Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1711: Homonymous hemianopia type of visual field defect is seen in all except which of the following?

A. Lateral geniculate body
B. Total optic radiation
C. Optic tract
D. Optic chiasm (Correct Answer)

Explanation: ***Optic chiasm*** - Lesions of the **optic chiasm** typically cause **bitemporal hemianopia**, due to damage to the crossing nasal fibers from both eyes [1]. - Homonymous hemianopia involves the loss of vision in the **same visual field half** of both eyes, which is caused by post-chiasmal lesions [1]. *Lateral geniculate body* - Lesions in the **lateral geniculate body** interrupt visual pathways after the optic chiasm, leading to **contralateral homonymous hemianopia** [1]. - The lateral geniculate body is the primary relay center for visual information from the optic tract to the visual cortex [1]. *Total optic radiation* - Complete lesions of the **optic radiation** (also known as geniculocalcarine tract) result in **contralateral homonymous hemianopia**, often with macular sparing [1]. - The optic radiations carry visual information from the lateral geniculate body to the primary visual cortex in the occipital lobe [1]. *Optic tract* - Damage to the **optic tract** results in **contralateral homonymous hemianopia** because it contains fibers from the temporal retina of the ipsilateral eye and the nasal retina of the contralateral eye, both representing the opposite visual field [1]. - The optic tract is located after the optic chiasm, meaning any lesion here will affect vision from the same side of the visual field in both eyes [1].

Question 1712: A female presents with loss of vision in the right halves of both eyes. Where is the lesion located in the optic pathway?

A. Left optic tract (Correct Answer)
B. Optic radiation
C. Optic chiasma
D. Right optic tract

Explanation: Left optic tract - A lesion in the **left optic tract** causes **right homonymous hemianopsia**, meaning loss of vision in the right halves of both eyes [1]. - This is because the left optic tract carries visual information from the **nasal retina of the right eye** and the **temporal retina of the left eye**, both of which process the right visual field [1]. *Optic radiation* - A lesion in the optic radiation would also cause a **homonymous hemianopsia** but depending on the specific location within the radiation, it could result in a **quadrantanopia** (loss of a quarter visual field) rather than a complete hemianopsia. - The optic radiation projects from the **lateral geniculate nucleus** to the **visual cortex**, and damage here affects the post-chiasmatic visual pathway [1]. *Optic chiasma* - A lesion at the **optic chiasma** typically results in **bitemporal hemianopsia**, which is the loss of vision in the **temporal halves of both eyes** [1]. - This occurs because the **crossing nasal fibers** from both eyes, which carry information from the temporal visual fields, are affected [1]. *Right optic tract* - A lesion in the **right optic tract** would result in **left homonymous hemianopsia**, meaning loss of vision in the **left halves of both eyes** [1]. - This is due to the right optic tract carrying fibers from the **nasal retina of the left eye** and the **temporal retina of the right eye**, both of which process the left visual field [1].

Question 1713: A 70-year-old male patient presents with high-frequency hearing loss. It was noted that the basilar membrane was affected. Which of the following structures lies near the affected structure?

A. Stria vascularis (Correct Answer)
B. Modiolus
C. Helicotrema
D. Oval window

Explanation: ***Stria vascularis*** - The **stria vascularis** is a highly vascularized epithelial layer located on the lateral wall of the **scala media**, directly adjacent to the **basilar membrane**. - It is crucial for maintaining the high potassium concentration in the **endolymph** which is essential for the function of hair cells in the **organ of Corti** and thus hearing [2]. *Modiolus* - The **modiolus** is the central, conical bony pillar of the cochlea, around which the cochlear duct spirals. - While it houses the **spiral ganglion** and auditory nerve fibers, it is structurally distinct from and not immediately adjacent to the basilar membrane. *Helicotrema* - The **helicotrema** is the small opening at the apex of the cochlea where the **scala vestibuli** and **scala tympani** communicate [1]. - It is located at the very end of the cochlea, far from the main vibratory portion of the basilar membrane responsible for high-frequency sounds. *Oval window* - The **oval window** is the opening in the bony labyrinth into which the **stapes** footplate fits, transmitting vibrations from the middle ear to the inner ear [2]. - While critical for hearing, it is located at the base of the cochlea and is not an immediate neighbor of the basilar membrane in the context of its function in sound transduction within the cochlear duct.

Question 1714: Which structure is located at the floor of the 4th ventricle?

