Head And Neck – 2020

The prosencephalic organizing centre (located in the developing forebrain or prosencephalon) plays a crucial inductive role in the early formation of the face.

• It releases key signaling molecules such as Sonic hedgehog (SHH) and fibroblast growth factors (FGFs) that guide the formation of:

  • Frontonasal prominence

  • Facial placodes

  • Facial midline structures

• Disruptions in these signals can lead to midline facial defects such as holoprosencephaly or cleft lip.

❌ Why the Other Options Are Incorrect:

Neural tube

• Gives rise to the central nervous system, but not specifically responsible for inducing facial primordia.

Notochord

• Important for inducing the neural tube and vertebral column, but not directly involved in facial development.

Mesencephalic organizing centre

• Involved in patterning of the midbrain, not the facial primordia.

Stomodeum

• The primitive oral cavity; it receives inductive signals, but does not send the inductive signals guiding facial formation.

Genioglossus is Correct:

• The genioglossus originates from the superior mental spine (genial tubercles) on the inner surface of the body of the mandible.

• It fans out into the tongue and inserts throughout its length.

• Functionally, it:

  • Protrudes the tongue (sticks it out)

  • Helps depress the central part

• It is the primary muscle responsible for tongue movements like sticking it out or pushing it forward.

❌ Why the Others Are Incorrect:

Hyoglossus

• Originates from the greater horn and body of the hyoid bone, not the mandible.

Geniohyoid

• Attaches to the inferior mental spine of the mandible, but it’s not a tongue muscle—it elevates the hyoid.

Styloglossus

• Originates from the styloid process of the temporal bone.

Palatoglossus

• Arises from the palatine aponeurosis of the soft palate—not connected to the mandible.

The majority of retinal ganglion cell axons go to the lateral geniculate body (for conscious visual processing).

• However, some fibers take a different route:

  • They go to the superior colliculus in the midbrain.

• The superior colliculus is involved in:

  • Visual reflexes (e.g., turning your head toward a flash of light)

  • Coordinating eye and head movements

  • Pupillary light reflex pathway (indirectly via the pretectal area)

❌ Why the Other Options Are Incorrect:

Inferior colliculus

• Part of the auditory pathway, not visual. Receives input from cochlear nuclei → sends info to medial geniculate body.

Optic radiation

• These are axons from the lateral geniculate body to the visual cortex. Ganglion cells do not synapse here.

Lateral geniculate body

• Main site for conscious visual processing, but it is in the thalamus, not midbrain. Question specifically asks about midbrain synapse.

Medial geniculate body

• Part of the auditory pathway, not involved in vision.

The deep facial vein connects the facial vein to the pterygoid venous plexus, located in the infratemporal fossa.

• This is another important route for spread of infection from superficial to deep venous systems.

❌ Why the Others Are Incorrect:

Facial vein communicates with inferior ophthalmic vein

• ❌ Incorrect. It communicates with the superior ophthalmic vein, not the inferior.

Facial vein drains into external jugular vein

• ❌ Incorrect. It typically drains into the internal jugular vein via the common facial vein.

Facial vein has unidirectional valves

• ❌ Incorrect. The facial vein is valveless, allowing bidirectional flow—this is why infections can spread to the brain.

The tensor tympani muscle is located in the middle ear and functions to dampen loud sounds by tightening the tympanic membrane.

• It is innervated by a branch of the mandibular nerve (V₃)—the third division of the trigeminal nerve (CN V).

• This follows the rule: “tensor = trigeminal (V₃)”, like:

  • Tensor veli palatini

  • Tensor tympani

❌ Why the Other Options Are Incorrect:

Vestibulocochlear nerve (CN VIII)

• Sensory only. For hearing and balance. No motor supply to muscles.

Facial nerve (CN VII)

• Supplies stapedius (the other middle ear muscle), but not tensor tympani.

Glossopharyngeal nerve (CN IX)

• Innervates stylopharyngeus muscle, not involved in middle ear function.

Maxillary nerve (V₂)

• Sensory only. No motor branches to any muscles.

The nucleus of the tractus solitarius (NTS), located in the medulla oblongata, is the main sensory nucleus for taste.

• It receives afferent taste fibers from:

  • Facial nerve (CN VII) – anterior 2/3 of the tongue

  • Glossopharyngeal nerve (CN IX) – posterior 1/3

  • Vagus nerve (CN X) – epiglottis and pharynx

• It processes taste and visceral sensory inputs before relaying them to higher centers (e.g., thalamus → gustatory cortex).

❌ Why the Other Options Are Incorrect:

Dorsal nuclei

• Vague term; possibly refers to dorsal motor nucleus of the vagus, which handles parasympathetic output, not taste.

Nucleus ambiguus

• Motor nucleus involved in swallowing and phonation—supplies muscles of pharynx, larynx via CN IX, X, and XI.

Nucleus of pneumotaxic centre

• Located in the pons, regulates breathing rhythm, not sensory input.

Vasomotor centre

• Part of medullary centers that control blood pressure and heart rate, not taste.

 Bitter is Correct:

• Vallate (circumvallate) papillae are large, dome-shaped structures located at the posterior part of the tongue (in a V-shape).

• They house a large number of taste buds (more than other papillae).

• These taste buds are most sensitive to bitter tastes, which:

  • Are often associated with toxins or harmful substances.

  • Trigger a protective response like gagging or rejection—hence located near the oropharynx, just before swallowing.

❌ Why the Other Options Are Incorrect:

Umami

• Detected primarily on the anterior and posterior tongue, but not specifically by vallate papillae.

Sour

• Detected by foliate papillae and lateral tongue areas.

Sweet

• Best detected at the tip of the tongue, primarily by fungiform papillae.

Salty

• Detected at the anterolateral edges of the tongue, not primarily by vallate papillae.

Medulla Oblongata is Correct:

• The swallowing center is located in the medulla oblongata, within the reticular formation.

• It coordinates the phases of swallowing (oral, pharyngeal, and esophageal) by integrating signals from:

  • Cranial nerves V, VII, IX, X, and XII

  • Sensory input from the oropharynx and esophagus

• It sends motor commands to muscles of the tongue, pharynx, and esophagus to coordinate safe and efficient swallowing.

❌ Why the Other Options Are Incorrect:

Hypothalamus

• Regulates hunger, thirst, body temperature—not directly involved in motor coordination of swallowing.

Pons

• Involved in breathing and facial expression control, but not the primary center for swallowing.

Cerebellum

• Coordinates movement and balance, but does not initiate reflexive swallowing.

Midbrain

• Handles visual and auditory reflexes, not autonomic reflexes like swallowing.

Hair Cells Are Correct:

• The hair cells (inner and outer) in the organ of Corti are the actual sensory receptors for hearing.

• Located on the basilar membrane, they are mechanoreceptors that:

  • Detect movement of the basilar membrane due to sound-induced vibrations.

  • Convert these mechanical signals into electrical impulses via deflection of their stereocilia.

  • Inner hair cells primarily send signals to the brain via the cochlear division of CN VIII.

❌ Why the Other Options Are Incorrect:

Perilymph

• Fluid in the scala vestibuli and scala tympani. Supports vibration transmission but is not a sensory structure.

Spiral ganglion

• Contains cell bodies of auditory nerve fibers, which receive input from hair cells, but does not detect sound itself.

Basal (Basilar) membrane

• Supports the organ of Corti and vibrates in response to sound—but it is not the sensory unit itself.

Endolymph

• Fluid in the scala media (cochlear duct), rich in K⁺, surrounds hair cells but is not a receptor.

When rhodopsin absorbs light, it undergoes a series of photoisomerization changes, forming intermediates:

• 1. Rhodopsin

  2. Bathorhodopsin

  3. Lumirhodopsin

  4. Metarhodopsin I

  5. Metarhodopsin II (also called activated rhodopsin)

• The key activating step for vision is Lumirhodopsin → Metarhodopsin, especially Metarhodopsin II, which:

  • Activates transducin (G-protein)

  • Triggers the phototransduction cascade

  • Ultimately leads to closure of Na⁺ channels and hyperpolarization

❌ Why the Other Options Are Incorrect:

• All-trans retinol to all-trans retinal
  ❌ Wrong chemical context — this step occurs after photoactivation during retinoid recycling, not during immediate light absorption.

