Nervous system MCQ Quiz in বাংলা - Objective Question with Answer for Nervous system - বিনামূল্যে ডাউনলোড করুন [PDF]

The correct answer is a-i, b-ii, c-iii, d-iv

Explanation:

a. C fibers are Non-myelinated, which means conduction is slower compared to myelinated fibers.

• Conduction velocity ranges from 0.5–2 m/s.
• Involved in transmitting dull, aching pain and temperature sensations.
• These fibers are responsible for the delayed pain after an injury.

b. Aγ fibers are Myelinated fibers.

• Conduction velocity ranges from 15–30 m/s.
• Found in the motor fibers of muscle spindles, responsible for regulating muscle tone and reflexes.
• Play a role in maintaining muscle sensitivity to stretch during movement.

c. Aα fibers are Myelinated fibers with the fastest conduction velocity, ranging from 80–120 m/s.

• Found in motor nerves controlling skeletal muscles.
• Also involved in transmitting proprioceptive information (e.g., position and movement sense).
• These fibers allow for rapid and precise control of muscle activity.

d. Aδ fibers are Myelinated fibers with a conduction velocity of 5–30 m/s.

• Transmit sharp, localized pain and temperature sensations.
• These fibers are responsible for the immediate sharp pain felt after an injury.

The correct answer is C and D.

Explanation:

• Statement A: Correct. The depolarization of a neuron is caused by the influx of Na⁺ ions through voltage-gated sodium channels. This leads to the inside of the neuron becoming more positive, which initiates the action potential.
• Statement B: Correct. The repolarization phase involves the efflux of K⁺ ions through voltage-gated potassium channels, which helps return the membrane potential back toward the resting state after the depolarization.
• Statement C: Incorrect. The threshold potential is the membrane potential at which voltage-gated sodium channels open, not when potassium channels begin to open. Potassium channels start to open later in the action potential, typically during or after depolarization, contributing to repolarization. When the membrane potential reaches this threshold (typically around -55 mV), it triggers the opening of these sodium channels, leading to the rapid influx of Na⁺ ions and thus depolarization.
• Statement D: Incorrect. During the refractory period, a second action potential can only be triggered by a stronger-than-normal stimulus. This is due to the inactivation of sodium channels during the absolute refractory period and the need for the membrane potential to return to a more negative value for the relative refractory period. However, it does not account for the absolute refractory period, where a second action potential cannot be initiated regardless of stimulus strength. Therefore, this statement is incomplete as it does not fully capture the nature of the refractory periods.

Conclusion: The incorrect statements are C and D

The correct answer is B and C.

Explanation:

• Statement A: Correct. Odorant molecules bind to specific G protein-coupled receptors (GPCRs) on the olfactory receptor neurons located in the olfactory cilia. This binding activates the G protein (G_olf), which in turn activates adenylate cyclase. This enzyme converts ATP into cyclic AMP (cAMP). The increase in cAMP levels is a crucial step in the signal transduction pathway.
• Statement B: Incorrect. The activation of cAMP in olfactory receptor cells primarily opens cation channels (such as Na⁺ and Ca²⁺ channels), leading to depolarization. However, the opening of Na⁺ and Ca²⁺ channels does not directly result in membrane depolarization via the simple influx of these ions; other ions, like chloride (Cl⁻), also play a role in the signaling process, especially as they work in coordination with cAMP-mediated changes.
• Statement C: Incorrect.  Olfactory receptor cells primarily signal through the influx of Na⁺ and Ca²⁺ ions, leading to membrane depolarization, not hyperpolarization. While Cl^- ions do play a role in olfactory transduction, it is secondary. In some cases, Cl^- ions can exit the cell through calcium-activated chloride channels due to the high intracellular Cl^- concentration, which would further depolarize the membrane rather than hyperpolarize it.
• Statement D: Correct. The spatial arrangement of olfactory receptor neurons in the olfactory bulb plays a crucial role in odor identification. Olfactory receptor neurons expressing the same type of olfactory receptor converge their axons onto specific structures in the olfactory bulb called glomeruli. Each glomerulus represents a specific odorant receptor type, and the spatial pattern of activated glomeruli encodes the identity of the odor.

Fig: A schematic diagram of olfactory signal transduction

Conclusion: The incorrect statements are B and C, so the correct answer is B and C.

The correct answer is C and D.

Concept:

Phototransduction is the process by which light signals are converted into electrical signals in the retina, specifically within the photoreceptor cells known as rods and cones.This process is crucial for vision, allowing the visual information captured as light to be sent to the brain for interpretation.

