Neuroanatomy — MCQs
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In adults, the spinal cord normally ends at what level?
The fibers from the contralateral nasal hemiretina project to the following layers of the lateral geniculate nucleus:
Which of the following statements regarding chorda tympani is false?
What is the primary function of the superior cervical ganglion?
Which of the following cranial nerves does not have a parasympathetic component?
Following a head injury, a man lost his tears from both eyes. Absence of lacrimation is due to injury to which structure?
Lacrimal gland receives postganglionic innervation through?
In the central nervous system, which cells are responsible for the formation of the myelin sheath of neurons?
What is the primary function of Schwann cells?
A patient presents with a brachial plexus injury and exhibits signs of Horner's syndrome. Which nerve root level is primarily involved?
Neuroanatomy Indian Medical PG Practice Questions and MCQs
Question 1791: In adults, the spinal cord normally ends at what level?
- A. Lower border of L3
- B. Lower border of S1
- C. Lower border of L5
- D. Lower border of L1 (Correct Answer)
Explanation: ***Lower border of L1*** - In adults, the **spinal cord** typically terminates at the level of the **L1 vertebral body**, or specifically, its lower border [1]. - This marks the anatomical transition from the solid spinal cord to the **conus medullaris**, which then continues as the **cauda equina** [1]. *Lower border of L3* - While the spinal cord in **newborns** can extend as low as L3, it retracts with growth, and this level is incorrect for adults. - An adult spinal cord ending at L3 would be considered an **abnormal finding**, potentially indicating a **tethered cord syndrome**. *Lower border of S1* - The spinal cord never extends to the S1 level in healthy individuals, even in newborns. - The **sacrum (S1-S5)** is well below the normal termination point of the spinal cord. *Lower border of L5* - The spinal cord typically terminates well above L5 in adults. - The **cauda equina**, not the spinal cord itself, extends through the lumbar and sacral regions to L5 and beyond.
Question 1792: The fibers from the contralateral nasal hemiretina project to the following layers of the lateral geniculate nucleus:
- A. Layers 4, 5 & 6.
- B. Layers 2, 3 & 5.
- C. Layers 1, 2 & 6.
- D. Layers 1, 4 & 6. (Correct Answer)
Explanation: ***Layers 1, 4 & 6.*** - The **contralateral nasal hemiretina** projects to layers 1, 4, and 6 of the lateral geniculate nucleus (LGN) [1]. - These layers receive input from the **magnocellular (layer 1)** and **parvocellular (layers 4 and 6)** pathways originating from the contralateral eye. *Layers 2, 3 & 5.* - This option incorrectly combines layers from both contralateral and ipsilateral projections. - Layers 2, 3, and 5 receive input from the **ipsilateral temporal hemiretina**, not the contralateral nasal hemiretina [1]. *Layers 1, 2 & 6.* - While layers 1 and 6 receive contralateral input, layer 2 specifically receives input from the **ipsilateral eye**. - This combination is not exclusively for contralateral nasal hemiretinal projection. *Layers 4, 5 & 6.* - This option includes layer 5, which receives input from the **ipsilateral temporal hemiretina**. - Layers 4 and 6 do receive contralateral input, but layer 5 makes this answer incorrect for an exclusive contralateral projection.
Question 1793: Which of the following statements regarding chorda tympani is false?
- A. Contains secretomotor nerves that supply salivary gland
- B. Contains motor nerves that supply facial muscles (Correct Answer)
- C. Passes through the petrotympanic fissure
- D. Contains sensory neurons that supply anterior 2/3rd of tongue
Explanation: ***Contains motor nerves that supplies facial muscles*** - The chorda tympani carries special visceral afferent fibers for **taste from the anterior two-thirds of the tongue** [1] and preganglionic parasympathetic fibers to the **submandibular and sublingual glands**. - It does not contain **motor nerves that supply facial muscles**; those are supplied directly by the main trunk of the facial nerve (CN VII) after it exits the stylomastoid foramen. *Contains secretomotor nerves that supply salivary gland* - The chorda tympani contains **preganglionic parasympathetic fibers** that synapse in the submandibular ganglion. - These postganglionic fibers then innervate the **submandibular and sublingual salivary glands**, promoting saliva production. *Passes through the petrotympanic fissure* - The chorda tympani nerve exits the temporal bone via the **petrotympanic fissure (Glaserian fissure)**. - This is its exit point from the middle ear cavity to join the **lingual nerve**. *Contains sensory neurons that supply anterior 2/3rd of tongue* - The chorda tympani carries **special visceral afferent (taste) fibers** from the taste buds on the anterior two-thirds of the tongue [1]. - These fibers are part of the **facial nerve (CN VII)** pathway for taste sensation [1].