• Metarhodopsin to bathorhodopsin
  ❌ This is the reverse direction; light absorption pushes forward toward metarhodopsin, not backward.

• Bathorhodopsin to rhodopsin
  ❌ Rhodopsin is the starting molecule, and bathorhodopsin forms after light hits it.

• Lumirhodopsin to bathorhodopsin
  ❌ Again, this is the reverse direction of the actual photochemical sequence.

 Why This is Incorrect:

• The mucous membrane of the tongue—especially on the dorsal surface—is firmly bound to the underlying muscle. This allows it to withstand friction during chewing and speaking.

• The ventral surface, while smoother, still has its mucosa tightly adherent, especially centrally.

• So saying it is loosely bound is incorrect for the tongue (though true for parts of the cheek or lips).

✅ Why the Other Statements Are Correct:

• Posterior one third of tongue is irregular with lymphoid aggregations called lingual tonsils
  ✔ True — these form part of Waldeyer’s ring.

• It is firmly bound to underlying muscle
  ✔ True — ensures functional movement and durability.

• Anterior two third of tongue is covered by small projections called papillae
  ✔ True — includes filiform, fungiform, circumvallate, and foliate papillae.

• Ventral surface of tongue is covered by a smooth mucosa
  ✔ True — it lacks papillae and is smoother compared to the dorsal surface.

The retromandibular vein is formed in front of the ear (inside the parotid gland) by the joining of the superficial temporal vein and the maxillary vein. This is its true anatomical origin.

❌ Incorrect Answers:

• • It drains the side of head and superficial aspects of temporal muscles
    → That’s mainly done by the superficial temporal vein, not the retromandibular vein itself.

  • It joins with the common facial vein to form external jugular vein
    → Wrong vein. The posterior division of the retromandibular vein joins the posterior auricular vein to form the external jugular vein.

  • It is formed posterior to the ear by the union of the superficial temporal and maxillary veins
    → Incorrect location. It’s formed anterior to the ear, not behind it.

  • It ultimately drains into internal jugular vein
    → Only the anterior division (via common facial vein) drains into the internal jugular, not the entire retromandibular vein.

 Ultimobranchial Body is Correct:

• Parafollicular cells (C-cells) produce calcitonin, a hormone that lowers blood calcium.

• These cells originate from the ultimobranchial body, which is derived from the 5th pharyngeal pouch (often considered a rudimentary part of the 4th pouch).

• The ultimobranchial body fuses with the developing thyroid gland, and its cells integrate into the thyroid as C-cells.

• These cells are also influenced by neural crest cells, giving them a unique embryological origin compared to thyroid follicular cells.

❌ Why the Other Options Are Incorrect:

Second pharyngeal pouch

• Gives rise to the palatine tonsils, not thyroid components.

Third pharyngeal arch

• Contributes to muscles and cartilage of the hyoid region, not to thyroid development.

First pharyngeal pouch

• Forms the middle ear and eustachian tube, not thyroid tissue.

Second pharyngeal cleft

• This is ectoderm, not endoderm. Normally obliterated during development.

 Maxillary Vein is Correct:

• The pterygoid venous plexus is located around the lateral pterygoid muscle, in the infratemporal fossa.

• It is an extensive, interconnected network that receives blood from facial, deep facial, infraorbital, and ophthalmic veins.

• It ultimately drains into the maxillary vein, which then joins the retromandibular vein, and further drains into the external jugular system.

❌ Why the Other Options Are Incorrect:

Inferior ophthalmic vein

• It drains into the pterygoid venous plexus, not the other way around.

Superior ophthalmic vein

• Connects to the cavernous sinus, but is not a drainage point for the pterygoid plexus.

Facial vein

• Communicates with the pterygoid plexus via the deep facial vein, but is not the final drainage vein.

Cavernous sinus

• It has indirect connections (via ophthalmic veins), but the main drainage route of the pterygoid plexus is into the maxillary vein, not the sinus.

📝 Clinical Pearl:

• The pterygoid venous plexus can serve as a route for infection spread between the face and the cavernous sinus, due to its valveless connections—especially relevant in cases of “danger triangle of the face” infections.

• The piriform aperture is the anterior nasal opening of the skull.

• It is shaped like an inverted pear and is bounded by:

  • Superiorly: the nasal bones

  • Laterally and inferiorly: the frontal processes and body of the maxilla

• This aperture is where the cartilaginous framework of the nose attaches.

❌ Why the Other Options Are Incorrect:

Maxillary and zygomatic bones

• Zygomatic bones are lateral to the orbit and do not form part of the piriform aperture.

Lacrimal and nasal bones

• Lacrimal bones are very small and form part of the medial wall of the orbit, not the piriform aperture.

Nasal and zygomatic bones

• Zygomatic bones are unrelated to the nasal opening.

Frontal and nasal bones

• The frontal bone lies superior to the nasal bones and does not bound the piriform aperture.

Superior Portion is Correct:

• The olfactory epithelium is found in the superior portion of the nasal cavity, specifically:

  • The roof of the nasal cavity

  • The superior nasal concha

  • The upper part of the nasal septum

• This specialized area contains olfactory receptor neurons, supporting cells, and basal stem cells.

• It connects with the olfactory bulb through the cribriform plate of the ethmoid bone.

❌ Why the Other Options Are Incorrect:

Inferior portion of the nasal cavity

• Lined by respiratory epithelium, not involved in smell.

It is not present in the nasal cavity

• Incorrect—olfactory epithelium is in the nasal cavity.

Posterior and lateral portion of nasal cavity

• Also lined by respiratory epithelium; not the olfactory zone.

Anterior and lateral portion of nasal cavity

• Mostly vestibule and respiratory areas—not olfactory.

• An oblique facial cleft is a rare and severe congenital anomaly.

• It results from the failure of fusion between the maxillary prominence and the lateral nasal prominence during facial development.

• This leads to a cleft running diagonally from the upper lip to the medial aspect of the eye.

• Often associated with exposed nasolacrimal duct, since this duct forms in the groove between these two structures.

❌ Why the Others Are Incorrect:

Two medial nasal prominences with each other

• Their failure results in median cleft lip, not oblique cleft.

Two maxillary prominences with each other

• These fuse across the upper jaw but are not responsible for oblique clefts.

Two mandibular prominences with each other

• Their failure causes midline mandibular clefts, not facial ones.

Maxillary prominence with medial nasal prominence

• Failure of this fusion results in a unilateral or bilateral cleft lip, not an oblique facial cleft.

 11-cis Retinal is Correct:

• Rhodopsin is a light-sensitive pigment found in rods, composed of:

  • Scotopsin (the protein part)

  • 11-cis retinal (the light-sensitive chromophore)

• 11-cis retinal is the active, bent form of vitamin A aldehyde.

• Upon exposure to light, it isomerizes to all-trans retinal, initiating the visual signal cascade.

• This is the first step in phototransduction.

❌ Why the Others Are Incorrect:

11-cis retinol

• Alcohol form of vitamin A, not the aldehyde form that binds to scotopsin.

All-trans retinol

• The storage form of vitamin A; not used directly in rhodopsin formation.

13-cis retinol

• Not involved in normal visual cycle; biologically less relevant in vision.

All-trans retinal

• Form after light exposure—does not bind to scotopsin to form rhodopsin.

Horizontal Cells Are Correct:

• Horizontal cells are interneurons in the retina that connect photoreceptors (rods and cones) laterally.

• They inhibit neighboring photoreceptors via GABAergic synapses, reducing the signal in adjacent cells.

• This mechanism sharpens visual contrast, enhances edge detection, and is a textbook example of lateral inhibition.

❌ Why the Others Are Incorrect:

Ganglionic cells

• Final output cells of the retina. They send signals to the brain but don’t perform lateral inhibition.

Amacrine cells

• Act at the inner plexiform layer, mainly modulate signals between bipolar and ganglion cells, especially in motion detection and light adaptation—not lateral inhibition of photoreceptors.

