Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 781: Which of the following is the MOST accurate statement about CSF?

A. Formed by the choroid plexus in the ventricles. (Correct Answer)
B. Normally contains no neutrophils
C. pH is less than that of plasma
D. Removal of CSF during dural tap can cause a headache due to the change in pressure.

Explanation: ***Formed by the choroid plexus in the ventricles.*** * The **choroid plexus**, located in the ventricles of the brain, is primarily responsible for the production of **cerebrospinal fluid (CSF)**. * Specialized epithelial cells of the choroid plexus filter blood plasma to produce CSF, which then circulates through the central nervous system. *Normally contains no neutrophils* * Normal CSF should contain **virtually no neutrophils**; their presence typically indicates an inflammatory or infectious process, such as **bacterial meningitis**. * While normal CSF doesn't have neutrophils, this option isn't as broadly accurate as the choroid plexus statement because the presence of other cell types like lymphocytes in small numbers is normal. *pH is less than that of plasma* * The pH of CSF is typically **slightly lower than that of plasma** (around 7.31 compared to 7.40), but the statement "less than" is broad and the degree of difference can be variable and is a less defining characteristic than its formation site. * This slight difference in pH is important for regulating **respiration** through chemoreceptors, but it's not the most accurate or fundamental statement about CSF properties. *Removal of CSF during dural tap can cause a headache due to the change in pressure.* * A **post-dural puncture headache** (PDPH) is a well-known complication of a dural tap (lumbar puncture), caused by the leakage of CSF from the puncture site, leading to **intracranial hypotension**, not simply a change in pressure. * This decrease in CSF volume and pressure causes a traction on pain-sensitive structures within the cranium, resulting in a headache that is typically **worse when upright** and relieved by lying down.

Question 782: Which sensory modalities are most directly affected by lesions of the primary somatosensory cortex?

A. Pain, temperature, and touch
B. Vibration and proprioception
C. Localization and two-point discrimination (Correct Answer)
D. All of the options

Explanation: ***Localization and two-point discrimination*** - Lesions in the **primary somatosensory cortex** (S1) lead to profoundly impaired **discriminative touch**, which includes the ability to precisely localize tactile stimuli and distinguish between two closely spaced points. - These are the **most characteristic deficits** of S1 lesions, representing the cortex's unique role in processing **spatial discrimination and fine sensory analysis**. - S1 is essential for the **integrative functions** that allow precise spatial mapping of sensory inputs. *Pain, temperature, and touch* - Basic touch perception is affected, but **pain and temperature** are primarily mediated by the **spinothalamic tracts** with substantial processing in the thalamus, insular cortex, and anterior cingulate cortex rather than S1. - Crude touch sensation remains relatively preserved with S1 lesions; it is the **discriminative quality** that is lost. - These modalities are NOT the most directly affected by isolated S1 lesions. *Vibration and proprioception* - **Vibration** and **proprioception** are indeed significantly impacted by S1 lesions as S1 receives thalamic projections from the **dorsal column-medial lemniscus (DCML) pathway**. - However, these modalities have substantial **subcortical representation** in the thalamus and can be partially preserved even with cortical damage. - In contrast, **localization and two-point discrimination** are purely cortical functions with no subcortical processing, making them the MOST directly and exclusively dependent on S1 integrity. *All of the options* - This is incorrect because pain and temperature perception is NOT most directly affected by S1 lesions—these are primarily processed by other pathways and cortical areas (spinothalamic system, insular cortex).

Question 783: Normal cerebrospinal fluid pressure is

A. 5-10 mmH2O
B. 180-300 mmH2O
C. 110-180 mmH2O (Correct Answer)
D. 200-400 mmH2O

Explanation: ***110-180 mmH2O*** - This range represents the **upper portion of normal CSF pressure** and is the best answer among the given options. - Complete normal **cerebrospinal fluid (CSF) pressure**, as measured during lumbar puncture in lateral decubitus position, is typically **60-180 mmH2O** (or 50-180 mmH2O per some references). - While 110 mmH2O is slightly higher than the traditional lower limit, this option is acceptable as it falls within normal range and is clearly superior to the other choices. - Normal CSF pressure is crucial for maintaining **brain homeostasis** and protecting it from injury. *180-300 mmH2O* - This range indicates **elevated CSF pressure (intracranial hypertension)**, exceeding normal limits. - Such pressures may be seen in disorders like **idiopathic intracranial hypertension** or **hydrocephalus**. - Values above 200-250 mmH2O are generally considered significantly elevated. *200-400 mmH2O* - This represents **severely elevated CSF pressure**, indicating significant intracranial hypertension. - Pressures this high demand urgent medical attention as they can lead to **brain herniation** and irreversible neurological damage. - This is clearly pathological and well above normal range. *5-10 mmH2O* - This is significantly **lower than normal CSF pressure** and indicates **intracranial hypotension**. - Normal CSF pressure should not fall below 50-60 mmH2O. - Low CSF pressure can cause symptoms such as **postural headaches**, nausea, and dizziness, often seen after lumbar puncture or CSF leak.

