Sensory Systems Practice Questions

Q: Which of the following best describes the electrical response of the rods to light?

Hyperpolarization. ***Hyperpolarization*** - Light causes **rhodopsin** to activate a G-protein cascade, leading to the closure of **cGMP-gated Na+ channels**. - This closure reduces the influx of positive ions (Na+), resulting in the cell becoming **more negative** (hyperpolarized). *Depolarization* - **Depolarization** occurs in the dark due to the continuous influx of Na+ ions through open cGMP-gated channels. - This is the "dark current" which is interrupted by light, leading to hyperpolarization, not depolarization. *Action potential* - **Rods and cones** do not generate action potentials; they produce graded potentials in response to light. - Action potentials are generated by **ganglion cells** further down the visual pathway. *Capacitive discharge* - **Capacitive discharge** is a term related to electrical components and does not describe the physiological electrical response of photoreceptor cells. - This term is irrelevant to the **neurobiological process** of phototransduction.

Q: According to Weber-Fechner's law, the perceived intensity of a stimulus is proportional to:

Logarithm of stimulus intensity. ***Logarithm of stimulus intensity*** - **Weber-Fechner's Law** states that the perceived intensity of a sensation (**psychological magnitude**) is directly proportional to the logarithm of the physical stimulus intensity. - This law describes how the **just noticeable difference (JND)** between two stimuli is proportional to the magnitude of the original stimulus, meaning that as a stimulus gets stronger, an even greater change is needed for it to be noticed. *Number of neurons stimulated* - While the number of neurons stimulated can correlate with stimulus intensity, Weber-Fechner's law specifically quantifies the **perceived intensity** in relation to the **stimulus magnitude**, not directly the neural count. - The activation of more neurons typically leads to a stronger signal, but the mathematical relationship described by the law is different. *Number of receptors stimulated* - The number of receptors stimulated contributes to the overall signal received by the nervous system, but it is an earlier step in the sensory pathway. - Weber-Fechner's law describes the **psychophysical relationship** at a higher level of processing, not simply the initial receptor activation. *Amplitude of action potential* - The **amplitude of action potentials** is generally **all-or-none** and does not vary with stimulus intensity; rather, the *frequency* of action potentials increases with stronger stimuli. - Therefore, the amplitude of a single action potential does not directly reflect the perceived intensity according to Weber-Fechner's law.

Q: What are the primary receptor cells of hearing?

Hair cell. ***Hair cell*** - **Hair cells** are the specialized receptor cells located in the **organ of Corti** within the inner ear. - They transduce mechanical vibrations caused by sound waves into electrical signals that the brain interprets as sound. *Tectorial membrane* - The **tectorial membrane** is an extracellular matrix that overlies the **organ of Corti** and is involved in stimulating the stereocilia of hair cells. - It is not a receptor cell itself but rather a crucial component in the mechanical transduction process. *Supporting cell* - **Supporting cells** (e.g., pillar cells, Deiters' cells) provide structural and metabolic support to the **hair cells** in the organ of Corti. - They do not directly detect sound vibrations or convert them into electrical signals. *Tunnel of corti* - The **tunnel of Corti** is a fluid-filled space within the **organ of Corti**, formed by the pillar cells. - It serves as a structural landmark and separates the inner and outer hair cells but does not contain receptor cells for hearing.

Q: Which structure in the inner ear is responsible for converting sound waves into electrical signals that can be interpreted by the brain?