Rods

• Photoreceptors that detect dim light, do not perform any inhibitory functions themselves.

Bipolar cells

• Relay signals from photoreceptors to ganglion cells. They don’t inhibit laterally.

Pars Optica Retinae is Correct:

• The optic cup forms during early eye development from an outgrowth of the diencephalon.

• The inner layer of the posterior optic cup becomes the pars optica retinae.

• This region gives rise to the neural (sensory) retina, containing:

  • Photoreceptors (rods and cones)

  • Bipolar cells

  • Ganglion cells

• It’s the functional visual part of the retina responsible for processing light signals.

❌ Why the Other Options Are Incorrect:

Pars caeca retinae

• Non-visual part of the retina (anterior portion), contributes to ciliary body and iris epithelium.

Pars iridica retinae

• Forms the pigmented epithelium of the iris, not involved in vision.

Outer layer of optic cup

• Becomes the retinal pigment epithelium (RPE)—supportive, but not sensory.

Pars ciliaris retinae

• Part of the pars caeca, contributes to ciliary body—again, not sensory.

📝 Summary:

Muscular Triangle is Correct:

• The muscular triangle is one of the subdivisions of the anterior triangle of the neck.

• It contains the infrahyoid (strap) muscles, which include:

  • Sternohyoid

  • Sternothyroid

  • Thyrohyoid

  • Omohyoid (superior belly)

• These muscles are involved in depressing the hyoid bone and larynx during swallowing and speech.

❌ Why the Others Are Incorrect:

Submental triangle

• Contains submental lymph nodes and anterior jugular vein, not infrahyoid muscles.

Submandibular triangle

• Contains submandibular gland, facial artery/vein, and lymph nodes.

Posterior triangle

• Contains accessory nerve (CN XI), brachial plexus, external jugular vein, and scalene muscles—not infrahyoid muscles.

Carotid triangle

• Contains carotid sheath structures: common carotid artery, internal jugular vein, vagus nerve—but not the infrahyoid group.

“Hyoid arch” (2nd pharyngeal arch) is Correct:

• The stapes is the auditory ossicle that attaches to the oval window.

• The stapes develops from the second pharyngeal arch, also called the hyoid arch.

• The facial nerve (CN VII) is the nerve of the second arch—this is also the nerve that runs near the stapedius muscle, which attaches to the stapes.

• Hence, the correct embryological origin of the ossicle touching the oval window is the hyoid arch.

❌ Why the Others Are Incorrect:

Mandibular arch / 1st pharyngeal arch

• Gives rise to the malleus and incus, not the stapes.

• Associated with mandibular nerve (CN V₃).

3rd pharyngeal arch

• Contributes to stylopharyngeus muscle and parts of the hyoid bone, not ear ossicles.

4th pharyngeal arch

• Forms laryngeal cartilages, pharyngeal muscles—not involved in ossicles.

📝 Summary of Auditory Ossicle Origins:

 Why This is Incorrect:

• Most minor salivary glands (like labial, buccal, palatine, and lingual) are mucous or mixed (mostly mucous with some serous).

• They are responsible for mucus secretion to keep the oral cavity moist—not for producing digestive enzymes.

• Saying all are “serous” is incorrect—they are predominantly mucous, with a few exceptions like von Ebner’s glands (which are purely serous).

✅ Why the Other Statements Are Correct:

Serous cells are predominant cells of submandibular gland

• True. Submandibular gland is a mixed gland, but serous cells predominate (≈90%).

Intercalated ducts are wider and longer in the parotid gland

• True. Parotid gland is purely serous with well-developed ductal systems, including prominent intercalated ducts.

All minor salivary glands are not encapsulated

• True. Minor salivary glands are scattered, unencapsulated, and located throughout the oral mucosa.

Demilune cells secrete lysozyme in sublingual gland

• True. In mucous acini, serous demilunes cap the mucous cells and secrete lysozyme and other antimicrobial proteins.

📝 Summary:

Stapedius is Correct:

• The stapedius is the smallest skeletal muscle in the human body.

• It is located in the posterior wall of the middle ear and inserts on the stapes bone.

• Its function: stabilizes the stapes and dampens vibrations to protect the inner ear from loud sounds (acoustic reflex).

• It is innervated by a branch of the facial nerve (CN VII).

❌ Why the Others Are Incorrect:

Posterior auricular, Superior auricular, Anterior auricular

• These are muscles of facial expression, located outside the ear, and while they are supplied by the facial nerve, they are not muscles of the middle ear.

Tensor tympani

• A middle ear muscle, but innervated by the mandibular nerve (CN V₃), not the facial nerve.

• It inserts on the malleus and also dampens sound—but not supplied by CN VII.

Internal Branch of Superior Laryngeal Nerve is Correct:

• This nerve is a branch of the vagus nerve (CN X).

• It pierces the thyrohyoid membrane and provides sensory innervation to:

  • The laryngopharynx

  • The mucosa above the vocal cords (supraglottic larynx)

  • The posterior tongue and upper laryngeal inlet

• The laryngopharynx, being the area behind the larynx and below the oropharynx, falls under its territory.

❌ Why the Others Are Incorrect:

External laryngeal nerve

• Also a branch of the superior laryngeal nerve.

• Provides motor innervation to cricothyroid, not sensory.

Recurrent laryngeal nerve

• Provides sensory innervation below the vocal cords and motor innervation to intrinsic laryngeal muscles.

• Does not supply the laryngopharynx.

Pharyngeal branch of maxillary nerve

• From CN V2, supplies part of the nasopharynx, not the laryngopharynx.

Glossopharyngeal nerve

• Supplies sensory innervation to the oropharynx (including palatine tonsils and posterior third of tongue), but not the laryngopharynx.

Fourth Pharyngeal Arch is Correct:

• The cricothyroid muscle is unique among intrinsic laryngeal muscles because it’s innervated by the external branch of the superior laryngeal nerve, a branch of the vagus nerve (CN X).

• This nerve is derived from the fourth pharyngeal arch, which gives rise to:

  • Muscles: cricothyroid, pharyngeal constrictors, levator veli palatini

  • Artery: part of the aortic arch and subclavian artery

• Thus, the cricothyroid originates embryologically from the 4th pharyngeal arch.

❌ Why the Others Are Incorrect:

Mandibular arch (1st arch)

• Gives rise to muscles of mastication, mylohyoid, anterior belly of digastric, etc.

• Innervated by mandibular nerve (CN V₃).

Hyoid arch (2nd arch)

• Gives rise to muscles of facial expression, posterior belly of digastric, etc.

• Innervated by facial nerve (CN VII).

Sixth pharyngeal arch

• Gives rise to most intrinsic muscles of the larynx (e.g., posterior cricoarytenoid, lateral cricoarytenoid, thyroarytenoid).

• Innervated by the recurrent laryngeal nerve—not the cricothyroid.

Fifth pharyngeal arch

• Rudimentary or absent in humans. It typically regresses without contributing to adult structures.

Anterior Surface of Cornea is Correct:

• Refraction = bending of light to focus it on the retina.

• The anterior surface of the cornea is the first and most curved transparent layer the light encounters.

• It provides about two-thirds (≈70%) of the eye’s total refractive power.

• The cornea is air-to-cornea interface, which has the greatest difference in refractive index—this is why most bending happens here.

❌ Why the Others Are Incorrect:

Anterior surface of lens

• The lens does contribute to focusing (≈30%), but adjustable, not the main refractor at rest.

Posterior surface of lens

• Less involved in bending light compared to anterior lens surface; smaller interface difference.

Anterior surface of sclera

• Sclera is opaque, not involved in refraction at all.

Posterior surface of cornea

• Less curvature, and it’s within the aqueous humor, not exposed to a large refractive index change.

Foramen Spinosum is Correct:

• The middle meningeal artery, a branch of the maxillary artery, enters the cranial cavity via the foramen spinosum.

• It runs between the dura mater and the skull, supplying the meninges and calvaria.

• Its path makes it vulnerable in pterion fractures, leading to epidural hematoma—a classic clinical scenario.

