Auditory System — MCQs
A 70-year-old male patient presents with high-frequency hearing loss. It was noted that the basilar membrane was affected. Which of the following structures lies near the affected structure?
A 45-year-old gentleman reports decreased hearing in the right ear for the last two years. On testing with a 512 Hz tuning fork, the Rinne's test without masking is negative on the right ear and positive on the left ear. With the Weber's test, the tone is perceived as louder in the left ear. Patient most likely has -
Where is the organ of Corti located within the cochlea?
What is the primary mechanism by which a cholesteatoma leads to hearing loss?
Auditory pathway is mediated by:
Which of the following tests assesses resistance in the middle ear?
Stimulation of posterior semicircular canal produces -
Which of the following will occur in a girl who suddenly stops spinning after several seconds of spinning to the left?
Which of the following structures is responsible for detecting rotational acceleration?
Motor protein in organ of Corti -
Auditory System Indian Medical PG Practice Questions and MCQs
Question 1: A 70-year-old male patient presents with high-frequency hearing loss. It was noted that the basilar membrane was affected. Which of the following structures lies near the affected structure?
- A. Stria vascularis (Correct Answer)
- B. Modiolus
- C. Helicotrema
- D. Oval window
Explanation: ***Stria vascularis*** - The **stria vascularis** is a highly vascularized epithelial layer located on the lateral wall of the **scala media**, directly adjacent to the **basilar membrane**. - It is crucial for maintaining the high potassium concentration in the **endolymph** which is essential for the function of hair cells in the **organ of Corti** and thus hearing [2]. *Modiolus* - The **modiolus** is the central, conical bony pillar of the cochlea, around which the cochlear duct spirals. - While it houses the **spiral ganglion** and auditory nerve fibers, it is structurally distinct from and not immediately adjacent to the basilar membrane. *Helicotrema* - The **helicotrema** is the small opening at the apex of the cochlea where the **scala vestibuli** and **scala tympani** communicate [1]. - It is located at the very end of the cochlea, far from the main vibratory portion of the basilar membrane responsible for high-frequency sounds. *Oval window* - The **oval window** is the opening in the bony labyrinth into which the **stapes** footplate fits, transmitting vibrations from the middle ear to the inner ear [2]. - While critical for hearing, it is located at the base of the cochlea and is not an immediate neighbor of the basilar membrane in the context of its function in sound transduction within the cochlear duct.
Question 2: A 45-year-old gentleman reports decreased hearing in the right ear for the last two years. On testing with a 512 Hz tuning fork, the Rinne's test without masking is negative on the right ear and positive on the left ear. With the Weber's test, the tone is perceived as louder in the left ear. Patient most likely has -
- A. Right conductive hearing loss (Correct Answer)
- B. Right sensorineural hearing loss
- C. Left sensorineural hearing loss
- D. Left conductive hearing loss
Explanation: ***Right conductive hearing loss*** - A **negative Rinne's test** (bone conduction louder than air conduction) in the right ear indicates **conductive hearing loss** on that side - However, in true conductive hearing loss, **Weber should lateralize to the affected (right) ear** due to the occlusion effect, not to the left ear - The Weber lateralizing to the left ear with a negative Rinne on the right suggests this may be a **false negative Rinne** due to lack of masking, where sound crosses over to the better left ear - This combination is atypical for pure conductive loss and requires repeat testing with proper masking *Right sensorineural hearing loss* - In **sensorineural hearing loss**, Rinne's test should be **positive** (air conduction > bone conduction) on both sides, though both may be reduced on the affected side - **Weber lateralizes to the unaffected (left) ear**, which matches the given finding - The **negative Rinne on the right ear without masking** is likely a **false negative** due to sound crossing over to the better left ear during bone conduction testing - This is the **most consistent interpretation** when Rinne testing is done without masking, but traditionally the question frame suggests conductive loss *Left sensorineural hearing loss* - Would show **positive Rinne bilaterally** with reduced hearing on the left - **Weber would lateralize to the right ear** (the better ear), contradicting the given findings - This option is clearly inconsistent with the clinical findings *Left conductive hearing loss* - Would show **negative Rinne on the left** and positive on the right - Weber would lateralize to the left ear (affected side in conductive loss) - The **Rinne findings contradict this**, as the right ear shows negative Rinne, not the left
Question 3: Where is the organ of Corti located within the cochlea?