Question 784: Cranial nerve 8 palsy is associated with all of the following symptoms except:

A. Gag reflex (Correct Answer)
B. Hearing loss
C. Tinnitus
D. Vertigo

Explanation: ***Gag reflex*** - The **gag reflex** is primarily mediated by the **glossopharyngeal (CN IX)** and **vagus (CN X)** nerves. - CN VIII, the vestibulocochlear nerve, is solely responsible for hearing and balance, and thus has no role in the gag reflex. *Vertigo* - **Vertigo** is a common symptom of CN VIII palsy, specifically involving the **vestibular branch** of the nerve. - Damage to this branch can disrupt the sense of balance and spatial orientation. *Hearing loss* - **Hearing loss** is a hallmark symptom of CN VIII palsy, affecting the **cochlear branch** of the nerve. - This can manifest as conductive, sensorineural, or mixed hearing loss, depending on the specific pathology. *Tinnitus* - **Tinnitus**, the perception of sound when no external sound is present, is frequently associated with CN VIII palsy. - It often accompanies hearing loss and is a common complaint in conditions affecting the auditory system.

Question 785: Keyhole-shaped visual field defect is seen in a lesion involving which of the following regions?

A. Lesion of the lateral geniculate body
B. Lesion of the optic disk (Correct Answer)
C. Lesion of the optic chiasma
D. Lesion of the occipital lobe

Explanation: ***Lesion of the optic disk*** - A **keyhole-shaped visual field defect** is a **pathognomonic sign** of **optic disc lesions**, particularly in **glaucomatous optic neuropathy**. - This characteristic defect occurs due to damage to **retinal nerve fiber bundles** as they converge at the optic disc, respecting the **horizontal raphé**. - Arcuate scotomas (superior and inferior) can coalesce around the point of fixation, creating the distinctive **keyhole or dumbbell shape**. - The pattern reflects the anatomical organization of nerve fibers entering the optic nerve head. *Lesion of the lateral geniculate body* - Lesions of the **lateral geniculate body (LGB)** typically cause **incongruous homonymous hemianopias** or **quadrantanopias**, not keyhole defects. - The LGB has retinotopic organization with six layers, and partial lesions cause visual field defects affecting corresponding areas in both eyes. - Vascular lesions (from lateral choroidal artery branches) can cause sector-shaped or wedge-shaped defects, but not keyhole patterns. *Lesion of the optic chiasma* - A lesion of the optic chiasma typically leads to **bitemporal hemianopia**, where the temporal visual fields of both eyes are affected, usually due to compression from a **pituitary tumor**. - This is characterized by loss of vision in the outer halves of the visual field for both eyes, which is distinct from a keyhole defect. - The crossing nasal fibers are affected, resulting in bilateral temporal field loss. *Lesion of the occipital lobe* - Lesions in the occipital lobe, specifically the **primary visual cortex (V1)**, generally cause **homonymous hemianopia** or **quadrantanopia** respecting the vertical midline. - This means the same side of the visual field is affected in both eyes, and **macular sparing** may be present due to dual vascular supply. - Occipital lobe defects are typically congruous (identical in both eyes) and do not produce keyhole-shaped patterns.

Question 786: Nociceptive signals from the face and head are transmitted primarily to which of the following?

A. Nucleus caudalis (Correct Answer)
B. Limbic system
C. Reticular system
D. Superior cervical ganglion

Explanation: ***Nucleus caudalis*** - The **nucleus caudalis** (spinal trigeminal nucleus, pars caudalis) is the primary processing center for **nociceptive (pain)** information from the face and head, received via the trigeminal nerve. - It extends into the upper cervical spinal cord and is functionally analogous to the dorsal horn of the spinal cord for body pain. *Limbic system* - The **limbic system** is involved in the **emotional processing** of pain, memory, and motivation, but it does not receive primary nociceptive input directly from the face and head. - It receives projections from areas like the thalamus and somatosensory cortex after initial processing. *Reticular system* - The **reticular system** plays a role in alertness, sleep-wake cycles, and modulates pain perception, but it is not the primary relay for initial nociceptive signals. - It has diffuse connections throughout the brainstem and receives inputs from ascending sensory pathways. *Superior cervical ganglion* - The **superior cervical ganglion** is part of the **sympathetic nervous system** and is involved in controlling functions like pupillary dilation and salivary gland secretion. - It does not directly receive or process nociceptive signals from the face and head.

Question 787: Perception of ordinarily non-noxious stimuli as pain is better known as?