❌ Why the Others Are Incorrect:

Foramen ovale

• Transmits the mandibular nerve (V3), accessory meningeal artery, and lesser petrosal nerve—not the middle meningeal artery.

Foramen rotundum

• Passage for the maxillary nerve (V2)—no arteries pass through.

Foramen lacerum

• Mostly filled with cartilage. No major structures pass through it, though some structures cross over it.

Superior orbital fissure

• Transmits cranial nerves III, IV, V₁, VI, and ophthalmic vein to the orbit—not related to the middle meningeal artery.

Temporal Bone is Correct:

• The middle ear cavity (also called the tympanic cavity) is located in the petrous part of the temporal bone.

• It houses:

  • The ossicles (malleus, incus, stapes)

  • The tympanic membrane

  • The opening of the Eustachian tube

• It connects laterally to the external acoustic meatus and medially to the inner ear.

• The mastoid air cells, also part of the temporal bone, communicate with the middle ear via the aditus to mastoid antrum.

❌ Why the Others Are Incorrect:

Mastoid bone

• Not a separate bone—part of the temporal bone. Contains air cells, but not the cavity itself.

Sphenoid bone

• Located more anteriorly. Contains sphenoid sinus, not middle ear structures.

Greater wing of sphenoid

• Also part of the sphenoid bone, forms part of the orbit and skull base—not involved in hearing structures.

Occipital bone

• Forms the back and base of the skull, near the foramen magnum. No relation to the ear.

• The lesser palatine artery primarily supplies the soft palate and tonsils, not the nasal septum.

• It is not part of Kiesselbach’s plexus, which is the anterior septal region where most nosebleeds occur.

• Hence, lesser palatine artery does not contribute to the arterial anastomosis at the common nosebleed site.

❌ Why the Others Are Correct Participants:

Sphenopalatine artery

• A terminal branch of the maxillary artery, and primary supplier of the nasal septum.

• Major contributor to Kiesselbach’s plexus.

Anterior ethmoidal artery

• Branch of the ophthalmic artery, enters nasal cavity via ethmoidal foramina, supplies upper septum.

Greater palatine artery

• Ascends through the incisive canal to contribute to the anterior nasal septum, part of the plexus.

Superior labial artery

• Branch of the facial artery, sends septal branches upward into the anterior nasal septum.

📝 Summary:

🔴 Kiesselbach’s plexus = “Little’s Area”
It’s where branches from five arteries meet:

1. Anterior ethmoidal (ophthalmic)

2. Sphenopalatine (maxillary)

3. Greater palatine (maxillary)

4. Superior labial (facial)

5. Septal branch of artery of incisive canal (sometimes listed separately)

Sternocleidomastoid is Correct:

• The investing layer is the most superficial layer of the deep cervical fascia.

• It completely encloses two muscles:

  • The sternocleidomastoid (front-lateral neck)

  • The trapezius (posterior neck and upper back)

• This layer also helps form the roof of the anterior and posterior triangles of the neck.

• It lies deep to the platysma and superficial to most other deep structures.

❌ Why the Others Are Incorrect:

Digastric

• Only partially related to deep fascia; mainly enclosed in the submandibular triangle by pretracheal fascia, not the investing layer.

Geniohyoid

• Lies deep, above the mylohyoid, and is covered by pretracheal fascia, not the investing layer.

Mylohyoid

• Forms the floor of the oral cavity, not enclosed by the investing layer.

Omohyoid

• Pierces the investing layer, but is not enclosed by it. The fascia forms a sling to hold its intermediate tendon, but doesn’t wrap the whole muscle.

Lateral Grey Horn is Correct:

• The intermediate column lies between the anterior (motor) and posterior (sensory) horns.

• It gives rise to the lateral grey horn, which is seen in the thoracic and upper lumbar (T1–L2) regions of the spinal cord.

• The lateral horn contains preganglionic sympathetic neurons—so it plays a role in the autonomic nervous system.

• This region develops from the intermediate zone of the mantle layer during spinal cord development.

❌ Why the Others Are Incorrect:

Marginal layer

• Refers to the outermost layer of the developing spinal cord, forms the white matter, not grey matter structures.

Posterior grey horn

• Derived from the alar plate, associated with sensory input, not the intermediate column.

Anterior grey horn

• Derived from the basal plate, responsible for motor output, not autonomic.

Mantle layer

• A developmental layer, not a final structure; it gives rise to grey matter, but not equivalent to the intermediate column.

• In light adaptation, the eyes adjust to bright light by reducing sensitivity.

• This is achieved by the breakdown (bleaching) of photopigments, particularly rhodopsin in rods.

• Rhodopsin is split into its components: retinal and opsin, rendering the photoreceptor less sensitive to light.

• This helps the retina avoid overstimulation and glare in bright environments.

❌ Why the Other Options Are Incorrect:

The level of rhodopsin is high

• Opposite of what happens—rhodopsin levels decrease due to bleaching.

Bipolar cells transmit signals at the maximum rate

• Their activity adjusts based on photoreceptor input, but they do not constantly fire at maximum in light adaptation.

Vitamin A is converted into retinal

• True in dark adaptation, where retinal is regenerated.

• Not the primary event in light adaptation.

The size of pupil is increased

• In light, the pupil constricts to limit light entry.

• Pupil dilates in the dark.

 Red Cones is Correct:

• Protanope = type of red-green color blindness.

• It is due to the absence of red-sensitive cones (L-cones) in the retina.

• These cones normally detect long wavelengths (reds).

• As a result, protanopes have difficulty distinguishing red from green, and red may appear darker or even black.

❌ Why the Others Are Incorrect:

Rhodopsin

• Found in rods, used for dim light vision, not color.

• Irrelevant to colorblindness types like protanopia.

Green cones

• Absent in deuteranopia, not protanopia.

Blue cones

• Missing in tritanopia (very rare), not protanopia.

White cones

• There’s no such thing. White is a perceived combination of all wavelengths, not a photoreceptor type.

• Keratomalacia is a severe, advanced form of vitamin A deficiency.

• It causes destruction, softening, and ulceration of the cornea due to loss of epithelial integrity and mucous secretion.

• The condition is marked by dryness (xerosis) and clouding or opacification of the cornea.

• It can lead to permanent blindness if not treated.

❌ Why the Other Options Are Incorrect:

Localized thickening of conjunctiva

• Refers more to Bitot’s spots, a milder manifestation of vitamin A deficiency—not keratomalacia.

Dryness of conjunctiva and cornea

• This describes an earlier stage (xerophthalmia), not the advanced destructive changes seen in keratomalacia.

Unable to see in light or dark condition

• This is non-specific and not characteristic of keratomalacia or any known vitamin A issue.

Patient cannot see in low light or in near dark condition

• This is night blindness (nyctalopia), an early sign of vitamin A deficiency, not keratomalacia.

Atlantoaxial Joint is Correct:

• The atlantoaxial joint is located between the first cervical vertebra (C1, atlas) and the second cervical vertebra (C2, axis).

• C2 has the dens (odontoid process), which acts as a pivot around which the atlas (and thus the skull) rotates.

• This rotation allows you to move your head side-to-side, as in saying “no.”

• It is a pivot-type synovial joint.

❌ Why the Others Are Incorrect:

Atlantooccipital joint

• Located between the occipital bone and C1 (atlas).

• Allows nodding motion (“yes”), not rotation.

C2–C3 joint

• Normal intervertebral joint.

• Limited motion, not specialized for head rotation.

C3–C4 joint

• Similar to above—regular cervical vertebral articulation, no major role in head movement.

C7–T1 joint

• Transition from cervical to thoracic spine.

• Supports neck, but not involved in head rotation.

Presbycusis is Correct:

• Presbycusis is the progressive, bilateral sensorineural hearing loss that occurs with aging.

• It primarily affects high-frequency sounds first.

• It results from degeneration of the cochlea, especially the hair cells in the organ of Corti, or loss of neurons in the auditory pathway.

• Common in the elderly, with no associated pain, dizziness, or discharge.

