Nervous System — MCQs
Superior temporal gyrus lesion leads to?
What are the typical contents of a meningocele sac?
All are true regarding brachial plexus injury, except:
What is the primary symptom associated with a lesion in Wernicke's area?
Which of the following structures in the central nervous system contains major autonomic reflex centers?
Which spinal nerves are affected in Klumpke's paralysis?
Nerves of pharyngeal arch develop from
Which cells are responsible for myelination in the peripheral nervous system?
The infratentorial dura is supplied by branches of the ___?
A patient undergoing a minor surgical procedure is given lignocaine injection. Assertion: Local anaesthetics act by blocking nerve conduction. Reason: Small fibers and non-myelinated fibers are blocked more easily than large myelinated fibers.
Nervous System Indian Medical PG Practice Questions and MCQs
Question 1: Superior temporal gyrus lesion leads to?
- A. Anomic aphasia
- B. Broca's aphasia
- C. Wernicke's aphasia (Correct Answer)
- D. Non-fluent aphasia
Explanation: ***Wernicke's aphasia*** - A lesion in the **superior temporal gyrus** (Wernicke's area) leads to Wernicke's aphasia, characterized by impaired **comprehension of language** [1]. - Patients with Wernicke's aphasia exhibit **fluent but meaningless speech** (word salad) and are often unaware of their deficits [1]. *Anomic aphasia* - Characterized by difficulty finding words, particularly nouns and verbs, and is often associated with lesions in the **angular gyrus** or **temporal lobe** [1]. - Speech remains fluent and grammatically correct, but it is marked by frequent pauses and circumlocutions as the individual struggles to retrieve specific words. *Broca's aphasia* - Results from damage to **Broca's area** in the posterior inferior frontal gyrus, causing **non-fluent speech** and difficulty with speech production [1]. - While comprehension is relatively preserved, patients struggle to form complete sentences and may exhibit agrammatism. *Non-fluent aphasia* - A broad category of aphasias, including Broca's aphasia, where speech production is notably impaired, and the output is effortful and characterized by **agrammatism** and **short, telegraphic sentences**. - **Wernicke's aphasia** is typically considered a **fluent aphasia**, as speech production itself is not interrupted, though its content is often incomprehensible [1].
Question 2: What are the typical contents of a meningocele sac?
- A. Spinal cord
- B. Meninges and CSF (Correct Answer)
- C. Dura mater
- D. Cauda equina
Explanation: ***Meninges and CSF*** - A meningocele is a neural tube defect characterized by herniation of the **meninges (all three layers: dura mater, arachnoid mater, and pia mater) and cerebrospinal fluid (CSF)** through a bony defect in the skull or vertebral column. - The sac contains meninges and CSF but **does NOT contain neural tissue** (spinal cord or nerve roots), which distinguishes it from myelomeningocele. - This is typically covered by skin or a thin membrane. *Dura mater* - While the dura mater is present as the outermost layer forming part of the sac wall, it is only **one component** of the meninges. - The complete answer must include all three meningeal layers (dura, arachnoid, pia) **plus CSF**, not just the dura alone. - Stating only "dura mater" is incomplete and does not accurately describe the typical contents of a meningocele. *Spinal cord* - The presence of **spinal cord tissue** within the herniated sac indicates a more severe defect called **myelomeningocele** (or meningomyelocele). - A simple meningocele by definition does **not** contain neural tissue. *Cauda equina* - The **cauda equina** consists of spinal nerve roots below the level of L1-L2. - Its presence within the herniated sac would indicate a **myelomeningocele**, not a meningocele. - Meningocele contains only meninges and CSF, with no neural elements.
