Chapter: Neurophysiology; Topic: Special Senses: Vision; Subtopic: Parallel Processing in the Visual System
Key Definitions & Concepts
Parvocellular Pathway (P-pathway): The "What" pathway originating from midget ganglion cells in the retina; specialized for high spatial resolution, color vision, and fine detail.
Magnocellular Pathway (M-pathway): The "Where" pathway originating from parasol ganglion cells; specialized for high temporal resolution, motion detection, and depth perception.
Lateral Geniculate Nucleus (LGN): The thalamic relay center for vision. Layers 1-2 receive Magnocellular input; Layers 3-6 receive Parvocellular input.
Ventral Stream: The cortical continuation of the P-pathway into the temporal lobe, responsible for object recognition ("What is it?").
Dorsal Stream: The cortical continuation of the M-pathway into the parietal lobe, responsible for spatial awareness and motion ("Where is it?").
Cones: Photoreceptors concentrated in the fovea responsible for color and acuity; they provide the primary input to the P-pathway.
Spatial Summation: Low in the P-pathway (small receptive fields) allowing fine detail; High in the M-pathway (large receptive fields) increasing sensitivity to dim light/motion.
Temporal Resolution: The ability to detect rapid changes (flicker). The M-pathway has high temporal resolution; the P-pathway has low (sustained response).
Color Opponency: A feature of P-cells (Red-Green, Blue-Yellow) allowing for color discrimination; M-cells are color blind.
Koniocellular Pathway: A third, minor pathway (K-pathway) involved in blue-yellow color vision and possibly blindsight.
[Image of Visual pathways diagram P and M]
Lead Question - 2016
Parvocellular pathway for vision is concerned with?
a) Fine details of object
b) Movements of object
c) Flickering features
d) Depth of vision
Explanation: The visual system is divided into two parallel processing streams starting from the retina. The Parvocellular (P) pathway originates from small (midget) ganglion cells that receive input primarily from cones in the fovea. These cells have very small receptive fields and show a sustained response to stimuli. This physiology makes them ideally suited for analyzing the Fine details of objects (high visual acuity), form, texture, and color ("What" the object is). In contrast, the Magnocellular (M) pathway is specialized for detecting movement, flicker, and depth ("Where" the object is). Therefore, the correct answer is a) Fine details of object.
1. The Parvocellular layers of the Lateral Geniculate Nucleus (LGN) are layers:
a) 1 and 2
b) 3, 4, 5, and 6
c) 1, 4, and 6
d) 2, 3, and 5
Explanation: The Lateral Geniculate Nucleus (LGN) has a distinct laminar structure consisting of 6 principal layers. The two ventral layers (Layers 1 and 2) contain large cell bodies and are called the Magnocellular layers. The four dorsal layers (Layers 3, 4, 5, and 6) contain small cell bodies and are called the Parvocellular layers. These layers receive the axons from the P-ganglion cells of the retina. This anatomical segregation ensures that color/form information (P-pathway) remains separate from motion information (M-pathway) before reaching the cortex. Therefore, the correct answer is b) 3, 4, 5, and 6.
2. Which visual function is exclusively mediated by the Magnocellular pathway?
a) Color perception
b) High acuity form recognition
c) Motion perception
d) Face recognition
Explanation: The Magnocellular (M) pathway is "color blind" (achromatic) and has poor spatial resolution due to large receptive fields. However, it excels at detecting rapid changes in the visual scene. Its ganglion cells have transient (phasic) responses and high conduction velocities. This makes the M-pathway the exclusive system for Motion Perception and the detection of low-contrast, rapidly changing stimuli (flicker). Damage to the dorsal stream (M-pathway continuation) leads to Akinetopsia (motion blindness). Color and form are P-pathway functions. Therefore, the correct answer is c) Motion perception.
3. The "Ventral Stream" of visual processing projects to the Temporal Lobe and is primarily an extension of the:
a) Magnocellular pathway
b) Parvocellular pathway
c) Koniocellular pathway
d) Retinotectal pathway
Explanation: After V1 (Primary Visual Cortex), visual information splits. The Ventral Stream ("What" pathway) projects ventrally to the Inferior Temporal Cortex. It is involved in object recognition, face recognition, and color processing. This stream receives its dominant input from the Parvocellular pathway (P-blobs and P-interblobs in V1). Conversely, the Dorsal Stream ("Where" pathway) projects to the Parietal lobe and is dominated by the Magnocellular input for spatial awareness and motion guidance. Therefore, the correct answer is b) Parvocellular pathway.
4. Compared to Magnocellular cells, Parvocellular neurons have:
a) Larger receptive fields and faster conduction
b) Larger receptive fields and slower conduction
c) Smaller receptive fields and slower conduction
d) Smaller receptive fields and faster conduction
Explanation: Structure dictates function. P-cells are small ("Parvo"). They receive input from very few photoreceptors (sometimes 1:1 in the fovea). This results in Smaller receptive fields, which provides high spatial resolution (acuity). Their axons are thinner, leading to Slower conduction velocities compared to the thick M-cell axons. This slower speed is an acceptable trade-off for the high-detail analysis required for reading or recognizing faces, where speed is less critical than precision. M-cells are large, fast, and have large fields. Therefore, the correct answer is c) Smaller receptive fields and slower conduction.
5. A specific deficit in detecting "Flicker" at high frequencies (Critical Fusion Frequency) would suggest damage to the:
a) Parvocellular system
b) Magnocellular system
c) Rods only
d) S-cones
Explanation: The ability to resolve stimuli that change rapidly in time (Temporal Resolution) is a property of the Magnocellular system. M-cells respond transiently to stimulus onset and offset. They can follow rapid flickering lights up to high frequencies. If the M-pathway is damaged (e.g., in early Glaucoma or Dyslexia theories), the ability to detect high-frequency flicker is impaired. P-cells are "sustained" responders; they are sluggish and blur rapid flicker, making them poor at temporal resolution. Therefore, the correct answer is b) Magnocellular system.
6. Color vision defects (specifically Red-Green) are most likely to arise from dysfunction in the:
a) Magnocellular layers of LGN
b) Parvocellular layers of LGN
c) Superior Colliculus
d) Pulvinar nucleus
Explanation: Color vision relies on the comparison of signals from different cone types (L, M, S cones). This process, known as Color Opponency (e.g., Red vs. Green), is computed by the P-ganglion cells and transmitted via the Parvocellular layers of the LGN. The M-pathway sums inputs from all cones (L+M) to detect luminance (brightness) but discards the spectral difference (color) information. Therefore, the P-pathway is the exclusive carrier of Red-Green color data. (Blue-Yellow involves the Koniocellular path). Therefore, the correct answer is b) Parvocellular layers of LGN.
7. The "Blobs" (Cytochrome Oxidase Blobs) found in the Primary Visual Cortex (V1) are specially dedicated to processing:
a) Motion
b) Depth (Stereopsis)
c) Color
d) Orientation
Explanation: When V1 is stained for the metabolic enzyme Cytochrome Oxidase, a pattern of dark spots ("Blobs") and pale intervening areas ("Interblobs") appears in layers 2/3. The P-pathway projects to both. The Blobs are specifically rich in cells that are color-sensitive but not orientation-selective. They process Color information. The Interblobs contain cells that are orientation-selective (for form/edges) but not color-sensitive. M-pathway input goes to layer 4B and is distinct from the blob system. Therefore, the correct answer is c) Color.
8. Contrast sensitivity for stationary, high-spatial-frequency gratings (fine patterns) is a function of the:
a) M-pathway
b) P-pathway
c) Scotopic system
d) Vestibulo-ocular reflex
Explanation: Visual stimuli can be described by contrast and spatial frequency (detail). M-pathway: High contrast sensitivity (sees faint objects) but only for low spatial frequencies (coarse patterns). P-pathway: Low contrast sensitivity (needs distinct boundaries) but excellent for High spatial frequencies (fine detail/patterns). Therefore, perceiving a stationary, finely detailed pattern (high spatial frequency) is the domain of the P-pathway. Therefore, the correct answer is b) P-pathway.
9. Stereopsis (Depth Perception) relies heavily on disparity cues processed by the:
a) Parvocellular pathway mainly
b) Magnocellular pathway mainly
c) Koniocellular pathway
d) Auditory pathway
Explanation: Depth perception involves analyzing the small differences (disparities) between the images on the two retinas. While both pathways contribute, the Magnocellular pathway is generally considered the dominant system for stereopsis, particularly for coarse depth and depth-from-motion. M-cells project to cortical area V5/MT and the thick stripes of V2, which are rich in disparity-tuned neurons. The P-pathway contributes to fine depth, but the "Where" (Dorsal stream/Magnocellular) system is the primary locator of objects in 3D space. Therefore, the correct answer is b) Magnocellular pathway mainly.
10. Which neurotransmitter is used by the Photoreceptors (Rods and Cones) to signal the Bipolar cells at the beginning of these pathways?
a) GABA
b) Glycine
c) Glutamate
d) Dopamine
Explanation: In the dark, photoreceptors are depolarized and continuously release their neurotransmitter. This neurotransmitter is Glutamate. When light strikes the receptor, it hyperpolarizes, and Glutamate release decreases. This drop in glutamate has different effects on downstream cells: it hyperpolarizes OFF-bipolar cells (which have ionotropic glutamate receptors) and depolarizes ON-bipolar cells (which have metabotropic receptors that invert the signal). This divergence creates the ON and OFF channels that feed into the M and P pathways. Therefore, the correct answer is c) Glutamate.
Chapter: Head and Neck; Topic: Orbit and Eyelid; Subtopic: Extraocular Muscles and Eyelid Innervation
Key Definitions & Concepts
Orbicularis Oculi: The sphincter muscle of the eyelids responsible for closing the eye (blinking and tight closure), innervated by the Facial Nerve (CN VII).
