Neuroanatomy Practice Questions

Q: Purely somatic efferent nerves are all except:

Trigeminal. 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].

Q: Taste sensation from anterior part of tongue is mediated by:

7th CN. ***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.

Q: All of the following are true about grey communicans except:

Preganglionic. ***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).

Q: TRUE regarding upper motor neuron VIIth nerve paralysis is:

Contralateral lower face paresis. ***Contralateral lower face paresis*** - The **upper face** receives **bilateral innervation** from both cerebral hemispheres, meaning a unilateral upper motor neuron (UMN) lesion will spare the upper face [1]. - The **lower face** receives **contralateral innervation** only; therefore, a UMN lesion on one side of the brain will result in weakness of the lower facial muscles on the opposite side of the face. *Ipsilateral lower face paresis* - This would occur with a **lower motor neuron (LMN) lesion**, such as in Bell's palsy, affecting the facial nerve nucleus or nerve itself [1]. - An LMN lesion typically causes **ipsilateral weakness** of both the upper and lower face due to the loss of all motor innervation on that side. *Ipsilateral upper face paresis* - This is characteristic of a **lower motor neuron (LMN) lesion**, which affects the entire facial nerve including both upper and lower facial muscles on the same side. - UMN lesions generally spare the upper face due to its bilateral cortical innervation [1]. *Contralateral upper face paresis* - This is generally not observed in isolated UMN facial nerve paralysis due to the **bilateral cortical innervation** of the upper facial muscles. - Only a very rare and extensive bilateral UMN lesion or an LMN lesion would cause such a presentation.

Q: Auditory pathway is mediated by:

Medial geniculate body. ***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.

Q: Lesion of facial nerve at level of stylomastoid foramen leads to:

Paralysis of orbicularis oculi muscle. ***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.

Q: Blood supply to spinal nerve roots is derived from?

All of the options. ***All of the options*** - The **spinal nerve roots** receive their blood supply from a **complex vascular network** involving multiple arterial sources. - All three arteries listed contribute to the perfusion of nerve roots at different levels of the spinal cord. **Each contributing artery:** ***Anterior spinal artery*** - Forms from the union of branches from the **vertebral arteries** - Supplies the **anterior two-thirds** of the spinal cord and gives off branches to the **ventral (anterior) nerve roots** - Provides the primary blood supply to motor nerve roots ***Posterior spinal arteries*** - Typically arise from the **vertebral arteries** or **PICA** (posterior inferior cerebellar artery) - Supply the **posterior one-third** of the spinal cord and contribute to the **dorsal (posterior) nerve roots** - Provide vascular support to sensory nerve roots ***Ascending cervical artery*** - Branch of the **inferior thyroid artery** (from the thyrocervical trunk of the subclavian artery) - Provides **segmental radicular branches** that reinforce the blood supply to the **cervical spinal cord and nerve roots** - Part of the extensive collateral circulation supporting the spinal vasculature **Key concept:** The spinal nerve roots are supplied by a **redundant vascular network** to ensure continuous perfusion, involving longitudinal vessels (ASA, PSA) and segmental feeders (radicular arteries including ascending cervical).

Q: Lesion of the marked structure affects all EXCEPT

Superior oblique. ***Superior oblique*** - The **superior oblique** muscle is innervated by the **trochlear nerve (CN IV)**. - A lesion affecting the **oculomotor nerve (CN III)**, which usually controls the marked structure, would therefore **not** affect the superior oblique. *Superior rectus* - The **superior rectus** muscle is innervated by the **oculomotor nerve (CN III)**. - A lesion of the oculomotor nerve would impair its function, leading to difficulty in **elevating** and **adducting** the eye. *Inferior oblique* - The **inferior oblique** muscle is innervated by the **oculomotor nerve (CN III)**. - Damage to this nerve would result in compromised function of the inferior oblique, affecting **extorsion** and **elevation** of the eye. *Medial rectus* - The **medial rectus** muscle is innervated by the **oculomotor nerve (CN III)**. - A lesion of the oculomotor nerve would lead to an inability to perform **adduction** (moving the eye inward).

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

Dorsal root ganglion. ***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].

Q: Ptosis results from trauma to which nerve?

III. 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.

Question 1

Purely somatic efferent nerves are all except:

Accepted Answer

Trigeminal

Answer

Abducent

Answer

Trochlear

Answer

Oculomotor

Question 2

Taste sensation from anterior part of tongue is mediated by:

Accepted Answer

7th CN

Answer

10th CN

Answer

12th CN

Answer

5th CN

Question 3

All of the following are true about grey communicans except:

Accepted Answer

Preganglionic

Answer

Connects to spinal nerves

Answer

Unmyelinated

Answer

Present at all spinal levels

Question 4

TRUE regarding upper motor neuron VIIth nerve paralysis is:

Accepted Answer

Contralateral lower face paresis

Answer

Ipsilateral lower face paresis

Answer

Ipsilateral upper face paresis

Answer

Contralateral upper face paresis

Question 5

Auditory pathway is mediated by:

Accepted Answer

Medial geniculate body

Answer

Lateral lemniscus

Answer

Medial lemniscus

Answer

Lateral geniculate body

Question 6

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

Accepted Answer

Paralysis of orbicularis oculi muscle

Answer

Loss of innervation to stapedius

Answer

Loss of taste sensation from Ant. 2/3 of tongue

Answer

Loss of Lacrimal secretion

Question 7

Blood supply to spinal nerve roots is derived from?

Accepted Answer

All of the options

Answer

Posterior spinal artery

Answer

Anterior spinal artery

Answer

Ascending cervical artery

Question 8

Lesion of the marked structure affects all EXCEPT

Accepted Answer

Superior oblique

Answer

Superior rectus

Answer

Inferior oblique

Answer

Medial rectus

Question 9

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

Accepted Answer

Dorsal root ganglion

Answer

Dorsal gray horn

Answer

Spinal cord

Answer

Brain

Question 10

Ptosis results from trauma to which nerve?

Accepted Answer

III

Answer

VII

Answer

VIII

Answer

VI

Neuroanatomy — MCQs

Neuroanatomy — MCQs

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