Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 671: Fine touch and position sense is carried by

A. Lateral spinothalamic tract
B. Anterior spinothalamic tract
C. Spinocerebellar tract
D. Dorsal column (Correct Answer)

Explanation: ***Dorsal column*** - The **dorsal column-medial lemniscus pathway** is responsible for transmitting **fine touch**, **vibration**, **proprioception**, and **two-point discrimination** from the body to the brain. - This pathway includes the **fasciculus gracilis** (lower body) and **fasciculus cuneatus** (upper body) in the spinal cord. *Lateral spinothalamic tract* - The **lateral spinothalamic tract** primarily transmits sensations of **pain** and **temperature**. - It decussates (crosses) at the level of entry in the spinal cord and ascends contralaterally. *Anterior spinothalamic tract* - The **anterior spinothalamic tract** carries information about **crude touch** and **pressure**. - Like the lateral spinothalamic tract, it decussates at the spinal cord level and ascends contralaterally. *Spinocerebellar tract* - The **spinocerebellar tracts** (anterior and posterior) convey unconscious **proprioceptive** information to the **cerebellum**. - This information helps in coordinating muscle movements and maintaining posture, but it does not carry conscious fine touch or position sense.

Question 672: Pain and temperature are carried by:

A. Lateral spinothalamic tract (Correct Answer)
B. Dorsal column pathway
C. Anterior spinothalamic tract
D. Ventral column pathway

Explanation: ***Lateral spinothalamic tract*** - The **lateral spinothalamic tract** is primarily responsible for transmitting **pain** and **temperature** sensations from the body to the brain. - This pathway decussates (crosses) at the level of the spinal cord segment where the sensory neuron enters, then ascends contralaterally. *Dorsal column pathway* - The **dorsal column pathway** (also known as the posterior column-medial lemniscus pathway) is responsible for **fine touch, vibration, and proprioception**. - It ascends ipsilaterally in the spinal cord and decussates in the medulla oblongata. *Anterior spinothalamic tract* - The **anterior spinothalamic tract** primarily carries information related to **crude touch** and **pressure**. - While part of the spinothalamic system, it does not carry pain and temperature as its primary function. *Ventral column pathway* - The term **ventral column pathway** is not a standard, precise neuroanatomical classification for a specific sensory tract. - While parts of the spinothalamic tracts (anterior and lateral) are located in the ventral/anterior funiculus of the spinal cord, "ventral column pathway" itself is not a primary sensory pathway.

Question 673: Stimulation by touching or pulling on which structure is least likely to cause a painful sensation?

A. The postcentral gyrus (Correct Answer)
B. The dura overlying the postcentral gyrus
C. Branches of the middle cerebral artery that supply the postcentral gyrus
D. Branches of the middle meningeal artery that lie between the skull and dura over the postcentral gyrus

Explanation: ***The postcentral gyrus*** - The **brain parenchyma**, including the postcentral gyrus, **lacks pain receptors (nociceptors)**. Therefore, direct stimulation or manipulation of brain tissue itself does not elicit a sensation of pain. - Patients can be fully conscious during some brain surgeries without pain from the brain tissue being operated on, though they may experience other sensations or deficits depending on the stimulated area. *The dura overlying the postcentral gyrus* - The **dura mater** is highly innervated by **nociceptors**, particularly in certain areas like the anterior and middle cranial fossae. Traction or irritation of the dura can cause significant pain, often referred to specific head regions. - This pain is mediated by cranial nerves, such as the trigeminal and vagus nerves, and cervical spinal nerves. *Branches of the middle cerebral artery that supply the postcentral gyrus* - The **blood vessels** supplying the brain, including branches of the **middle cerebral artery**, are invested with **pain fibers**. - Stretching or irritation of these blood vessels, especially during procedures or in pathological conditions like **vasospasm**, can cause referred pain sensations. *Branches of the middle meningeal artery that lie between the skull and dura over the postcentral gyrus* - The **middle meningeal artery** and its branches run in the **epidural space** (between the skull and dura mater) and contribute to pain sensation in this region. - Like the dura itself, these vessels and their surrounding tissues contain **nociceptors**, and their manipulation or irritation can cause significant pain, often perceived as a headache.

