Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1631: Ptosis in Horner syndrome is due to the involvement of which muscle?

A. Müller muscle (Correct Answer)
B. Levator aponeurosis
C. Horner's muscle
D. Orbicularis oculi

Explanation: ***Müller muscle*** - **Ptosis** in **Horner syndrome** results from the paralysis of the **smooth muscle fibers** of the Müller muscle (also known as the superior tarsal muscle), which is innervated by the **sympathetic nervous system**. - This muscle contributes a small amount to upper eyelid elevation, and its denervation causes a **mild unilateral ptosis**. *Levator aponeurosis* - The **levator aponeurosis** is involved in eyelid elevation but is primarily innervated by the **oculomotor nerve (III cranial nerve)**, not the sympathetic system. - Damage to the oculomotor nerve or the aponeurosis itself would cause a more **severe ptosis** than seen in Horner syndrome. *Horner's muscle* - **Horner's muscle**, also known as the **lacrimal part of the orbicularis oculi muscle**, is involved in the drainage of tears, not eyelid elevation. - It does not play a role in the ptosis associated with **Horner syndrome**. *Orbicularis oculi* - The **orbicularis oculi muscle** is responsible for **eyelid closure** and is innervated by the **facial nerve (VII cranial nerve)**. - Its dysfunction would lead to difficulty closing the eye, not ptosis or an inability to open it.

Question 1632: Arrange the following in the sequence of auditory pathway: 1. Cochlear nucleus 2. Spiral ganglion 3. Superior olivary nucleus 4. Inferior colliculus 5. Medial geniculate body

A. 5-4-3-2-1
B. 3-4-5-1-2
C. 2-1-3-4-5 (Correct Answer)
D. 1-2-3-4-5

Explanation: ***2-1-3-4-5*** - The auditory pathway begins with the **spiral ganglion**, which contains the cell bodies of the first-order neurons that innervate the hair cells of the cochlea. - Signals then proceed to the **cochlear nucleus** in the brainstem, followed by the **superior olivary nucleus**, the **inferior colliculus**, and finally the **medial geniculate body** in the thalamus before reaching the auditory cortex [1]. *5-4-3-2-1* - This sequence represents a nearly reverse order of the ascending auditory pathway, starting from a higher processing center (medial geniculate body) and moving backward, which is incorrect for sensory input. - The **medial geniculate body** is the thalamic relay for auditory information, receiving input from lower centers and projecting to the auditory cortex [1]. *3-4-5-1-2* - This sequence incorrectly places the **superior olivary nucleus** as the initial processing stage, preceding the lower-level **spiral ganglion** and **cochlear nucleus**. - Auditory information must first be transduced by hair cells and then relayed by the spiral ganglion neurons to the cochlear nucleus before further processing in the olivary complex. *1-2-3-4-5* - This sequence incorrectly places the **cochlear nucleus** before the **spiral ganglion**. - The **spiral ganglion** contains the primary afferent neurons that receive input from the hair cells and project their axons to the cochlear nucleus.

Question 1633: A 45-year-old patient presents with difficulty speaking and swallowing following a stroke. MRI reveals an infarct in the medulla. Which of the following cranial nerve nuclei is most likely affected?

A. Vestibulocochlear nucleus
B. Trigeminal nerve nucleus
C. Facial nerve nucleus
D. Nucleus ambiguus (Correct Answer)

Explanation: ***Nucleus ambiguus*** - The **nucleus ambiguus** is located in the **medulla** and contains motor neurons that innervate muscles involved in **speaking** and **swallowing**, specifically those of the pharynx, larynx, and soft palate via cranial nerves IX, X, and XI [1]. - An infarct in the medulla causing difficulty speaking and swallowing strongly implicates damage to this nucleus, leading to **dysarthria** and **dysphagia** [1]. *Vestibulocochlear nucleus* - This nucleus is primarily involved in **hearing** and **balance**, which would manifest as dizziness, hearing loss, or nystagmus, not directly difficulty speaking and swallowing. - While located in the brainstem, damage to this nucleus typically does not cause the specific symptoms of dysarthria and dysphagia described. *Trigeminal nerve nucleus* - The trigeminal nerve is responsible for sensory innervation of the face, and motor innervation for **mastication** (chewing). - Damage would primarily affect facial sensation or jaw movement, not the act of deglutition or phonation. *Facial nerve nucleus* - This nucleus, located in the **pons**, controls the muscles of **facial expression** and taste for the anterior two-thirds of the tongue. - Damage would lead to facial weakness or paralysis, not the profound difficulty with speaking and swallowing affecting pharyngeal and laryngeal function.