A. Vagal triangle (Correct Answer)
B. Infundibulum
C. Tuber cinereum
D. Mammillary body

Explanation: ***Vagal triangle*** - The **vagal triangle** is a prominent anatomical landmark located on the **floor of the fourth ventricle**, specifically within the medullary region, inferior to the hypoglossal triangle. - It overlies the dorsal nucleus of the **vagus nerve (cranial nerve X)**, providing a superficial indication of its underlying nuclear complex. *Infundibulum* - The **infundibulum** is a funnel-shaped stalk that connects the **hypothalamus** to the posterior pituitary gland. - It is located near the base of the brain, not in the floor of the fourth ventricle. *Tuber cinereum* - The **tuber cinereum** is a part of the **hypothalamus**, forming the floor of the third ventricle. - It is involved in regulating various homeostatic functions and has no direct anatomical relation to the fourth ventricle's floor. *Mammillary body* - **Mammillary bodies** are a pair of small, rounded prominences on the **ventral surface of the hypothalamus**, posterior to the tuber cinereum. - They are part of the limbic system, primarily involved in memory, and are not found in the floor of the fourth ventricle.

Question 1715: Organ of Corti is situated in?

A. Basilar membrane (Correct Answer)
B. Utricle
C. Saccule
D. Reissner's membrane

Explanation: ***Basilar membrane*** - The **Organ of Corti**, which is the **sensory organ for hearing**, rests directly on the **basilar membrane** within the cochlea [2]. - Vibrations of the basilar membrane, caused by sound waves, stimulate the **hair cells** of the Organ of Corti, leading to the generation of nerve impulses [4]. *Utricle* - The **utricle** is part of the **vestibular system** in the inner ear, responsible for detecting **linear acceleration** and **head tilt** in the horizontal plane [1], [3]. - It plays no direct role in the process of hearing or housing the Organ of Corti. *Saccule* - The **saccule** is also a part of the **vestibular system**, specifically detecting **linear acceleration** and **head tilt** in the vertical plane [1], [3]. - Like the utricle, it is involved in balance and spatial orientation, not hearing. *Reissner's membrane* - **Reissner's membrane** (vestibular membrane) forms the **roof of the scala media** in the cochlea, separating it from the scala vestibuli. - While it is an important structure in the cochlea, the Organ of Corti sits on the **basilar membrane**, which forms the floor of the scala media, not on Reissner's membrane.

Question 1716: What is the nerve root value of the supinator reflex (brachioradialis reflex)?

A. C3 C4
B. C5 C6 (Correct Answer)
C. C8 T1
D. C4 C5

Explanation: ***C5 C6*** - The supinator reflex, also known as the **brachioradialis reflex**, is primarily mediated by the **C5 and C6 nerve roots**. - Tapping the **brachioradialis tendon** elicits a reflexive forearm supination and elbow flexion, confirming the integrity of this root level. *C3 C4* - These nerve roots are primarily involved with the **diaphragm** (via the phrenic nerve) and neck muscles. - They do not contribute significantly to the innervation of the muscles involved in the supinator reflex. *C4 C5* - While C5 is involved, C4 primarily innervates muscles of the **neck and shoulder girdle** such as the **levator scapulae** and **supraspinatus**. - The main contribution to the supinator reflex arc requires the combined input from C5 and C6. *C8 T1* - These nerve roots are primarily responsible for the innervation of the **intrinsic hand muscles** and some forearm flexors. - They are tested by reflexes such as the **triceps reflex (C7)** and finger flexion reflexes, not the supinator reflex.

Question 1717: Which of the following is part of the membranous labyrinth and not the bony labyrinth?

A. Vestibule
B. Cochlea
C. Utricle (Correct Answer)
D. Semicircular canal

Explanation: ***Utricle*** - The **utricle** is a component of the **membranous labyrinth** within the vestibule, housing **maculae** responsible for detecting linear acceleration and head tilt [2]. - It contains **endolymph** and is surrounded by perilymph, acting as the primary connection point for the semicircular ducts. *Cochlea* - The **cochlea** is a part of both the **bony** and **membranous labyrinths**, comprising the bony cochlear canal and the membranous cochlear duct within it [3]. - While it contains the **organ of Corti** for hearing, the term "cochlea" itself refers to the entire structure, including its bony housing [3]. *Vestibule* - The **vestibule** is part of the **bony labyrinth**, a central chamber housing the **saccule** and **utricle**, which are themselves part of the membranous labyrinth [2]. - It is an anatomical region rather than a specific membranous structure, primarily consisting of bone. *Semicircular canal* - The **semicircular canals** are part of the **bony labyrinth**, forming three loops that house the membranous **semicircular ducts** [1]. - These bony structures surround the ducts, which contain the **cristae ampullares** for rotational head movement detection [1].

