Neuroanatomy — MCQs
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Where are mitral cells primarily located?
The tensor tympani muscle is innervated by:
Following a penetrating injury in the submandibular triangle, the tongue of a 45-year-old patient deviates to the left on protrusion. Which of the following nerves is likely injured?
Which of the following is a characteristic feature of the axon hillock that distinguishes it from the neuronal cell body?
Action of the right superior oblique muscle is:
What are the root values of the phrenic nerve?
Which of the following is a draining channel of the cavernous sinus?
Facial nerve does not supply which structure of the face?
Which of the following is an example of a non-macroglial cell?
Abnormal regeneration of which nerve is the cause of crocodile tears?
Neuroanatomy Indian Medical PG Practice Questions and MCQs
Question 1761: Where are mitral cells primarily located?
- A. Kidney
- B. Mitral valve
- C. Olfactory bulb (Correct Answer)
- D. Optic nerve
Explanation: Olfactory bulb - **Mitral cells** are the primary projection neurons in the **olfactory bulb**, receiving extensive input from olfactory sensory neurons [1]. - They play a crucial role in processing and transmitting **olfactory information** from the nose to higher brain regions [1]. *Kidney* - The kidney contains various specialized cells for filtration and reabsorption (e.g., **podocytes**, **tubular cells**), but no mitral cells. - Its primary function is maintaining **fluid and electrolyte balance** and waste excretion, unrelated to olfaction. *Mitral valve* - The **mitral valve** is located in the heart, separating the left atrium and left ventricle. - It consists of connective tissue and endothelial cells and is essential for regulating **blood flow**, not scent perception. *Optic nerve* - The **optic nerve** transmits visual information from the retina to the brain and is composed of retinal ganglion cell axons [2]. - Its function is entirely distinct from olfaction, involving **light perception** and visual processing [2].
Question 1762: The tensor tympani muscle is innervated by:
- A. Vagus nerve
- B. Facial nerve
- C. Maxillary nerve
- D. Mandibular nerve (V3) (Correct Answer)
Explanation: ***Mandibular nerve (V3)*** - The tensor tympani muscle is a derivative of the **first pharyngeal arch**. - Muscles derived from the first pharyngeal arch are innervated by the **mandibular division of the trigeminal nerve (V3)**. *Vagus nerve* - The vagus nerve (cranial nerve X) primarily innervates muscles of the **larynx and pharynx**, and plays a major role in **parasympathetic innervation** of thoracic and abdominal organs. - It does not innervate muscles within the middle ear. *Facial nerve* - The facial nerve (cranial nerve VII) innervates the **stapedius muscle** in the middle ear, as well as muscles of **facial expression** and carries taste sensation. - It does not innervate the tensor tympani. *Maxillary nerve* - The maxillary nerve (V2) is a sensory nerve that provides sensation to the **midface, upper teeth, and palate**. - It does not have motor innervation to any middle ear muscles.
Question 1763: Following a penetrating injury in the submandibular triangle, the tongue of a 45-year-old patient deviates to the left on protrusion. Which of the following nerves is likely injured?
- A. Left hypoglossal nerve (Correct Answer)
- B. Right glossopharyngeal nerve
- C. Left glossopharyngeal nerve
- D. Right accessory nerve
Explanation: ***Left hypoglossal nerve*** - Injury to the **hypoglossal nerve (CN XII)** on one side causes weakness and **atrophy** of the ipsilateral intrinsic and extrinsic muscles of the tongue. - **Key clinical rule**: The tongue deviates **toward the side of the lesion** on protrusion. - This occurs because the **genioglossus muscle** (innervated by CN XII) normally protrudes the tongue to the **opposite side**. When the left CN XII is injured, the **unopposed right genioglossus** pushes the tongue to the left (toward the weak side). - Location: The hypoglossal nerve courses through the **submandibular triangle**, making it vulnerable to penetrating injuries in this region. *Right glossopharyngeal nerve* - The glossopharyngeal nerve (CN IX) primarily mediates **taste from the posterior one-third of the tongue**, **general sensation from the pharynx**, and motor innervation to the **stylopharyngeus muscle**. - Its injury would result in difficulty swallowing, loss of gag reflex, and altered taste, **not tongue deviation on protrusion**. *Left glossopharyngeal nerve* - Similar to a right glossopharyngeal nerve injury, a left-sided injury would manifest as dysphagia, absent gag reflex, and sensory deficits in the pharynx and posterior tongue. - It does **not control the motor function** of the tongue muscles responsible for protrusion. *Right accessory nerve* - The accessory nerve (CN XI) innervates the **sternocleidomastoid** and **trapezius muscles**, controlling head and shoulder movements. - Injury would lead to weakness in shrugging the shoulder and turning the head, with **no impact on tongue movement** or deviation.
Question 1764: Which of the following is a characteristic feature of the axon hillock that distinguishes it from the neuronal cell body?
