Sensory Systems Practice Questions

Q: Destruction of the right labyrinth causes nystagmus to:

Left side. ***Left side*** - Destruction of the right labyrinth leads to a **reduction in tonic firing** from the right vestibular nerve. This creates an **imbalance** where the left labyrinth's signals are now relatively stronger. - The brain interprets this imbalance as if the head is turning to the left, causing **vestibulo-ocular reflex** to induce nystagmus with its **fast phase** to the left (away from the side of the lesion and towards the relatively intact labyrinth). *Rotatory nystagmus* - While nystagmus can have a rotatory component, the predominant direction of acceleration or slow phase will be either horizontal or vertical and indicates the **direction of the lesion** or excitation. - Describing nystagmus purely as "rotatory" does not specify the **direction of the fast component** in relation to the lesion. *No nystagmus* - **Unilateral destruction** of a labyrinth creates an acute imbalance in vestibular input, which **always results in nystagmus**. - Nystagmus is a key clinical sign of acute **vestibular dysfunction**, as the brain perceives an ongoing head movement that isn't occurring. *Right side* - A fast phase directed towards the right would imply either **excitation** of the right labyrinth or **destruction** of the left labyrinth. - In this case, destruction of the right labyrinth leads to nystagmus with its **fast phase away from the lesion**, meaning to the left.

Q: Which substance is most likely to increase in the rods of the retina when the light is turned on?

Metarhodopsin II. ***Metarhodopsin II*** - When **light strikes rhodopsin**, it undergoes a conformational change, forming **metarhodopsin II**, which is the active form that initiates the phototransduction cascade. - **Metarhodopsin II** activates a **G-protein (transducin)**, leading to a decrease in cGMP and subsequent rod hyperpolarization. *Cyclic guanosine monophosphate (cGMP)* - **Light activation** of rhodopsin triggers a cascade that **decreases cGMP concentration** in the rods, leading to closing of cGMP-gated sodium channels. - In the **dark**, cGMP levels are high, keeping the sodium channels open and the rod depolarized. *Cyclic adenosine monophosphate (cAMP)* - **cAMP** is a significant second messenger in many cellular processes but is **not directly involved in the primary phototransduction pathway** in rods. - Its levels do not acutely increase in response to light in the same manner as molecules in the phototransduction cascade. *Rhodopsin* - **Rhodopsin** is the **light-sensitive pigment** located in the rod outer segment membranes. - When light is turned on, rhodopsin is **converted** into its active form, metarhodopsin II, meaning the amount of intact rhodopsin itself will decrease, not increase.

Q: Colour vision is with the help of:

Cones. ***Cones*** - **Cones** are photoreceptor cells in the retina responsible for **color vision** and high spatial acuity in bright light conditions. - There are three types of cones, each sensitive to different wavelengths of light (red, green, and blue). *Cortex* - The **visual cortex** in the brain processes visual information, including color, but it relies on input from the photoreceptors. - The cortex itself does not initially detect color; it interprets signals sent from the retina. *Optic disc* - The **optic disc** is the point where the optic nerve leaves the eye, and it contains no photoreceptor cells. - This area is therefore known as the "blind spot" and cannot detect light or color. *Rods* - **Rods** are photoreceptor cells primarily responsible for **scotopic (low-light) vision** and peripheral vision. - They are highly sensitive to light but do not detect color, only shades of gray.

Q: The parvocellular pathway, from the lateral geniculate nucleus to the visual cortex, carries signals for the detection of

Color vision, shape and fine details.. ***Color vision, shape and fine details.*** - The **parvocellular pathway** is specialized for processing **detailed visual information**, including **color vision**, **fine spatial resolution** (shape), and **texture**. - Its neurons have **small receptive fields** and a sustained response, making them ideal for precise analysis of stationary objects and their features. *Luminance contrast* - While the parvocellular pathway contributes to luminance contrast, it is not its primary or most distinguishing feature compared to its role in color and fine detail. - Both parvocellular and **magnocellular pathways** process luminance contrast, but **magnocellular** is more involved in rapid changes. *Temporal frequency.* - **Temporal frequency** (detecting changes over time, like motion or flicker) is primarily processed by the **magnocellular pathway**. - The **parvocellular pathway** has a relatively **slow, sustained response** and is less adept at detecting rapid temporal changes. *Movement, depth and flicker.* - **Movement**, **depth perception**, and **flicker detection** are predominantly functions of the **magnocellular pathway**. - This pathway has large receptive fields and responds transiently to stimuli, making it optimized for detecting motion and rapid changes in the visual scene.

