Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 691: EEG waves prominent in occipital lobe are

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

Explanation: ***Alpha*** - **Alpha waves** are typically most prominent in the **occipital and parietal lobes** when an individual is awake but in a relaxed state with their eyes closed. - They are associated with a state of **relaxed awareness** and tend to disappear when the eyes open or during mental activity or sleep. *Gamma* - **Gamma waves** are the fastest brain waves and are associated with **higher-level cognitive functions**, such as learning, memory, and information processing across different brain regions. - While present throughout the brain, they are not specifically prominent in the occipital lobe in isolation during baseline resting states. *Beta* - **Beta waves** are characteristic of an **alert, awake state** and are often recorded over the frontal and central regions of the brain. - They are associated with active thinking, problem-solving, and concentration, and tend to be suppressed in the occipital region during rest. *Theta* - **Theta waves** are typically associated with **sleep stages 1 and 2**, as well as deep meditation and certain emotional states. - While they can be observed in various brain regions during specific activities or sleep, they are not primarily prominent in the occipital lobe during awake, relaxed states.

Question 692: Most afferent fibers from the lateral geniculate nucleus terminate in which layer of the primary visual cortex:

A. Layer 2 & 3
B. Layer 1
C. Layer 4 (Correct Answer)
D. Layer 5 & 6

Explanation: ***Layer 4*** - The **lateral geniculate nucleus (LGN)** is the primary thalamic relay for visual information. Its afferent fibers directly target and terminate in **Layer 4** (specifically Layer 4C) of the primary visual cortex (V1 or Brodmann area 17). - This layer is characterized by its dense population of **stellate cells**, which are crucial for initial visual processing and relaying information to other cortical layers. *Layer 2 & 3* - These layers (also known as the **supragranular layers**) receive input primarily from layer 4 and are involved in higher-order processing, such as **shape and object recognition**. - They contain **pyramidal neurons** that project to other cortical areas, but they are not the primary termination site for LGN afferents. *Layer 1* - This outermost layer, also known as the **molecular layer**, is relatively cell-sparse and plays a role in **cortical modulation** and integration of synaptic inputs. - It primarily contains axons and dendrites and does not receive direct strong input from the LGN. *Layer 5 & 6* - These layers (also known as the **infragranular layers**) are involved in output from the cortex. Layer 5 contains large **pyramidal cells** that project subcortically (e.g., to the superior colliculus). - Layer 6 projects back to the **thalamus**, including the LGN, thereby modulating its activity, but it is not the primary recipient of LGN afferents.

Question 693: All of the following are known functions of hypothalamus except

A. Temperature regulation
B. Hypophyseal control
C. Food intake
D. Increase in heart rate with exercise (Correct Answer)

Explanation: ***Increase in heart rate with exercise*** - The **hypothalamus** has an indirect role in cardiovascular responses during exercise, primarily through its influence on the **autonomic nervous system** to maintain homeostasis. - However, the primary control of increased heart rate during exercise originates from the **medulla oblongata** and the **motor cortex**, which directly modulates the sympathetic nervous system to increase cardiac output. *Temperature regulation* - The **hypothalamus** contains thermoregulatory centers that monitor and adjust body temperature through mechanisms such as **sweating** and **shivering**. - This function is a fundamental aspect of maintaining **homeostasis**. *Hypophyseal control* - The **hypothalamus** directly controls the **pituitary gland** (hypophysis) by producing releasing and inhibiting hormones that regulate the secretion of pituitary hormones. - This neuroendocrine function is crucial for controlling various **endocrine axes**. *Food intake* - The **hypothalamus** plays a key role in regulating appetite and satiety, with specific nuclei like the **arcuate nucleus** integrating signals related to hunger and fullness. - This control is essential for maintaining **energy balance**.

Question 694: Ablation of the somatosensory area I of the cerebral cortex leads to

A. Loss of tactile localization but not of two point discrimination
B. Loss of tactile localization and two point discrimination (Correct Answer)
C. Total loss of pain sensation
D. Total loss of touch sensation

Explanation: ***Loss of tactile localization and two point discrimination*** - The **somatosensory area I (S1)** is crucial for processing higher-order somatic sensations, including the **discriminative aspects of touch**. - Its ablation leads to deficits in distinguishing distinct points of touch (**two-point discrimination**) and precisely identifying where touch occurred (**tactile localization**). *Loss of tactile localization but not of two point discrimination* - This option incorrectly suggests that **two-point discrimination** would be preserved, which is not the case as S1 is essential for both functions. - While other cortical areas contribute to sensation, S1 is paramount for fine tactile distinctions. *Total loss of pain sensation* - **Pain sensation** is processed across multiple brain regions, including the **thalamus**, **insula**, and **anterior cingulate cortex**, not solely S1. - S1 primarily processes discriminatory aspects of somatosensation, not the affective component of pain. *Total loss of touch sensation* - A total loss of touch sensation implies a complete unawareness of touch, which would require more extensive damage than just S1 ablation, potentially affecting **thalamic pathways** or other cortical regions. - S1 ablation primarily affects the *quality* and *interpretation* of touch, rather than its complete absence.