Levator Palpebrae Superioris (LPS): The primary elevator of the upper eyelid responsible for opening the eye, innervated by the Oculomotor Nerve (CN III).
Antagonist Muscle: A muscle that opposes the action of another; LPS (opener) is the physiological antagonist to Orbicularis Oculi (closer).
Lagophthalmos: The inability to close the eyelids completely, commonly seen in Facial Nerve paralysis (Bell's Palsy).
Ptosis: Drooping of the upper eyelid, which can result from paralysis of the LPS (CN III palsy) or Müller's muscle.
Superior Tarsal Muscle (Müller's Muscle): A smooth muscle component assisting LPS in eyelid elevation, supplied by sympathetic fibers.
Palpebral Part: The inner portion of the orbicularis oculi involved in involuntary, gentle blinking.
Orbital Part: The outer, thicker portion of the orbicularis oculi involved in forceful closure (squinting).
Corneal Reflex: An involuntary blinking reflex elicited by stimulating the cornea; Afferent limb is CN V1, Efferent limb is CN VII.
Horner's Syndrome: A condition caused by sympathetic trunk damage, leading to partial ptosis, miosis, and anhidrosis.
[Image of Muscles of the eyelid anatomy]
Lead Question - 2016
Which muscle is antagonist to orbicularis oculi that is not supplied by facial nerve?
a) Levator Palpebrae superioris
b) Orbicularis oris
c) Superior oblique
d) Inferior oblique
Explanation: The question asks for the physiological antagonist to the Orbicularis Oculi. The function of the Orbicularis Oculi is to close the eyelids (sphincter action). Therefore, its antagonist must be a muscle that opens the eyelids (elevator). The primary elevator of the upper eyelid is the Levator Palpebrae Superioris (LPS). Crucially, the question specifies a muscle "not supplied by the facial nerve." The Orbicularis Oculi is supplied by the Facial Nerve (CN VII), whereas the Levator Palpebrae Superioris is supplied by the Oculomotor Nerve (CN III). The Orbicularis oris acts on the mouth. The Superior and Inferior obliques move the eyeball, not the eyelid. Therefore, the correct answer is a) Levator Palpebrae superioris.
1. A patient presents with complete inability to close the right eye. When asked to close the eyes tight, the right eyeball rolls upwards (Bell's Phenomenon). This condition is due to paralysis of which muscle?
a) Levator Palpebrae Superioris
b) Superior Rectus
c) Orbicularis Oculi
d) Frontalis
Explanation: The clinical sign described is Lagophthalmos, the inability to close the eyelid. This function is solely performed by the Orbicularis Oculi muscle. When the Facial Nerve (CN VII) is damaged (as in Bell's Palsy), the Orbicularis Oculi is paralyzed, and the eye remains open. The upward rolling of the eyeball (Bell's phenomenon) is a normal reflex that becomes visible because the eyelid fails to cover the eye. The Levator Palpebrae Superioris opposes this muscle; if it were paralyzed, the eye would be closed (ptosis). The Superior Rectus moves the eye, not the lid. Therefore, the correct answer is c) Orbicularis Oculi.
2. The Levator Palpebrae Superioris (LPS) splits into a superficial and deep lamella anteriorly. The smooth muscle component, known as Müller's muscle, is located in the deep lamella. Loss of innervation to this specific smooth muscle results in:
a) Complete Ptosis
b) Lagophthalmos
c) Partial Ptosis
d) Retraction of the eyelid
Explanation: The eyelid elevation is primarily achieved by the skeletal muscle portion of the LPS (supplied by CN III). However, the Superior Tarsal Muscle (Müller's muscle), which is smooth muscle located underneath the LPS, provides additional tonic elevation (about 1-2 mm). This muscle is innervated by the sympathetic nervous system. Paralysis of Müller's muscle, as seen in Horner's Syndrome, leads to a mild drooping of the eyelid, known as Partial Ptosis. Complete ptosis occurs only when the main LPS or CN III is damaged. Lagophthalmos is the opposite condition. Therefore, the correct answer is c) Partial Ptosis.
3. Which part of the Orbicularis Oculi muscle is primarily responsible for the involuntary, gentle closure of the eyelids, such as during blinking?
a) Orbital part
b) Lacrimal part
c) Palpebral part
d) Temporal part
Explanation: The Orbicularis Oculi is divided into three parts: orbital, palpebral, and lacrimal. The Palpebral part is contained within the eyelids themselves and consists of thin, pale fibers. It is responsible for gentle, involuntary closure, such as reflex blinking and sleeping. The Orbital part surrounds the orbital margin and is responsible for forceful, tight closure (squinting) to protect the eye from bright light or dust. The Lacrimal part (Horner's muscle) dilates the lacrimal sac to facilitate tear drainage. Differentiation between these parts is important in facial nerve assessment. Therefore, the correct answer is c) Palpebral part.
[Image of Orbicularis oculi parts]
4. A 50-year-old diabetic patient presents with a "down and out" position of the left eye and severe drooping of the left upper eyelid. The pupil is spared. Which nerve is most likely affected?
a) Trochlear nerve
b) Abducens nerve
c) Facial nerve
d) Oculomotor nerve
Explanation: The clinical picture of an eye deviated "down and out" combined with severe ptosis (drooping eyelid) is classic for an Oculomotor Nerve (CN III) palsy. CN III innervates the Levator Palpebrae Superioris (elevation of lid), as well as the Superior Rectus, Medial Rectus, Inferior Rectus, and Inferior Oblique muscles. The unopposed action of the Lateral Rectus (CN VI) and Superior Oblique (CN IV) pulls the eye down and out. Pupil sparing is common in diabetic microvascular infarction of the nerve, whereas compressive lesions (aneurysms) often involve the pupil. Therefore, the correct answer is d) Oculomotor nerve.
5. The nerve supply to the Levator Palpebrae Superioris travels through which division of the Oculomotor nerve?
a) Superior division
b) Inferior division
c) Ganglionic branch
d) Sympathetic root
Explanation: Upon entering the orbit through the Superior Orbital Fissure, the Oculomotor nerve (CN III) divides into a superior and an inferior division. The Superior division is the smaller of the two and ascends to supply the Superior Rectus muscle and the Levator Palpebrae Superioris (LPS). The Inferior division supplies the Medial Rectus, Inferior Rectus, and Inferior Oblique (and carries parasympathetics). Knowledge of this branching is crucial in orbital trauma or surgery, where specific divisions may be injured, causing isolated muscle deficits. Therefore, the correct answer is a) Superior division.
6. During a neurological exam, the physician touches the patient's cornea with a wisp of cotton. The patient blinks bilaterally. The efferent (motor) limb of this reflex arc is mediated by which nerve?
a) Ophthalmic nerve (V1)
b) Oculomotor nerve (III)
c) Facial nerve (VII)
d) Maxillary nerve (V2)
Explanation: The corneal reflex is a vital brainstem reflex. The afferent (sensory) limb carries sensation from the cornea via the nasociliary branch of the Ophthalmic division of the Trigeminal nerve (V1). The impulse goes to the sensory nucleus of V, then connects to the motor nucleus of VII bilaterally. The efferent (motor) limb, which causes the contraction of the Orbicularis Oculi muscles to produce the blink, is carried by the Facial nerve (VII). Loss of the reflex can indicate damage to V1, VII, or the brainstem connections. Therefore, the correct answer is c) Facial nerve (VII).
7. The Levator Palpebrae Superioris arises from the lesser wing of the sphenoid. What is its primary insertion point that allows it to elevate the eyelid?
a) Superior orbital margin
b) Superior Tarsal Plate and skin of upper eyelid
c) Sclera of the eyeball
d) Conjunctival fornix only
Explanation: The aponeurosis of the Levator Palpebrae Superioris (LPS) fans out anteriorly. Its primary and most functionally significant insertion is onto the anterior surface of the Superior Tarsal Plate and into the skin of the upper eyelid (creating the eyelid crease). It also has attachments to the conjunctiva. This insertion into the rigid tarsal plate allows the muscle to pull the eyelid structure upward effectively. If the aponeurosis detaches from the tarsal plate (dehiscence), it results in senile or involutional ptosis. Therefore, the correct answer is b) Superior Tarsal Plate and skin of upper eyelid.
8. A patient with a Pancoast tumor (apical lung tumor) presents with a constricted pupil (miosis), lack of sweating (anhidrosis) on one side of the face, and a mild drooping of the eyelid. Which muscle's dysfunction is responsible for the eyelid drooping in this case?
a) Orbicularis Oculi
b) Levator Palpebrae Superioris
c) Superior Tarsal (Müller's) Muscle
d) Frontalis
Explanation: The clinical presentation is classic for Horner's Syndrome, caused by the interruption of the sympathetic chain (often by a lung tumor at the thoracic inlet). While the main elevator of the lid is the LPS (CN III), the sympathetic nerves innervate the Superior Tarsal (Müller's) Muscle. This smooth muscle assists in holding the eye open. Loss of sympathetic tone results in paralysis of Müller's muscle, leading to a mild (1-2mm) ptosis. It is distinct from the severe ptosis of CN III palsy. Therefore, the correct answer is c) Superior Tarsal (Müller's) Muscle.