Q: At what intensity does the sound of a normal voice reach the ear from a distance of 1 meter?

60 dB. **60 dB** - A **normal conversational voice** at a distance of about 1 meter typically has an intensity around **60 decibels (dB)**. - This level is considered moderate and easily audible without discomfort in a quiet environment. *80 dB* - An intensity of **80 dB** is significantly louder, comparable to a **garbage disposal** or a **loud alarm clock**. - While audible, it would generally be perceived as quite loud for a normal conversational voice. *20 dB* - An intensity of **20 dB** is very quiet, equivalent to a **whisper** or the **rustling of leaves**. - It would be too low for a normal conversational voice to be heard clearly at 1 meter. *40 dB* - An intensity of **40 dB** is softer than typical conversation, similar to the sound of a **quiet office** or **refrigerator hum**. - While audible, it would likely be considered a **soft voice** rather than a normal conversational level.

Q: Red cones in fovea have peak sensitivity at which wavelength?

560nm. ***560nm*** - Red cones (also known as **L-cones** for long wavelength) are most sensitive to light with a wavelength around **560 nanometers (nm)**, which corresponds to the reddish-yellow part of the visible spectrum. - This peak sensitivity allows them to detect red and distinguish it from other colors when combined with signals from other cone types. *520nm* - This wavelength represents the approximate peak sensitivity for **green cones** (M-cones, for medium wavelength), which are responsible for detecting green hues. - While red cones have some sensitivity at 520nm, it is not their peak or primary wavelength of maximal response. *460nm* - This wavelength is close to the peak sensitivity of **blue cones** (S-cones, for short wavelength), which are responsible for detecting blue and violet light. - Red cones have very limited or no significant sensitivity at such short wavelengths. *480nm* - This wavelength falls in the blue-green region of the spectrum, where both blue and green cones show significant sensitivity. - It is not the peak sensitivity for red cones, which are predominantly responsive to longer wavelengths.

Q: Sensory organ for responding to texture is:

Meissner corpuscles. ***Meissner corpuscles*** - These are **mechanoreceptors** located in the **dermal papillae** of glabrous (hairless) skin, particularly abundant in fingertips, palms, and soles. - They are responsible for detecting **light touch**, discrimination of two points, and are crucial for sensing **texture** and fine tactile discrimination. *Pacinian corpuscles* - These are large **mechanoreceptors** located deeper in the dermis and subcutaneous tissue. - They detect **vibration** and **pressure**, rather than texture or sustained light touch. *Ruffini corpuscles* - These are **mechanoreceptors** found in the deep layers of the dermis and joint capsules. - They are primarily responsible for detecting **skin stretch** and **sustained pressure**. *Merkel cells* - These are **mechanoreceptors** located in the **basal layer of the epidermis**. - They are involved in sensing **sustained pressure** and **light touch**, contributing to static tactile discrimination, but Meissner corpuscles are more specialized for texture.

Q: Endolymph in the ear is equivalent to

ICF. ***ICF*** - **Endolymph** is characterized by a **high potassium concentration** and a **low sodium concentration**, mirroring the ionic composition of intracellular fluid (**ICF**). - This unique ionic composition is crucial for the generation of the **endocochlear potential**, which drives the transduction of sound and head movements into electrical signals. *CSF* - **Cerebrospinal fluid (CSF)** has a relatively **high sodium concentration** and a **low potassium concentration**, more closely resembling extracellular fluid. - Its primary role is to cushion the brain and spinal cord, and it is found in the subarachnoid space and ventricles, not the inner ear. *Lymph* - **Lymph** is essentially filtered blood plasma and thus has an ionic composition similar to **extracellular fluid**, with **high sodium** and **low potassium**. - It circulates throughout the lymphatic system and plays a role in immunity and fluid balance, distinctly different from endolymph's function. *Blood* - **Blood plasma** also has a **high sodium concentration** and a **low potassium concentration**, typical of extracellular fluid. - Its primary functions include transport of oxygen, nutrients, hormones, and waste products, and it does not directly come into contact with the structures of the inner ear.