A. Hyperalgesia (increased pain response)
B. Hyperesthesia (increased sensitivity to stimuli)
C. Radiculopathy (nerve root compression)
D. Allodynia (pain from non-painful stimuli) (Correct Answer)

Explanation: ***Allodynia (pain from non-painful stimuli)*** - This term precisely describes the phenomenon where a typically **non-painful stimulus**, such as light touch or brushing, is perceived as painful. - It results from **altered processing** of sensory information, often due to central or peripheral sensitization. *Hyperalgesia (increased pain response)* - This refers to an **exaggerated response** to a stimulus that is *normally painful*, meaning the pain is felt more intensely than expected. - Unlike allodynia, the stimulus itself is inherently noxious, but the patient's reaction is disproportionately severe. *Hyperesthesia (increased sensitivity to stimuli)* - This is a general term for **increased sensitivity** to *any* sensory stimulus, which could include touch, temperature, or sound. - It does not specifically denote pain from non-noxious stimuli, but rather an amplified perception of normal sensations. *Radiculopathy (nerve root compression)* - This is a neurological condition caused by the **compression or irritation of a nerve root**, typically in the spine. - While it can cause pain, numbness, or weakness in the distribution of the affected nerve, it is a diagnosis of the *cause* of symptoms, not a description of the *type* of pain perception itself like allodynia.

Question 788: Berger waves (alpha waves) of EEG have a rhythm of how many Hz?

A. 0-4 Hz
B. 4-7 Hz
C. 8-13 Hz (Correct Answer)
D. 13-30 Hz

Explanation: ***8-13 Hz*** - **Berger waves**, also known as **alpha waves**, are defined by their frequency range of **8 to 13 Hz** in the electroencephalogram (EEG). - These waves are typically observed when a person is in a relaxed, awake state with their eyes closed. *0-4 Hz* - This frequency range corresponds to **delta waves**, which are characteristic of deep sleep and certain brain pathologies. - Delta waves are much slower and have higher amplitude compared to alpha waves. *4-7 Hz* - This frequency range is associated with **theta waves**, commonly seen during light sleep, drowsiness, and some meditative states. - Theta waves are slower than alpha waves and indicate a state of reduced alertness. *13-30 Hz* - This frequency range represents **beta waves**, which are associated with active thinking, problem-solving, and alertness with open eyes. - Beta waves are faster and typically have lower amplitude than alpha waves.

Question 789: Which of the following Brodmann areas is primarily associated with Broca's motor aphasia?

A. 44 (Correct Answer)
B. 4
C. 22
D. 17

Explanation: ***Brodmann Area 44*** - **Brodmann area 44**, also known as **Broca's area**, is located in the inferior frontal gyrus and is critical for **speech production**. - Damage to this area typically leads to **Broca's motor aphasia** (also called expressive aphasia), characterized by **non-fluent speech**, difficulty forming words, and impaired grammar while comprehension remains relatively intact. *Brodmann Area 4* - **Brodmann area 4** corresponds to the **primary motor cortex**, responsible for executing voluntary movements. - While essential for motor control, it is not directly involved in the cognitive aspects of language production that define Broca's aphasia. *Brodmann Area 22* - **Brodmann area 22** is primarily associated with **Wernicke's area**, which is located in the superior temporal gyrus and is crucial for **language comprehension**. - Damage to this area results in **Wernicke's aphasia** (receptive aphasia), characterized by fluent but meaningless speech and impaired comprehension. *Brodmann Area 17* - **Brodmann area 17** is the **primary visual cortex**, responsible for processing visual information. - It plays no direct role in language processing or speech production; damage here would primarily cause visual field deficits.

Question 790: In the context of motor coordination, Purkinje cells from the cerebellum end in which of the following?

A. Extrapyramidal system
B. Cranial nerve nuclei
C. Cerebellar nuclei (Correct Answer)
D. Cerebral cortex

Explanation: ***Cerebellar nuclei*** - **Purkinje cells** are the primary output neurons of the **cerebellar cortex** and are GABAergic (inhibitory). - They project exclusively to the **deep cerebellar nuclei** (fastigial, globose, emboliform, and dentate nuclei), where they inhibit the nuclear neurons, which then project out of the cerebellum. *Extrapyramidal system* - The **extrapyramidal system** refers to neural networks involved in the modulation of movement, distinct from the corticospinal (pyramidal) tracts, and includes structures like the basal ganglia and brainstem nuclei. - While the cerebellum indirectly influences the extrapyramidal system through its projections from the deep cerebellar nuclei to brainstem nuclei, Purkinje cells do not directly terminate there. *Cranial nerve nuclei* - **Cranial nerve nuclei** are located in the brainstem and control the functions of the cranial nerves. - Purkinje cells do not directly project to these nuclei; rather, cerebellar output influences them indirectly through pathways that first involve the deep cerebellar nuclei. *Cerebral cortex* - The **cerebral cortex** is the outer layer of the cerebrum, responsible for higher cognitive functions and voluntary movements. - Purkinje cells do not project directly to the cerebral cortex; instead, cerebellar output reaches the cortex indirectly via the **thalamus**.

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

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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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