9. While performing surgery on the eyelid, a surgeon must be aware of the "Gray Line" on the eyelid margin. This anatomical landmark corresponds to which structure?
a) The junction of skin and conjunctiva
b) The muscle of Riolan (Part of Orbicularis Oculi)
c) The openings of the Meibomian glands
d) The insertion of the LPS aponeurosis
Explanation: The Gray Line is a crucial surgical landmark located on the intermarginal strip of the eyelid. It marks the avascular plane between the anterior lamella (skin and orbicularis muscle) and the posterior lamella (tarsal plate and conjunctiva). Anatomically, it corresponds to the pretarsal portion of the orbicularis oculi muscle, specifically a marginal bundle known as the Muscle of Riolan. Incision along this line allows the surgeon to split the eyelid into its anterior and posterior halves without excessive bleeding. Therefore, the correct answer is b) The muscle of Riolan (Part of Orbicularis Oculi).
10. Which branch of the Facial Nerve is primarily responsible for innervating the Orbicularis Oculi muscle to ensure eye closure?
a) Cervical branch
b) Marginal Mandibular branch
c) Temporal and Zygomatic branches
d) Buccal branch
Explanation: The Facial nerve branches into five terminal divisions within the parotid gland: Temporal, Zygomatic, Buccal, Marginal Mandibular, and Cervical. The Orbicularis Oculi covers the orbit and requires innervation from the upper branches. The Temporal and Zygomatic branches cross the zygomatic arch to supply the orbicularis oculi. The temporal branch supplies the upper part, and the zygomatic branch supplies the lower/lateral part. Injury to these specific branches during face-lift surgery or trauma can lead to inability to close the eye (lagophthalmos). Therefore, the correct answer is c) Temporal and Zygomatic branches.
Chapter: Histology; Topic: Exocrine Glands; Subtopic: Lacrimal Gland Structure
Keyword Definitions:
Lacrimal Gland: A serous, tubuloacinar gland producing tears.
Serous Cells: Pyramidal secretory cells with round basal nuclei and apical secretory granules.
Acini/Alveoli: Secretory units lined by serous pyramidal cells arranged around a lumen.
Myoepithelial Cells: Contractile cells lying between basement membrane and secretory cells, aiding secretion.
Duct System: Intercalated and striated ducts conducting lacrimal secretion to ocular surface.
1) Lead Question – 2016
What is the lining of the lacrimal gland alveoli?
A) Ciliated columnar cells
B) Pyramidal cells
C) Non-keratinizing squamous epithelium
D) None
Answer: B) Pyramidal cells
Explanation: Lacrimal glands are serous tubuloacinar glands whose secretory alveoli are lined by serous pyramidal cells. These cells have a basally located round nucleus, abundant rough endoplasmic reticulum, and apically stored secretory granules. They secrete the watery component of tears. Ciliated columnar epithelium lines respiratory structures, not lacrimal alveoli. Squamous epithelium is not found in lacrimal glands. Therefore, option B is correct. Recognizing serous pyramidal cells helps identify lacrimal gland histology and differentiate it from mixed glands like salivary glands.
2) Lacrimal gland secretion is primarily–
A) Mucous
B) Serous
C) Mixed
D) Keratinous
Answer: B) Serous
Explanation: Lacrimal gland is purely serous, producing watery tears with lysozyme and IgA. Thus, B is correct.
3) Which nerve provides parasympathetic supply to lacrimal gland?
A) Glossopharyngeal nerve
B) Facial nerve
C) Trigeminal nerve
D) Vagus nerve
Answer: B) Facial nerve
Explanation: Parasympathetic fibers arise from facial nerve via greater petrosal nerve. Thus, B is correct.
4) Myoepithelial cells in lacrimal glands lie between–
A) Duct epithelium and lumen
B) Basement membrane and secretory cells
C) Stroma and ducts
D) Lumen and stroma
Answer: B) Basement membrane and secretory cells
Explanation: Myoepithelial cells assist secretion by contracting around acini. Thus, B is correct.
5) A patient with Sjögren syndrome typically shows–
A) Destruction of lacrimal gland acini
B) Hyperplasia of lacrimal ducts
C) Increase in mucus secretion
D) Normal tear secretion
Answer: A) Destruction of lacrimal gland acini
Explanation: Autoimmune attack destroys serous acini causing dry eyes. Thus, A is correct.
6) The lacrimal gland resembles which salivary gland histologically?
A) Sublingual
B) Submandibular
C) Parotid
D) Von Ebner's glands
Answer: C) Parotid
Explanation: Both parotid and lacrimal glands are purely serous with similar acini. Thus, C is correct.
7) Which Ig is predominantly secreted in lacrimal fluid?
A) IgE
B) IgA
C) IgM
D) IgD
Answer: B) IgA
Explanation: IgA provides mucosal immunity in tears. Thus, B is correct.
8) Tear fluid drains first into which structure?
A) Nasolacrimal duct
B) Lacrimal sac
C) Canaliculi
D) Puncta
Answer: D) Puncta
Explanation: Tears enter puncta before canaliculi and lacrimal sac. Thus, D is correct.
9) Serous cells contain abundant–
A) Mucin granules
B) Zymogen granules
C) Lipid droplets
D) Keratohyalin granules
Answer: B) Zymogen granules
Explanation: Serous cells store protein-rich secretory granules. Thus, B is correct.
10) Lacrimal gland acini are surrounded by–
A) Dense irregular connective tissue
B) Smooth muscle bundles
C) Myoepithelial cells
D) Stratified squamous epithelium
Answer: C) Myoepithelial cells
Explanation: Myoepithelial cells facilitate tear secretion. Thus, C is correct.
11) Which duct drains lacrimal gland secretions into conjunctival sac?
A) Interlobular duct
B) Striated duct
C) Excretory duct
D) Collecting duct
Answer: C) Excretory duct
Explanation: Lacrimal gland excretory ducts open into superior fornix of conjunctiva. Thus, C is correct.
Topic: Special Senses; Subtopic: Visual Cycle and Phototransduction
Keyword Definitions:
• Visual cycle: Biochemical pathway converting light into electrical signals in photoreceptor cells.
• Opsin: Protein component of visual pigment that binds retinal.
• Retinal: Light-sensitive derivative of vitamin A, existing in 11-cis and all-trans forms.
• Phototransduction: Conversion of light energy into a neural signal in rods and cones.
• Rhodopsin: Visual pigment in rod cells composed of opsin and 11-cis-retinal.
• Isomerization: Conversion of 11-cis-retinal to all-trans-retinal upon light absorption initiating vision.
Lead Question - 2015
True about visual cycle cascade ?
a) Associated with conformational change in opsin
b) Light causes isomerization of all-trans-retinol to 11 Cis-retinol
c) Retinol [alcohol] is involved
d) All are true
Explanation (Answer: a) Associated with conformational change in opsin)
The visual cycle begins when light strikes rhodopsin, converting 11-cis-retinal to all-trans-retinal, causing a conformational change in opsin that triggers a phototransduction cascade. Retinal, not retinol, is the active aldehyde form involved in vision. Light does not directly convert all-trans-retinol to 11-cis-retinol. Hence, the true statement is that the cascade is associated with opsin’s conformational change during photon absorption.
1. The visual pigment in rods is:
a) Iodopsin
b) Melanin
c) Rhodopsin
d) Photopsin
Explanation (Answer: c) Rhodopsin)
Rhodopsin is the visual pigment present in rod cells, responsible for scotopic (night) vision. It consists of the protein opsin bound to 11-cis-retinal. When light hits rhodopsin, 11-cis-retinal is converted to all-trans-retinal, initiating the phototransduction cascade. Iodopsin and photopsin are cone pigments for color vision, while melanin reduces light scatter.
2. Light absorption by rhodopsin leads to:
a) Hyperpolarization of photoreceptor
b) Depolarization of photoreceptor
c) Opening of sodium channels
d) Increased glutamate release
Explanation (Answer: a) Hyperpolarization of photoreceptor)
Upon light exposure, rhodopsin activation closes sodium channels via the cyclic GMP pathway, leading to hyperpolarization of the photoreceptor membrane. This reduces glutamate release at the synapse, signaling light perception. In darkness, sodium channels remain open, maintaining depolarization. Thus, light induces the opposite electrical state compared to dark conditions.
3. Which of the following converts all-trans-retinal back to 11-cis-retinal?
a) Retinal isomerase
b) Retinol dehydrogenase
c) Opsinase
d) Transducin
Explanation (Answer: a) Retinal isomerase)
Retinal isomerase in the retinal pigment epithelium catalyzes the conversion of all-trans-retinal back to 11-cis-retinal, regenerating the visual pigment. Retinol dehydrogenase interconverts retinal and retinol but not isomers. Transducin is a G-protein in the phototransduction cascade. This recycling ensures sustained visual function after exposure to light.
4. In vitamin A deficiency, which symptom appears first?
a) Night blindness
b) Photophobia
c) Conjunctival xerosis
d) Keratomalacia
Explanation (Answer: a) Night blindness)
Night blindness (nyctalopia) is the earliest sign of vitamin A deficiency because rods cannot regenerate rhodopsin without adequate 11-cis-retinal. Persistent deficiency leads to xerophthalmia, Bitot’s spots, and keratomalacia. Vitamin A is vital for the visual cycle and epithelial maintenance. Early treatment reverses night blindness completely.
5. The G-protein involved in phototransduction is:
a) Transducin
b) Rhodopsin
c) Retinal-binding protein
d) Guanylate cyclase
Explanation (Answer: a) Transducin)
Transducin is the G-protein activated by photoexcited rhodopsin (metarhodopsin II). It activates phosphodiesterase, which reduces cGMP levels, leading to closure of sodium channels and hyperpolarization. Rhodopsin is the receptor, not the G-protein. Guanylate cyclase restores cGMP in darkness, helping reset the cycle.