Question 1794: What is the primary function of the superior cervical ganglion?
- A. Is the largest cervical ganglion
- B. Supplies sympathetic fibers to the dilator pupillae muscle (Correct Answer)
- C. Deep petrosal nerve of pterygopalatine ganglion is derived from plexus around internal carotid artery
- D. Left superior cervical cardiac branch goes to deep cardiac plexus
Explanation: Supplies sympathetic fibers to the dilator pupillae muscle - The superior cervical ganglion is the primary source of postganglionic sympathetic fibers to the head and neck. - One of its key functions is providing sympathetic innervation to the dilator pupillae muscle [1] via the long ciliary nerves, causing mydriasis (pupil dilation) [2]. - This represents a clear physiological function of the ganglion in autonomic control of the eye. Is the largest cervical ganglion - While the superior cervical ganglion is indeed the largest of the three cervical sympathetic ganglia, this is an anatomical characteristic, not a function. - Size is a structural feature, not a physiological role. Left superior cervical cardiac branch goes to deep cardiac plexus - The superior cervical ganglion does contribute cardiac branches to the cardiac plexus for sympathetic innervation of the heart. - However, this describes an anatomical pathway rather than the primary function itself, and specifying "left" and "deep cardiac plexus" makes it overly specific rather than addressing overall function. Deep petrosal nerve of pterygopalatine ganglion is derived from plexus around internal carotid artery - The superior cervical ganglion does send postganglionic fibers forming a plexus around the internal carotid artery, which contributes to the deep petrosal nerve. - However, this is an anatomical derivation/pathway, not a functional description of what the ganglion does physiologically.
Question 1795: Which of the following cranial nerves does not have a parasympathetic component?
- A. Oculomotor nerve
- B. Abducens nerve (Correct Answer)
- C. Facial nerve
- D. Vagus nerve
Explanation: Abducens nerve - The abducens nerve (CN VI) is a purely motor nerve, primarily responsible for innervating the lateral rectus muscle of the eye. - Its function is to cause abduction (outward movement) of the eye, and it does not carry any parasympathetic fibers. Oculomotor nerve - The oculomotor nerve (CN III) contains parasympathetic fibers that control the pupillary constrictor muscles and the ciliary muscles [1]. - These fibers originate from the Edinger-Westphal nucleus and cause pupillary constriction (miosis) and accommodation [1]. Facial nerve - The facial nerve (CN VII) has parasympathetic components that innervate the submandibular and sublingual salivary glands, as well as the lacrimal glands. - These fibers are crucial for tear production and salivation. Vagus nerve - The vagus nerve (CN X) is a major parasympathetic nerve, carrying widespread innervation to the thoracic and abdominal viscera. - It regulates heart rate, digestion, respiration, and other autonomic functions in organs like the heart, lungs, and gastrointestinal tract.
Question 1796: Following a head injury, a man lost his tears from both eyes. Absence of lacrimation is due to injury to which structure?
- A. Greater petrosal nerve (Correct Answer)
- B. Supraorbital nerve
- C. Tympanic plexus
- D. Nasociliary nerve
Explanation: ***Greater petrosal nerve*** - The **greater petrosal nerve** carries **parasympathetic preganglionic fibers** from the facial nerve (CN VII) that are destined for the **lacrimal gland**. - Damage to this nerve before it synapses in the **pterygopalatine ganglion** would result in the loss of **lacrimation**. *Supraorbital nerve* - The **supraorbital nerve** is a branch of the **ophthalmic division of the trigeminal nerve (CN V1)** and provides **sensory innervation** to the forehead, upper eyelid, and scalp. - It does not carry fibers for lacrimal gland function. *Tympanic plexus* - The **tympanic plexus** is formed by branches of the **glossopharyngeal nerve (CN IX)** and provides **parasympathetic innervation to the parotid gland** for salivation. - It plays no role in lacrimal gland function. *Nasociliary nerve* - The **nasociliary nerve** is a branch of the **ophthalmic division of the trigeminal nerve (CN V1)** and provides **sensory innervation** to the eyeball, conjunctiva, and part of the nasal mucosa. - It does not carry fibers for lacrimal gland secretion.
Question 1797: Lacrimal gland receives postganglionic innervation through?