Question 695: Which of the following acts as the major neurotransmitter in the substantia nigra?

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

Explanation: ***Dopamine*** - The **substantia nigra** is a critical midbrain structure, and its pars compacta (SNc) is the primary site for **dopaminergic neurons** that project to the striatum (nigrostriatal pathway). - The degeneration of these **dopamine-producing neurons** is the hallmark pathology of **Parkinson's disease**. *Serotonin* - While serotonin (5-HT) neurons are found throughout the brain, their primary concentrations are in the **raphe nuclei**, not the substantia nigra. - Serotonin is involved in mood, sleep, appetite, and other functions, but it is not the major neurotransmitter of the substantia nigra. *Acetylcholine* - **Acetylcholine (ACh)** is crucial for muscle contraction, learning, memory, and is prominent in the **basal forebrain** and **brainstem cholinergic nuclei**. - Although it plays a role in basal ganglia function, particularly in the striatum, it is not the major neurotransmitter in the substantia nigra itself. *Noradrenaline* - **Noradrenaline (norepinephrine)** is primarily produced in the **locus coeruleus** in the brainstem and projects widely to the cerebral cortex. - It is involved in arousal, attention, and the stress response, but it is not the dominant neurotransmitter within the substantia nigra.

Question 696: True statement about cerebrospinal fluid is

A. More in ventricle than in subarachnoid space
B. Maximum secreted by choroid plexus (Correct Answer)
C. Flows from lateral ventricles to 3rd ventricle through aqueduct of sylvius
D. CSF formation and absorption are equal at 68 mm CSF pressure

Explanation: ***Maximum secreted by choroid plexus*** - The **choroid plexus**, located within the ventricles, is the primary site of cerebrospinal fluid (CSF) production, responsible for approximately **70-80%** of its secretion. - Cells of the choroid plexus actively transport ions and solutes, drawing water into the ventricular system to form CSF. *More in ventricle than in subarachnoid space* - The majority of CSF volume, approximately **120-150 mL**, is found in the **subarachnoid space** surrounding the brain and spinal cord, not within the ventricles. - The ventricles, while producing CSF, serve more as a conduit for its circulation. *Flows from lateral ventricles to 3rd ventricle through aqueduct of sylvius* - CSF flows from the lateral ventricles to the third ventricle through the **foramina of Monro (interventricular foramina)**, not the aqueduct of Sylvius. - The **aqueduct of Sylvius (cerebral aqueduct)** connects the third ventricle to the fourth ventricle. *CSF formation and absorption are equal at 68 mm CSF pressure* - CSF formation and absorption typically achieve equilibrium at a pressure of approximately **130 mm H2O (or about 10 mmHg)** in a recumbent adult, not 68 mm. - Fluctuations outside this range can indicate issues with CSF circulation or absorption.

Question 697: The rigidity seen in Parkinson's disease is due to

A. Excessive stimulation of alpha motor neurons of all the muscles.
B. Loss of dopaminergic inhibition from substantia nigra. (Correct Answer)
C. Basal ganglia dysfunction affecting muscle tone regulation.
D. Increased sensitivity of stretch reflex.

Explanation: ***Loss of dopaminergic inhibition from substantia nigra.*** - The **loss of dopaminergic neurons** in the **substantia nigra pars compacta** is the fundamental pathophysiological mechanism underlying Parkinsonian rigidity. - This dopamine depletion leads to **altered basal ganglia output**, causing disinhibition of the globus pallidus interna (GPi) and increased inhibitory output to the thalamus. - The result is **continuous co-contraction of agonist and antagonist muscles**, producing the characteristic **lead-pipe rigidity** (uniform resistance throughout range of motion) or **cogwheel rigidity** (when superimposed with tremor). - Unlike spasticity, Parkinsonian rigidity is **not velocity-dependent** and does not show a clasp-knife phenomenon. *Excessive stimulation of alpha motor neurons of all the muscles.* - While there is increased alpha motor neuron activity contributing to muscle stiffness, this is a **downstream effect** of the dopamine loss, not the primary mechanism. - The rigidity results from complex alterations in **basal ganglia-thalamo-cortical circuits**, not simply excessive alpha motor neuron firing. - This option describes a consequence rather than the underlying cause. *Basal ganglia dysfunction affecting muscle tone regulation.* - This statement is **correct but too vague** to be the best answer. - While basal ganglia dysfunction is indeed involved, the **specific mechanism** is the loss of dopaminergic inhibition from the substantia nigra. - In medical education, the more precise pathophysiological mechanism is preferred over general statements. *Increased sensitivity of stretch reflex.* - This is **incorrect** and describes **spasticity**, not Parkinsonian rigidity. - **Spasticity** (from upper motor neuron lesions) shows velocity-dependent resistance and hyperactive stretch reflexes. - **Parkinsonian rigidity** shows uniform resistance independent of velocity and does **not** involve hyperactive stretch reflexes. - The stretch reflex is actually **normal or slightly increased** in Parkinson's disease, but this is not the mechanism of rigidity.