6. The vitamin required for regeneration of visual pigment is:
a) Vitamin D
b) Vitamin E
c) Vitamin A
d) Vitamin K
Explanation (Answer: c) Vitamin A)
Vitamin A (retinol) is the precursor for retinal, the light-sensitive molecule in the visual cycle. Its deficiency prevents regeneration of rhodopsin, impairing dark adaptation. Vitamin D regulates calcium, E is antioxidant, and K assists in coagulation. Thus, adequate vitamin A is essential for normal vision and photoreceptor function.
7. Retinol is converted to retinal by:
a) Alcohol dehydrogenase
b) Retinol dehydrogenase
c) Retinal isomerase
d) Transducin
Explanation (Answer: b) Retinol dehydrogenase)
Retinol dehydrogenase oxidizes retinol (vitamin A alcohol) into retinal (vitamin A aldehyde). This reaction is reversible and part of the visual cycle. Retinal combines with opsin to form rhodopsin. Alcohol dehydrogenase acts mainly on ethanol, while retinal isomerase converts isomers of retinal, not retinol itself.
8. Which event occurs first in the visual cycle after photon absorption?
a) Activation of transducin
b) Isomerization of 11-cis-retinal to all-trans-retinal
c) Breakdown of cGMP
d) Closure of Na⁺ channels
Explanation (Answer: b) Isomerization of 11-cis-retinal to all-trans-retinal)
The first event after light absorption is isomerization of 11-cis-retinal to all-trans-retinal, altering opsin’s structure and initiating the phototransduction cascade. This leads to activation of transducin, cGMP hydrolysis, and Na⁺ channel closure. Hence, this photochemical reaction is the key trigger converting light to an electrical signal.
9. During dark adaptation, rhodopsin levels:
a) Increase
b) Decrease
c) Remain constant
d) Fluctuate randomly
Explanation (Answer: a) Increase)
In darkness, rhodopsin synthesis increases as 11-cis-retinal is regenerated, enhancing rod sensitivity. This adaptation restores scotopic vision, enabling detection of dim light. In bright light, rhodopsin breaks down rapidly. Vitamin A deficiency prevents proper regeneration, delaying dark adaptation and causing night blindness.
10. Visual cycle defect causing congenital stationary night blindness involves:
a) Mutation in transducin gene
b) Rhodopsin kinase defect
c) Retinal isomerase deficiency
d) Opsin overproduction
Explanation (Answer: c) Retinal isomerase deficiency)
Congenital stationary night blindness occurs when retinal isomerase is deficient, preventing regeneration of 11-cis-retinal. This disrupts rhodopsin formation, impairing rod photoreceptor response. Mutations in transducin or rhodopsin kinase affect signaling but not regeneration. The result is lifelong poor night vision without progression.
11. Bleaching of rhodopsin refers to:
a) Conversion of 11-cis-retinal to all-trans-retinal
b) Destruction of opsin
c) Breakdown of retinal to retinol
d) Inactivation of transducin
Explanation (Answer: a) Conversion of 11-cis-retinal to all-trans-retinal)
Bleaching is the process where light converts 11-cis-retinal to all-trans-retinal, leading to loss of pigment color in rhodopsin. This initiates the visual cascade, producing metarhodopsin II and activating transducin. Bleaching reverses when all-trans-retinal is converted back to 11-cis-retinal in the retinal pigment epithelium, restoring visual sensitivity.
Chapter: Neuroanatomy; Topic: Cranial Nerve Nuclei; Subtopic: Oculomotor Nucleus and Its Location
Key Definitions:
• Oculomotor nerve (III): The third cranial nerve, responsible for most of the eye movements, eyelid elevation, and pupillary constriction.
• Oculomotor nucleus: The motor nucleus located in the midbrain that gives rise to the somatic motor fibers of the oculomotor nerve.
• Edinger–Westphal nucleus: The parasympathetic nucleus associated with the oculomotor nerve, controlling pupillary constriction and accommodation.
• Midbrain: The uppermost part of the brainstem containing nuclei for cranial nerves III and IV and serving as a pathway for motor and sensory tracts.
Lead Question (NEET PG 2015):
1. Oculomotor nucleus is located in -
a) Forebrain
b) Midbrain
c) Pons
d) Medulla
Answer: b) Midbrain
Explanation: The oculomotor nucleus is located in the midbrain at the level of the superior colliculus, near the midline, anterior to the cerebral aqueduct. It gives rise to fibers that form the oculomotor nerve, which exits the brainstem through the interpeduncular fossa. The associated Edinger–Westphal nucleus provides parasympathetic fibers to the sphincter pupillae and ciliary muscle. Together, these nuclei coordinate eye movements, eyelid elevation, and pupillary constriction, essential for visual focus and light reflexes.
Guessed Questions (Related to Oculomotor Nerve and Brainstem Nuclei):
2. The Edinger–Westphal nucleus is responsible for which of the following functions?
a) Eye abduction
b) Pupillary constriction
c) Eye depression
d) Eye elevation
Answer: b) Pupillary constriction
Explanation: The Edinger–Westphal nucleus provides preganglionic parasympathetic fibers that travel via the oculomotor nerve to the ciliary ganglion, which in turn innervates the sphincter pupillae for pupillary constriction.
3. The oculomotor nerve exits the brainstem through which area?
a) Pons
b) Interpeduncular fossa
c) Olive of medulla
d) Middle cerebellar peduncle
Answer: b) Interpeduncular fossa
Explanation: The oculomotor nerve emerges on the ventral aspect of the midbrain from the interpeduncular fossa, located between the cerebral peduncles, before entering the cavernous sinus and orbit.
4. A lesion in the oculomotor nerve results in which clinical feature?
a) Ptosis, mydriasis, and eye deviation down and out
b) Miosis, enophthalmos, and anhidrosis
c) Loss of corneal reflex
d) Nystagmus
Answer: a) Ptosis, mydriasis, and eye deviation down and out
Explanation: Oculomotor nerve palsy leads to paralysis of most extraocular muscles (except lateral rectus and superior oblique), causing the eye to deviate downward and outward, along with ptosis and a dilated pupil.
5. Which of the following cranial nerves emerges from the dorsal aspect of the brainstem?
a) Oculomotor nerve
b) Trochlear nerve
c) Abducent nerve
d) Trigeminal nerve
Answer: b) Trochlear nerve
Explanation: The trochlear nerve (cranial nerve IV) is the only cranial nerve to emerge dorsally from the brainstem, specifically from the dorsal midbrain below the inferior colliculus.
6. The oculomotor nerve supplies all extraocular muscles except:
a) Superior rectus
b) Lateral rectus
c) Inferior rectus
d) Medial rectus
Answer: b) Lateral rectus
Explanation: The oculomotor nerve innervates superior rectus, inferior rectus, medial rectus, and inferior oblique muscles. The lateral rectus is supplied by the abducent nerve (VI).
7. The oculomotor nerve nucleus lies at the level of which structure?
a) Superior colliculus
b) Inferior colliculus
c) Pons
d) Medulla oblongata
Answer: a) Superior colliculus
Explanation: The oculomotor nucleus lies in the midbrain at the level of the superior colliculus, adjacent to the midline, and anterior to the cerebral aqueduct.
8. Compression of the oculomotor nerve due to posterior communicating artery aneurysm leads to:
a) Miosis and enophthalmos
b) Ptosis and mydriasis
c) Diplopia only
d) Loss of corneal reflex
Answer: b) Ptosis and mydriasis
Explanation: Aneurysm of the posterior communicating artery compresses the oculomotor nerve, affecting parasympathetic fibers and causing pupillary dilation (mydriasis) and eyelid drooping (ptosis).
9. Which nucleus is involved in the accommodation reflex of the eye?
a) Oculomotor nucleus
b) Edinger–Westphal nucleus
c) Abducent nucleus
d) Trochlear nucleus
Answer: b) Edinger–Westphal nucleus
Explanation: The Edinger–Westphal nucleus mediates the parasympathetic component of the accommodation reflex by controlling ciliary muscle contraction and pupillary constriction for near vision.
10. A lesion in the midbrain affecting the oculomotor nucleus results in:
a) Contralateral lateral rectus paralysis
b) Ipsilateral oculomotor palsy
c) Bilateral visual loss
d) Horner’s syndrome
Answer: b) Ipsilateral oculomotor palsy
Explanation: A lesion involving the oculomotor nucleus or its fibers in the midbrain produces ipsilateral paralysis of the extraocular muscles supplied by CN III and loss of parasympathetic control to the pupil.
11. The parasympathetic fibers of the oculomotor nerve synapse in which ganglion?
a) Pterygopalatine ganglion
b) Otic ganglion
c) Submandibular ganglion
d) Ciliary ganglion
Answer: d) Ciliary ganglion
Explanation: The Edinger–Westphal nucleus sends preganglionic fibers via the oculomotor nerve to the ciliary ganglion, where they synapse before supplying the sphincter pupillae and ciliary muscle.
Chapter: Neuroanatomy; Topic: Cranial Nerves; Subtopic: Trochlear Nerve and Its Anatomical Course
Key Definitions:
• Trochlear nerve (IV): The smallest cranial nerve that supplies the superior oblique muscle of the eye and is the only nerve to emerge dorsally from the brainstem.
• Intracranial course: The distance traveled by a cranial nerve within the cranial cavity before it exits through a foramen.
• Superior oblique muscle: An extraocular muscle responsible for depression and intorsion of the eyeball.
• Brainstem exit: The trochlear nerve uniquely emerges from the dorsal aspect of the midbrain and decussates completely before doing so.
Lead Question (NEET PG 2015):
1. The nerve which has the longest intracranial course is:
a) Fourth cranial nerve
b) Third cranial nerve
c) Sixth cranial nerve
d) Fifth cranial nerve
Answer: a) Fourth cranial nerve
Explanation: The trochlear nerve (cranial nerve IV) has the longest intracranial course among all cranial nerves. It arises from the dorsal aspect of the midbrain, decussates completely within the midbrain, and courses anteriorly around the brainstem to enter the cavernous sinus. It then enters the orbit through the superior orbital fissure to supply the superior oblique muscle. Despite being the thinnest cranial nerve, its long intracranial course makes it highly susceptible to trauma, especially in head injuries involving shearing forces.
