Physiology of Smell and Taste — MCQs
Sensory fibers from the taste buds in the back of the tongue and soft palate travel along:
Which tongue papillae do not have taste buds?
The roof of the olfactory region is formed by?
A patient was admitted with skull base trauma. The doctor was testing the marked structure in the pharyngeal region. Which of the following nerves was being tested?
Match the following: A) Glossopharyngeal nerve B) Spinal accessory nerve C) Facial nerve D) Mandibular nerve 1) Shrugging of shoulder 2) Touch sensation from the posterior one-third of the tongue 3) Chewing 4) Taste from the anterior two-thirds of the tongue
Among the following trigeminal nerve divisions, which one is involved in orbital apex syndrome?
Impulses generated in the taste buds of the tongue reach the cerebral cortex via the
An absent gag reflex can result from injury to which of the following nerves?
End tracheostomy is performed in patients undergoing surgery for which of the following conditions?
Mild hoarseness with stridor is seen in:
Physiology of Smell and Taste Indian Medical PG Practice Questions and MCQs
Question 1: Sensory fibers from the taste buds in the back of the tongue and soft palate travel along:
- A. Facial nerve
- B. Trigeminal nerve
- C. Vagus nerve
- D. Glossopharyngeal nerve (Correct Answer)
Explanation: ***Glossopharyngeal nerve*** - The **glossopharyngeal nerve** (cranial nerve IX) innervates the **posterior one-third of the tongue** for general sensation and taste, as well as the **palatoglossal arch** and **soft palate** [1]. - This nerve carries taste sensations from taste buds located in these regions to the brainstem [1]. *Trigeminal nerve* - The **trigeminal nerve** (cranial nerve V) is primarily responsible for **general sensation** from the face, oral cavity, and anterior two-thirds of the tongue, but it does **not** carry taste fibers. - It also provides motor innervation to the muscles of mastication. *Facial nerve* - The **facial nerve** (cranial nerve VII) carries taste sensation from the **anterior two-thirds of the tongue** via the chorda tympani, not the posterior tongue or soft palate. - It also controls the muscles of facial expression. *Vagus nerve* - The **vagus nerve** (cranial nerve X) plays a minor role in taste, primarily innervating taste buds in the **epiglottis** and **pharynx**, which are not specified in this question [1]. - Its main functions include parasympathetic innervation to many visceral organs.
Question 2: Which tongue papillae do not have taste buds?
- A. Fungiform
- B. Filiform (Correct Answer)
- C. Circumvallate
- D. Foliate
- E. Conical
Explanation: ***Filiform*** - **Filiform papillae** are the most abundant type of papillae on the tongue and are responsible for the **mechanical action of gripping food**, due to their cone-shaped, abrasive structure of keratinized epithelium. - Unlike other papillae, they **lack taste buds** and thus do not play a role in taste sensation. *Fungiform* - **Fungiform papillae** are mushroom-shaped and are scattered among the filiform papillae, primarily on the tip and sides of the tongue. - These papillae **contain taste buds** on their superior surface and are involved in sensing taste stimuli. *Circumvallate* - **Circumvallate papillae** are large, dome-shaped structures arranged in a V-shape at the back of the tongue. - They are surrounded by a trench into which salivary glands empty, and their walls contain a **large number of taste buds**. *Foliate* - **Foliate papillae** are leaf-like folds located on the lateral margins of the posterior tongue. - They are **well-developed in young children** and contain taste buds, though they tend to degenerate with age. *Conical* - **Conical** is not a recognized classification of tongue papillae. While filiform papillae have a conical (cone-shaped) structure, "conical papillae" is not an anatomical term used to describe a distinct type of papilla.
Question 3: The roof of the olfactory region is formed by?
- A. Nasal bone
- B. Sphenoid
- C. Temporal bone
- D. Cribriform plate of ethmoid (Correct Answer)
Explanation: ***Cribriform plate of ethmoid*** - The **cribriform plate** of the ethmoid bone forms the superior boundary, or roof, of the nasal cavity specifically in the olfactory region [1]. - It is perforated by numerous **olfactory foramina** through which the olfactory nerves pass from the nasal cavity to the olfactory bulb of the brain [2]. *Nasal bone* - The **nasal bones** form part of the bridge of the nose and contribute to the anterior part of the bony framework of the external nose. - They do not form the roof of the olfactory region within the nasal cavity. *Sphenoid* - The **sphenoid bone** is a complex bone at the base of the skull, contributing to the posterior wall of the nasal cavity and parts of the cranial floor. - It does not directly form the roof of the olfactory region. *Temporal bone* - The **temporal bones** are located on the sides and base of the skull, housing structures related to hearing and balance. - They are not involved in forming the roof of the nasal cavity or the olfactory region.