- A. Basilar membrane (Correct Answer)
- B. Utricle
- C. Saccule
- D. Reissner's membrane
Explanation: ***Basilar membrane*** - The **organ of Corti** is the sensory organ of hearing, and it sits directly on the **basilar membrane** within the cochlea [2]. - The vibratory movements of the basilar membrane, induced by sound waves, stimulate the **hair cells** of the organ of Corti [2], [4]. - This membrane separates the scala media from the scala tympani and is critical for the transduction of mechanical vibrations into neural signals. *Utricle* - The **utricle** is part of the **vestibular system** and is located in the **membranous labyrinth** of the inner ear [1], [3]. - Its primary function is to detect **linear acceleration** and **head tilts** in the horizontal plane, contributing to balance, not hearing [1], [3]. *Saccule* - The **saccule** is also a component of the **vestibular system**, similar to the utricle [1], [3]. - It specifically detects **linear acceleration** and **head tilts** in the vertical plane, contributing to balance rather than auditory perception [3]. *Reissner's membrane* - **Reissner's membrane** (vestibular membrane) separates the **scala vestibuli** from the **scala media** in the cochlea [2]. - While it is part of the cochlear structure, the organ of Corti is located on the basilar membrane, not Reissner's membrane.
Question 4: What is the primary mechanism by which a cholesteatoma leads to hearing loss?
- A. Auditory nerve compression
- B. Ossicle erosion causing conductive loss (Correct Answer)
- C. Recurrent middle ear infections
- D. Direct cochlear damage
Explanation: ***Ossicle erosion causing conductive loss*** - Cholesteatomas are destructive, expanding growths of **squamous epithelium** that can erode the surrounding bone. - This erosion commonly affects the **ossicles (malleus, incus, stapes)**, leading to their destruction and disruption of sound conduction, resulting in a **conductive hearing loss**. - This is the **primary mechanism** by which cholesteatomas cause hearing loss. *Auditory nerve compression* - While a cholesteatoma can expand significantly, it does not typically cause hearing loss through direct **compression of the auditory nerve**. - **Auditory nerve damage** is more characteristic of **sensorineural hearing loss** caused by inner ear pathologies or tumors like acoustic neuromas. *Recurrent middle ear infections* - While cholesteatomas often lead to **recurrent middle ear infections** (otitis media), these infections themselves are not the primary mechanism of hearing loss in cholesteatoma. - The infections are a complication, and the **erosive nature** of the cholesteatoma itself is what directly damages the sound-transmitting structures. *Direct cochlear damage* - Cholesteatomas are primarily associated with **conductive hearing loss** due to ossicular chain damage, not direct cochlear damage. - While in very advanced cases, they can indirectly affect the cochlea through **inflammatory mediators** or create a **labyrinthine fistula**, this is not the primary mechanism for the typical hearing loss presentation. - Direct cochlear damage would result in **sensorineural hearing loss**, which is not the characteristic presentation of cholesteatoma.