Organ of Corti. ***Organ of Corti*** - The **organ of Corti** is located on the **basilar membrane** within the **cochlea** of the inner ear and is the primary structure responsible for **auditory transduction**. - It contains specialized **hair cells** (inner and outer) that convert mechanical vibrations from sound waves into **electrical signals** through **mechanotransduction**. - When sound waves cause the basilar membrane to vibrate, the hair cells' stereocilia bend, opening **mechanically-gated ion channels** and generating **receptor potentials** that trigger action potentials in the **auditory nerve (cranial nerve VIII)**. *Semicircular canals* - These are part of the **vestibular system** responsible for detecting **rotational movements** and maintaining **balance**, not for hearing. - They contain **ampullae with cristae** that detect angular acceleration but do not convert sound waves into electrical signals. *Vestibule* - The vestibule contains the **utricle and saccule**, which are part of the **vestibular system** responsible for detecting **linear acceleration** and **head position** relative to gravity. - These structures are involved in **balance and spatial orientation**, not in the conversion of sound waves. *Tympanic membrane* - The **tympanic membrane (eardrum)** is located in the **middle ear**, not the inner ear. - While it vibrates in response to sound waves and transmits these vibrations to the **ossicles**, it does not convert sound into electrical signals—it only serves as a mechanical transducer.

Q: Stimulation of posterior semicircular canal produces

Vertical nystagmus. ***Vertical nystagmus*** - Stimulation of the **posterior semicircular canal** primarily produces **vertical nystagmus** with a torsional (rotatory) component. - The posterior canal detects rotation in the sagittal plane and its activation triggers the **vestibulo-ocular reflex (VOR)**, causing predominantly **vertical eye movements** (typically downbeating) with associated torsion. - The posterior canal connects via the **vestibular nerve** to the **vestibular nuclei**, which project to the **oculomotor nuclei** to produce eye movements in the plane of the stimulated canal. *Rotatory nystagmus* - While the posterior canal does produce a **torsional (rotatory) component** accompanying the vertical nystagmus, **purely rotatory nystagmus** alone is not the most characteristic response. - Isolated rotatory nystagmus is more commonly associated with **anterior semicircular canal** pathology or combined canal involvement. *Horizontal nystagmus* - **Horizontal nystagmus** is specifically associated with stimulation of the **horizontal (lateral) semicircular canal**, which detects rotation in the horizontal plane. - Posterior canal stimulation does not produce horizontal eye movements as it operates in a different anatomical plane. *All of the options* - This option is incorrect because isolated stimulation of the **posterior semicircular canal** produces a specific pattern: primarily **vertical nystagmus with a torsional component**, not all types of nystagmus. - Horizontal nystagmus is distinctly absent with isolated posterior canal stimulation.

Q: Which of the following has cyclic GMP mediated action?

Photochemical reactions of visual cycle. ***Photochemical reactions of visual cycle*** - The **photochemical reactions** in the visual cycle, particularly in **rod cells**, are mediated by **cyclic GMP (cGMP)**. - Light stimulation activates **rhodopsin**, which in turn activates **transducin**, leading to the activation of **cGMP phosphodiesterase**, which hydrolyzes cGMP, causing **hyperpolarization** of the photoreceptor cell. *Thyroid hormone action* - **Thyroid hormone (T3 and T4)** action is mediated by **intracellular receptors** that act as **transcription factors**, directly regulating gene expression. - Their mechanism typically does not involve **second messengers** like cGMP. *Steroidogenesis* - **Steroidogenesis** is the process of producing **steroid hormones**, which is primarily regulated by **intracellular signaling pathways** involving **G protein-coupled receptors** (e.g., ACTH stimulating cortisol synthesis) and ultimately gene expression, but not typically cGMP. - While some steroid hormones can influence cGMP levels, cGMP is not the primary mediator for the *process* of steroidogenesis itself. *Recruitment of glucose transporters to cell membrane* - The recruitment of **glucose transporters** (e.g., GLUT4) to the cell membrane, particularly in response to **insulin**, is mediated by **insulin receptor** signaling pathways, involving **tyrosine kinase activity** and downstream protein phosphorylation cascades. - This process primarily uses **intracellular signaling molecules** like **PIP3** and **Akt**, not cGMP.