Question 4: A patient was admitted with skull base trauma. The doctor was testing the marked structure in the pharyngeal region. Which of the following nerves was being tested?
- A. Trigeminal nerve
- B. Facial nerve
- C. Glossopharyngeal nerve (Correct Answer)
- D. Vagus
- E. Hypoglossal nerve
Explanation: ***Glossopharyngeal nerve*** - The image shows a probe stimulating the posterior part of the **pharynx**, which elicits the **gag reflex**. - The afferent limb of the **gag reflex** is mediated primarily by the **glossopharyngeal nerve (CN IX)**, which detects sensation from the posterior tongue and pharynx. *Trigeminal nerve* - The **trigeminal nerve (CN V)** primarily mediates sensation from the face, teeth, and anterior two-thirds of the tongue, and motor control of the **muscles of mastication**. - It does not have a primary role in the sensation or reflex of the posterior pharyngeal wall. *Facial nerve* - The **facial nerve (CN VII)** is responsible for the **muscles of facial expression**, taste from the anterior two-thirds of the tongue, and parasympathetic innervation to several glands. - While it contributes to some aspects of swallowing, it is not the main sensory nerve for the gag reflex from the posterior pharynx. *Vagus* - The **vagus nerve (CN X)** provides the efferent limb of the gag reflex, causing pharyngeal muscle contraction. - However, the sensory input from the posterior pharynx (the afferent limb being tested by the probe) is primarily carried by the **glossopharyngeal nerve**. *Hypoglossal nerve* - The **hypoglossal nerve (CN XII)** provides motor innervation to the intrinsic and extrinsic muscles of the tongue. - While it is relevant in skull base trauma, it does not mediate sensation from the pharynx or the gag reflex being tested in the image.
Question 5: Match the following: A) Glossopharyngeal nerve B) Spinal accessory nerve C) Facial nerve D) Mandibular nerve 1) Shrugging of shoulder 2) Touch sensation from the posterior one-third of the tongue 3) Chewing 4) Taste from the anterior two-thirds of the tongue
- A. A-3 , B-1 , C-4 , D-2
- B. A-2 , B-3 , C-4 , D-1
- C. A-4 , B-1 , C-2 , D-3
- D. A-2 , B-1 , C-4 , D-3 (Correct Answer)
Explanation: ***A-2 , B-1 , C-4 , D-3*** - **A) Glossopharyngeal nerve (CN IX)** is responsible for **general sensation and taste from the posterior one-third of the tongue** [1]. (2). - **B) Spinal Accessory nerve (CN XI)** innervates the **sternocleidomastoid** and **trapezius muscles**, which are involved in shrugging the shoulders (1). - **C) Facial nerve (CN VII)** carries **taste sensation from the anterior two-thirds of the tongue** [1] (4) via the chorda tympani. - **D) Mandibular nerve (V3)**, a branch of the trigeminal nerve, innervates the muscles of mastication, enabling **chewing** (3). *A-3 , B-1 , C-4 , D-2* - This option incorrectly associates the **glossopharyngeal nerve** with chewing, which is a function of the mandibular nerve (V3). - It also incorrectly associates the **mandibular nerve** with touch sensation from the posterior one-third of the tongue, which is a function of the glossopharyngeal nerve [1]. *A-2 , B-3 , C-4 , D-1* - This option incorrectly links the **spinal accessory nerve** with chewing; this nerve primarily controls shoulder and neck movements. - It also incorrectly assigns shrugging of the shoulder to the **mandibular nerve** instead of the spinal accessory nerve. *A-4 , B-1 , C-2 , D-3* - This choice incorrectly attributes **taste from the anterior two-thirds of the tongue** to the glossopharyngeal nerve, which supplies the posterior one-third [1]. - It also incorrectly links **touch sensation from the posterior one-third of the tongue** to the facial nerve, which is involved in taste from the anterior two-thirds [1].
Question 6: Among the following trigeminal nerve divisions, which one is involved in orbital apex syndrome?