❌ Why the Other Options Are Incorrect:

Otitis media

• A middle ear infection, usually in children.

• Associated with pain, fluid buildup, and possibly conductive hearing loss, not age-related.

Conductive deafness

• Involves outer or middle ear problems (e.g., wax, otosclerosis).

• Age-related hearing loss is sensorineural, not conductive.

Sensorineural hearing loss

• True that presbycusis is a type of sensorineural hearing loss.

• But this option is too broad—the question asks specifically about age-related hearing loss.

Ménière’s disease

• Involves episodic vertigo, tinnitus, and fluctuating hearing loss, typically in one ear.

• It’s a disorder of endolymph (fluid imbalance), not related to aging.

• Taste buds are barrel-shaped sensory structures located in the epithelium.

• The apex (top) of each taste bud opens into the oral cavity via a taste pore.

• Through this taste pore, dissolved food substances can reach the gustatory (taste) receptor cells, allowing chemoreception.

❌ Why the Other Options Are Incorrect:

They are mainly located on the soft palate but few on the ventral surface of tongue

• Wrong: Majority of taste buds are on the dorsal surface of the tongue, especially on fungiform, foliate, and circumvallate papillae.

• Soft palate has some, ventral surface has none.

A taste bud consists of 10–12 cells

• Incorrect: Each taste bud typically contains 50–100 cells, including gustatory cells, supporting (sustentacular) cells, and basal cells.

Sustentacular cells of taste buds are also known as gustatory cells

• Incorrect: These are two distinct cell types.

  • Gustatory cells = sensory receptor cells.

  • Sustentacular cells = supportive cells, not involved in taste transduction.

Taste buds are embedded within epithelium covering the filiform papillae

• Wrong: Filiform papillae are the only papillae without taste buds.

• Taste buds are found in fungiform, foliate, and circumvallate papillae.

Ophthalmic is Correct:

• The ophthalmic nerve is a branch of the trigeminal nerve (CN V₁), not the facial nerve (CN VII).

• It provides sensory innervation to the forehead, upper eyelid, and parts of the nose.

• It does not control muscles of facial expression.

❌ Why the Others Are Facial Nerve Branches:

Temporal

• Innervates frontalis, orbicularis oculi, and part of scalp muscles.

Zygomatic

• Controls muscles around the eye (e.g., orbicularis oculi).

Buccal

• Supplies muscles around the mouth and nose (e.g., buccinator, upper orbicularis oris).

Marginal mandibular

• Controls muscles of the lower lip and chin (e.g., depressor anguli oris).

💡 Memory Tip:

Facial nerve terminal branches often follow this mnemonic:
“To Zanzibar By Motor Car”
Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical

 K⁺ is Correct:

• Endolymph, found in the cochlear duct, has an unusually high concentration of potassium and low sodium—opposite of most extracellular fluids.

• When stereocilia of hair cells bend, K⁺ flows into the hair cells through mechanically gated channels.

• This influx of K⁺ depolarizes the cell (instead of Na⁺, like in typical neurons).

• Depolarization then triggers opening of voltage-gated Ca²⁺ channels for neurotransmitter release.

❌ Why the Others Are Incorrect:

Mg²⁺

• Not involved in depolarizing auditory hair cells. More involved in enzymatic reactions and NMDA receptor function.

Cl⁻

• Usually contributes to hyperpolarization, not depolarization. No role in this specific process.

Ca²⁺

• Important after depolarization (enters to help with neurotransmitter release), but it doesn’t cause the depolarization.

Na⁺

• Typically causes depolarization in most neurons, but not in hair cells. Endolymph is low in Na⁺.

Glossopharyngeal Nerve is Correct:

• It supplies the posterior one-third of the tongue.

• Provides both general sensation and taste in this region.

• Also involved in gag reflex and innervates part of the pharynx.

• Cranial Nerve IX (9).

❌ Why the Others Are Incorrect:

Facial nerve

• Supplies anterior 2/3rd taste only (via chorda tympani).

• No role in posterior tongue.

Olfactory nerve

• Responsible for smell, not taste or tongue sensation.

Trigeminal nerve

• Supplies anterior 2/3rd general sensation (not taste).

• Does not reach the posterior 1/3rd.

Vagus nerve

• Supplies epiglottis and lower pharynx for taste.

• Can supply a small area of the tongue base, but not the posterior 1/3rd specifically.

Larynx is Correct:

• Contains vocal cords that vibrate to produce sound.

• Generates the basic tone used for speech.

• Adjusts pitch and volume.

• It’s the main voice-producing organ.

❌ Why the Others Are Incorrect:

Tongue

• Shapes and articulates speech (e.g., forming letters),

• Doesn’t generate tone.

Pharynx

• Acts as a resonating chamber.

• Modifies sound but doesn’t produce it.

Nasal cavity

• Affects resonance (especially nasal sounds like “m” or “n”).

• No role in generating tone.

Tonsils

• Lymphoid tissue involved in immune defense.

• No function in sound or speech production.

The soft palate is a muscular structure located posterior to the hard palate. It does not undergo ossification, which makes it the correct answer.

✔️ Why the Soft Palate does not ossify:

• It is composed primarily of skeletal muscle fibers, connective tissue, mucous glands, and is covered by mucosa.

• Unlike the hard palate, it lacks a bony framework and thus remains flexible to function during swallowing, speech, and breathing.

• The term “soft” reflects its non-ossified, muscular nature.

❌ Why the Other Options Are Incorrect:

• • Hard palate
  🔴 Contains palatine processes of the maxilla and horizontal plates of the palatine bones — these undergo intramembranous ossification.

• • Middle ear cavity
  🔴 Contains the auditory ossicles (malleus, incus, stapes), which are among the first bones to ossify during fetal development.

• • Nasal septum
  🔴 Formed from both cartilage and bone, particularly the vomer and perpendicular plate of the ethmoid, which undergo ossification.

• • Lateral leg compartment
  🔴 Muscles in this compartment (e.g., fibularis longus and brevis) are attached to bones like the fibula, which form through endochondral ossification.

The musculature of the tongue is not derived from ectoderm — this statement is anatomically and embryologically incorrect.

✔️ Correct Embryological Origin of Tongue Muscles:

• Tongue muscles (intrinsic and most extrinsic) are derived from occipital somites, which are mesodermal in origin, specifically paraxial mesoderm.

• These myoblasts migrate into the tongue during development.

• They are innervated by the hypoglossal nerve (cranial nerve XII).

✅ Why the Other Statements Are Correct:

• • Anterior two-thirds of the tongue is innervated differently from the posterior one-third
  ✔️ True — The anterior 2/3 receives general sensation from the mandibular branch of CN V (V3) and taste from the chorda tympani (branch of CN VII). The posterior 1/3 is innervated by the glossopharyngeal nerve (CN IX) for both general sensation and taste.

• • Foramen cecum is the site of thyroid migration
  ✔️ True — The foramen cecum marks the origin of the thyroglossal duct, through which the thyroid gland migrates downward during embryonic development.

• • Anterior two-thirds of the tongue is formed by lateral lingual swellings
  ✔️ True — These swellings arise from the first pharyngeal arch and merge to form the anterior 2/3 of the tongue, overgrowing the tuberculum impar.

• • Taste buds develop on the dorsal surface of tongue
  ✔️  True — Taste buds are primarily located on the dorsal surface of the tongue, especially on structures like fungiform, foliate, and circumvallate papillae.

The patient’s primary complaint is inability to lift his shoulder, which strongly suggests weakness or paralysis of the trapezius muscle — a muscle primarily responsible for shoulder elevation.

The trapezius (along with the sternocleidomastoid) is innervated by the spinal accessory nerve (cranial nerve XI).

✔️ Spinal accessory nerve (CN XI):

• Exits the skull through the jugular foramen, along with cranial nerves IX (glossopharyngeal) and X (vagus).

• A lesion at the jugular foramen can affect the accessory nerve, resulting in weakness in shoulder shrugging and difficulty turning the head against resistance.

❌ Why the Other Options Are Incorrect:

• • Foramen ovale
   Transmits the mandibular nerve (V3), not involved in shoulder movement. A lesion here would affect mastication muscles, not the trapezius.

