Neuroanatomy — MCQs
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Wernicke's encephalopathy involves which part of the CNS?
Branches from the Anterior division of the Mandibular nerve supplies all of the following muscles, EXCEPT:
Frey's syndrome occurs due to aberrant regeneration of parasympathetic nerve fibers following parotid surgery, leading to gustatory sweating. The nerve directly involved in this aberrant reinnervation is:
Which is the MOST FALSE about grey rami communicantes?
TRUE statement regarding nerve supply of adrenal gland:
Which of the following sensations is NOT perceived by spinal nucleus of trigeminal nerve?
The tensor veli palatini muscle is innervated by which nerve?
Root value of cremaster reflex is
Which cranial nerve emerges from the dorsal aspect of the brainstem?
Substantia nigra is connected to which part of the basal ganglia?
Neuroanatomy Indian Medical PG Practice Questions and MCQs
Question 1671: Wernicke's encephalopathy involves which part of the CNS?
- A. Thalamus and Frontal lobe
- B. Mammillary body and Thalamus (Correct Answer)
- C. Mammillary body only
- D. Mammillary body and Frontal lobe
Explanation: ***Correct: Mammillary body and Thalamus*** - **Wernicke's encephalopathy** is characterized by damage to specific brain regions due to **thiamine (vitamin B1) deficiency**, most notably the **mammillary bodies** and **dorsomedial thalamus**. - These areas are crucial for memory formation and processing, explaining the classic triad of symptoms: **ataxia**, **ophthalmoplegia**, and **confusion/altered mental status**. - Other affected regions include the **periaqueductal gray matter**, **tectal plate**, and **floor of the fourth ventricle**. *Incorrect: Thalamus and Frontal lobe* - While the **thalamus** is indeed involved (specifically the dorsomedial nuclei), the **frontal lobe** is not a primary site of acute damage in Wernicke's encephalopathy. - Frontal lobe dysfunction may occur secondarily in chronic cases or in Korsakoff syndrome, but it is not part of the characteristic pathological findings. *Incorrect: Mammillary body only* - Although the **mammillary bodies** are the most consistently and severely affected structures, damage is **not confined to them alone**. - The **thalamus** (particularly dorsomedial nuclei) and other **periventricular structures** are also characteristically involved in the pathology. *Incorrect: Mammillary body and Frontal lobe* - The **frontal lobe** is not a characteristic region of acute damage in Wernicke's encephalopathy. - This option incorrectly substitutes the **thalamus** (which is actually affected) with the frontal lobe, providing an inaccurate picture of the pathological distribution.
Question 1672: Branches from the Anterior division of the Mandibular nerve supplies all of the following muscles, EXCEPT:
- A. Lateral Pterygoid
- B. Masseter
- C. Medial Pterygoid (Correct Answer)
- D. Temporalis
Explanation: ***Medial Pterygoid*** - The nerve to the **medial pterygoid** branches directly off the main trunk of the **mandibular nerve (V3)** before its division into anterior and posterior branches. - This muscle is responsible for **elevating the mandible**, assisting in chewing. *Lateral Pterygoid* - The nerve to the **lateral pterygoid** originates from the **anterior division** of the mandibular nerve. - This muscle is crucial for **protruding** and **depressing the mandible**, and for **side-to-side movements**. *Masseter* - The **masseteric nerve**, which supplies the **masseter muscle**, is a branch of the **anterior division** of the mandibular nerve. - The masseter is a powerful muscle involved in **closing the jaw** (mandibular elevation). *Temporalis* - The **deep temporal nerves**, which innervate the **temporalis muscle**, arise from the **anterior division** of the mandibular nerve. - The temporalis muscle is responsible for **elevating** and **retracting the mandible**.
Question 1673: Frey's syndrome occurs due to aberrant regeneration of parasympathetic nerve fibers following parotid surgery, leading to gustatory sweating. The nerve directly involved in this aberrant reinnervation is:
- A. Trigeminal nerve
- B. Facial nerve
- C. GlossoPharyngeal nerve
- D. Auriculotemporal nerve (Correct Answer)
Explanation: ***Auriculotemporal nerve*** - Frey's syndrome, or **gustatory sweating**, occurs due to damage to the **auriculotemporal nerve**, typically during parotidectomy. - Aberrant regeneration leads to misdirection of parasympathetic fibers meant for the parotid gland to the sweat glands in the preauricular and temporal regions. *Trigeminal nerve* - The trigeminal nerve (CN V) is primarily responsible for **sensory innervation of the face** and **motor innervation of the muscles of mastication**. - It does not directly provide secretomotor innervation to the parotid gland or sweat glands. *Facial nerve* - The facial nerve (CN VII) innervates the **muscles of facial expression** and provides taste sensation to the anterior two-thirds of the tongue, and secretomotor innervation to the submandibular and sublingual glands. - While it passes through the parotid gland, it does not provide secretomotor innervation to the parotid gland itself. *GlossoPharyngeal nerve* - The glossopharyngeal nerve (CN IX) provides presynaptic parasympathetic fibers to the **otic ganglion**, which then synapse with postsynaptic fibers carried by the auriculotemporal nerve to the parotid gland. - Although it is the origin of the parasympathetic innervation for the parotid, the direct aberrant reinnervation in Frey's syndrome involves the auriculotemporal nerve, not the glossopharyngeal nerve itself.