Question 1634: During an examination of the cranial nerves, a patient shows inability to move their eye laterally past the midline. Which of the following structures in the cavernous sinus is most likely affected?

A. Oculomotor nerve
B. Trochlear nerve
C. Ophthalmic nerve
D. Abducens nerve (Correct Answer)

Explanation: ***Abducens nerve*** - The **abducens nerve (CN VI)** innervates the **lateral rectus muscle**, responsible for **abduction** (lateral movement) of the eye [1]. - Inability to move the eye laterally past the midline indicates paralysis or weakness of the lateral rectus muscle, directly implicating the abducens nerve [1]. *Oculomotor nerve* - The **oculomotor nerve (CN III)** controls most **extraocular muscles** (superior, inferior, medial rectus, inferior oblique) and the levator palpebrae superioris, as well as pupillary constriction [1], [2]. - Damage to this nerve would primarily affect **adduction**, elevation, depression, and eyelid opening, not isolated lateral gaze. *Trochlear nerve* - The **trochlear nerve (CN IV)** innervates the **superior oblique muscle**, which depresses and internally rotates the eye [1]. - A lesion here typically presents with **vertical diplopia**, particularly when reading or descending stairs, due to impaired eye depression and intorsion. *Ophthalmic nerve* - The **ophthalmic nerve (V1)** is one of the three divisions of the trigeminal nerve and is purely **sensory**. - It provides sensation to the forehead, upper eyelid, cornea, and nose, and does not control any eye movements.

Question 1635: Which part of thalamus is related to motor control?

A. Ventrolateral thalamus (Correct Answer)
B. Ventral posteromedial
C. Ventral posterolateral
D. Lateral geniculate nucleus

Explanation: ***Ventrolateral thalamus*** - The **ventrolateral (VL) nucleus** of the thalamus is a key relay station for **motor control**, receiving input from the **basal ganglia** and **cerebellum** and projecting to the motor cortex [1]. - It plays a crucial role in the planning, initiation, and coordination of **voluntary movements**. *Ventral posteromedial* - The **ventral posteromedial (VPM) nucleus** is involved in processing **somatosensory information** from the face and taste sensations. - It does not primarily contribute to motor control pathways. *Ventral posterolateral* - The **ventral posterolateral (VPL) nucleus** relays **somatosensory information** from the body (limbs and trunk) to the primary somatosensory cortex. - Its main function is sensory perception, not motor control. *Lateral geniculate nucleus* - The **lateral geniculate nucleus (LGN)** is exclusively involved in the **visual pathway**, receiving input from the retina and projecting to the primary visual cortex. - It has no direct role in motor control.

Question 1636: Tibial and common peroneal nerves supply which of the following muscles?

A. Gracilis
B. Adductor longus
C. Biceps femoris (Correct Answer)
D. Adductor magnus

Explanation: **Biceps femoris** - The **long head** of the biceps femoris is supplied by the **tibial nerve**. - The **short head** of the biceps femoris is supplied by the **common peroneal nerve**. *Gracilis* - The gracilis muscle is solely innervated by the **obturator nerve**. - It participates in **hip adduction** and **knee flexion**, but its innervation is distinct. *Adductor longus* - The adductor longus muscle is innervated exclusively by the **obturator nerve**. - Its primary function is **adduction of the thigh**. *Adductor magnus* - The adductor magnus has a dual innervation, but not by the tibial and common peroneal nerves. - Its **adductor part** is innervated by the **obturator nerve**, while its **hamstring part** is supplied by the **tibial nerve**.

Question 1637: The cranial nerve passing through cavernous sinus is

A. Olfactory
B. Abducens (Correct Answer)
C. Facial
D. Optic

Explanation: ***Abducens*** - The **abducens nerve (CN VI)** is the only cranial nerve that travels **through the substance of the cavernous sinus** itself, running alongside the internal carotid artery. - This unique intracavernous location makes it the most vulnerable cranial nerve to injury from cavernous sinus pathology (thrombosis, tumors, aneurysms). - Other nerves (CN III, IV, V1, V2) run in the **lateral wall** of the sinus, not through it. *Olfactory* - The **olfactory nerve (CN I)** runs from the nasal cavity through the cribriform plate to the olfactory bulb. - It does not traverse the cavernous sinus. *Facial* - The **facial nerve (CN VII)** exits the skull via the stylomastoid foramen and has a complex course through the temporal bone. - It does not pass through the cavernous sinus. *Optic* - The **optic nerve (CN II)** exits the orbit through the optic canal to reach the optic chiasm. - It does not travel through the cavernous sinus, though it is in close anatomical proximity to structures anterior to it.