Guessed Questions (Related to Trochlear and Other Cranial Nerves):
2. Which cranial nerve is the only one to emerge from the dorsal aspect of the brainstem?
a) Oculomotor nerve
b) Trochlear nerve
c) Abducent nerve
d) Optic nerve
Answer: b) Trochlear nerve
Explanation: The trochlear nerve is unique as it emerges dorsally from the midbrain, below the inferior colliculus. It completely decussates before exiting, supplying the contralateral superior oblique muscle.
3. Which cranial nerve has the longest extracranial course?
a) Facial nerve
b) Vagus nerve
c) Abducent nerve
d) Glossopharyngeal nerve
Answer: b) Vagus nerve
Explanation: The vagus nerve (cranial nerve X) has the longest extracranial course, extending from the medulla oblongata to the thoracic and abdominal organs, influencing heart rate, digestion, and respiratory function.
4. A lesion of the trochlear nerve leads to which of the following clinical features?
a) Diplopia on looking up
b) Diplopia on looking down and in
c) Loss of lateral gaze
d) Ptosis and mydriasis
Answer: b) Diplopia on looking down and in
Explanation: The trochlear nerve supplies the superior oblique muscle, which depresses and intorts the eyeball. Lesion results in vertical diplopia, especially noticeable when the patient looks down and in (e.g., reading or walking downstairs).
5. The trochlear nerve supplies which extraocular muscle?
a) Superior rectus
b) Inferior oblique
c) Superior oblique
d) Medial rectus
Answer: c) Superior oblique
Explanation: The trochlear nerve supplies only the superior oblique muscle, which acts to depress, abduct, and intort the eyeball, especially when the eye is adducted.
6. Which cranial nerve nucleus is located at the level of the inferior colliculus?
a) Oculomotor nucleus
b) Trochlear nucleus
c) Abducent nucleus
d) Facial nucleus
Answer: b) Trochlear nucleus
Explanation: The trochlear nucleus is situated in the midbrain at the level of the inferior colliculus. Fibers from this nucleus decussate in the midbrain before emerging dorsally to form the trochlear nerve.
7. A patient presents with head tilt to the opposite side and vertical diplopia. Which nerve is most likely affected?
a) Oculomotor nerve
b) Trochlear nerve
c) Abducent nerve
d) Trigeminal nerve
Answer: b) Trochlear nerve
Explanation: In trochlear nerve palsy, patients tilt their head to the side opposite the lesion to minimize diplopia caused by paralysis of the superior oblique muscle, which normally intorts the eye.
8. Which of the following cranial nerves decussates completely before emerging from the brainstem?
a) Optic nerve
b) Trochlear nerve
c) Abducent nerve
d) Facial nerve
Answer: b) Trochlear nerve
Explanation: The trochlear nerve is the only cranial nerve that undergoes complete decussation within the brainstem. Each trochlear nucleus supplies the contralateral superior oblique muscle.
9. Which nerve passes through the cavernous sinus along with the internal carotid artery?
a) Trochlear nerve
b) Abducent nerve
c) Optic nerve
d) Olfactory nerve
Answer: b) Abducent nerve
Explanation: The abducent nerve (VI) passes through the cavernous sinus close to the lateral wall of the internal carotid artery, making it vulnerable to injury in cavernous sinus thrombosis.
10. Which cranial nerve lesion produces both ptosis and mydriasis?
a) Trochlear nerve
b) Oculomotor nerve
c) Abducent nerve
d) Optic nerve
Answer: b) Oculomotor nerve
Explanation: The oculomotor nerve supplies the levator palpebrae superioris (eyelid elevation) and carries parasympathetic fibers to the sphincter pupillae. A lesion causes ptosis and pupil dilation (mydriasis).
11. The thinnest cranial nerve is:
a) Trochlear nerve
b) Oculomotor nerve
c) Abducent nerve
d) Optic nerve
Answer: a) Trochlear nerve
Explanation: The trochlear nerve is the smallest in diameter among cranial nerves but has the longest intracranial course. Despite its small size, it plays a crucial role in eye movement control, particularly in depression during adduction.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of the Optic Cup
Keyword Definitions:
• Optic Cup: A double-layered structure derived from the optic vesicle, forming retina and related structures.
• Retina: Neural tissue responsible for photoreception and visual transmission.
• Lens: Transparent, biconvex structure focusing light on the retina.
• Cornea: Transparent front part of the eye formed from surface ectoderm and neural crest.
• Sclera: Dense connective tissue forming the outer protective layer of the eyeball, derived from mesoderm and neural crest.
Lead Question - 2014
Optic cup give rise to ?
a) Lens
b) Retina
c) Cornea
d) Sclera
Explanation:
The optic cup, derived from neural ectoderm, gives rise to the retina — both its neural and pigmented layers. The inner layer forms the neural retina, while the outer layer becomes the retinal pigment epithelium. It also contributes to the iris and ciliary body epithelium. Thus, the correct answer is Retina.
1) The outer layer of the optic cup forms?
a) Neural retina
b) Pigmented retina
c) Cornea
d) Lens capsule
Explanation: The optic cup has two layers — the outer layer forms the retinal pigment epithelium, and the inner layer becomes the neural retina. This double-walled cup structure is essential for visual function. Therefore, the correct answer is Pigmented retina.
2) The ciliary body epithelium develops from?
a) Surface ectoderm
b) Neural ectoderm of optic cup
c) Neural crest
d) Mesoderm
Explanation: The epithelium of the ciliary body arises from the anterior extension of both layers of the optic cup, which is of neural ectodermal origin. The connective tissue and muscles of the ciliary body are derived from neural crest cells. Thus, the correct answer is Neural ectoderm of optic cup.
3) Which of the following structures is derived from the inner layer of the optic cup?
a) Retinal pigment epithelium
b) Neural retina
c) Corneal endothelium
d) Lens fibers
Explanation: The inner layer of the optic cup forms the neural retina, which contains photoreceptor cells, bipolar cells, and ganglion cells responsible for vision. Hence, the correct answer is Neural retina.
4) During eye development, lens formation is induced by?
a) Optic vesicle
b) Optic cup
c) Surface ectoderm
d) Neural crest
Explanation: The optic vesicle induces the overlying surface ectoderm to form the lens placode, which invaginates to form the lens vesicle. This inductive interaction is a classic example of epithelial-mesenchymal signaling. Thus, the correct answer is Optic vesicle.
5) A developmental defect in closure of the optic fissure leads to?
a) Aniridia
b) Coloboma
c) Microphthalmia
d) Glaucoma
Explanation: Failure of the embryonic optic fissure to close leads to coloboma, a cleft-like defect usually seen in the iris, choroid, or retina. It may affect one or both eyes. Thus, the correct answer is Coloboma.
6) The iris pigment epithelium develops from?
a) Surface ectoderm
b) Mesoderm
c) Neural ectoderm of optic cup
d) Neural crest
Explanation: The iris pigment epithelium originates from the outer layer of the optic cup, which is neural ectoderm in origin. The connective tissue of the iris is derived from neural crest cells. Hence, the correct answer is Neural ectoderm of optic cup.
7) A neonate presents with a cleft in the inferior iris. The most likely developmental defect is?
a) Failure of optic cup formation
b) Non-closure of choroidal fissure
c) Persistence of hyaloid artery
d) Absent lens placode
Explanation: Non-closure of the choroidal (optic) fissure during embryogenesis causes coloboma, presenting as a notched iris. It results from incomplete fusion of the optic cup margins. Thus, the correct answer is Non-closure of choroidal fissure.
8) Which germ layer gives rise to the corneal epithelium?
a) Surface ectoderm
b) Neural ectoderm
c) Mesoderm
d) Neural crest
Explanation: The corneal epithelium originates from surface ectoderm, while its stroma and endothelium develop from neural crest cells. The cornea is vital for light refraction and transparency. Thus, the correct answer is Surface ectoderm.
9) Failure of lens vesicle separation leads to?
a) Congenital aphakia
b) Persistent lens stalk
c) Microcornea
d) Coloboma
Explanation: Incomplete separation of the lens vesicle from the surface ectoderm causes persistent lens stalk, potentially forming epithelial pearls. It interferes with corneal development. Hence, the correct answer is Persistent lens stalk.
10) Neural crest cells contribute to all except?
a) Sclera
b) Corneal stroma
c) Retina
d) Iris connective tissue
Explanation: Neural crest cells form the sclera, corneal stroma, corneal endothelium, and connective tissue of the iris and ciliary body. The retina, however, is derived from neural ectoderm. Thus, the correct answer is Retina.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of Germ Layers in Eye Formation
Keyword Definitions:
• Optic Cup: A double-walled structure formed from the optic vesicle that gives rise to the retina.
• Neural Ectoderm: Layer of ectoderm giving rise to the brain, spinal cord, retina, and posterior pituitary.
• Surface Ectoderm: Gives rise to lens, corneal epithelium, and eyelid skin.
• Mesoderm: Forms extraocular muscles and vascular components of the eye.
• Neural Crest Cells: Contribute to corneal stroma, sclera, choroid, and ciliary muscles.
Lead Question - 2014
Optic cup is derived from ?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation:
The optic cup is derived from the neural ectoderm, which originates as an outpouching from the diencephalon. The outer layer of the optic cup becomes the pigmented layer of the retina, and the inner layer forms the neural retina. This dual-layered cup induces lens formation from surface ectoderm. Thus, the correct answer is Neural ectoderm.