• • Foramen magnum
   Though the spinal root of CN XI enters the skull here, a lesion at this site would likely cause more extensive neurological deficits, including motor/sensory impairment due to spinal cord involvement — not isolated shoulder weakness.

• • Foramen rotundum
   Transmits the maxillary nerve (V2), which is purely sensory to the midface — completely unrelated to motor control of the shoulder.

• • None of these
   Incorrect — the correct site is jugular foramen, as explained above.

Myopia, commonly known as nearsightedness, is a refractive error where close objects appear clear, but distant objects appear blurry. This happens because:

• The eyeball is too long, or

• The cornea is too curved, causing light rays to focus in front of the retina instead of on it.

✅ Concave Lens (Diverging Lens):

• A concave lens spreads out (diverges) the light rays before they enter the eye.

• This effectively moves the focal point backward, allowing the light to focus directly on the retina.

• Concave lenses are used in glasses or contact lenses specifically designed for myopic patients.

❌ Why the Other Options Are Incorrect:

• • Convex
  🔴 Convex lenses converge light and are used for hypermetropia (farsightedness), not myopia. They would worsen the myopic condition.

• • None of these
  🔴 Incorrect — concave lenses are the standard treatment for myopia.

• • Imaginary
  🔴 Not a valid term in optics. Lenses used in corrective eyewear are real, physical lenses.

• • Mixed
  🔴 Vague and non-specific. Lens correction must be precise — either concave or convex based on the refractive error. “Mixed” doesn’t describe a real lens type used in clinical correction.

Hypermetropia, also known as farsightedness, is a common refractive error where distant objects can be seen more clearly than near objects. This condition occurs due to one of the following anatomical factors:

• The eyeball is too short (from front to back), or

• The cornea is too flat, reducing its refractive power.

As a result, light rays from nearby objects focus behind the retina, instead of directly on it.

✅ Convex Lens (Converging Lens):

• A convex lens bends (converges) light rays inward, helping them focus on the retina rather than behind it.

• It increases the overall converging power of the eye, compensating for the lack of natural refraction in hypermetropic eyes.

• Convex lenses are used in spectacles or contact lenses for correction.

❌ Why the Other Options Are Incorrect:

• • Concave lens
  🔴 Used for myopia (nearsightedness) because it diverges light rays. It would worsen hypermetropia.

• • None of these
  🔴 Incorrect — convex lenses are a well-established treatment.

• • Contact lens
  🔴 While contact lenses can be used to correct hypermetropia, the type of contact lens needed is convex. This option is too vague and does not answer the question properly.

• • Concavo-convex lens
  🔴 This is a general shape descriptor (could be converging or diverging depending on curvature). It lacks specificity — in the treatment of hypermetropia, a convex (converging) lens is precisely what’s required.

• Umami taste is primarily triggered by L-glutamate, a naturally occurring amino acid.

• It is commonly found in protein-rich foods like meat, cheese, mushrooms, and especially in additives such as monosodium glutamate (MSG).

• Taste receptor cells responsible for umami have T1R1 + T1R3 receptors, which specifically bind to glutamate.

• The binding of glutamate to these receptors initiates a signal that is transmitted to the brain via facial (VII), glossopharyngeal (IX), and vagus (X) cranial nerves, depending on the region of the tongue.

❌ Why the Other Options Are Incorrect:

• • Alkaloids
   These are typically bitter-tasting compounds (e.g., caffeine, quinine), not umami.

• • Acetic acid
   Acetic acid is associated with the sour taste, not umami.

• • Organic substances containing nitrogen
   While amino acids (like glutamate) contain nitrogen, not all nitrogen-containing organics elicit the umami taste. This option is too broad and non-specific.

• • Fructose
   This is a sugar and is associated with the sweet taste, not umami.

• Horizontal cells are interneurons in the retina that connect laterally between photoreceptors (rods and cones).

• They receive input from multiple photoreceptors and provide inhibitory feedback to neighboring photoreceptors and bipolar cells.

• This mechanism sharpens spatial contrast in the image by inhibiting adjacent photoreceptor signals, making the borders of light and dark areas more distinct — a phenomenon known as lateral inhibition.

• The effect increases the contrast at edges, which enhances our ability to detect object boundaries clearly.

❌ Why the Other Options Are Incorrect:

• • Bipolar cells
  🔴 These cells relay signals from photoreceptors to ganglion cells but do not mediate lateral inhibition. Their role is more vertical than lateral.

• • Amacrine cells
  🔴 These modulate signals between bipolar and ganglion cells, primarily affecting temporal resolution and contrast over time, not spatial contrast enhancement.

• • Photoreceptors
  🔴 These are the initial light-sensing cells (rods and cones) and do not perform lateral inhibition themselves.

• • Ganglionic cells
  🔴 These receive visual information from bipolar cells and send signals to the brain via the optic nerve, but do not inhibit neighboring ganglion cells in the way required for contrast enhancement.

This statement is true.

• The lingual glands (found beneath the tongue) include anterior lingual glands (of Blandin and Nuhn) and posterior lingual glands (of von Ebner and Weber).

• Most lingual glands, especially those near the tip and underside of the tongue, are mucous-secreting.

• Von Ebner’s glands, near the vallate papillae, are serous, but these are minor in quantity compared to the mucous lingual glands.

❌ Why the Other Options Are Incorrect:

• • Submandibular gland secretions are mainly mucus
  🔴 Incorrect. The submandibular gland produces mixed secretions, but they are predominantly serous, not mucous.

• • The submandibular gland is the largest salivary gland
  🔴 Incorrect. The parotid gland is the largest salivary gland, not the submandibular.

• • 20% of salivary secretions are produced by small salivary glands
  🔴 Incorrect. Minor salivary glands contribute less than 10% of the total saliva volume.

• • Parotid gland secretions are seromucous
  🔴 Incorrect. The parotid gland produces purely serous secretions, rich in amylase and electrolytes.

Muscles of the tongue are not derived from ectoderm.

• Instead, they originate from mesoderm, specifically from occipital somites (paraxial mesoderm).

• These mesodermal cells migrate into the developing tongue and form skeletal muscles.

• The innervation by the hypoglossal nerve (CN XII) reflects their somite origin.

Thus, the statement “Muscles of the tongue are derived from ectoderm” is factually incorrect.

❌ Why the Other Statements Are Correct:

• • “Lateral swellings merge and overlap tuberculum impar to form the anterior 2/3rd of the tongue”
  ✅ Correct. The anterior two-thirds of the tongue arises from first pharyngeal arch structures, including lateral lingual swellings which overgrow the tuberculum impar.

• • “The development of tongue begins in the fourth week of embryonic life”
  ✅ Correct. Tongue development initiates during the 4th week, marked by the appearance of the tuberculum impar.

• • “The tuberculum impar eventually degenerates”
  ✅ Correct. It plays a transient role and is overgrown by the expanding lateral lingual swellings.

• • “Hypobranchial eminence is derived from the 3rd and 4th pharyngeal arch”
  ✅ Correct. The posterior third of the tongue arises from the hypobranchial eminence, which is formed by the 3rd and 4th pharyngeal arches.

The pterygopalatine fossa is a small, inverted pyramid-shaped space located deep in the face, behind the maxilla and below the apex of the orbit. It acts as a key neurovascular crossroad, connecting various regions including the orbit, nasal cavity, pharynx, and oral cavity.

✅ 3rd part of the maxillary artery

• The third (pterygopalatine) part of the maxillary artery is a direct content of the pterygopalatine fossa.

• It enters the fossa through the pterygomaxillary fissure and gives rise to branches that supply the nasal cavity, palate, and pharynx.

• These branches include the infraorbital artery, sphenopalatine artery, and descending palatine artery, among others.

❌ Why the Other Options Are Incorrect:

• • Infraorbital nerve
  → While the infraorbital nerve (a branch of the maxillary nerve, CN V2) passes through the pterygopalatine fossa, it is technically not a primary content but rather a structure that traverses it on its path to the infraorbital canal.