- A. Olfactory nerve
- B. Mandibular division of trigeminal nerve
- C. Maxillary division of trigeminal nerve
- D. Ophthalmic division of trigeminal nerve (Correct Answer)
Explanation: ***Ophthalmic division of trigeminal nerve*** - Orbital apex syndrome involves deficits of nerves passing through the **superior orbital fissure** and **optic canal**, which includes the ophthalmic division of the trigeminal nerve (CN V1). - Involvement of CN V1 leads to **sensory loss** in the forehead, upper eyelid, and side of the nose. *Olfactory nerve* - The **olfactory nerve (CN I)** is responsible for the sense of smell and does not pass through the orbital apex. - Its involvement would manifest as **anosmia**, which is not a characteristic feature of orbital apex syndrome. *Maxillary division of trigeminal nerve* - The **maxillary division (CN V2)** exits the skull through the **foramen rotundum** and innervates the midface. - It is generally **not involved** in orbital apex syndrome, as its anatomical course is distinct from the structures within the orbital apex. *Mandibular division of trigeminal nerve* - The **mandibular division (CN V3)** exits the skull through the **foramen ovale** and innervates the lower face and muscles of mastication. - Its involvement is **not associated** with orbital apex syndrome, as it is anatomically distant from the orbital apex.
Question 7: Impulses generated in the taste buds of the tongue reach the cerebral cortex via the
- A. Thalamus (Correct Answer)
- B. Dorsal roots of the first cervical spinal nerve
- C. Hypoglossal nerve
- D. Lingual nerve
Explanation: ***Thalamus*** - The **thalamus** acts as a crucial relay station for almost all sensory information, including taste, before it reaches the **cerebral cortex** for conscious perception. - Taste signals from the cranial nerves (facial, glossopharyngeal, vagus) travel to the **nucleus of the solitary tract** in the brainstem, then to the **ventral posteromedial (VPM) nucleus of the thalamus**, and finally to the **gustatory cortex**. *Dorsal roots of the first cervical spinal nerve* - The dorsal roots of cervical spinal nerves are involved in transmitting **somatosensory information** (touch, pain, temperature, proprioception) from the neck and head region, not taste. - These nerves carry signals from the spinal cord to the brain, whereas taste pathways originate from cranial nerves in the head. *Hypoglossal nerve* - The **hypoglossal nerve (CN XII)** is primarily a **motor nerve** responsible for controlling the muscles of the tongue, essential for speech and swallowing. - It has no direct role in transmitting taste sensations to the cerebral cortex. *Lingual nerve* - The **lingual nerve** is a branch of the **trigeminal nerve (CN V)** and carries **general sensation** (touch, pain, temperature) from the anterior two-thirds of the tongue. - While it runs with the **chorda tympani** (a branch of the facial nerve that carries taste), the lingual nerve itself does not transmit taste signals to the brain.
Question 8: An absent gag reflex can result from injury to which of the following nerves?
- A. Cranial Nerve VII (Facial) and Cranial Nerve V (Trigeminal)
- B. Cranial Nerve V (Trigeminal) and Cranial Nerve IX (Glossopharyngeal)
- C. Cranial Nerve IX (Glossopharyngeal) and Cranial Nerve X (Vagus) (Correct Answer)
- D. Cranial Nerve X (Vagus) and Cranial Nerve VII (Facial)
- E. Cranial Nerve XII (Hypoglossal) and Cranial Nerve X (Vagus)
Explanation: ***Cranial Nerve IX (Glossopharyngeal) and Cranial Nerve X (Vagus)*** - The **gag reflex** is a protective reflex that involves both sensory and motor components. - The **glossopharyngeal nerve (CN IX)** is responsible for the **afferent (sensory)** limb, detecting stimulation of the posterior pharynx. The **vagus nerve (CN X)** is responsible for the **efferent (motor)** limb, causing contraction of pharyngeal muscles. *Cranial Nerve VII (Facial) and Cranial Nerve V (Trigeminal)* - The **facial nerve (CN VII)** primarily controls muscles of **facial expression** and taste from the anterior two-thirds of the tongue. - The **trigeminal nerve (CN V)** mediates sensation to the face, mastication, and corneal reflex, but not the gag reflex. *Cranial Nerve V (Trigeminal) and Cranial Nerve IX (Glossopharyngeal)* - While **CN IX** is indeed involved in the **sensory component of the gag reflex**, the **trigeminal nerve (CN V)** is not directly involved in either the sensory or motor pathway of the gag reflex. - The trigeminal nerve's primary roles are facial sensation and mastication. *Cranial Nerve X (Vagus) and Cranial Nerve VII (Facial)* - The **vagus nerve (CN X)** is crucial for the **motor component** of the gag reflex. - However, the **facial nerve (CN VII)** is not involved in the gag reflex; its functions relate to facial movement and taste. *Cranial Nerve XII (Hypoglossal) and Cranial Nerve X (Vagus)* - While the **vagus nerve (CN X)** does provide the **motor component** of the gag reflex, the **hypoglossal nerve (CN XII)** is not involved in this reflex. - The **hypoglossal nerve (CN XII)** controls intrinsic and extrinsic muscles of the tongue, important for tongue movement and speech, but not for the pharyngeal muscle contraction required for the gag reflex.