Question 1674: Which is the MOST FALSE about grey rami communicantes?
- A. Fibres are non-myelinated
- B. Present medial to white rami communicantes
- C. Connected to spinal nerve
- D. Carries pre-ganglionic fibres (Correct Answer)
Explanation: ***Carries pre-ganglionic fibres*** - Grey rami communicantes are primarily composed of **unmyelinated post-ganglionic sympathetic fibers** that return to the spinal nerve for distribution to target organs. - They do **not** carry **pre-ganglionic fibers**; pre-ganglionic fibers are found in the white rami communicantes [1]. - This is the **most definitively false** statement as it represents a fundamental misunderstanding of autonomic nervous system organization [1]. *Fibres are non-myelinated* - This statement is **true** because grey rami communicantes are indeed made up of **unmyelinated post-ganglionic sympathetic fibers**. - Their lack of myelin gives them their characteristic grey appearance. *Present medial to white rami communicantes* - This statement is **false**. Grey rami communicantes are typically positioned **lateral or posterolateral** to white rami communicantes in anatomical arrangement. - White rami are more medial as they carry pre-ganglionic fibers from the spinal nerve to the sympathetic ganglion [1]. - However, this is less consistently false than the preganglionic fiber statement, as some anatomical variations may occur. *Connected to spinal nerve* - This statement is **true**. Grey rami communicantes arise from the **sympathetic ganglia** and re-join the corresponding **spinal nerve** to distribute post-ganglionic fibers to peripheral structures [1]. - This connection allows sympathetic innervation to reach widespread target tissues. - Grey rami are present at **all spinal levels** (unlike white rami which are only at T1-L2).
Question 1675: TRUE statement regarding nerve supply of adrenal gland:
- A. Adrenal cortex has no nerve supply
- B. Adrenal medulla has no nerve supply
- C. Release of catecholamines is not affected by nerve supply
- D. Preganglionic fibres from lower thoracic spinal segments bypass sympathetic chain (Correct Answer)
Explanation: ***Preganglionic fibres from lower thoracic & upper lumbar spinal segments bypass sympathetic chain*** - The adrenal medulla is innervated by **preganglionic sympathetic fibers** originating from the **T5-T11 spinal cord segments**, which travel through the splanchnic nerves and synapse directly on chromaffin cells, effectively bypassing the sympathetic chain ganglia [1], [2]. - This direct innervation allows for a **rapid, systemic catecholamine release** in response to stress. *Adrenal cortex has no nerve supply* - The **adrenal cortex** receives some **autonomic innervation**, primarily sympathetic, though it is less dense and its direct role in steroidogenesis is not fully understood. - While hormonal signals are primary for cortical regulation, nerve fibers are present and may modulate blood flow or cellular activity. *Adrenal medulla has no nerve supply* - The **adrenal medulla** is a modified sympathetic ganglion whose **chromaffin cells** are directly innervated by **preganglionic sympathetic fibers** [1], [2]. - This direct neural input is crucial for its rapid response in releasing **catecholamines** into the bloodstream. *Release of catecholamines is not affected by nerve supply* - The release of **catecholamines** (epinephrine and norepinephrine) from the **adrenal medulla** is directly and primarily controlled by **preganglionic sympathetic innervation** [1], [2]. - Without this nerve supply, the stress-induced release of these hormones would be severely impaired, highlighting the critical role of neural input.
Question 1676: Which of the following sensations is NOT perceived by spinal nucleus of trigeminal nerve?
- A. Pain
- B. Temperature
- C. Proprioception (Correct Answer)
- D. Fine touch
Explanation: ***Proprioception*** - The **spinal nucleus of the trigeminal nerve** processes **pain and temperature** from the face, while **proprioception** from the face and masticatory muscles is processed by the **mesencephalic nucleus of the trigeminal nerve** [1]. - **Proprioceptive fibers** from the trigeminal nerve bypass the spinal trigeminal nucleus entirely. *Pain* - The **spinal nucleus of the trigeminal nerve** is the primary sensory nucleus responsible for processing **pain** sensations originating from the face and oral cavity [1]. - Pain fibers synapse here before ascending to higher brain centers. *Temperature* - Similar to pain, **temperature** sensations from the face are conveyed to and processed by the **spinal nucleus of the trigeminal nerve** [1]. - Both warm and cold thermoreceptors project to this nucleus. *Fine touch* - While some general touch information might be processed elsewhere, the **principal sensory nucleus of the trigeminal nerve** is primarily responsible for **fine touch and discriminative touch** from the face. - The spinal nucleus's role is largely focused on nociception and thermoreception.
Question 1677: The tensor veli palatini muscle is innervated by which nerve?
