Neuroanatomy — MCQs

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: What is the primary function of the hypoglossal nerve?

A. Sensory innervation to the posterior third of the tongue
B. Sensory innervation to the anterior two-thirds of the tongue
C. Taste sensation from the posterior one-third of the tongue
D. Motor innervation to the intrinsic and extrinsic muscles of the tongue (except palatoglossus) (Correct Answer)

Explanation: ***Motor innervation to all of the muscles of the tongue both intrinsic and extrinsic*** [2] - The hypoglossal nerve (**CN XII**) is a purely **motor cranial nerve**. [2] - It supplies all the **extrinsic muscles of the tongue** (genioglossus, hyoglossus, styloglossus, palatoglossus is innervated by vagus) and all the **intrinsic muscles of the tongue** (superior longitudinal, inferior longitudinal, transverse, and vertical), enabling tongue movement crucial for speech and swallowing. [2] *Sensory innervation to the posterior third of the tongue* - Sensory innervation to the posterior third of the tongue is primarily provided by the **glossopharyngeal nerve (CN IX)**. [1] - This nerve mediates general sensation and taste from this region. [1] *Sensory innervation to the anterior two-thirds of the tongue* - General sensory innervation to the anterior two-thirds of the tongue is supplied by the **lingual nerve**, a branch of the **trigeminal nerve (CN V3)**. - Taste sensation from this area is carried by the chorda tympani, a branch of the facial nerve (CN VII). [1] *Taste sensation from the posterior one-third of the tongue* - Taste sensation from the posterior one-third of the tongue is also mediated by the **glossopharyngeal nerve (CN IX)**. [1] - This nerve is responsible for both general sensation and taste in the posterior tongue. [1]

Question 1769: 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 1770: 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.

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