml* - 800 ml is an **excessively large** volume for the total CSF in an adult human and would indicate a severe condition of **hydrocephalus**. - This volume is far beyond the normal physiological capacity for circulating CSF.

Question 743: Which of the following is a primary function of the cerebellum?

A. Coordination of voluntary movements (Correct Answer)
B. None of the options
C. Regulation of muscle tone
D. Planning and initiation of movement

Explanation: ***Coordination of voluntary movements*** - The cerebellum plays a crucial role in **coordinating voluntary movements**, ensuring they are smooth, precise, and fluid. - It receives sensory input from the body and motor commands from the cortex, integrating this information to **adjust ongoing movements** for accuracy. - This is considered the **most prominent and primary function** of the cerebellum in clinical and physiological contexts. *Regulation of muscle tone* - The cerebellum **does regulate muscle tone** and is part of the classical triad of cerebellar functions (coordination, equilibrium, and muscle tone). - However, when compared to coordination of voluntary movements, this is considered a **secondary or supporting function**. - Cerebellar lesions typically cause **hypotonia** (reduced muscle tone), demonstrating its role in tone regulation. - In the context of "primary function," coordination takes precedence over tone regulation. *Planning and initiation of movement* - **Planning and initiation of movement** are primarily functions of the **cerebral cortex**, particularly the supplementary motor area and premotor cortex, along with the basal ganglia. - The cerebellum contributes to motor planning but does not initiate the movement itself. *None of the options* - This option is incorrect because the cerebellum has a clear and primary function as described in the correct option.

Question 744: Which of the following is the primary excitatory neurotransmitter in the central nervous system?

A. GABA
B. Glycine
C. Glutamate (Correct Answer)
D. Aspartate

Explanation: ***Glutamate*** - **Glutamate** is the primary **excitatory neurotransmitter** in the central nervous system - It acts on ionotropic receptors (AMPA, NMDA, kainate) and metabotropic receptors to **depolarize** the postsynaptic membrane - Increases the likelihood of postsynaptic neuron firing by opening ligand-gated ion channels - Plays a crucial role in **synaptic plasticity**, learning, and memory *GABA* - **GABA (gamma-aminobutyric acid)** is the primary **inhibitory neurotransmitter** in the CNS - Hyperpolarizes the postsynaptic membrane by opening chloride channels - Reduces neuronal excitability throughout the brain *Glycine* - **Glycine** is the primary **inhibitory neurotransmitter** in the spinal cord and brainstem - Acts via glycine receptors (chloride channels) leading to hyperpolarization - Important for motor and sensory processing in the spinal cord *Aspartate* - **Aspartate** is also an **excitatory neurotransmitter** acting on NMDA receptors - However, it is **much less abundant** and less important than glutamate - Glutamate is considered the main excitatory neurotransmitter due to its widespread distribution and predominant role

Question 745: At what gestational age does the swallowing-breathing reflex first appear in the fetus?

A. 14 weeks
B. 12 weeks
C. 16 weeks (Correct Answer)
D. Appear in all above period

Explanation: ***16 weeks*** - The **swallowing-breathing reflex** is a crucial protective mechanism that ensures coordination between swallowing and breathing to prevent aspiration. - This reflex is considered to fully develop and become consistently observable in the fetus around **16 weeks of gestation**. *14 weeks* - While some rudimentary swallowing movements may be observed earlier, the integrated and mature **swallowing-breathing reflex** is not fully established at 14 weeks. - The coordination required for this reflex is still developing during this period. *12 weeks* - At 12 weeks, the fetal swallowing mechanism is even less mature, and the **swallowing-breathing reflex** is not yet present. - Fetal development at this stage is primarily focused on organogenesis and basic motor functions. *Appear in all above period* - This statement is incorrect because the **swallowing-breathing reflex** has a specific developmental timeline and is not consistently functional at all gestational ages mentioned. - Its full emergence is a hallmark of more mature neuromuscular coordination.

Question 746: Horizontal acceleration with forward movement in the sagittal plane is detected by ?

A. Macula of Saccule
B. Macula of Utricle (Correct Answer)
C. Lateral semicircular canal
D. Posterior semicircular canal

Explanation: ***Macula of Utricle*** - The **utricle** is primarily responsible for detecting **horizontal linear acceleration**, such as forward/backward and side-to-side movements in the **sagittal and coronal planes**. - Its **macula** is oriented **horizontally**, making it the ideal structure for sensing horizontal acceleration with forward movement in the sagittal plane. - The utricle contains otoliths (calcium carbonate crystals) that shift with linear acceleration, stimulating hair cells that signal movement direction. *Macula of Saccule* - The **saccule** is primarily responsible for detecting **vertical linear acceleration** of the head, such as moving up and down in an elevator. - Its macula is oriented **vertically**, not horizontally, making it unsuitable for detecting horizontal forward movement. - While it may have minor secondary roles in certain head positions, it is NOT the primary detector for horizontal sagittal plane movement. *Lateral semicircular canal* - The **lateral semicircular canal** detects **rotational acceleration** primarily in the **horizontal plane**, such as turning the head from side to side (yaw rotation). - It does **not** detect linear acceleration like forward movement—only angular/rotational movements. *Posterior semicircular canal* - The **posterior semicircular canal** detects **rotational acceleration** when the head moves in the **sagittal plane**, like nodding (pitch rotation). - It works in conjunction with the anterior semicircular canal to detect head rotations, not linear acceleration.

Question 747: While walking or standing, posture is maintained by?