Question 5: Auditory pathway is mediated by:
- A. Medial geniculate body (Correct Answer)
- B. Lateral lemniscus
- C. Medial lemniscus
- D. Lateral geniculate body
Explanation: ***Medial geniculate body*** - The **medial geniculate body (MGB)** is a thalamic relay nucleus that serves as the final subcortical processing station for **auditory information** before it reaches the cerebral cortex [1], [3]. - It receives input from the **inferior colliculus** and projects to the **primary auditory cortex** (Heschl's gyrus) in the temporal lobe [1]. *Lateral lemniscus* - The **lateral lemniscus** is an ascending tract of the **auditory pathway** in the brainstem, carrying auditory information from the cochlear nuclei to the inferior colliculus [1]. - While it's part of the auditory pathway, it is a **fiber tract** and not the primary mediating structure that refers to the main relay nucleus in the thalamus. *Medial lemniscus* - The **medial lemniscus** is an ascending sensory pathway in the brainstem that primarily transmits **fine touch, vibration, proprioception, and two-point discrimination** from the fasciculus gracilis and cuneatus to the thalamus. - It is part of the **somatosensory system** and is not involved in auditory processing. *Lateral geniculate body* - The **lateral geniculate body (LGB)** is a thalamic relay nucleus for the **visual pathway** [2]. - It receives input from the **retina** via the optic tract and projects to the **primary visual cortex** (Brodmann area 17) in the occipital lobe.
Question 6: Which of the following tests assesses resistance in the middle ear?
- A. Pure tone audiometry
- B. Caloric test
- C. BERA (Brainstem evoked response audiometry)
- D. Impedance audiometry (Correct Answer)
Explanation: ***Impedance audiometry*** - This test measures the **impedance** (resistance) of the middle ear and the mobility of the **tympanic membrane** and **ossicular chain** - It also assesses the **acoustic reflex**, which is the contraction of the middle ear muscles in response to loud sound, providing information about the middle ear and auditory pathways *Pure tone audiometry* - This test measures an individual's **hearing sensitivity** across different frequencies - It assesses the **thresholds of hearing** for air conduction and bone conduction, but does not directly measure middle ear resistance *Caloric test* - The caloric test evaluates the function of the **vestibular system** and the **horizontal semicircular canal** - It involves introducing warm or cold water/air into the ear canal to induce nystagmus, but does not assess middle ear resistance *BERA (Brainstem evoked response audiometry)* - BERA measures the **electrical activity** in the auditory pathway from the cochlea to the brainstem in response to auditory stimuli - It is used to assess hearing in infants, differentiate between **sensory** and **neural hearing loss**, and detect neurological disorders, but does not measure middle ear impedance
Question 7: Stimulation of posterior semicircular canal produces -
- A. Rotatory nystagmus
- B. Vertical nystagmus (Correct Answer)
- C. Horizontal nystagmus
- D. None of the options
Explanation: ***Vertical nystagmus*** - Stimulation of the **posterior semicircular canal** produces **vertical-torsional nystagmus** with the vertical component being predominant. - The posterior canal is oriented at approximately 45° to the sagittal plane and detects angular acceleration in the RALP plane (Right Anterior-Left Posterior). - Stimulation typically causes **downbeat nystagmus** (fast phase downward) with a torsional component, activating the **superior oblique** and **inferior rectus muscles** on the ipsilateral side. - The vertical component is the primary clinical feature observed. *Rotatory nystagmus* - While posterior canal stimulation does produce a **torsional (rotatory) component**, it is not purely rotatory. - The torsional component accompanies the vertical nystagmus but is **secondary to the vertical component**. - Pure rotatory nystagmus is rare and would suggest involvement of multiple canals or central pathology. *Horizontal nystagmus* - **Horizontal nystagmus** is specifically produced by stimulation of the **horizontal (lateral) semicircular canal**. - It indicates activation of the horizontal canal system, which lies in a different plane than the posterior canal. - The medial and lateral rectus muscles are primarily involved in horizontal nystagmus. *None of the options* - This option is incorrect because **vertical nystagmus with torsional component** is the characteristic and well-documented response to posterior semicircular canal stimulation. - Each semicircular canal produces a specific directional nystagmus corresponding to its anatomical plane of orientation.
Question 8: Which of the following will occur in a girl who suddenly stops spinning after several seconds of spinning to the left?