- A. Has a conical shape leading into the axon
- B. Contains dense Nissl granules
- C. Contains no Nissl granules (Correct Answer)
- D. Is located at the beginning of dendrites
Explanation: Correct: Contains no Nissl granules - The **axon hillock** is a specialized region of the neuron that is devoid of rough endoplasmic reticulum and free ribosomes, which constitute **Nissl granules (Nissl substance)** [1] - This absence of Nissl granules distinguishes it from the cell body and dendrites where active protein synthesis occurs [1] - Its primary function is **action potential generation** and initiation, requiring a specific distribution of voltage-gated sodium channels rather than protein synthesis machinery [1] - This is the key **cytological feature** that differentiates the axon hillock from the soma [1] *Incorrect: Contains dense Nissl granules* - **Nissl granules** are abundant in the neuronal cell body (soma) and proximal dendrites, indicating active protein synthesis for neuronal maintenance and function [1] - The axon hillock specifically **lacks** these structures, which is one of its defining histological characteristics [1] - This absence can be demonstrated with Nissl staining (cresyl violet or toluidine blue) *Incorrect: Is located at the beginning of dendrites* - The **axon hillock** is located at the junction of the **cell body (soma)** and the **axon**, not at the beginning of dendrites [1] - Dendrites are receptive regions that receive synaptic input and extend from the cell body in multiple directions [1] - The axon hillock integrates inputs to determine whether an action potential will be initiated *Incorrect: Has a conical shape leading into the axon* - While the axon hillock does have a conical/funnel shape tapering into the axon, this is a **morphological description** rather than a distinguishing characteristic [1] - Many neuronal structures have specific shapes, but the **absence of Nissl granules** is the specific cytological feature that functionally distinguishes the axon hillock - The shape facilitates efficient action potential propagation but is not the defining histological feature
Question 1765: Action of the right superior oblique muscle is:
- A. Laevoelevation
- B. Laevodepression
- C. Dextroelevation
- D. Dextrodepression (Correct Answer)
Explanation: ***Dextrodepression*** - The **right superior oblique muscle** has three primary actions: **depression** (downward movement), **abduction** (outward/lateral movement), and **intorsion** (internal rotation) [1]. - In the context of conjugate gaze movements, the right superior oblique contributes to **dextrodepression** (downward and rightward gaze) by depressing and abducting the right eye. - When the eye is **adducted** (looking nasally toward the nose), the superior oblique acts as the **primary depressor**, making its depressive action most evident [1]. - The combination of **depression + abduction** of the right eye aligns with the dextrodepression movement pattern [1]. *Laevoelevation* - This refers to upward and leftward gaze movement, which involves **elevation** (not depression). - The right superior oblique is a **depressor**, not an elevator, so it does not contribute to laevoelevation. - This movement is primarily mediated by elevators like the **left inferior oblique** and other elevating muscles [1]. *Laevodepression* - This refers to downward and leftward gaze movement. - While the right superior oblique is a depressor, it causes **abduction** (lateral movement) of the right eye, moving it **rightward/temporally**, not leftward [1]. - Laevodepression is primarily controlled by the **left superior oblique** and other muscles that depress while moving the eyes leftward. *Dextroelevation* - This refers to upward and rightward gaze movement, involving **elevation**. - The right superior oblique is a **depressor**, not an elevator, so it cannot contribute to elevation movements. - This movement is mainly caused by elevating muscles like the **right inferior oblique** [1].
Question 1766: What are the root values of the phrenic nerve?
- A. C2, C3, C4
- B. C4, C5, C6
- C. C5, C6, T1
- D. C3, C4, C5 (Correct Answer)
Explanation: ***C3, C4, C5*** - The **phrenic nerve** primarily originates from the cervical spinal nerves C3, C4, and C5. - This nerve is crucial as it provides **motor innervation to the diaphragm**, which is essential for breathing. - Remembered by the mnemonic: "C3, 4, 5 keeps the diaphragm alive." *C2, C3, C4* - While C3 and C4 contribute to the phrenic nerve, C2 is not considered a primary root value. - **C2** is more involved in innervation of the neck muscles and sensation in the head and neck. *C4, C5, C6* - Although C4 and C5 contribute significantly, **C6 is not a typical root value** for the phrenic nerve. - C6 primarily contributes to the brachial plexus, innervating muscles of the upper limb. *C5, C6, T1* - This combination represents root values that are more characteristic of the **brachial plexus**, which primarily innervates the upper limb. - C5 does contribute to the phrenic nerve, but **C6 and T1 are unrelated** to phrenic nerve innervation.
Question 1767: Which of the following is a draining channel of the cavernous sinus?