1) The lens of the eye is derived from?
a) Surface ectoderm
b) Neural ectoderm
c) Neural crest
d) Mesoderm
Explanation: The crystalline lens develops from the surface ectoderm, which forms the lens placode in response to induction from the optic vesicle. This placode invaginates to form the lens vesicle. Thus, the correct answer is Surface ectoderm.
2) The retina is derived from?
a) Surface ectoderm
b) Neural ectoderm
c) Neural crest
d) Mesoderm
Explanation: Both the neural and pigmented layers of the retina originate from the neural ectoderm, which forms the optic vesicle and subsequently the optic cup. Therefore, the correct answer is Neural ectoderm.
3) Corneal endothelium develops from?
a) Neural crest cells
b) Neural ectoderm
c) Mesoderm
d) Surface ectoderm
Explanation: Neural crest cells migrate between the lens and surface ectoderm to form the corneal endothelium and stroma. The corneal epithelium arises from surface ectoderm. Thus, the correct answer is Neural crest cells.
4) Which of the following eye structures arises from mesoderm?
a) Iris
b) Lens
c) Extraocular muscles
d) Retina
Explanation: The extraocular muscles and blood vessels of the eye arise from mesoderm, contributing to movement and vascularization of the eye. Hence, the correct answer is Extraocular muscles.
5) A defect in closure of the optic fissure leads to?
a) Anophthalmos
b) Coloboma
c) Cyclopia
d) Glaucoma
Explanation: Failure of the embryonic optic fissure to close results in coloboma, a keyhole-shaped defect in the iris, retina, or choroid. This occurs during the 5th week of development. Thus, the correct answer is Coloboma.
6) A baby born with absence of lens most likely had developmental failure of?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation: The lens develops from the surface ectoderm via the lens placode. Failure of placode induction or invagination results in congenital aphakia (absence of lens). Thus, the correct answer is Surface ectoderm.
7) Which structure induces lens formation in the embryo?
a) Optic cup
b) Surface ectoderm
c) Neural crest
d) Mesoderm
Explanation: The optic cup derived from neural ectoderm induces the overlying surface ectoderm to form the lens placode through epithelial-mesenchymal interactions. Thus, the correct answer is Optic cup.
8) The sclera and choroid are derived from?
a) Surface ectoderm
b) Mesoderm and neural crest
c) Neural ectoderm
d) Endoderm
Explanation: The sclera and choroid develop mainly from neural crest cells, with mesodermal contribution to vascular structures. They form the fibrous and vascular coats of the eyeball. Hence, the correct answer is Mesoderm and neural crest.
9) A neonate presents with a cleft in the iris and retina. The developmental cause is?
a) Failure of lens vesicle separation
b) Persistence of hyaloid artery
c) Nonclosure of optic fissure
d) Overgrowth of choroid
Explanation: Nonclosure of the embryonic optic fissure results in coloboma affecting iris or retina. It manifests as a characteristic cleft defect. Thus, the correct answer is Nonclosure of optic fissure.
10) Neural crest cells contribute to which ocular structure?
a) Corneal stroma
b) Lens capsule
c) Retina
d) Iris epithelium
Explanation: Neural crest cells form corneal stroma, corneal endothelium, sclera, and ciliary muscles. They do not contribute to retina or lens. Hence, the correct answer is Corneal stroma.
Chapter: Nervous System; Topic: Cranial Nerves; Subtopic: Parasympathetic Pathways to Lacrimal Gland
Keyword Definitions:
Lacrimal gland: Exocrine gland that secretes tears to lubricate and protect the eye.
Parasympathetic supply: Autonomic fibers responsible for secretory stimulation of glands.
Greater petrosal nerve: A branch of the facial nerve that carries parasympathetic fibers to the lacrimal gland.
Pterygopalatine ganglion: A parasympathetic ganglion where preganglionic fibers from the facial nerve synapse before reaching the lacrimal gland.
Lead Question - 2014
Parasympathetic supply to lacrimal glands are passed through?
a) Lesser petrosal nerve
b) Chorda tympani
c) Greater petrosal nerve
d) Lingual nerve
Explanation:
The parasympathetic fibers to the lacrimal gland originate from the superior salivatory nucleus of the facial nerve. They travel via the greater petrosal nerve, synapse in the pterygopalatine ganglion, and then reach the lacrimal gland through the zygomatic and lacrimal nerves. This pathway controls tear secretion. Hence, the correct answer is c) Greater petrosal nerve.
1) Which ganglion is involved in the parasympathetic pathway to the lacrimal gland?
a) Ciliary ganglion
b) Otic ganglion
c) Pterygopalatine ganglion
d) Submandibular ganglion
The pterygopalatine ganglion (also called sphenopalatine) is where the preganglionic parasympathetic fibers from the greater petrosal nerve synapse. Postganglionic fibers then reach the lacrimal gland via the zygomatic branch of the maxillary nerve. Hence, the correct answer is c) Pterygopalatine ganglion.
2) The greater petrosal nerve is a branch of which cranial nerve?
a) Trigeminal
b) Facial
c) Glossopharyngeal
d) Vagus
The greater petrosal nerve arises from the facial nerve (cranial nerve VII) at the geniculate ganglion. It carries preganglionic parasympathetic fibers to the pterygopalatine ganglion, which later innervate the lacrimal and nasal glands. Hence, the correct answer is b) Facial nerve.
3) Which nerve carries postganglionic fibers to the lacrimal gland?
a) Zygomatic nerve
b) Auriculotemporal nerve
c) Lingual nerve
d) Nasociliary nerve
After synapsing in the pterygopalatine ganglion, postganglionic fibers travel via the zygomatic nerve (branch of V2) and join the lacrimal nerve (branch of V1) to reach the lacrimal gland. Hence, the correct answer is a) Zygomatic nerve.
4) Which cranial nucleus gives origin to fibers supplying the lacrimal gland?
a) Inferior salivatory nucleus
b) Superior salivatory nucleus
c) Edinger-Westphal nucleus
d) Dorsal motor nucleus of vagus
The superior salivatory nucleus of the pons provides preganglionic parasympathetic fibers that travel through the facial nerve and greater petrosal nerve to reach the lacrimal gland, promoting tear secretion. Hence, the correct answer is b) Superior salivatory nucleus.
5) (Clinical) Damage to the greater petrosal nerve results in?
a) Loss of taste
b) Dryness of eyes
c) Hyperlacrimation
d) Facial palsy
Injury to the greater petrosal nerve disrupts parasympathetic innervation to the lacrimal gland, leading to dryness of the eye due to reduced tear secretion. This may occur in facial nerve lesions proximal to the geniculate ganglion. Hence, the correct answer is b) Dryness of eyes.
6) (Clinical) A lesion at the geniculate ganglion affects which functions?
a) Lacrimation and taste
b) Hearing only
c) Facial sensation
d) Eye movements
A lesion at the geniculate ganglion affects both lacrimation (greater petrosal nerve) and taste (chorda tympani). Patients may present with dry eyes and loss of taste on the anterior two-thirds of the tongue. Hence, the correct answer is a) Lacrimation and taste.
7) (Clinical) Which symptom indicates greater petrosal nerve damage in facial palsy?
a) Loss of corneal reflex
b) Decreased lacrimation
c) Hyperacusis
d) Vertigo
In facial palsy affecting the segment proximal to the greater petrosal nerve, decreased lacrimation occurs due to interruption of parasympathetic fibers to the lacrimal gland. Hence, the correct answer is b) Decreased lacrimation.
8) (Clinical) A patient with Bell’s palsy complains of dry eyes. Which structure is likely involved?
a) Chorda tympani
b) Greater petrosal nerve
c) Stapedius branch
d) Temporal branch of facial nerve
Dry eyes in Bell’s palsy suggest involvement of the greater petrosal nerve due to interruption of parasympathetic supply to the lacrimal gland. This differentiates proximal from distal facial nerve lesions. Hence, the correct answer is b) Greater petrosal nerve.
9) (Clinical) Which condition may cause excessive tearing (epiphora) despite normal nerve function?
a) Blocked nasolacrimal duct
b) Facial nerve palsy
c) Damage to pterygopalatine ganglion
d) Geniculate ganglion lesion
Excessive tearing, or epiphora, usually results from a blocked nasolacrimal duct, preventing proper tear drainage into the nasal cavity. The parasympathetic pathway remains intact. Hence, the correct answer is a) Blocked nasolacrimal duct.
10) (Clinical) Which condition is characterized by dry eyes and mouth due to autoimmune destruction of lacrimal and salivary glands?
a) Myasthenia gravis
b) Sjögren’s syndrome
c) Bell’s palsy
d) Sarcoidosis
Sjögren’s syndrome causes autoimmune destruction of lacrimal and salivary glands, leading to dry eyes (xerophthalmia) and dry mouth (xerostomia). Parasympathetic pathways remain intact, but glandular tissue is damaged. Hence, the correct answer is b) Sjögren’s syndrome.
Chapter: Anatomy of Eye; Topic: Glands of Eyelid; Subtopic: Sweat and Sebaceous Glands near Eyelid Margin
Keyword Definitions:
Moll’s gland: Modified apocrine sweat glands located near eyelash follicles at the eyelid margin.
Zeis gland: Sebaceous glands associated with eyelash follicles.
Meibomian gland: Large sebaceous glands in the tarsal plate secreting oily film to prevent tear evaporation.
Krause gland: Accessory lacrimal gland contributing to tear secretion.