Question 1718: Vidian nerve is formed by union of?

A. Superficial petrosal nerve and deep petrosal nerve
B. Greater petrosal nerve and superficial petrosal nerve
C. Greater petrosal nerve and deep petrosal nerve (Correct Answer)
D. Greater petrosal nerve and external petrosal nerve

Explanation: ***Greater petrosal nerve and deep petrosal nerve*** - The **Vidian nerve**, also known as the **nerve of the pterygoid canal**, is formed by the union of the **greater petrosal nerve** and the **deep petrosal nerve**. - This union occurs **at the anterior aspect of the foramen lacerum**, and the Vidian nerve then passes through the **pterygoid canal** to reach the pterygopalatine ganglion. - The **greater petrosal nerve** carries **parasympathetic fibers** from the facial nerve (CN VII), while the **deep petrosal nerve** carries **sympathetic fibers** from the internal carotid plexus. *Superficial petrosal nerve and deep petrosal nerve* - The term **superficial petrosal nerve** is not the correct anatomical name for the preganglionic parasympathetic component that forms the Vidian nerve. - The correct parasympathetic component is the **greater petrosal nerve**, which carries fibers from the facial nerve (CN VII). *Greater petrosal nerve and superficial petrosal nerve* - This option incorrectly uses the term "superficial petrosal nerve" as a distinct component from the "greater petrosal nerve." - The **greater petrosal nerve** is itself a superficial branch of the facial nerve, but it unites with the **deep petrosal nerve**, not another "superficial petrosal nerve." *Greater petrosal nerve and external petrosal nerve* - The **external petrosal nerve** is not a commonly recognized or primary component contributing to the formation of the Vidian nerve. - The deep petrosal nerve, a sympathetic nerve from the carotid plexus, is the correct component that joins the greater petrosal nerve.

Question 1719: A patient presents with the complaint of inability to close the eye, drooling of saliva, and deviation of the angle of the mouth. Which of the following nerves is most likely to be affected?

A. Facial nerve (Correct Answer)
B. Trigeminal nerve
C. Oculomotor nerve
D. Glossopharyngeal nerve

Explanation: ***Facial nerve*** - The **facial nerve (cranial nerve VII)** controls the muscles of facial expression, including those for eye closure and mouth movement. - Damage to the facial nerve leads to **unilateral facial weakness or paralysis**, causing inability to close the eye, drooling from the corner of the mouth, and deviation of the mouth. *Trigeminal nerve* - The **trigeminal nerve (cranial nerve V)** is primarily responsible for **facial sensation** and **mastication (chewing)**. - Dysfunction typically presents as facial numbness, pain, or difficulty chewing, not facial muscle paralysis. *Oculomotor nerve* - The **oculomotor nerve (cranial nerve III)** controls most **extraocular muscles** (eye movements), pupillary constriction, and lifts the eyelid. - Damage would result in ptosis (drooping eyelid), dilated pupil, and outward and downward deviation of the eye. *Glossopharyngeal nerve* - The **glossopharyngeal nerve (cranial nerve IX)** is involved in **taste from the posterior tongue**, **swallowing**, and sensation from the pharynx. - Its impairment can lead to difficulty swallowing, loss of gag reflex, or altered taste, but not facial paralysis.

Question 1720: Nerve injured in Frey’s syndrome is:

A. Auriculotemporal Nerve (Correct Answer)
B. Great auricular nerve
C. Lingual Nerve
D. Inferior alveolar nerve

Explanation: ***Auriculotemporal Nerve*** - Frey's syndrome (also known as **auriculotemporal syndrome**) results from damage and aberrant regeneration of the **auriculotemporal nerve**. - This leads to **sweating and flushing** in the pre-auricular and temporal regions in response to salivary stimuli (e.g., eating). *Great auricular nerve* - The great auricular nerve primarily provides **sensory innervation** to the skin over the parotid gland, mastoid process, and auricle. - While it can be injured during parotid surgery, its damage typically causes **sensory deficits** (numbness) rather than gustatory sweating. *Lingual Nerve* - The lingual nerve provides **general sensation** and **taste** to the anterior two-thirds of the tongue and innervates the submandibular and sublingual glands. - Injury to this nerve leads to issues with **taste and sensation of the tongue**, not gustatory sweating in the face. *Inferior alveolar nerve* - The inferior alveolar nerve provides **sensory innervation** to the lower teeth and lower lip, and its mental branch supplies the chin. - Damage to this nerve is typically associated with **numbness or altered sensation** in the lower dental arch, lip, and chin, not Frey's syndrome.

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