Question 9: End tracheostomy is performed in patients undergoing surgery for which of the following conditions?
- A. Laryngectomy (Correct Answer)
- B. Laryngofissure surgery
- C. Oropharyngeal growth
- D. Obstructive sleep apnea with stridor
Explanation: **Explanation:** **1. Why Laryngectomy is Correct:** An **End Tracheostomy** (also known as a permanent tracheostomy) is performed when the entire larynx is surgically removed (Total Laryngectomy). In this procedure, the distal tracheal stump is brought out to the skin of the neck and sutured to the margins of the skin incision. This creates a permanent stoma where the airway is completely separated from the pharynx and esophagus. Since the larynx (the connection between the upper and lower airway) is gone, the patient breathes exclusively through this stoma for the rest of their life. **2. Why Other Options are Incorrect:** * **Laryngofissure surgery:** This is a thyrotomy where the larynx is opened to access the vocal cords. It usually requires a **temporary/prolonged tracheostomy** to maintain the airway during postoperative edema, but the larynx remains intact. * **Oropharyngeal growth:** These patients may require a **temporary tracheostomy** to bypass an upper airway obstruction or for anesthesia access, but the tracheal opening is not permanent. * **Obstructive Sleep Apnea (OSA) with stridor:** Tracheostomy is a treatment of last resort for OSA. It is a **temporary/permanent-in-situ** tracheostomy (the larynx is preserved), not an "End" tracheostomy. **3. Clinical Pearls for NEET-PG:** * **End vs. Side Tracheostomy:** In an "End" tracheostomy, the trachea is severed and the end is brought to the skin. In a standard "Side" tracheostomy, an opening is made in the anterior wall of the trachea while the rest of the airway remains in continuity. * **Post-Laryngectomy:** Because the airway and food passage are separated, these patients **cannot aspirate** through the stoma, but they also cannot perform a Valsalva maneuver effectively. * **High-Yield Fact:** The most common indication for Total Laryngectomy (and thus End Tracheostomy) is advanced (T3/T4) Squamous Cell Carcinoma of the larynx.
Question 10: Mild hoarseness with stridor is seen in:
- A. Unilateral abductor palsy
- B. Bilateral abductor palsy (Correct Answer)
- C. Laryngomalacia
- D. Tracheal stenosis
Explanation: ### Explanation The clinical presentation of **Bilateral Abductor Palsy** (usually due to injury to both recurrent laryngeal nerves) is characterized by the vocal cords being fixed in the **median or paramedian position**. 1. **Why the correct answer is right:** In bilateral abductor palsy, the vocal cords cannot move away from the midline. Because the cords are positioned very close to each other, the **glottic airway is severely compromised**, leading to inspiratory **stridor**. However, because the cords are in a near-normal position for phonation (close together), the **voice remains remarkably good or only mildly hoarse**. This "good voice but poor airway" paradox is a classic diagnostic hallmark. 2. **Why the incorrect options are wrong:** * **Unilateral abductor palsy:** Usually presents with mild hoarseness or breathiness, but the unaffected cord compensates. Stridor is typically absent because the airway remains adequate. * **Laryngomalacia:** The most common cause of congenital stridor. It presents with an inspiratory "crowing" sound that improves when the infant is prone. Hoarseness is not a feature as the vocal cords function normally. * **Tracheal stenosis:** Presents with biphasic stridor and dyspnea. Since the pathology is below the level of the larynx, the voice is typically normal unless there is associated glottic involvement. ### Clinical Pearls for NEET-PG: * **Most common cause** of bilateral abductor palsy: Thyroid surgery (injury to bilateral Recurrent Laryngeal Nerves). * **Management:** Emergency tracheostomy is often required to secure the airway, followed by permanent procedures like lateralization of the cord (Woodman’s operation) or posterior cordotomy. * **Semon’s Law:** States that in progressive lesions of the recurrent laryngeal nerve, the abductor fibers are affected before the adductor fibers.
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