- A. Facial nerve
- B. Vagus nerve
- C. Glossopharyngeal nerve
- D. Mandibular nerve (Correct Answer)
Explanation: ***Mandibular nerve*** - The **tensor veli palatini** muscle plays a crucial role in tensing the **soft palate** and opening the **Eustachian tube**. - Its innervation is by a branch of the **mandibular division of the trigeminal nerve (V3)**, specifically the nerve to the medial pterygoid. *Facial nerve* - The **facial nerve (cranial nerve VII)** primarily innervates the muscles of **facial expression**, not the muscles of the soft palate. - It also supplies the **lacrimal, submandibular, and sublingual glands** and carries **taste sensation** from the anterior two-thirds of the tongue. *Vagus nerve* - The **vagus nerve (cranial nerve X)** innervates most muscles of the **pharynx and larynx**, and some muscles of the soft palate such as the **levator veli palatini**, **palatopharyngeus**, and **palatoglossus**. - It does not, however, innervate the **tensor veli palatini**. *Glossopharyngeal nerve* - The **glossopharyngeal nerve (cranial nerve IX)** innervates the **stylopharyngeus muscle** and provides sensation to the posterior one-third of the tongue. - While it has functions related to the pharynx, it does not directly innervate the **tensor veli palatini**.
Question 1678: Root value of cremaster reflex is
- A. S3, S4
- B. S1, S2
- C. L2, L3
- D. L1, L2 (Correct Answer)
Explanation: L1, L2 - The cremaster reflex arc involves sensory fibers that travel via the ilioinguinal nerve (L1) and motor fibers that innervate the cremaster muscle via the genitofemoral nerve (L1, L2). - Stimulation of the upper inner thigh (L1 dermatome) results in contraction of the cremaster muscle, elevating the testis on the ipsilateral side. S3, S4 - These spinal segments are primarily involved in the pudendal nerve and control functions related to the perineum, bladder, and bowel, such as the anal reflex. - They are not associated with the cremasteric reflex. S1, S2 - These segments are primarily responsible for the Achilles reflex (ankle jerk) and innervate muscles of the foot and lower leg. - They do not contribute to the cremaster reflex arc. L2, L3 - These segments are primarily involved in the patellar reflex (knee jerk) and innervate the quadriceps femoris muscle. - While L2 is part of the genitofemoral nerve, the complete arc of the cremaster reflex also significantly involves L1.
Question 1679: Which cranial nerve emerges from the dorsal aspect of the brainstem?
- A. Trigeminal nerve
- B. Trochlear nerve (Correct Answer)
- C. Abducens nerve
- D. Oculomotor nerve
Explanation: ***Trochlear nerve*** - The **trochlear nerve (CN IV)** is unique among cranial nerves as it emerges from the **dorsal aspect of the brainstem** (specifically, the posterior surface of the midbrain). - It also has the longest intracranial course and is the only cranial nerve that **decussates** completely before innervating its target muscle. *Trigeminal nerve* - The trigeminal nerve (CN V) emerges from the **ventrolateral aspect of the pons**, not the dorsal brainstem. - It is a mixed nerve providing sensation to the face and motor innervation to muscles of mastication. *Abducens nerve* - The abducens nerve (CN VI) emerges from the **junction of the pons and medulla** (pontomedullary sulcus) on the ventral surface of the brainstem. - It is a purely motor nerve that innervates the **lateral rectus muscle** of the eye, responsible for abduction. *Oculomotor nerve* - The oculomotor nerve (CN III) emerges from the **ventral aspect of the midbrain**, specifically from the interpeduncular fossa. [1] - This nerve controls most of the eye movements and pupil constriction. [1]
Question 1680: Substantia nigra is connected to which part of the basal ganglia?
- A. Thalamus
- B. Pallidum
- C. Striatum (Correct Answer)
- D. Subthalamic nucleus
Explanation: ***Striatum*** - The **substantia nigra pars compacta (SNc)** provides **dopaminergic input** to the striatum via the **nigrostriatal pathway**, which is crucial for motor control [1]. - This connection establishes the direct and indirect pathways of the basal ganglia, modulating **movement initiation** and **inhibition** [1]. *Thalamus* - The thalamus acts as a **relay station** for information leaving the basal ganglia, but it is not directly connected to the substantia nigra as a primary input or output structure within the basal ganglia circuitry [1]. - The basal ganglia influence the thalamus, which then projects to the **motor cortex**, but the direct connection from substantia nigra is to the striatum. *Pallidum* - The **pallidum (globus pallidus)** receives input from the striatum and projects to the thalamus, but it is not directly connected to the substantia nigra as the **primary recipient** of nigral efferents [1]. - While it's part of the basal ganglia, the substantia nigra's main direct projection is to the **striatum**. *Subthalamic nucleus* - The **subthalamic nucleus (STN)** is an excitatory component of the basal ganglia that receives input from the cortex and projects to the globus pallidus. - While there are some indirect connections, the STN is not the primary target of the **nigrostriatal dopaminergic projections** from the substantia nigra [1].
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