Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1651: Purely somatic efferent nerves are all except:

A. Abducent
B. Trochlear
C. Oculomotor
D. Trigeminal (Correct Answer)

Explanation: The trigeminal nerve (CN V) is primarily a mixed nerve, containing both sensory fibers from the face and motor fibers to the muscles of mastication. While it has motor components, its significant sensory function and innervation of different structures classify it differently from the purely somatic efferent cranial nerves. *Abducent* - The abducent nerve (CN VI) is a somatic efferent nerve that exclusively innervates the lateral rectus muscle of the eye [1]. - Its sole function is to cause abduction (lateral movement) of the eyeball [1]. *Trochlear* - The trochlear nerve (CN IV) is also a somatic efferent nerve, innervating only the superior oblique muscle of the eye [1]. - This muscle allows for downward and outward rotation of the eye [1]. *Occulomotor* - The oculomotor nerve (CN III) contains somatic efferent fibers that innervate most of the extraocular muscles (medial, superior, inferior rectus, and inferior oblique) [1]. - It also carries parasympathetic fibers to the pupillary sphincter and ciliary muscles, but its primary motor components are somatic efferent [2].

Question 1652: Taste sensation from anterior part of tongue is mediated by:

A. 7th CN (Correct Answer)
B. 10th CN
C. 12th CN
D. 5th CN

Explanation: ***7th CN*** - The **facial nerve (CN VII)** mediates taste sensation from the **anterior two-thirds of the tongue** via the **chorda tympani** branch [1]. - This sensory information travels to the **solitary nucleus** in the brainstem [1]. *10th CN* - The **vagus nerve (CN X)** innervates a small area for taste sensation in the **epiglottis** and laryngeal pharynx, not the anterior tongue [1]. - It is primarily involved in parasympathetic regulation of visceral organs. *12th CN* - The **hypoglossal nerve (CN XII)** is a **motor nerve** responsible for the movement of the tongue muscles. - It does **not** carry taste or general sensation from any part of the tongue. *5th CN* - The **trigeminal nerve (CN V)** mediates **general sensation** (touch, pain, temperature) from the anterior two-thirds of the tongue. - It does **not** carry taste fibers from the tongue.

Question 1653: All of the following are true about grey communicans except:

A. Connects to spinal nerves
B. Unmyelinated
C. Preganglionic (Correct Answer)
D. Present at all spinal levels

Explanation: ***Preganglionic*** - The **grey rami communicantes** primarily carry **postganglionic unmyelinated sympathetic fibers** from the paravertebral ganglia back to spinal nerves [1]. - They are therefore **not preganglionic**; rather, they are the efferent pathway for sympathetic nerves after synapsing in the ganglion [1]. - This is the **false statement** and the correct answer to this EXCEPT question. *Connects to spinal nerves* - The grey rami communicantes connect the **sympathetic trunk ganglia** to all **31 pairs of spinal nerves**, allowing sympathetic innervation to reach widespread target organs. - These connections transmit postganglionic sympathetic fibers that then travel with the spinal nerves to their final destinations. *Unmyelinated* - Grey rami communicantes are composed of **unmyelinated axons**, giving them their characteristic grey appearance. - This contrasts with the white rami communicantes, which contain preganglionic myelinated fibers (found only at T1-L2/L3 levels) [1]. *Present at all spinal levels* - Grey rami communicantes are present at **all 31 spinal levels** (cervical, thoracic, lumbar, sacral, and coccygeal). - This distinguishes them from white rami communicantes, which are only present at T1-L2/L3 (thoracolumbar outflow).

Question 1654: Auditory pathway is mediated by:

A. Medial geniculate body (Correct Answer)
B. Lateral lemniscus
C. Medial lemniscus
D. Lateral geniculate body

Explanation: ***Medial geniculate body*** - The **medial geniculate body (MGB)** is a thalamic relay nucleus that serves as the final subcortical processing station for **auditory information** before it reaches the cerebral cortex [1], [3]. - It receives input from the **inferior colliculus** and projects to the **primary auditory cortex** (Heschl's gyrus) in the temporal lobe [1]. *Lateral lemniscus* - The **lateral lemniscus** is an ascending tract of the **auditory pathway** in the brainstem, carrying auditory information from the cochlear nuclei to the inferior colliculus [1]. - While it's part of the auditory pathway, it is a **fiber tract** and not the primary mediating structure that refers to the main relay nucleus in the thalamus. *Medial lemniscus* - The **medial lemniscus** is an ascending sensory pathway in the brainstem that primarily transmits **fine touch, vibration, proprioception, and two-point discrimination** from the fasciculus gracilis and cuneatus to the thalamus. - It is part of the **somatosensory system** and is not involved in auditory processing. *Lateral geniculate body* - The **lateral geniculate body (LGB)** is a thalamic relay nucleus for the **visual pathway** [2]. - It receives input from the **retina** via the optic tract and projects to the **primary visual cortex** (Brodmann area 17) in the occipital lobe.

Question 1655: A patient has a painful ulcer on the tip of his tongue. Which of the following cranial nerves carries the pain sensation he experiences?

A. XII
B. IX
C. VII
D. V (Correct Answer)

Explanation: ***V*** - The **trigeminal nerve (CN V)** is responsible for general sensation (touch, pain, temperature) from the anterior two-thirds of the tongue, including the tip [2]. - The **lingual nerve**, a branch of the mandibular division (V3) of the trigeminal nerve, innervates this area. *XII* - The **hypoglossal nerve (CN XII)** is primarily responsible for the motor innervation of the intrinsic and extrinsic muscles of the tongue, controlling tongue movement. - It does not carry sensory information like pain from the tongue. *IX* - The **glossopharyngeal nerve (CN IX)** provides general sensation and taste perception from the posterior one-third of the tongue. - It would not be involved in pain sensation from the tip of the tongue. *VII* - The **facial nerve (CN VII)**, specifically via its chorda tympani branch, carries taste sensation from the anterior two-thirds of the tongue [1]. - It does not carry general pain sensation from the tongue.

Question 1656: Lesion of facial nerve at level of stylomastoid foramen leads to:

A. Loss of innervation to stapedius
B. Paralysis of orbicularis oculi muscle (Correct Answer)
C. Loss of taste sensation from Ant. 2/3 of tongue
D. Loss of Lacrimal secretion

Explanation: ***Paralysis of orbicularis oculi muscle*** - The **facial nerve** is primarily responsible for innervating all **muscles of facial expression**, including the **orbicularis oculi**, after it exits the **stylomastoid foramen**. - A lesion at this level would therefore lead to paralysis of these muscles, causing an inability to close the eye on the affected side. *Loss of innervation to stapedius* - The nerve to the **stapedius muscle** branches off the facial nerve *before* it exits the stylomastoid foramen, within the **temporal bone**. - Therefore, a lesion *at* the stylomastoid foramen would occur *distal* to this branching point, sparing the nerve to the stapedius and preserving its function. *Loss of taste sensation from Ant. 2/3 of tongue* - **Taste sensation** from the anterior two-thirds of the tongue is carried by the **chorda tympani nerve**, which branches off the facial nerve *within the temporal bone*. - A lesion *at* the stylomastoid foramen would be *distal* to the origin of the chorda tympani, thus preserving taste sensation. *Loss of Lacrimal secretion* - **Lacrimal gland secretion** is mediated by parasympathetic fibers that branch off the facial nerve as the **greater petrosal nerve**, *much earlier and more proximally* within the temporal bone. - A lesion *at* the stylomastoid foramen would not affect the function of the greater petrosal nerve or lacrimal secretion.

Question 1657: Largest parasympathetic peripheral ganglion is?

A. Sphenopalatine ganglion (Correct Answer)
B. Ciliary ganglion
C. Otic ganglion
D. None of the options

Explanation: ***Sphenopalatine ganglion*** - The **sphenopalatine ganglion** is the largest parasympathetic ganglion in the head and neck. - It receives preganglionic parasympathetic fibers from the **facial nerve** (via the greater petrosal nerve) and relays them to the lacrimal gland and mucous glands of the nasal cavity, palate, and pharynx. *Ciliary ganglion* - The **ciliary ganglion** is a small parasympathetic ganglion located in the orbit [1]. - It controls the **pupillary constrictor** and **ciliary muscles** for accommodation [1]. *Otic ganglion* - The **otic ganglion** is a small parasympathetic ganglion located medial to the mandibular nerve. - It supplies secretomotor fibers to the **parotid gland**. *None of the options* - This option is incorrect because the sphenopalatine ganglion is indeed the largest peripheral parasympathetic ganglion.