Question 674: Perception of normal (non-painful) sensory stimuli as painful is called

A. Causalgia
B. Hyperpathia
C. Hyperalgesia
D. Allodynia (Correct Answer)

Explanation: ***Allodynia*** - This is the experience of **pain from stimuli that are not typically painful**, such as light touch or brushing against the skin. - It arises from abnormal processing of sensory signals in the central nervous system, often seen in conditions like **neuropathic pain** and **fibromyalgia**. *Causalgia* - This term refers to **complex regional pain syndrome type II**, which is characterized by **burning pain** and often involves nerve injury. - While it involves severe pain, it typically results from a noxious stimulus becoming excessively painful, rather than a non-painful stimulus being perceived as painful. *Hyperpathia* - This describes an **exaggerated pain reaction to a painful stimulus**, often involving a raised threshold for pain alongside an increased and persistent response. - Unlike allodynia, the initial stimulus is already painful; hyperpathia simply makes the response more intense and prolonged. *Hyperalgesia* - This is an **increased pain response to a stimulus that is normally painful**, meaning a painful stimulus is perceived as even more painful than expected. - The key difference from allodynia is that the stimulus itself is already nociceptive (pain-producing), whereas in allodynia, a non-nociceptive stimulus elicits pain.

Question 675: The structure that integrates impulses for eye-hand coordination is:

A. Pretectal nucleus
B. Superior colliculus (Correct Answer)
C. Frontal eye field
D. Area 17

Explanation: ***Superior colliculus*** - The **superior colliculus** is a crucial midbrain structure that plays a significant role in integrating visual, auditory, and somatosensory information to direct **saccadic eye movements** and orienting behaviors. - Its output projects to motor centers, facilitating **eye-hand coordination** by linking visual targets with appropriate motor responses. *Pretectal nucleus* - The **pretectal nucleus** is primarily involved in mediating the **pupillary light reflex**, controlling pupil constriction in response to light. - While it processes visual information, its main function is not direct eye-hand coordination. *Frontal eye field* - The **frontal eye field** is a part of the cerebral cortex involved in the voluntary control of eye movements, particularly **saccades**. - It plans and initiates eye movements but does not directly integrate sensory input for eye-hand coordination in the same way the superior colliculus does. *Area 17* - **Area 17**, also known as the **primary visual cortex (V1)**, is responsible for the initial processing of visual information, including detecting edges, orientations, and colors. - It is foundational for vision but does not directly integrate multimodal sensory input for coordinating eye and hand movements.

Question 676: Dorsal column lesions are associated with loss of:

A. Loss of ankle jerk reflex
B. Loss of superficial abdominal reflexes
C. Loss of proprioception (Correct Answer)
D. Loss of knee jerk reflex

Explanation: ***Proprioception*** - The **dorsal column-medial lemniscus pathway** is responsible for transmitting fine touch, vibration, and **proprioception** from the body to the brain. - Damage to this pathway, such as in a **dorsal column lesion**, directly impairs the ability to sense the position and movement of body parts. *Loss of ankle jerk reflex* - The **ankle jerk reflex**primarily tests the integrity of the **S1 and S2 nerve roots** and the reflex arc involving the gastrocnemius and soleus muscles. - This reflex is generally not directly affected by isolated dorsal column lesions, as it is a **deep tendon reflex** that relies on sensory and motor neuron pathways distinct from the dorsal column. *Loss of superficial abdominal reflexes* - **Superficial abdominal reflexes** assess the integrity of the T7-T12 spinal cord segments and corresponding nerve pathways. - These reflexes involve different neurological pathways compared to the dorsal column, which is primarily sensory for conscious proprioception, vibration, and fine touch. *Loss of knee jerk reflex* - The **knee jerk reflex** (patellar reflex) tests the integrity of the **L2, L3, and L4 spinal nerve roots** and the quadriceps femoris muscle. - Like the ankle jerk, this is a **deep tendon reflex** whose arc is separate from the dorsal column's ascending sensory tracts.

Question 677: The normal concentration of protein in CSF at 4 weeks may be as high as-

A. 80mg%
B. 100mg%
C. 120mg%
D. 150mg% (Correct Answer)

Explanation: ***150mg%*** - In newborns and infants, the **blood-brain barrier** is not fully mature, leading to higher CSF protein levels than in adults. - At 4 weeks of age, CSF protein concentrations within the range of **100-170 mg/dL** (100-170 mg%) are considered normal. *80mg%* - While a normal CSF protein level for adults is typically **<45 mg/dL**, pediatric ranges are significantly higher. - **80 mg%** is lower than expected for a 4-week-old infant. *100mg%* - This value is at the **lower end of the normal range** for a 4-week-old infant. - While possible, it may reflect early maturation or be on the borderline. *120mg%* - This is within the normal limits, but the question asks for "as high as", implying the **upper limit of normal**. - **150mg%** better represents the potential maximum normal value at this age.