- A. Pterygopalatine ganglion (Correct Answer)
- B. Submandibular ganglion
- C. Otic ganglion
- D. Ciliary ganglion
Explanation: ***Pterygopalatine ganglion*** - The **lacrimal gland** receives **secretomotor parasympathetic innervation** from the pterygopalatine ganglion [2]. - The **postganglionic fibers** from this ganglion travel with the **zygomatic nerve** and then join the **lacrimal nerve** to reach the lacrimal gland [2]. *Submandibular ganglion* - This ganglion primarily provides **postganglionic parasympathetic innervation** to the **submandibular and sublingual salivary glands** [2]. - Its fibers are involved in saliva production, not tear secretion. *Otic ganglion* - The otic ganglion supplies **postganglionic parasympathetic innervation** to the **parotid salivary gland** [2]. - It is involved in mumps and is not associated with lacrimal gland function. *Ciliary ganglion* - The ciliary ganglion innervates the **sphincter pupillae** and **ciliary muscle** of the eye, controlling pupil constriction and accommodation [1], [2]. - It does not have a role in the innervation of the lacrimal gland.
Question 1798: In the central nervous system, which cells are responsible for the formation of the myelin sheath of neurons?
- A. Astrocytes
- B. Oligodendroglia cells (Correct Answer)
- C. Schwann cells
- D. Microglia
Explanation: ***Oligodendroglia cells*** - **Oligodendroglia cells (oligodendrocytes)** are responsible for forming the **myelin sheath** around axons in the **central nervous system** (CNS) [2]. - Each oligodendrocyte can myelinate **multiple axons** (up to 50 segments), providing insulation that speeds up nerve impulse conduction via **saltatory conduction** [3], [4]. - This is a key distinguishing feature from Schwann cells in the PNS [3]. *Astrocytes* - **Astrocytes** are star-shaped glial cells that play a crucial role in providing **nutritional support** to neurons, regulating the **blood-brain barrier**, and maintaining the **extracellular environment**. - They do not form myelin; instead, they are involved in structural support, repair within the CNS, and neurotransmitter recycling [1]. *Schwann cells* - **Schwann cells** are the myelin-forming cells of the **peripheral nervous system** (PNS) [2]. - Unlike oligodendrocytes, each Schwann cell typically myelinates only a **single segment of one axon** [3], [4]. - This is the key anatomical difference between CNS and PNS myelination. *Microglia* - **Microglia** are the resident **immune cells** of the CNS, derived from mesoderm [1]. - They act as macrophages, responding to injury and infection, but play no role in myelin formation [1], [3]. - They are involved in immune surveillance and phagocytosis of debris [1].
Question 1799: What is the primary function of Schwann cells?
- A. Form myelin sheath (Correct Answer)
- B. Part of the central nervous system
- C. Derived from neural crest cells
- D. Present in both myelinated and unmyelinated nerve fibers
Explanation: ***Form myelin sheath*** - **Schwann cells** are glial cells found in the **peripheral nervous system** that wrap around axons to form the myelin sheath [1], [3]. - The **myelin sheath** acts as an electrical insulator, increasing the speed of nerve impulse conduction via **saltatory conduction** [2]. - This is the **primary and most characteristic function** of Schwann cells in the PNS [3]. *Part of the central nervous system* - Schwann cells are exclusively found in the **peripheral nervous system (PNS)**, not the CNS [4]. - In the **central nervous system (CNS)**, **oligodendrocytes** are responsible for myelin formation [1], [4]. *Derived from neural crest cells* - While Schwann cells are indeed derived from **neural crest cells**, this describes their **embryological origin**, not their function. - Many other cell types (melanocytes, neurons of peripheral ganglia) are also neural crest derivatives. *Present in both myelinated and unmyelinated nerve fibers* - While Schwann cells are associated with both fiber types, this describes their **distribution**, not their primary function [1], [3]. - In unmyelinated fibers, Schwann cells envelop multiple axons without forming concentric myelin layers [1].
Question 1800: A patient presents with a brachial plexus injury and exhibits signs of Horner's syndrome. Which nerve root level is primarily involved?
- A. C5
- B. C6
- C. C7
- D. T1 (Correct Answer)
Explanation: ***T1*** - Involvement of the **T1 nerve root** is crucial because it carries **preganglionic sympathetic fibers** that ascend to the superior cervical ganglion [1]. - Damage to these fibers at the T1 level, often due to a **lower brachial plexus injury (Klumpke's palsy)**, interrupts the sympathetic pathway to the head, leading to **Horner's syndrome** [1]. *C5* - The **C5 nerve root** primarily contributes to the **upper trunk** of the brachial plexus and innervates muscles like the deltoid and biceps. - Injury to C5 typically results in deficits related to **shoulder abduction** and **elbow flexion**, not Horner's syndrome. *C6* - The **C6 nerve root** also contributes to the upper and middle trunks, innervating muscles responsible for **wrist extension** and **elbow flexion**. - Damage to C6 would primarily cause weakness in these movements and sensory loss in the thumb and index finger. *C7* - The **C7 nerve root** forms the middle trunk and innervates muscles like the triceps and wrist flexors. - Injury to C7 would lead to deficits in **elbow extension** and **wrist flexion**, and sensory loss in the middle finger.
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