Question 1658: Tic Douloureux is facial pain traveling through which of the following nerves?

A. Hypoglossal
B. Trigeminal (Correct Answer)
C. Vestibulocochlear
D. Facial

Explanation: ***Trigeminal*** - **Tic douloureux**, also known as **trigeminal neuralgia**, is a chronic pain condition affecting the **trigeminal nerve (cranial nerve V)** [1]. - This nerve is responsible for sensory innervation of the face, and the condition presents as sudden, severe, electric shock-like pains [1]. *Hypoglossal* - The **hypoglossal nerve (cranial nerve XII)** primarily controls the **movement of the tongue**. - Dysfunction of this nerve typically manifests as speech and swallowing difficulties, not facial pain. *Vestibulocochlear* - The **vestibulocochlear nerve (cranial nerve VIII)** is responsible for **hearing and balance**. - Problems with this nerve cause symptoms like vertigo, dizziness, and hearing loss. *Facial* - The **facial nerve (cranial nerve VII)** controls **facial expressions**, taste sensation from the anterior two-thirds of the tongue, and functions of several glands. - Disorders of the facial nerve, such as Bell's palsy, cause facial weakness or paralysis, not the characteristic lancinating pain of tic douloureux.

Question 1659: The cell body of general somatic and visceral sensory neurons is located within the

A. Dorsal gray horn
B. Dorsal root ganglion (Correct Answer)
C. Spinal cord
D. Brain

Explanation: ***Dorsal root ganglion*** - The **dorsal root ganglia** are collections of **nerve cell bodies** (ganglia) located outside the central nervous system, specifically along the dorsal roots of the spinal cord [3]. - They contain the **unipolar cell bodies** of all primary **general somatic and visceral sensory (afferent) neurons** that transmit sensory information from the periphery to the spinal cord [1],[4]. - **Note**: Special sensory neurons (vision, hearing, smell, taste) have cell bodies in different ganglia specific to their cranial nerves. *Dorsal gray horn* - The **dorsal gray horn** is a region within the gray matter of the spinal cord, primarily consisting of **interneurons** and the **synaptic terminals** of sensory neurons. - It does not contain the cell bodies of the primary sensory neurons themselves, but rather processes the sensory input received. *Spinal cord* - The **spinal cord** is a part of the central nervous system that serves as a conduit for sensory (afferent) and motor (efferent) signals [2]. - While sensory neurons project *into* the spinal cord, their cell bodies are located *outside* of it, in the dorsal root ganglia [3]. *Brain* - The **brain** is the primary control center of the nervous system, responsible for interpreting sensory information and initiating motor responses. - The cell bodies of general somatic and visceral sensory neurons are located in the **dorsal root ganglia**, not directly in the brain [3].

Question 1660: Ptosis results from trauma to which nerve?

A. VII
B. VIII
C. VI
D. III (Correct Answer)

Explanation: III - **Ptosis**, or drooping of the eyelid, occurs due to paralysis of the **levator palpebrae superioris muscle**, which is innervated by the **oculomotor nerve (III)**. [1] - Damage to the oculomotor nerve can also lead to other symptoms like **diplopia**, **strabismus**, and a **dilated pupil**. *VII* - The **facial nerve (VII)** primarily controls muscles of facial expression, including the **orbicularis oculi**, which closes the eye. - Damage to the facial nerve results in difficulty closing the eye, not drooping of the upper eyelid. *VIII* - The **vestibulocochlear nerve (VIII)** is responsible for **hearing** and **balance**. - Trauma to this nerve would cause symptoms like **hearing loss**, **tinnitus**, or **vertigo**, with no direct impact on eyelid function. *VI* - The **abducens nerve (VI)** innervates the **lateral rectus muscle**, which abducts the eye. [2] - Injury to the abducens nerve causes the eye to turn inward (**esotropia**) and results in **diplopia**, but not ptosis.

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