• • Otic ganglion
  → Located in the infratemporal fossa, not the pterygopalatine fossa. It is associated with the mandibular nerve (CN V3), not the maxillary nerve (CN V2).

• • 1st part of the maxillary artery
  → Found in the infratemporal fossa, before the artery enters the pterygomaxillary fissure.

• • 2nd part of the maxillary artery
  → Also lies in the infratemporal fossa, associated with the lateral pterygoid muscle.

The area around the tip of the nose and upper lip is part of the so-called “dangerous area of the face.” This region includes:

• The upper lip

• The lower part of the nose

• The medial angle of the eye

🔄 Why is it dangerous?

The facial vein, which drains this area, has connections with deep venous structures inside the skull:

• The facial vein communicates with the angular vein, which continues into the superior ophthalmic vein.

• The superior ophthalmic vein drains into the cavernous sinus, a venous sinus located at the base of the brain.

Importantly, these veins are valveless, meaning infection from the face can spread retrograde into the intracranial structures, particularly the cavernous sinus — leading to cavernous sinus thrombosis, a life-threatening condition.

💉 Clinical Relevance:

• Squeezing pimples or manipulating acne in this area can force bacteria or inflammatory material into the venous system, with potential intracranial spread.

• Doctors advise against such actions and may prescribe topical or systemic antibiotics or retinoids to safely manage infections here.

❌ Why the Other Options Are Incorrect:

• • None of these → Incorrect because a well-established anatomical reason exists.

• • This area requires more special care than the others → Vague and not anatomically specific.

• • This area is richly vascularized → While true, it’s not the key reason for the clinical concern.

• • This area is more prone to acne → Not particularly more prone; acne can appear in many facial areas.

The superior orbital fissure is a key opening in the sphenoid bone, located between the greater and lesser wings. It connects the middle cranial fossa with the orbit and transmits important nerves and vessels involved in ocular movement and function.

✅ Structures that pass through the superior orbital fissure include:

• Oculomotor nerve (CN III)

• Trochlear nerve (CN IV)

• Abducens nerve (CN VI)

• Lacrimal, frontal, and nasociliary branches of the ophthalmic division of the trigeminal nerve (V1)

• Superior ophthalmic vein

• Sympathetic fibers

❌ What does NOT pass through:

• The optic nerve (CN II) does not pass through the superior orbital fissure.

• It instead passes through the optic canal, which lies medial to the superior orbital fissure, accompanied by the ophthalmic artery.

❌ Why the Other Options Are Incorrect:

• Superior ophthalmic vein → Passes through the superior orbital fissure to drain into the cavernous sinus.

• Oculomotor nerve → Controls most extraocular muscles; enters via the superior orbital fissure.

• Trochlear nerve → Supplies the superior oblique muscle; also enters via the superior orbital fissure.

• Abducens nerve → Controls the lateral rectus muscle; enters through the superior orbital fissure.

Vitamin A exists in several forms:

• Retinol: the alcohol form — the transport and storage form.

• Retinal (retinaldehyde): the aldehyde form — essential for vision.

• Retinoic acid: the carboxylic acid form — acts as a hormone-like growth factor.

• Retinyl esters: storage form in the liver.

• Beta-carotene: a provitamin A carotenoid found in plants, converted into retinal in the body.

🔄 Interconversion:

• Retinol ⇌ Retinal
  This is a reversible reaction, catalyzed by retinol dehydrogenases. It’s easily interconverted depending on physiological needs, especially in the visual cycle and metabolism.

• Retinal → Retinoic acid
  This is an irreversible oxidation step. Once retinal becomes retinoic acid, it cannot go back — retinoic acid is used for gene regulation and growth.

• Retinol ⇌ Retinyl esters
  This is reversible, but it requires enzymatic esterification and hydrolysis, not as readily reversible as retinal ↔ retinol in most tissues.

• Beta-carotene → Retinal
  This conversion is unidirectional and occurs only in the intestinal mucosa and liver — it’s not reversible.

❌ Why the Other Options Are Incorrect:

• Retinoic acid and beta-carotene → No direct interconversion; they are in entirely different metabolic pathways.

• Retinol and retinoic acid → Conversion is irreversible from retinal to retinoic acid.

• Retinal and retinoic acid → Irreversible step; cannot go back to retinal.

• Retinol and retinyl esters → Reversible, but requires enzyme-mediated esterification and is less readily reversible compared to retinal ↔ retinol.

The semicircular canals are three fluid-filled, looped structures located in the inner ear and are part of the vestibular system. They are oriented in three planes (horizontal, anterior, and posterior), which allows them to detect rotational (angular) movements of the head.

• Inside each canal is a structure called the ampulla, which contains crista ampullaris — a sensory organ that detects rotational acceleration.

• The motion of endolymph fluid during head rotation stimulates hair cells, which send signals via the vestibular nerve to the brain to help maintain balance.

❌ Why the Other Options Are Incorrect:

• Cochlea → Involved in hearing, not balance. It converts sound waves into nerve impulses via hair cells in the organ of Corti.

• Cilia → While hair cells have cilia, “cilia” alone is too vague and not a structure that can be “defective” in the context of this specific function unless specified (e.g., stereocilia in vestibular hair cells).

• Eustachian tube → Equalizes air pressure in the middle ear but plays no role in balance.

• Vestibule → Contains the utricle and saccule, which detect linear acceleration and gravity (e.g., going up/down an elevator or forward/backward in a car), not rotational motion.

The orbicularis oculi is the muscle responsible for closing the eyelids. It has three parts, each with distinct functions:

🔸 Orbital part:

• Encircles the bony orbit.

• Responsible for forceful closure of the eyelids (e.g., during bright light exposure, wind, or irritation).

• Under voluntary control (e.g., squeezing the eyes shut tightly).

🔸 Palpebral part:

• Located within the eyelids.

• Responsible for gentle blinking or normal eye closure (like during sleep or blinking).

• Also voluntary and reflexive.

🔸 Lacrimal part:

• Located near the medial canthus of the eye.

• Helps with tear drainage by aiding in movement of tears through the nasolacrimal duct.

🔸 Procerus:

• Not involved in eyelid movement. It’s a small muscle over the bridge of the nose, responsible for wrinkling the skin between the eyebrows.

❌ Why the Other Options Are Incorrect:

• Procerus → Affects the skin between the eyebrows; has no role in eye closure.

• Palpebral part of orbicularis oculi → Causes gentle blinking or eye closure, not forceful.

• Lacrimal part of orbicularis oculi → Assists in tear drainage, not eyelid closure.

• None of them → Incorrect because orbital part clearly does cause forceful closure

The temporalis muscle is a broad, fan-shaped muscle on the lateral side of the skull. It originates from the temporal fossa and inserts onto the coronoid process of the mandible.

🔹 Functionally, its fibers are divided:

• Anterior fibers → Elevate the mandible (close the jaw)

• Middle fibers → Also aid in elevation

• Posterior fibers → Retract the mandible (pull the jaw backward)

This retraction is especially important after protrusion during chewing, helping reset the position of the mandible.

❌ Why the Other Options Are Incorrect:

• Middle fibers of temporalis → Primarily involved in elevation, not retraction.

• Masseter → A powerful elevator of the mandible. The deep fibers may assist slightly in protraction, not retraction.

• Lateral pterygoid → Functions in protrusion and depression of the mandible; it helps open the jaw and move it forward.

• Medial pterygoid → Like the masseter, it assists in elevation and protrusion, not retraction.

• This is the gradual, bilateral, and symmetrical sensorineural hearing loss that occurs with aging.

• Most commonly affects high-frequency sounds first.

• Caused by degeneration of hair cells in the organ of Corti, cochlear nerve fibers, or cochlear blood supply.

• It is non-preventable but can be managed with hearing aids or cochlear implants in severe cases.

❌ Why the Other Options Are Incorrect:

• Otitis media → Inflammation of the middle ear, common in children, and often causes conductive hearing loss, not age-related.

• Vestibular neuronitis → Inflammation of the vestibular nerve, causing vertigo, not hearing loss.