- A. Her eyes will move slowly to the right (Correct Answer)
- B. The hair cells in the right semicircular canal will depolarize
- C. When asked to point to a target, the girl will point to the right of the target
- D. The cupula in the right semicircular canal will move away from the utricle
Explanation: ***Her eyes will move slowly to the right*** - After spinning to the left and suddenly stopping, **post-rotatory nystagmus** occurs due to continued endolymph movement. - The endolymph continues to move to the LEFT due to **inertia**, creating a sensation of rotating to the **RIGHT**. - This produces **nystagmus** with the **slow phase to the right** (direction of perceived rotation) and fast corrective phase to the left. - The **vestibulo-ocular reflex** generates this nystagmus as the brain interprets the continued endolymph movement as actual rotation. *The hair cells in the right semicircular canal will depolarize* - This is incorrect. Upon stopping a left spin, the endolymph continues moving LEFT due to inertia. - In the **right horizontal canal**, this creates **ampullary-petal flow** (toward the ampulla), which causes **hyperpolarization**, not depolarization. - During the actual left spin, it was the **left canal** that was depolarized (ampullary-fugal flow in horizontal canals causes excitation). *When asked to point to a target, the girl will point to the right of the target* - After stopping from spinning left, the sensation is of spinning to the RIGHT, causing a **past-pointing phenomenon**. - This perceived rightward rotation causes the person to point to the **LEFT** of the target, not the right. - The brain compensates for the perceived motion in the wrong direction. *The cupula in the right semicircular canal will move away from the utricle* - Upon stopping, the endolymph in the right canal continues moving to the LEFT (original spin direction) due to inertia. - This deflects the cupula **toward the utricle** (ampullary-petal), not away from it. - Ampullary-petal deflection in horizontal canals causes hyperpolarization of hair cells.
Question 9: Which of the following structures is responsible for detecting rotational acceleration?
- A. Semicircular canals (Correct Answer)
- B. Cochlea
- C. Fovea centralis
- D. Saccule
Explanation: ***Semicircular canals*** - The **semicircular canals** are part of the inner ear and are specifically designed to detect **rotational acceleration** of the head. - They contain a fluid called **endolymph** and hair cells within the **ampulla** that are stimulated by the movement of this fluid during rotation. *Cochlea* - The **cochlea** is primarily responsible for processing **auditory (sound) information**, not head movement. - It contains the **organ of Corti**, which converts sound vibrations into electrical signals. *Fovea centralis* - The **fovea centralis** is a part of the **retina** responsible for sharp, central vision and **high visual acuity**. - It plays no role in detecting head acceleration or balance. *Saccule* - The **saccule** is part of the **otolith organs** (along with the utricle) and detects **linear acceleration** and the pull of gravity in the vertical plane. - It is involved in sensing up-and-down movements and static head tilt, not rotational acceleration.
Question 10: Motor protein in organ of Corti -
- A. Kinesin
- B. Myosin (Correct Answer)
- C. Albumin
- D. Dynein
Explanation: **Myosin** - **Myosin I** and **Myosin VIIa** are key motor proteins found in the **hair cells** of the organ of Corti. - They play crucial roles in **stereocilia bundle stiffness** and the **adaptation** process of mechanotransduction, which is essential for hearing. *Kinesin* - **Kinesin** is primarily involved in **anterograde axonal transport** of vesicles and organelles along microtubules in neurons. - It is not the primary motor protein responsible for the unique mechanical properties of hair cells in the organ of Corti. *Albumin* - **Albumin** is a major **plasma protein** primarily involved in maintaining **osmotic pressure** and transporting various substances in the bloodstream. - It is not a motor protein and does not have a direct role in the mechanical function of the organ of Corti. *Dynein* - **Dynein** is a microtubule-associated motor protein responsible for **retrograde axonal transport** and the movement of cilia and flagella. - While important for intracellular transport in many cells, it is not the primary motor protein driving the mechanical processes within the hair cells of the organ of Corti.
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