Question 1638: Hypoglossal nerve supplies all of these muscles except:-

A. Palatoglossus (Correct Answer)
B. Styloglossus
C. Genioglossus
D. Hyoglossus

Explanation: ***Palatoglossus*** - The **palatoglossus** muscle is innervated by the **pharyngeal plexus** (composed of contributions from the vagus and glossopharyngeal nerves), not the hypoglossal nerve. - It is the only extrinsic muscle of the tongue not supplied by the hypoglossal nerve, and its primary function is to elevate the posterior part of the tongue and narrow the oropharyngeal isthmus. *Styloglossus* - The **styloglossus** muscle is an **extrinsic tongue muscle** that originates from the styloid process and inserts into the side and undersurface of the tongue. - It is supplied by the **hypoglossal nerve** and acts to retract and elevate the tongue. *Genioglossus* - The **genioglossus** muscle is an **extrinsic tongue muscle** that originates from the mental spine of the mandible. - It is innervated by the **hypoglossal nerve** and is responsible for protruding and depressing the tongue, and its bilateral contraction is crucial in preventing airway obstruction during sleep (tongue falling back). *Hyoglossus* - The **hyoglossus** muscle is an **extrinsic tongue muscle** that originates from the hyoid bone and inserts into the side of the tongue. - It is supplied by the **hypoglossal nerve** and acts to depress and retract the tongue.

Question 1639: Sensory innervation of the cornea is by which nerve?

A. 5th (ophthalmic division of the trigeminal nerve) (Correct Answer)
B. 6th (Abducens nerve)
C. 3rd (Oculomotor nerve)
D. 4th (Trochlear nerve)

Explanation: ***5th (ophthalmic division of the trigeminal nerve)*** - The **trigeminal nerve (CN V)** is responsible for sensory innervation of the face, and its **ophthalmic division (V1)** specifically supplies the cornea. - This extensive sensory innervation explains the **extreme sensitivity of the cornea** to touch, temperature, and chemicals, and is crucial for the **corneal reflex**. *6th (Abducens nerve)* - The **abducens nerve (CN VI)** is a **motor nerve** responsible for innervating the **lateral rectus muscle**, which abducts the eye. - It has no role in the sensory innervation of the cornea. *3rd (Oculomotor nerve)* - The **oculomotor nerve (CN III)** is primarily a **motor nerve** responsible for innervating most of the **extraocular muscles** (superior, inferior, medial recti, inferior oblique) and the **levator palpebrae superioris**. - It also carries **parasympathetic fibers** for pupillary constriction and accommodation, but it does not provide sensory innervation to the cornea. *4th (Trochlear nerve)* - The **trochlear nerve (CN IV)** is a **motor nerve** that innervates the **superior oblique muscle**, which depresses and internally rotates the eye. - It has no function in corneal sensation.

Question 1640: Ventricles are lined by?

A. Schwann cells
B. Oligodendrocytes
C. Ependymal cells (Correct Answer)
D. Astrocytes

Explanation: Ependymal cells - Ependymal cells are a type of glial cell that form the epithelial lining of the ventricles of the brain and the central canal of the spinal cord [3]. - They possess cilia that help circulate the cerebrospinal fluid (CSF) and microvilli involved in CSF absorption. Schwann cells - Schwann cells are responsible for forming the myelin sheath around axons in the peripheral nervous system (PNS) [4]. - They do not line the ventricles, which are part of the central nervous system [2]. Oligodendrocytes - Oligodendrocytes are glial cells that form the myelin sheath around axons in the central nervous system (CNS) [1], [4]. - While they are CNS cells, their primary function is myelination, not lining the ventricular system [1]. Astrocytes - Astrocytes are the most abundant and diverse glial cells in the CNS, providing structural support, metabolic regulation, and forming the blood-brain barrier. - They are found throughout the brain parenchyma but do not directly line the ventricular cavities.

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