Lead Question (2014):
Sweat gland near the lid margins
a) Moll
b) Zeis
c) Meibomian
d) Krause
Explanation:
The sweat glands near the eyelid margin are Moll’s glands, which are modified apocrine sweat glands associated with the eyelashes. They help lubricate the eyelid margin and maintain ocular hygiene. Infections of these glands cause stye-like conditions. Answer: Moll’s gland. Understanding their anatomy aids in diagnosing eyelid pathologies such as hordeolum and blepharitis.
1) Blockage of Moll’s gland leads to which condition?
a) Chalazion
b) External hordeolum
c) Internal hordeolum
d) Dacryocystitis
Explanation:
Blockage or infection of Moll’s gland results in external hordeolum (stye), presenting as a painful, red swelling at the eyelid margin. It differs from chalazion, which involves Meibomian glands. Proper eyelid hygiene and warm compresses are preventive. Answer: External hordeolum. It reflects inflammation of apocrine glands near lashes.
2) Which gland is responsible for the lipid layer of tear film?
a) Krause
b) Moll
c) Meibomian
d) Zeis
Explanation:
The Meibomian glands secrete an oily (lipid) layer that prevents evaporation of tears. Dysfunction of these glands causes dry eye syndrome and ocular irritation. Their ducts open at the eyelid margin posterior to the lashes. Answer: Meibomian gland. Proper function maintains ocular surface stability and comfort during blinking.
3) Sebaceous glands associated with eyelash follicles are called:
a) Moll
b) Zeis
c) Krause
d) Wolfring
Explanation:
The Zeis glands are sebaceous glands connected to eyelash follicles, producing oily secretions that lubricate lashes. Infection leads to external hordeolum as well. They differ from Meibomian glands, which are embedded in the tarsal plate. Answer: Zeis gland. Their role is vital for lash protection and smooth movement of eyelids.
4) Accessory lacrimal glands of Krause are located in:
a) Conjunctival fornix
b) Eyelid margin
c) Tarsal plate
d) Caruncle
Explanation:
The glands of Krause are small accessory lacrimal glands found in the conjunctival fornix. They supplement tear secretion along with glands of Wolfring. Their secretions maintain ocular surface moisture and corneal transparency. Answer: Conjunctival fornix. Damage can lead to dry eye due to reduced tear volume.
5) A 35-year-old woman presents with a painful, red swelling at the eyelid margin near an eyelash follicle. Most likely involved gland is:
a) Meibomian
b) Krause
c) Moll
d) Wolfring
Explanation:
A Moll’s gland infection causes external hordeolum, presenting as a painful, red nodule near the eyelash base. It is bacterial, commonly due to Staphylococcus aureus. Warm compresses help drain infection. Answer: Moll’s gland. Clinically, location and tenderness distinguish it from internal hordeolum or chalazion.
6) Blockage of Meibomian gland results in:
a) Chalazion
b) Stye
c) Blepharitis
d) Dacryoadenitis
Explanation:
Obstruction of a Meibomian gland leads to a chalazion, a chronic, non-infective, granulomatous swelling within the tarsal plate. It appears firm and painless, unlike stye, which is acute and tender. Answer: Chalazion. Surgical drainage or steroid injection may be required if persistent, though small lesions may resolve spontaneously.
7) Glands of Wolfring are situated near:
a) Tarsal border
b) Conjunctival fornix
c) Caruncle
d) Limbus
Explanation:
The glands of Wolfring are accessory lacrimal glands located near the tarsal border. They provide continuous tear secretion to keep the cornea moist. Along with Krause glands, they supplement the main lacrimal gland. Answer: Tarsal border. Their dysfunction contributes to chronic dryness or irritation in ocular surface diseases.
8) A patient with chronic blepharitis develops recurrent chalazia. Which gland dysfunction is most likely?
a) Zeis
b) Meibomian
c) Krause
d) Moll
Explanation:
Chronic blepharitis causing recurrent chalazia is linked to Meibomian gland dysfunction. Blocked ducts lead to stagnation and lipogranulomatous inflammation. Long-standing inflammation alters tear composition. Answer: Meibomian gland. Regular lid hygiene and warm compresses are key to management. Antibiotics may be needed if secondary infection occurs.
9) Which gland opens near the base of eyelashes and secretes oily material?
a) Moll
b) Krause
c) Zeis
d) Meibomian
Explanation:
The Zeis glands open at the base of eyelashes and secrete oily material to lubricate lash follicles. Their blockage can cause external hordeolum. Answer: Zeis gland. Proper lubrication from these glands prevents eyelash brittleness and maintains smooth eyelid motion during blinking and protection from dust.
10) A 50-year-old diabetic presents with a firm, painless swelling in the tarsal plate lasting weeks. Diagnosis?
a) Internal hordeolum
b) Chalazion
c) External hordeolum
d) Dacryoadenitis
Explanation:
A chronic, firm, painless swelling in the tarsal plate indicates chalazion, due to Meibomian gland blockage. It is non-suppurative and commonly seen in diabetics and patients with seborrheic dermatitis. Answer: Chalazion. Histologically, it represents lipogranulomatous inflammation. Excision or intralesional corticosteroids may be needed for persistent cases.
Topic: Visual System
Subtopic: Retina and Photoreceptors
Keywords:
• Retina: Light-sensitive layer at the back of the eye.
• Cones: Photoreceptor cells responsible for color vision and visual acuity.
• Photoreceptor: Specialized cell that responds to light.
• Visual System: Structures and pathways involved in vision.
Lead Question - 2013 (September 2008)
Number of cones in Retina?
a) 3-5 millions
b) 10-20 millions
c) 25-50 millions
d) 50-100 millions
Answer and Explanation:
Correct answer is a) 3-5 millions. The human retina contains approximately 3 to 5 million cone photoreceptors concentrated in the central region called the fovea. These cones enable high-resolution color vision under bright light (photopic) conditions and are essential for tasks requiring fine visual detail. (50 words)
1. Rod cells are responsible for:
a) Color vision
b) Low-light vision
c) High-resolution vision
d) Motion detection
Explanation:
Rod cells are specialized for low-light (scotopic) vision, providing black and white images in dim conditions, with high sensitivity but low spatial resolution. (Answer: b)
2. Fovea centralis contains predominantly:
a) Rods
b) Cones
c) Bipolar cells
d) Ganglion cells
Explanation:
The fovea centralis contains the highest concentration of cone cells, essential for sharp central vision and color discrimination in bright light. (Answer: b)
3. Cone cells are most sensitive to which type of light?
a) Dim light
b) Bright light
c) Infrared light
d) Ultraviolet light
Explanation:
Cone cells function optimally in bright light conditions, enabling high acuity and color perception. (Answer: b)
4. Total number of rod cells in human retina is approximately:
a) 120 million
b) 6 million
c) 3 million
d) 1 million
Explanation:
The human retina contains around 120 million rod cells, which mediate vision in low-light conditions and are more numerous than cone cells. (Answer: a)
5. The three types of cones are sensitive to:
a) Red, Green, Blue wavelengths
b) Ultraviolet, Infrared, Visible
c) Alpha, Beta, Gamma
d) Rod, Cone, Bipolar
Explanation:
Cone cells are categorized into three types based on spectral sensitivity to red (long), green (medium), and blue (short) wavelengths, enabling color vision. (Answer: a)
6. Clinical condition related to cone dysfunction is called:
a) Night blindness
b) Color blindness
c) Glaucoma
d) Cataract
Explanation:
Color blindness is caused by defective or absent cone cells, impairing color discrimination, typically inherited and most commonly affecting red-green perception. (Answer: b)
7. Which layer of retina contains photoreceptors?
a) Ganglion cell layer
b) Inner nuclear layer
c) Outer nuclear layer
d) Plexiform layer
Explanation:
The photoreceptors, including rods and cones, are located in the outer nuclear layer of the retina, where they transduce light into neural signals. (Answer: c)
8. Cone density is maximum at:
a) Optic disc
b) Peripheral retina
c) Fovea centralis
d) Macula lutea
Explanation:
Cone density peaks in the fovea centralis, the central region of the retina, responsible for sharp and detailed central vision. (Answer: c)
9. Cone cells mediate which type of vision?
a) Scotopic
b) Photopic
c) Mesopic
d) None
Explanation:
Cone cells mediate photopic vision, functioning under bright light conditions, essential for color perception and high visual acuity. (Answer: b)
10. Cone dysfunction may lead to which of the following disorders?
a) Glaucoma
b) Achromatopsia
c) Retinitis pigmentosa
d) Optic neuritis
Explanation:
Achromatopsia is a congenital condition caused by cone dysfunction, resulting in color blindness, poor visual acuity, and photophobia. (Answer: b)
Topic: Eye Anatomy
Subtopic: Lacrimal Apparatus
Keywords:
Lacrimal Punctum: Small openings on the medial aspect of the eyelids that drain tears into the lacrimal canaliculi.
Upper Eyelid: The superior movable fold covering the eye, containing the upper lacrimal punctum near the medial canthus.
Lower Eyelid: The inferior movable fold, containing the lower lacrimal punctum near the medial canthus.
Lacrimal Canaliculi: Small channels that transport tears from the puncta to the lacrimal sac.
Lead Question - 2013:
Lacrimal punctum of upper and lower eyelids are?
a) They are opposed
b) No relation
c) Upper punctum is medial
d) Upper punctum is lateral
Answer & Explanation:
Correct answer: a) They are opposed.
Explanation: The lacrimal puncta of the upper and lower eyelids are located at the medial ends of the eyelid margins and face each other directly. They collect tears from the ocular surface and drain them into the canaliculi. Proper anatomical alignment ensures effective tear drainage and prevents epiphora.
MCQ 1:
Function of the lacrimal puncta is to:
a) Produce tears
b) Drain tears into canaliculi
c) Secrete mucus
d) Block tear drainage
Answer & Explanation:
Correct answer: b) Drain tears into canaliculi.