Question 3: All are true regarding brachial plexus injury, except:
- A. In Klumpke's palsy, Horner's syndrome may be present on the ipsilateral side
- B. Preganglionic lesions have a better prognosis than postganglionic lesions (Correct Answer)
- C. Erb's palsy causes paralysis of the abductors and external rotators of the shoulder
- D. Histamine test is useful to differentiate between the preganglionic and postganglionic lesions
Explanation: ***Preganglionic lesions have a better prognosis than postganglionic lesions*** - **Preganglionic lesions** involve the avulsion of nerve roots from the spinal cord, making nerve regeneration and surgical repair more challenging, therefore resulting in a **worse prognosis**. - In contrast, **postganglionic lesions** involve damage to the nerves distal to the dorsal root ganglion, which often allows for **spontaneous recovery** or more successful surgical intervention, leading to a better prognosis. *In Klumpke's palsy, Horner's syndrome may be present on the ipsilateral side* - **Klumpke's palsy** results from injury to the **lower trunk** of the brachial plexus (C8-T1), which can involve the sympathetic fibers that exit at T1. - Damage to these fibers can lead to **Horner's syndrome** (miosis, ptosis, anhydrosis) on the ipsilateral side. *Erb's palsy causes paralysis of the abductors and external rotators of the shoulder* - **Erb's palsy** involves injury to the **upper trunk** of the brachial plexus (C5-C6), affecting muscles innervated by these roots. - This results in paralysis of muscles such as the deltoid (abductor) and supraspinatus/infraspinatus (external rotators), leading to the characteristic "waiter's tip" posture. *Histamine test is useful to differentiate between the preganglionic and postganglionic lesions* - The **histamine test** (or histamine wheal test) is used to assess the integrity of peripheral unmyelinated postganglionic sympathetic fibers. - If a wheal and flare reaction occurs, it suggests intact postganglionic fibers, indicating a **preganglionic lesion**; absence of a reaction suggests a **postganglionic lesion**.
Question 4: What is the primary symptom associated with a lesion in Wernicke's area?
- A. Inability to understand language
- B. Inability to repeat phrases
- C. Fluent speech with poor comprehension (Correct Answer)
- D. Difficulty in forming sentences
Explanation: ***Fluent speech with poor comprehension*** - A lesion in **Wernicke's area** results in **Wernicke's aphasia**, where the individual can produce speech fluently but the content is often meaningless or nonsensical (word salad). [1] - The primary characteristic is a profound **difficulty in understanding** spoken and written language, despite intact hearing and vision. *Inability to understand language* - While an inability to understand language is a key component of Wernicke's aphasia, the description "fluent speech with poor comprehension" more comprehensively captures the clinical presentation by including the intact though often chaotic speech production. - This option alone does not fully encompass the unique **dissociation between fluency and comprehension** seen in Wernicke's aphasia. *Inability to repeat phrases* - The **inability to repeat phrases** is typically associated with **conduction aphasia**, which results from damage to the **arcuate fasciculus**, the connection between Wernicke's and Broca's areas. [1] - While repetition can be impaired in Wernicke's aphasia due to poor comprehension, it is not the primary defining symptom differentiating it from other aphasias. *Difficulty in forming sentences* - **Difficulty in forming sentences** and producing meaningful speech, often characterized by **non-fluent, effortful speech** and agrammatism, is a hallmark of **Broca's aphasia**. [1] - Broca's area is responsible for **speech production** and grammatical structure, not language comprehension.
Question 5: Which of the following structures in the central nervous system contains major autonomic reflex centers?
- A. Medulla oblongata (Correct Answer)
- B. Thalamus
- C. Cerebellum
- D. Hypothalamus
Explanation: ***Medulla oblongata*** - The **medulla oblongata** contains the most critical **vital autonomic reflex centers** including the cardiovascular center (regulating heart rate and blood pressure), respiratory center (controlling breathing rhythm), and vasomotor center - It also houses reflex centers for coughing, sneezing, swallowing, and vomiting - These are **immediate, life-sustaining reflexes** that operate without higher center input *Hypothalamus* - The **hypothalamus** is indeed a major autonomic control center and the **highest level integrator** of autonomic function - However, it functions more as a **regulatory and integrative center** rather than a direct reflex center - It modulates autonomic responses through connections with brainstem centers like the medulla *Cerebellum* - The **cerebellum** is primarily responsible for motor coordination, balance, and posture control - While it may influence some autonomic functions indirectly, it does not contain autonomic reflex centers *Thalamus* - The **thalamus** serves as a relay station for sensory information and plays a role in consciousness and alertness - It is not involved in autonomic reflex pathways
Question 6: Which spinal nerves are affected in Klumpke's paralysis?