Question 698: Mechanical stimulation of the pain-sensitive structures of the brain can cause headache. All of the following are pain-sensitive structures of the brain, EXCEPT?

A. Dural sheath surrounding vascular sinuses
B. Choroid plexus (Correct Answer)
C. Falx cerebri
D. Middle meningeal artery

Explanation: ***Choroid plexus*** - The choroid plexus is primarily involved in the production of **cerebrospinal fluid (CSF)** and does not contain **pain receptors**. - Its stimulation typically does not cause headache, distinguishing it from other structures. *Dural sheath surrounding vascular sinuses* - The dura mater, especially the dural sheath surrounding **venous sinuses** and major arteries, contains numerous **pain-sensitive nerve endings**. - **Distension or traction** on these structures can result in significant pain, contributing to headache. *Falx cerebri* - The **falx cerebri**, a dural fold, is richly innervated and highly **pain-sensitive**. - **Inflammation, traction, or displacement** of the falx can cause severe headache. *Middle meningeal artery* - The **meningeal arteries**, including the middle meningeal artery, are richly supplied with **nociceptive fibers**. - **Vasodilation or inflammation** of these vessels is a common cause of headache, such as in migraines.

Question 699: A patient came to OPD with a stamping gait. On examination,when he was asked to close his eyes and walk, he fails to walk. Which of the following tracts is most probably affected?

A. Rubrospinal tract
B. Vestibulospinal tract
C. Spinocerebellar tract
D. Posterior column tract (Correct Answer)

Explanation: ***Posterior column tract*** - A **stamping gait** (high-stepping gait where feet are lifted high and slapped down) combined with inability to walk with eyes closed (positive **Romberg's sign**) indicates loss of **conscious proprioception**. - The **posterior column (dorsal column) tract** carries conscious proprioception, fine touch, and vibration sense from the body to the brain. - Patients compensate for proprioceptive loss using visual input; when eyes are closed, they cannot maintain balance or coordinate movement. *Rubrospinal tract* - Controls **muscle tone** and **fine motor movements**, particularly of distal limb muscles. - Damage causes **flexor posturing** and altered tone, not sensory ataxia or stamping gait. *Vestibulospinal tract* - Maintains **postural stability** and **balance** using vestibular input from the inner ear. - Damage causes imbalance and ataxia, but patients typically have difficulty with balance even with eyes **open**, unlike pure proprioceptive loss where vision compensates. *Spinocerebellar tract* - Carries **unconscious proprioception** to the cerebellum for motor coordination. - Damage causes **cerebellar ataxia** with uncoordinated movements, but Romberg's sign remains **negative** because conscious proprioception (posterior columns) is intact, allowing patients to maintain posture with eyes closed.

Question 700: The EEG pattern in REM sleep is:

A. High amplitude, slow waves
B. Low amplitude, slow waves
C. High amplitude, rapid waves
D. Low amplitude, rapid waves (Correct Answer)

Explanation: ***Low amplitude, rapid waves*** - REM sleep is characterized by an **EEG pattern** that is very similar to wakefulness, featuring **desynchronized, low amplitude, high frequency (rapid) waves**. - This pattern reflects high brain activity despite the body being in a state of muscle paralysis (**atonia**), and is often referred to as **paradoxical sleep**. *High amplitude, slow waves* - This EEG pattern, indicative of **delta waves**, is characteristic of **deep non-REM (NREM) sleep** stages 3 and 4 (or N3 in newer classifications). - It signifies a highly synchronized brain state where neuronal firing is slow and highly rhythmic, unlike the active brain state of REM sleep. *Low amplitude, slow waves* - While low amplitude waves can be seen in wakefulness or some lighter NREM stages, the presence of **slow waves** does not align with the highly active and desynchronized nature of REM sleep. - Slow waves are more typical of deeper sleep stages or general drowsiness. *High amplitude, rapid waves* - Although REM sleep involves **rapid waves (high frequency)**, they are typically of **low amplitude**. High amplitude waves suggest synchronization, whereas REM is characterized by desynchronization. - **High amplitude rapid waves** are not a typical EEG characteristic of any sleep stage; rapid waves usually imply lower amplitude due to desynchronization.

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

Practice Questions

Cerebral Cortex Functions

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Electroencephalography

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Neuroplasticity

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Sleep and Wakefulness

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