Q: Pitch discrimination is best between:

1000-4000 Hz. ***1000-4000 Hz*** - Humans exhibit the **best pitch discrimination** in the **mid-to-high frequency range**, which corresponds to frequencies between approximately **1000 Hz and 4000 Hz**. - This range demonstrates the **smallest just-noticeable difference (JND)** for frequency changes, meaning the ear can detect the most subtle pitch variations. - This optimal range is crucial for **speech intelligibility**, as it encompasses the **formant frequencies** of vowels and many consonants. - The **cochlear mechanics** and **density of hair cells** are optimized for maximum frequency resolution in this range. *100-1000 Hz* - While pitch perception is functional in this range, the **discrimination ability is not as precise** as in the 1000-4000 Hz range. - This lower-mid frequency range is important for fundamental frequencies in speech and music, but **JND values are larger**. *20-20,000 Hz* - This represents the **entire human audible frequency range**, but it is too broad to describe the specific range of **optimal pitch discrimination**. - Pitch discrimination varies significantly across this spectrum, with **poorest discrimination at the extremes** (very low and very high frequencies). *0-100 Hz* - This range covers **very low frequencies**, where pitch discrimination is **poor**. - Sounds in this range are often perceived more as **vibrations** or **rhythmic pulses** rather than distinct musical pitches. - The **temporal resolution** rather than frequency resolution dominates perception at these low frequencies.

Q: Static equilibrium is due to -

Macula. ***Macula*** - The **macula** contains hair cells embedded in a gelatinous layer with otoliths, which respond to **linear acceleration** and **head tilt**, thus sensing static equilibrium. - It is located within the **utricle and saccule** of the inner ear, responsible for detecting the head's position relative to gravity. *End organ of corti* - The **organ of Corti** is the sensory organ for **hearing**, located within the cochlea, transducing sound vibrations into electrical signals. - It is not involved in balance or equilibrium, but rather with the perception of **sound**. *Cristae ampullaris* - The **cristae ampullaris** are sensory organs found within the **ampullae of the semicircular canals** and are primarily responsible for detecting **dynamic equilibrium** (angular acceleration). - They respond to rotational movements of the head, not static changes in head position or gravity. *Cupula* - The **cupula** is a gelatinous structure that covers the hair cells within the **cristae ampullaris**. - It moves with the endolymph during head rotation, stimulating the hair cells for **dynamic equilibrium**, not static equilibrium.

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.

Question 1

Which of the following best describes the electrical response of the rods to light?

Accepted Answer

Hyperpolarization

Answer

Depolarization

Answer

Action potential

Answer

Capacitive discharge

Question 2

According to Weber-Fechner's law, the perceived intensity of a stimulus is proportional to:

Accepted Answer

Logarithm of stimulus intensity

Answer

Number of neurons stimulated

Answer

Number of receptors stimulated

Answer

Amplitude of action potential

Question 3

What are the primary receptor cells of hearing?

Accepted Answer

Hair cell

Answer

Tectorial membrane

Answer

Supporting cell

Answer

Tunnel of Corti

Question 4

Which structure in the inner ear is responsible for converting sound waves into electrical signals that can be interpreted by the brain?

Accepted Answer

Organ of Corti

Answer

Semicircular canals

Answer

Vestibule

Answer

Tympanic membrane

Question 5

Stimulation of posterior semicircular canal produces

Accepted Answer

Vertical nystagmus

Answer

Rotatory nystagmus

Answer

Horizontal nystagmus

Answer

All of the options

Question 6

Which of the following has cyclic GMP mediated action?

Accepted Answer

Photochemical reactions of visual cycle

Answer

Thyroid hormone action

Answer

Steroidogenesis

Answer

Recruitment of glucose transporters to cell membrane

Question 7

Pitch discrimination is best between:

Accepted Answer

1000-4000 Hz

Answer

20-20,000 Hz

Answer

100-1000 Hz

Answer

0-100 Hz

Question 8

Static equilibrium is due to -

Accepted Answer

Macula

Answer

Organ of Corti

Answer

Cristae ampullaris

Answer

Cupula

Question 9

Destruction of the right labyrinth causes nystagmus to:

Accepted Answer

Left side

Answer

Rotatory nystagmus

Answer

No nystagmus

Answer

Right side

Question 10

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

Sensory Systems — MCQs

Sensory Systems — MCQs

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