- A. C3-C6
- B. C6-C7
- C. C8-T1 (Correct Answer)
- D. C4-C5
Explanation: ***C8-T1*** - **Klumpke's paralysis** results from damage to the lower trunks of the brachial plexus, specifically involving the **C8 and T1 spinal nerves**. - This injury often leads to a characteristic "claw hand" deformity due to paralysis of the **intrinsic hand muscles** and **flexors of the wrist and fingers**, along with potential **Horner's syndrome** if the T1 sympathetic fibers are affected. *C3-C6* - Involvement of these spinal nerves would typically affect the **upper and middle trunks of the brachial plexus**, leading to different patterns of paralysis, such as those seen in **Erb's palsy**. - This range does not specifically define Klumpke's paralysis, which is localized to the lower brachial plexus. *C6-C7* - Injury to these nerves primarily affects the **upper and middle trunks**, responsible for movements like shoulder abduction and elbow flexion. - This pattern of involvement is associated with different neurological deficits and is not characteristic of Klumpke's paralysis. *C4-C5* - Damage to these spinal nerves would primarily affect the **upper trunk of the brachial plexus**, leading to conditions like **Erb's palsy**. - This would result in paralysis of the shoulder and biceps muscles, distinct from the hand and wrist deficits seen in Klumpke's paralysis.
Question 7: Nerves of pharyngeal arch develop from
- A. Mesoderm
- B. Neural crest cells (Correct Answer)
- C. Neuroectoderm
- D. Ectoderm
Explanation: ***Neural crest cells*** - **Neural crest cells** are a multipotent, migratory population of cells that arise from the dorsal part of the neural tube and contribute to a wide array of tissues, including the nerves of the pharyngeal arches (clefts). [1] - They give rise to components of the peripheral nervous system, including **sensory ganglia**, autonomic ganglia, and some cranial nerves associated with the pharyngeal arches. [2] *Mesoderm* - **Mesoderm** is one of the three primary germ layers that forms during early embryonic development. - It primarily gives rise to muscle, bone, connective tissue, and the circulatory system, but not the nerves of the pharyngeal structures. *Neuroectoderm* - **Neuroectoderm** refers to the part of the ectoderm that gives rise to the nervous system, but specifically it differentiates into the neural tube and neural crest. - While neural crest cells originate from neuroectoderm, the direct derivative for the pharyngeal nerves are the **neural crest cells** themselves after migration. *Ectoderm* - The **ectoderm** is the outermost of the three germ layers and gives rise to the epidermis, hair, nails, and the nervous system. - While the nervous system originates from ectoderm, the specific cell type for pharyngeal arch nerves is the **neural crest**, which is a specialized derivative of the ectoderm.
Question 8: Which cells are responsible for myelination in the peripheral nervous system?
- A. Oligodendrocytes
- B. Schwann cells (Correct Answer)
- C. Astrocytes
- D. Microglia
Explanation: ***Schwann cells*** - **Schwann cells** are specialized glial cells that form the **myelin sheath** around axons in the **peripheral nervous system (PNS)** [2], [3]. - Each Schwann cell typically myelinates a single segment of one axon, providing insulation and speeding up nerve impulse transmission [3]. *Oligodendrocytes* - **Oligodendrocytes** are responsible for myelination, but they do so in the **central nervous system (CNS)** (brain and spinal cord) [2], [3]. - A single oligodendrocyte can myelinate multiple axons or multiple segments of one axon [3]. *Astrocytes* - **Astrocytes** are star-shaped glial cells found in the **CNS** that provide metabolic support, regulate the external chemical environment, and contribute to the **blood-brain barrier** [1]. - They do not form myelin sheaths. *Microglia* - **Microglia** are the resident **immune cells** of the **CNS**, acting as the primary form of active immune defense [1]. - They function as macrophages, clearing cellular debris and pathogens, but are not involved in myelination [1].