A. Basal ganglia
B. Hypothalamus
C. Cerebellum (Correct Answer)
D. Amygdala

Explanation: ***Cerebellum*** - The **cerebellum** plays a crucial role in maintaining **balance and posture** by coordinating muscular activity, regulating muscle tone, and integrating sensory input. - It receives information about planned movements from the motor cortex and current body position from sensory receptors, allowing it to make real-time adjustments for stable locomotion and standing. *Basal ganglia* - The **basal ganglia** are primarily involved in the **initiation and control of voluntary movements**, motor learning, and routine behaviors. - While they influence movement, their direct role in the instantaneous maintenance of posture is less prominent than that of the cerebellum. *Hypothalamus* - The **hypothalamus** is a key brain region for regulating **autonomic functions**, hormone release, and maintaining homeostasis (e.g., body temperature, hunger, thirst). - It does not have a direct or primary role in the control of conscious posture or balance during walking or standing. *Amygdala* - The **amygdala** is a central component of the **limbic system**, primarily involved in processing emotions, particularly fear, and emotional memory. - It has no direct involvement in the motor control mechanisms required for maintaining posture during locomotion.

Question 748: Feed forward inhibition synapse is seen in:

A. Medulla
B. Basal ganglia
C. Hypothalamus
D. Cerebellum (Correct Answer)

Explanation: ***Cerebellum*** - The **cerebellum** is well-known for its role in motor control and learning, utilizing intricate neural circuits, including **feedforward inhibition**. - **Granule cells** excite **Purkinje cells** (the output neurons of the cerebellar cortex) and also excite **Golgi cells**, which then inhibit granule cells, creating a feedforward inhibitory loop to regulate granule cell activity. *Medulla* - The **medulla oblongata** is primarily involved in vital autonomic functions like respiration, heart rate, and blood pressure, and typically features different types of neural circuits. - While inhibition is crucial in medullary circuits, the prominent **feedforward inhibitory synapse** structure described in motor control is not its defining characteristic. *Basal ganglia* - The **basal ganglia** are involved in voluntary motor control, procedural learning, and habit formation, characterized by direct and indirect pathways that are largely modulatory. - While it has complex inhibitory and excitatory loops, the specific architecture of a **feedforward inhibitory synapse** that modulates the same input neuron, as seen in the cerebellum, is not its primary organizational principle. *Hypothalamus* - The **hypothalamus** is a key control center for endocrine and autonomic functions, regulating things like hunger, thirst, and body temperature. - Its neural circuitry is focused on hormonal regulation and homeostatic control, rather than elaborate motor coordination networks that prominently feature **feedforward inhibition** for precise timing.

Question 749: Which of the following statements about cerebellar neuronal connections is correct?

A. Mossy fibers provide inhibitory input to granule cells.
B. Climbing fibers provide inhibitory input to Purkinje cells.
C. Climbing fibers originate from the inferior olivary nucleus and project to Purkinje cells. (Correct Answer)
D. Mossy fibers originate only from the pontine nuclei and synapse with Purkinje cells.

Explanation: *Mossy fibers provide inhibitory input to granule cells.* - **Mossy fibers** provide **excitatory input** to granule cells, not inhibitory. - They also synapse on **Golgi cells**, which then provide inhibitory input to granule cells, forming a feedback loop. *Climbing fibers provide inhibitory input to Purkinje cells.* - **Climbing fibers** provide **excitatory input** to Purkinje cells, not inhibitory. - This **excitatory input** is strong and direct, leading to complex spikes in Purkinje cells. ***Climbing fibers originate from the inferior olivary nucleus and project to Purkinje cells.*** - **Climbing fibers** are crucial for motor learning and coordination, directly **synapsing** onto Purkinje cells. - They provide a very powerful excitatory input to **Purkinje cells**, causing complex spike discharges. *Mossy fibers originate only from the pontine nuclei and synapse with Purkinje cells.* - **Mossy fibers** originate from various sources, including the **pontine nuclei**, spinal cord, and vestibular nuclei; they do not originate only from pontine nuclei. - They do not directly synapse with Purkinje cells but instead synapse with **granule cells** in the cerebellar cortex.

Question 750: Which of the following sensations is carried by pathways that relay through the thalamus via the spinothalamic tract?

A. Proprioception
B. Tactile sensations
C. Pressure
D. Pain & temperature (Correct Answer)

Explanation: ***Pain & temperature*** - The **spinothalamic tracts** (lateral and anterior) are the primary pathways for relaying **pain** and **temperature** sensations from the periphery to the **thalamus**. - These sensations synapse in the **thalamus** before being projected to the somatosensory cortex for conscious perception. *Proprioception* - **Proprioception** (sense of body position) is primarily relayed through the **dorsal column-medial lemniscus pathway**, which also synapses in the thalamus. - However, the thalamic relay is crucial for all conscious somatic sensations, but pain and temperature are most *classically* and *exclusively* associated with dedicated spinothalamic tracts. *Tactile sensations* - **Crude touch** (general tactile sensation) is carried by the anterior spinothalamic tract, but **fine touch** and **discriminative touch** are primarily carried by the **dorsal column-medial lemniscus pathway**. - While tactile sensations involve thalamic relay, the pathways are more diverse compared to the distinct spinothalamic tracts for pain and temperature. *Pressure* - **Pressure sensation** is also primarily carried by the **dorsal column-medial lemniscus pathway**, similar to proprioception. - While it relays through the thalamus, it shares a pathway with other mechanoreceptive sensations rather than having a distinct, classic dedicated pathway like pain and temperature.

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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