Q: Weber-Fechner law is related with:

Stimulus discrimination. ***Stimulus discrimination*** - The **Weber-Fechner Law** describes the relationship between the **physical magnitude of a stimulus** and the **perceived intensity** of that stimulus. - It posits that the **just noticeable difference (JND)** between two stimuli is a constant proportion of the original stimulus, which is critical for **sensory discrimination**. *Amplitude* - While amplitude is a characteristic of some stimuli (e.g., sound waves), the Weber-Fechner Law is not exclusively about amplitude. - It refers to the **overall intensity** of a stimulus in relation to its perception, not just its amplitude. *Surface area* - **Surface area** might be relevant in terms of the body area stimulated (e.g., touch), but it is not directly related to the core principle of proportional change in stimulus intensity as described by the Weber-Fechner Law. - The law focuses on the **relative change in intensity** needed to perceive a difference, regardless of the absolute surface area involved. *Number of sensory fibre involvement* - The **number of sensory fibers** involved is related to the **encoding and transmission of sensory information**, but the Weber-Fechner Law describes the **psychophysical relationship** between the physical stimulus and its perception. - It's a **higher-level psychophysical law**, not a physiological description of nerve fiber recruitment.

Q: Exposure to 90 dB and 4000 Hz noise for a short duration results in -

Temporary hearing loss. ***Temporary hearing loss*** - Exposure to **90 dB** for about 8 hours can lead to noise-induced hearing loss, but prolonged exposure above 85 dB for several hours is usually required for **permanent damage**. - Moderate noise exposure (below the threshold for permanent damage) typically causes a **temporary threshold shift** or **auditory fatigue**, from which the ear can recover. *Auditory fatigue* - While auditory fatigue is a component of noise exposure, the intensity and frequency mentioned (**90 dB, 4000 Hz**) are more specifically associated with a measurable **temporary hearing loss** rather than just fatigue. - Auditory fatigue is generally a precursor to temporary hearing loss, but the term **temporary hearing loss** better encapsulates the measurable shift in hearing threshold. *Permanent hearing loss* - **Permanent hearing loss** typically results from **chronic exposure to high-intensity noise** (e.g., >85 dB for many years) or very intense, short bursts of sound. - A single exposure to **90 dB** at 4000 Hz for a relatively short duration (implied if not specified as chronic) is more likely to cause temporary rather than permanent damage. *Rupture of tympanic membrane* - **Tympanic membrane rupture** usually requires a **sudden, very high-intensity sound pressure** (e.g., an explosion or blast injury), typically in the range of **160-190 dB** or higher. - **90 dB** is below the threshold for causing direct mechanical damage like a tympanic membrane rupture, although it is sufficient to cause sensorineural hearing damage.

Question 1

Destruction of the right labyrinth causes nystagmus to:

Accepted Answer

Left side

Answer

Rotatory nystagmus

Answer

No nystagmus

Answer

Right side

Question 2

Which substance is most likely to increase in the rods of the retina when the light is turned on?

Accepted Answer

Metarhodopsin II

Answer

Cyclic guanosine monophosphate (cGMP)

Answer

Cyclic adenosine monophosphate (cAMP)

Answer

Rhodopsin

Question 3

Colour vision is with the help of:

Accepted Answer

Cones

Answer

Cortex

Answer

Optic disc

Answer

Rods

Question 4

The parvocellular pathway, from the lateral geniculate nucleus to the visual cortex, carries signals for the detection of

Accepted Answer

Color vision, shape and fine details.

Answer

Luminance contrast

Answer

Temporal frequency

Answer

Movement, depth and flicker.

Question 5

At what intensity does the sound of a normal voice reach the ear from a distance of 1 meter?

Accepted Answer

60 dB

Answer

80 dB

Answer

20 dB

Answer

40 dB

Question 6

Red cones in fovea have peak sensitivity at which wavelength?

Accepted Answer

560nm

Answer

520nm

Answer

460nm

Answer

480nm

Question 7

Sensory organ for responding to texture is:

Accepted Answer

Meissner corpuscles

Answer

Pacinian corpuscles

Answer

Ruffini corpuscles

Answer

Merkel cells

Question 8

Endolymph in the ear is equivalent to

Accepted Answer

ICF

Answer

CSF

Answer

Lymph

Answer

Blood

Question 9

Weber-Fechner law is related with:

Accepted Answer

Stimulus discrimination

Answer

Amplitude

Answer

Surface area

Answer

Number of sensory fibre involvement

Question 10

Exposure to 90 dB and 4000 Hz noise for a short duration results in -

Accepted Answer

Temporary hearing loss

Answer

Auditory fatigue

Answer

Permanent hearing loss

Answer

Rupture of tympanic membrane

Sensory Systems — MCQs

Sensory Systems — MCQs

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