- A. Inferior petrosal sinus (Correct Answer)
- B. Inferior ophthalmic vein
- C. Sphenoparietal sinus
- D. Superior ophthalmic vein
Explanation: ***Inferior petrosal sinus*** - The **inferior petrosal sinus** is a major venous channel that drains blood directly from the **cavernous sinus** inferiorly into the internal jugular vein. - It courses along the petrous part of the temporal bone to exit the skull through the **jugular foramen**. *Inferior ophthalmic vein* - The **inferior ophthalmic vein** primarily drains into the **pterygoid plexus** and sometimes directly into the **cavernous sinus**, but it is more of an afferent (draining into) rather than an efferent (draining from) channel of the cavernous sinus. - It contributes to the blood supply of the cavernous sinus from the orbit, rather than acting as its main outflow tract. *Sphenoparietal sinus* - The **sphenoparietal sinus** is located along the lesser wing of the sphenoid bone and drains into the **cavernous sinus**, acting as an **afferent channel**. - It is not a draining channel of the cavernous sinus to other major veins but rather an input source. *Superior ophthalmic vein* - The **superior ophthalmic vein** is a primary afferent (draining into) channel of the **cavernous sinus**, bringing blood from the orbit. - It connects the angular vein and facial vein systems to the cavernous sinus, serving as a significant route for potential spread of infection.
Question 1768: Facial nerve does not supply which structure of the face?
- A. Posterior belly of digastric muscle
- B. Submandibular gland
- C. Parotid gland (Correct Answer)
- D. Auricular muscle
Explanation: ***Parotid gland*** - While the facial nerve (CN VII) passes *through* the parotid gland, it does not provide motor innervation to the gland itself. - The parotid gland receives parasympathetic innervation for **salivation** primarily from the **glossopharyngeal nerve (CN IX)** via the otic ganglion. *Posterior belly of digastric muscle* - The **facial nerve (CN VII)** provides motor innervation to the posterior belly of the digastric muscle. - This muscle is involved in **depressing the mandible** and **elevating the hyoid bone**. *Submandibular gland* - The facial nerve (CN VII) provides parasympathetic secretomotor innervation to the submandibular gland via the **chorda tympani** and submandibular ganglion. - This innervation controls **salivation** from the submandibular gland. *Auricular muscle* - The facial nerve (CN VII) supplies the **auricular muscles**, which are muscles of facial expression around the ear. - These muscles contribute to minor **ear movements**.
Question 1769: Which of the following is an example of a non-macroglial cell?
- A. Schwann cells
- B. Oligodendrocytes
- C. None of the options (Correct Answer)
- D. Astrocytes
Explanation: ***None of the options*** - All three listed cell types (Schwann cells, oligodendrocytes, and astrocytes) are **macroglial cells** [1]. - **Macroglia** refers to glial cells of **ectodermal origin** and includes both CNS glia (astrocytes, oligodendrocytes, ependymal cells) and PNS glia (Schwann cells) [1]. - **Non-macroglial cells** would include **microglia**, which are derived from mesodermal/hematopoietic lineage and function as immune cells of the CNS [1]. *Schwann cells* - Schwann cells are **macroglial cells** of the peripheral nervous system (PNS) [1]. - They are derived from neural crest (ectodermal origin) and responsible for myelinating axons in the PNS [1], [3]. - They are the PNS equivalent of oligodendrocytes in the CNS [2]. *Oligodendrocytes* - Oligodendrocytes are **macroglial cells** in the central nervous system (CNS) [1]. - Their primary function is to myelinate multiple axons within the CNS [2], [3]. *Astrocytes* - Astrocytes are the most abundant type of **macroglial cell** in the CNS [1]. - They provide structural support, maintain the blood-brain barrier, and provide metabolic support for neurons.
Question 1770: Abnormal regeneration of which nerve is the cause of crocodile tears?
- A. Facial Nerve (Correct Answer)
- B. Glossopharyngeal Nerve
- C. Mandibular Nerve (V3)
- D. Vagus Nerve (CN X)
Explanation: Facial Nerve - **Crocodile tears**, or Bogorad's syndrome, result from aberrant regeneration of the **facial nerve (CN VII)** after injury, often occurring after Bell's palsy or trauma. - During regeneration, parasympathetic secretomotor fibers that should reinnervate salivary glands mistakenly regrow to innervate the **lacrimal gland**, leading to tearing (lacrimation) during salivation or eating. - The mechanism involves misdirected regeneration of fibers from the **greater petrosal nerve** or **chorda tympani** branches of CN VII. *Mandibular Nerve (V3)* - The mandibular nerve is a branch of the **trigeminal nerve (CN V)** and is primarily responsible for motor innervation to the muscles of mastication and sensory innervation to the lower face and mouth. - Its fibers are not involved in **lacrimal gland innervation** nor does its aberrant regeneration lead to crocodile tears. *Vagus Nerve (CN X)* - The vagus nerve is responsible for extensive innervation of the **visceral organs**, including the heart, lungs, and gastrointestinal tract, and plays a role in swallowing and speech. - It does not contain fibers that innervate the **lacrimal gland** or significantly contribute to facial gland secretion. *Glossopharyngeal Nerve* - The glossopharyngeal nerve (CN IX) primarily provides **sensory innervation** to the posterior tongue and pharynx, and motor innervation to the stylopharyngeus muscle. - It also carries parasympathetic fibers to the **parotid salivary gland**, but its aberrant regeneration does not cause lacrimation with salivation.
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