Explanation: The lacrimal puncta serve as entry points for tears to drain from the eye's surface into the lacrimal canaliculi, proceeding to the lacrimal sac and nasolacrimal duct. Proper function prevents tear overflow (epiphora) and maintains ocular surface health by facilitating tear clearance.
MCQ 2:
The lacrimal puncta are located at the:
a) Lateral canthus
b) Medial canthus
c) Center of eyelid margin
d) Superior orbital rim
Answer & Explanation:
Correct answer: b) Medial canthus.
Explanation: Both upper and lower lacrimal puncta are situated at the medial canthus of the eyelids, where they collect tears and drain them into the canaliculi. Their correct position ensures effective tear drainage, and abnormalities can lead to tearing disorders or infections like dacryocystitis.
MCQ 3:
The lacrimal canaliculi drain into the:
a) Lacrimal sac
b) Nasolacrimal duct
c) Conjunctival sac
d) Orbit
Answer & Explanation:
Correct answer: a) Lacrimal sac.
Explanation: The upper and lower lacrimal canaliculi drain tears from the puncta into the lacrimal sac, which then drains into the nasolacrimal duct. This anatomical route is essential for proper tear drainage and maintaining a healthy ocular surface, preventing tear stagnation and infection.
MCQ 4 (Clinical):
A patient with epiphora may have obstruction at which structure?
a) Lacrimal puncta
b) Lacrimal gland
c) Retina
d) Cornea
Answer & Explanation:
Correct answer: a) Lacrimal puncta.
Explanation: Epiphora, or excessive tearing, often results from blockage of the lacrimal puncta or canaliculi, preventing proper tear drainage. Clinical examination of the puncta for patency is vital to diagnose causes of tearing and guide appropriate management, such as dilation or surgery.
MCQ 5:
Which part of the lacrimal apparatus produces tears?
a) Lacrimal sac
b) Lacrimal gland
c) Lacrimal puncta
d) Canaliculi
Answer & Explanation:
Correct answer: b) Lacrimal gland.
Explanation: The lacrimal gland, located in the superolateral orbit, produces the aqueous component of tears. Tears are distributed across the ocular surface and drained by the lacrimal puncta and canaliculi. Understanding this system aids in diagnosing dry eye and tear drainage disorders.
MCQ 6 (Clinical):
A patient with infection around the medial canthus may have involvement of which structure?
a) Lacrimal puncta
b) Eyelid margin
c) Nasolacrimal duct
d) Retina
Answer & Explanation:
Correct answer: a) Lacrimal puncta.
Explanation: Infections such as canaliculitis or dacryocystitis often involve the lacrimal puncta, leading to swelling, redness, and tenderness near the medial canthus. Timely recognition and treatment prevent spread of infection and maintain tear drainage function, highlighting the importance of punctal assessment in clinical exams.
MCQ 7:
The direction of lacrimal flow is from:
a) Canaliculi → Puncta → Lacrimal sac
b) Eye surface → Puncta → Canaliculi → Lacrimal sac
c) Lacrimal sac → Puncta → Eye surface
d) Lacrimal gland → Lacrimal sac → Canaliculi
Answer & Explanation:
Correct answer: b) Eye surface → Puncta → Canaliculi → Lacrimal sac.
Explanation: Tears produced by the lacrimal gland flow over the ocular surface, enter the upper and lower lacrimal puncta, pass into the canaliculi, and drain into the lacrimal sac. This unidirectional flow is crucial to tear clearance and ocular surface health.
MCQ 8 (Clinical):
Which symptom suggests lacrimal punctal stenosis?
a) Sudden vision loss
b) Persistent watery eyes
c) Eye pain
d) Eyelid drooping
Answer & Explanation:
Correct answer: b) Persistent watery eyes.
Explanation: Lacrimal punctal stenosis refers to narrowing of the punctal openings, causing impaired tear drainage and chronic tearing (epiphora). Diagnosis involves slit-lamp examination and punctal dilation tests. Recognizing this prevents complications like conjunctivitis and helps in planning corrective procedures.
MCQ 9:
The upper and lower lacrimal puncta are located:
a) On the lateral aspect of the eyelids
b) At the medial eyelid margin
c) Centrally on the eyelid
d) On the superior orbital rim
Answer & Explanation:
Correct answer: b) At the medial eyelid margin.
Explanation: The upper and lower lacrimal puncta are small openings situated at the medial ends of the eyelid margins. They collect tears from the ocular surface and direct them into the canaliculi, crucial for tear drainage and ocular surface health maintenance.
MCQ 10 (Clinical):
A blocked lacrimal punctum leads to:
a) Dry eyes
b) Epiphora
c) Visual loss
d) Glaucoma
Answer & Explanation:
Correct answer: b) Epiphora.
Explanation: Blockage of the lacrimal punctum impairs tear drainage, resulting in overflow of tears onto the cheeks, known as epiphora. Identifying this condition is critical in clinical practice to prevent chronic tearing and secondary infections, often treated by punctal dilation or surgery.
Chapter: Head & Neck Anatomy
Topic: Arterial Supply
Subtopic: Ophthalmic Artery
Keywords:
Ophthalmic artery: First branch of the internal carotid artery after it enters the cranial cavity.
Internal carotid artery (ICA): Major artery supplying the brain and orbit.
Cavernous part of ICA: Segment traversing the cavernous sinus.
Cerebral part of ICA: Also called supraclinoid part, gives rise to ophthalmic artery.
Middle cerebral artery (MCA): Largest branch of ICA, supplies lateral cerebral hemisphere.
Facial artery: Branch of external carotid artery, supplies face.
1) Lead Question - 2012
Ophthalmic artery is a branch of?
a) Cavernous part of ICA
b) Cerebral part of ICA
c) MCA
d) Facial artery
Explanation: The ophthalmic artery arises from the cerebral (supraclinoid) part of the internal carotid artery just after it emerges from the cavernous sinus. It enters the orbit through the optic canal along with the optic nerve. Hence, the correct answer is cerebral part of ICA.
2) A patient presents with sudden monocular blindness. The most likely artery involved is?
a) Ophthalmic artery
b) Middle cerebral artery
c) Posterior communicating artery
d) Basilar artery
Explanation: Monocular blindness is commonly due to embolism or occlusion of the ophthalmic artery, a branch of the internal carotid artery. Retinal artery occlusion can cause sudden painless loss of vision. Correct answer is ophthalmic artery.
3) The central artery of retina is a branch of?
a) Middle cerebral artery
b) Ophthalmic artery
c) Basilar artery
d) External carotid artery
Explanation: The central artery of retina is a crucial end artery supplying the inner retina. It arises from the ophthalmic artery. Occlusion results in irreversible blindness. Correct answer is ophthalmic artery.
4) In cavernous sinus thrombosis, which artery is most closely related?
a) Maxillary artery
b) Ophthalmic artery
c) Internal carotid artery
d) Vertebral artery
Explanation: The cavernous sinus contains the cavernous part of ICA along with cranial nerves. Infection may spread to ICA leading to complications. Correct answer is internal carotid artery.
5) Which artery supplies the extraocular muscles?
a) Lacrimal artery
b) Muscular branches of ophthalmic artery
c) Posterior cerebral artery
d) Anterior cerebral artery
Explanation: Extraocular muscles receive blood supply from muscular branches of the ophthalmic artery. These branches ensure adequate perfusion of recti and oblique muscles. Correct answer is muscular branches of ophthalmic artery.
6) Which artery passes through the optic canal along with optic nerve?
a) Central retinal artery
b) Ophthalmic artery
c) Middle meningeal artery
d) Anterior cerebral artery
Explanation: The ophthalmic artery travels with the optic nerve through the optic canal to enter the orbit. This close relation explains visual loss in ICA occlusion. Correct answer is ophthalmic artery.
7) The lacrimal gland is mainly supplied by?
a) Facial artery
b) Lacrimal branch of ophthalmic artery
c) Posterior auricular artery
d) Maxillary artery
Explanation: The lacrimal gland receives its primary supply from the lacrimal artery, a branch of ophthalmic artery. It also anastomoses with infraorbital and middle meningeal arteries. Correct answer is lacrimal branch of ophthalmic artery.
8) Which artery forms an anastomosis with branches of external carotid artery on the face?
a) Central retinal artery
b) Supraorbital and supratrochlear branches of ophthalmic artery
c) Middle meningeal artery
d) Basilar artery
Explanation: The supraorbital and supratrochlear arteries, branches of ophthalmic artery, anastomose with superficial temporal and facial arteries, forming important ICA–ECA collateral channels. Correct answer is supraorbital and supratrochlear branches of ophthalmic artery.
9) Which part of ICA gives rise to posterior communicating artery?
a) Petrous part
b) Cavernous part
c) Cerebral (supraclinoid) part
d) Cervical part
Explanation: The posterior communicating artery arises from the cerebral (supraclinoid) part of ICA, connecting anterior circulation with posterior circulation. Correct answer is cerebral part.
10) Aneurysm of which artery commonly causes third nerve palsy?
a) Posterior communicating artery
b) Ophthalmic artery
c) Basilar artery
d) Anterior communicating artery
Explanation: Posterior communicating artery aneurysm compresses the oculomotor nerve leading to ptosis, diplopia, and pupillary dilation. Correct answer is posterior communicating artery.
11) A patient with severe facial trauma has massive epistaxis. Which artery is most likely responsible?
a) Ophthalmic artery
b) Sphenopalatine artery
c) Basilar artery
d) Internal carotid artery
Explanation: The sphenopalatine artery (terminal branch of maxillary artery, ECA system) is the main arterial source of severe posterior epistaxis. Correct answer is sphenopalatine artery.