• Otitis sclerosis (more correctly otosclerosis) → Abnormal bone growth around the stapes, causing conductive hearing loss, typically in younger adults, not elderly.

• Labyrinthitis → Inflammation of the labyrinth (inner ear), may cause hearing loss and vertigo, but usually acute and not age-related.

The ductal system in salivary glands (including the lingual glands) consists of several levels of ducts, each with its own histological features:

1. Intralobular ducts

• Includes intercalated and striated ducts

• Lined by simple cuboidal or low columnar epithelium

2. Interlobular ducts

• Located between lobules

• Typically lined by pseudostratified columnar epithelium

3. Excretory (main) ducts

• As ducts approach the oral cavity surface

• Lined by stratified columnar epithelium, sometimes becoming stratified squamous near the opening

❌ Why the Other Options Are Incorrect:

• Stratified columnar, simple cuboidal, pseudostratified columnar → Incorrect order and mismatch of duct levels

• All three are stratified columnar → Histologically inaccurate; duct epithelium varies based on location and function

• Simple cuboidal, simple cuboidal, stratified columnar → Interlobar ducts are not lined by simple cuboidal; should be pseudostratified

• Simple cuboidal, stratified columnar, stratified columnar → Interlobar is pseudostratified, not stratified columnar

• Filiform papillae are the most numerous.

• Found exclusively on the anterior 2/3rd.

• Provide the rough texture to the tongue.

• Important for mechanical functions, not taste.

Damage to the anterior 2/3rd would result in loss of filiform papillae, along with some taste sensation from fungiform papillae.

❌ Why the Other Options Are Incorrect:

• Vallate papillae → Located near sulcus terminalis, at the junction of anterior and posterior tongue. Not within the anterior 2/3rd proper.

• Fungiform papillae → Also in anterior 2/3rd, but not the only one affected; filiform are more numerous and distinctive to this region.

• Lingual papillae → General term including all types; too non-specific.

• Foliate papillae → Located at the posterolateral border, mostly in the posterior 1/3rd or near the margin.

Anatomy of the Posterior Triangle:

The posterior triangle of the neck is bordered by:

• Anteriorly: Posterior border of sternocleidomastoid (SCM)

• Posteriorly: Anterior border of trapezius

• Inferiorly: Middle third of clavicle

It contains:

• Nerves:

  • Spinal accessory nerve (CN XI) – supplies trapezius and SCM

  • Branches of the cervical plexus, including:

    • Great auricular nerve

    • Transverse cervical nerve

    • Supraclavicular nerves

These nerves emerge from behind the midpoint of SCM, often referred to as Erb’s point.

❌ Why the Other Options Are Incorrect (i.e., they are in the posterior triangle):

• Great auricular nerve → Sensory branch of cervical plexus; runs upward across SCM. ✅ Present.

• Spinal part of accessory nerve (CN XI) → Traverses the posterior triangle to innervate trapezius. ✅ Present.

• Transverse cervical nerve → Runs horizontally across SCM. ✅ Present.

• Supraclavicular nerve → Sensory nerves that descend into the supraclavicular region. ✅ Present.

❌ Why Recurrent Laryngeal Nerve Is Not Present:

• It is a branch of the vagus nerve (CN X).

• Courses in the tracheoesophageal groove, deep in the anterior compartment of the neck.

• Innervates all intrinsic muscles of the larynx (except cricothyroid).

• It is not part of the posterior triangle — hence, correct answer.

• Xerophthalmia is a spectrum of ocular manifestations resulting from vitamin A deficiency.

• Vitamin A is essential for:

  • Maintaining healthy epithelial tissues, including the conjunctiva and cornea.

  • Producing mucins that keep the eye surface moist.

• Without adequate vitamin A:

  • Conjunctival and corneal epithelia become keratinized and dry.

  • This leads to xerosis (dryness) of both the conjunctiva and cornea.

  • It may progress to Bitot’s spots, corneal ulceration, and even blindness in severe cases.

❌ Why the Other Options Are Incorrect:

• Poor vision in dim light → Describes nyctalopia (night blindness), an earlier symptom of vitamin A deficiency, but not xerophthalmia itself.

• Thickening of a part of cornea → Vague and nonspecific; not the hallmark of xerophthalmia.

• Poor vision at night → Same as above — refers to night blindness, not xerophthalmia.

• Dryness of cornea along with cloudy appearance → May occur in advanced xerophthalmia, but this option is less precise and doesn’t include the conjunctival involvement, which is central to the condition.

• Presbyopia is an age-related condition in which the lens of the eye loses its elasticity.

• This loss affects the ability of the eye to accommodate, meaning it can no longer easily adjust its focus from distant to near objects.

• Typically becomes noticeable in the mid-40s and progresses with age.

• Individuals often need reading glasses or bifocals as a result.

❌ Why the Other Options Are Incorrect:

• Anosmia → Loss of sense of smell, not related to vision or the lens.

• Aguesia → Loss of taste, unrelated to ocular function.

• Insomnia → Difficulty sleeping, not a sensory or visual issue.

• Presbycusis → Age-related hearing loss, not vision.

  • Though similar in terminology to presbyopia, it affects the cochlea and auditory system.

Types of acini:

• Serous cells → produce a watery, enzyme-rich secretion (e.g., amylase).

• Mucous cells → produce a thick, glycoprotein-rich mucus.

• Mixed acini → contain both serous and mucous cells, sometimes with serous demilunes (serous cells capping mucous acini).

Sublingual Gland Specifics:

• Smallest of the three major salivary glands.

• Histologically, it contains:

  • Predominantly mucous acini

  • Some serous cells in the form of demilunes → so it is technically mixed, but overwhelmingly mucous.

• Therefore, the correct classification is: Predominantly mucous.

❌ Why the Other Options Are Incorrect:

• Predominantly serous → Applies to the parotid gland, not sublingual.

• Seromucous → Describes submandibular gland (mixed, mostly serous).

• Serous → Too restrictive; not accurate for sublingual.

• Mucous → Not entirely wrong, but doesn’t acknowledge the small serous component. “Predominantly mucous” is more precise.

• Photoreceptor cells (rods and cones) are depolarized in the dark because:

  • cGMP binds to cyclic nucleotide-gated (CNG) Na⁺ channels, keeping them open.

  • This allows a continuous inward flow of Na⁺ (“dark current”).

• When light is absorbed by rhodopsin:

  1. Rhodopsin activates transducin (a G-protein).

  2. Transducin activates phosphodiesterase (PDE).

  3. PDE breaks down cGMP to GMP.

  4. Lower cGMP levels cause Na⁺ channels to close.

  5. This leads to hyperpolarization of the photoreceptor cell and reduced neurotransmitter release.

❌ Why the Other Options Are Incorrect:

• Increase in the number of open Na⁺ channels
  → False. Light reduces cGMP, which closes Na⁺ channels, not opens them.

• Increased Ca²⁺ conductance
  → Incorrect. Ca²⁺ enters through the same cGMP-gated channels as Na⁺, so when these close in light, Ca²⁺ influx also decreases.

• Decreased phosphodiesterase activity
  → Opposite of what happens. In light, PDE activity increases, degrading cGMP.

• Decreased transducin activity
  → Wrong. Light activates transducin, which in turn activates PDE.

Pharyngeal Plexus:

• Formed primarily by:

  • Vagus nerve (CN X) – motor fibers

  • Glossopharyngeal nerve (CN IX) – sensory fibers

  • Sympathetic fibers from the superior cervical ganglion

• Motor function: Supplies all muscles of the pharynx except one.

  ✔️ Supplied by pharyngeal plexus:

  • Superior constrictor

  • Middle constrictor

  • Inferior constrictor

  • Palatopharyngeus

  • Salpingopharyngeus

  • Levator veli palatini (also in soft palate)

❌ Exception – Stylopharyngeus:

• NOT supplied by the pharyngeal plexus.

• Instead, it is directly innervated by the glossopharyngeal nerve (CN IX) — and this is unique because:

  • Stylopharyngeus is the only muscle innervated by CN IX.

  • It serves as an important landmark in neuroanatomy.