Question 678: Complete transection of the spinal cord at the C7 level produces all of the following effects except:

A. Areflexia below the level of the lesion (Correct Answer)
B. Limited respiratory effort
C. Anesthesia below the level of the lesion
D. Hypotension

Explanation: ***Areflexia below the level of the lesion*** - While immediate **spinal shock** after a complete transection would cause areflexia, over time, the segments below the lesion often develop **hyperreflexia** and spasticity due to the loss of descending inhibitory control. - Therefore, sustained areflexia is an *unlikely* long-term effect of a complete spinal cord transection at C7. *Limited respiratory effort* - A C7 lesion would affect the **intercostal muscles** (innervated by T1-T11) and the **abdominal muscles** (innervated by T7-L1), which are crucial for forceful exhalation and coughing. - While the diaphragm (C3-C5) would be spared, breathing would still be significantly compromised, leading to a limited respiratory effort. *Anesthesia below the level of the lesion* - Complete transection interrupts all ascending sensory pathways, including the **spinothalamic tracts** (pain and temperature) and the **dorsal columns** (fine touch, vibration, proprioception), resulting in a complete loss of sensation below the C7 dermatome. - This is a hallmark of a complete spinal cord injury. *Hypotension* - Complete transection at C7 would disrupt the **sympathetic nervous system** pathways originating in the thoracolumbar region (T1-L2). - This leads to a loss of sympathetic tone to blood vessels, causing **vasodilation** and subsequent neurogenic shock, characterized by severe hypotension and bradycardia.

Question 679: Which of the following is true regarding cerebrospinal fluid?

A. Virtually glucose free
B. Is actively secreted by choroid plexus (Correct Answer)
C. Has the same pH of arterial blood
D. It is a major source of brain nutrition

Explanation: **Is actively secreted by choroid plexus** - **Cerebrospinal fluid (CSF)** is primarily produced by the **choroid plexus** via a combination of active transport and ultrafiltration processes. - The epithelial cells of the **choroid plexus** actively secrete ions and water, contributing to the formation and composition of CSF. *Virtually glucose free* - CSF normally contains **glucose**, although its concentration is about two-thirds of the plasma glucose concentration. - Significant reduction or absence of glucose in CSF often indicates a pathological process, such as **bacterial meningitis**. *Has the same pH of arterial blood* - The pH of CSF is typically slightly lower than that of arterial blood, usually around **7.31-7.34**, compared to plasma pH of 7.35-7.45. - This difference is crucial for maintaining the delicate acid-base balance within the central nervous system. *It is a major source of brain nutrition* - While CSF provides some nutrients, the primary source of brain nutrition is the **blood supply** through the cerebral vasculature. - Its main roles include providing **buoyancy**, **protection**, and acting as a medium for metabolite exchange, rather than direct substantial nutrition.

Question 680: A lesion of ventrolateral part of spinal cord will lead to loss of which of the following sensation below the level of lesion?

A. Proprioception on the contralateral side
B. Proprioception on the ipsilateral side
C. Pain sensation on the ipsilateral side
D. Pain sensation on the contralateral side (Correct Answer)

Explanation: ***Pain sensation on the contralateral side*** - The **ventrolateral part of the spinal cord** contains the **spinothalamic tract**, which transmits **pain and temperature** sensations. - Fibers of the spinothalamic tract **decussate (cross over)** at the level of entry into the spinal cord, meaning a lesion will cause loss of pain sensation on the **contralateral side** below the lesion. *Proprioception on the contralateral side* - **Proprioception** is primarily carried by the **dorsal columns**, which are located more posteriorly in the spinal cord. - Fibers for proprioception from the dorsal columns **decussate in the medulla**, not at the spinal cord level, so a spinal cord lesion would generally affect ipsilateral proprioception. *Proprioception on the ipsilateral side* - While proprioception is indeed carried primarily by the **dorsal columns** (located dorsally), a lesion limited to the ventrolateral part of the spinal cord would primarily affect the spinothalamic tract, not the dorsal columns. - Therefore, isolated **ventrolateral damage** would spare ipsilateral proprioception. *Pain sensation on the ipsilateral side* - This is incorrect because the **spinothalamic tract** fibers transmitting pain sensation **decussate** in the spinal cord close to their entry point. - Therefore, a lesion in the ventrolateral spinal cord would affect the already-crossed fibers, leading to **contralateral**, not ipsilateral, pain loss.

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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