Question 9: The infratentorial dura is supplied by branches of the ___?
- A. Accessory nerve and upper cervical nerves
- B. Only vagus nerve
- C. Upper cervical spinal nerves and vagus nerve (Correct Answer)
- D. Only upper cervical nerves
Explanation: ***Upper cervical spinal nerves and vagus nerve*** - The **infratentorial dura mater**, particularly the posterior fossa, receives its sensory innervation primarily from the **recurrent meningeal branches** of the upper cervical spinal nerves (C1-C3), which ascend through the foramen magnum. - The **vagus nerve (CN X)** also contributes to the sensory supply of the infratentorial dura, specifically to the posterior fossa, through its sensory branches. *Accessory nerve and upper cervical nerves* - The **accessory nerve (CN XI)** is primarily a motor nerve, responsible for innervating the sternocleidomastoid and trapezius muscles, and does not directly supply the dura mater. - While upper cervical nerves do contribute, the **vagus nerve** is also a significant contributor to infratentorial dural innervation. *Only vagus nerve* - While the **vagus nerve (CN X)** does contribute to the sensory innervation of the infratentorial dura, it is not the sole source. - The **upper cervical spinal nerves** also play a crucial role in providing sensory fibers to this region. *Only upper cervical nerves* - The **upper cervical spinal nerves** (C1-C3) are indeed a significant source of innervation for the infratentorial dura mater. - However, the **vagus nerve (CN X)** also provides sensory branches to this region, making the answer "only upper cervical nerves" incomplete.
Question 10: A patient undergoing a minor surgical procedure is given lignocaine injection. Assertion: Local anaesthetics act by blocking nerve conduction. Reason: Small fibers and non-myelinated fibers are blocked more easily than large myelinated fibers.
- A. Assertion is false, but Reason is true
- B. Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion (Correct Answer)
- C. Both Assertion and Reason are true, and Reason is the correct explanation for Assertion
- D. Assertion is true, but Reason is false
Explanation: ***Both Assertion and Reason are true, and Reason is NOT the correct explanation for Assertion*** - The **Assertion** is true: Local anesthetics (like lignocaine) block nerve conduction by inhibiting **voltage-gated sodium channels**, preventing the depolarization necessary for action potential propagation - The **Reason** is also true: Small diameter and non-myelinated fibers (like C and Aδ pain fibers) are blocked more easily than large myelinated fibers (like Aα motor fibers), which explains the **differential blockade** pattern seen clinically - However, the **Reason does NOT explain WHY** local anesthetics block nerve conduction—it describes **WHICH** nerve fibers are blocked preferentially. The mechanism of blocking conduction is sodium channel inhibition, not fiber size selectivity - The differential sensitivity is a consequence of fiber characteristics (surface area-to-volume ratio, number of nodes of Ranvier), not the explanation for the blocking mechanism itself *Both Assertion and Reason are true, and Reason is the correct explanation for Assertion* - While both statements are individually true, the Reason does not explain the **mechanism** by which local anesthetics block nerve conduction - The Reason addresses fiber **selectivity**, which is a separate pharmacological property from the **mechanism of action** (sodium channel blockade) *Assertion is true, but Reason is false* - The Assertion is demonstrably true—local anesthetics block nerve conduction - The Reason is also true—this is well-established pharmacology: autonomic (small) > sensory (medium) > motor (large) fiber blockade sequence *Assertion is false, but Reason is true* - The Assertion is fundamentally correct and represents the primary pharmacological action of local anesthetics - Blocking nerve conduction is the therapeutic goal of local anesthetic administration
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