In the Dark:

• In the absence of light, the photoreceptors are in a depolarized state.
• High levels of cyclic guanosine monophosphate (cGMP) keep cGMP-gated Na+ channels open.
• Na+ ions continually enter the cell, causing depolarization which maintains the release of the neurotransmitter glutamate.

In Response to Light:

• Light activates a photopigment (rhodopsin in rods and photopsins in cones).
• This activation leads to the activation of a G-protein called transducin.
• Transducin activates cGMP-phosphodiesterase (PDE).
• PDE breaks down cGMP into GMP, reducing the cGMP concentration.
• The decrease in cGMP causes cGMP-gated Na+ channels to close, leading to the hyperpolarization of the photoreceptor.
• Hyperpolarization reduces the release of glutamate.

Fig-Phototransduction in the outer segments of rod photoreceptors is initiated when rhodopsin absorbs a photon and triggers the exchange of GDP for GTP on the G-protein, transducin (Gt )

Explanation:

• Statement A: Correct. In photoreceptors (both rods and cones), light leads to hyperpolarization, which is caused by the closure of Na⁺ channels. Light reduces the levels of cGMP, leading to the closing of cGMP-gated Na⁺ channels and hyperpolarization.
• Statement B: Correct. In rods, the phototransduction cascade involves the activation of cGMP-phosphodiesterase, which decreases cGMP levels. This decrease causes the closure of cGMP-gated Na⁺ channels, leading to hyperpolarization of the cell.
• Statement C: Incorrect. The phototransduction process in cones does not involve the direct activation of K⁺ channels by light. Instead, cones also rely on the activation of cGMP-phosphodiesterase to reduce cGMP levels, leading to the closure of cGMP-gated ion channels (mainly Na⁺ channels), similar to rods.
• Statement D: Incorrect. The conversion of light to electrical signals in photoreceptors does not require the presence of cAMP. Phototransduction primarily involves a cascade of events where the reduction of cGMP (not cAMP) leads to the closure of cGMP-gated ion channels, resulting in hyperpolarization.

Conclusion: The incorrect statements are C and D, so the correct answer is C and D.

The correct answer is A, C, and D.

Explanation:

• Statement A: Correct. Touch receptors (mechanoreceptors) rely on mechanosensitive ion channels. These channels respond to mechanical deformation of the cell membrane, leading to ion influx and subsequent depolarization.
• Statement B: Incorrect. Light absorption by rhodopsin in rods leads to the closure, not opening, of cGMP-gated Na⁺ channels. This occurs because light triggers a cascade that reduces cGMP levels, resulting in hyperpolarization of the photoreceptor.
• Statement C: Correct. Pain receptors (nociceptors) can respond to mechanical, thermal, or chemical stimuli through the activation of ionotropic pathways (e.g., TRP channels) or metabotropic pathways (e.g., GPCRs).
• Statement D: Correct. Cold receptors are activated by TRP channels (e.g., TRPM8) that are sensitive to decreases in temperature. These channels allow ion influx, leading to depolarization and signaling cold sensation.

Conclusion: The correct combination is A, C, and D.

The correct answer is A,B and D.

Explanation:

Sensory receptors are specialized cells that convert physical stimuli into electrical signals that the nervous system can use. The mechanism of activation for different types of sensory receptors depends on the type of stimulus they detect

• Statement A: Correct: Nociceptors are a type of sensory receptor that detect signals from damaged tissue or the threat of damage and is associated with pain. They are activated by mechanical, thermal, or chemical stimuli, leading to the opening of non-selective cation channels, which allow various ions to enter the nerve endings and generate an action potential.
• Statement B: Different taste modalities involve different mechanisms. For example, salty and sour tastes often involve the direct passage of ions through channels, while sweet, bitter, and umami tastes typically involve G-protein-coupled receptor (GPCR) pathways.
• Statement C: Incorrect. Rod photoreceptors hyperpolarize in response to light, not depolarize. Light reduces the levels of cGMP, causing closure of Na⁺ channels, leading to hyperpolarization and a decrease in glutamate release.
• Statement D: Correct. Warmth receptors are activated by specific non-selective cation channels, such as TRP channels (e.g., TRPV1), which are sensitive to increases in temperature. These channels allow the influx of cations like Na⁺ and Ca²⁺, leading to depolarization.

Conclusion: The correct combination is A,B and D.

The correct answer is A and B.

Explanation:

1. Statement A: Correct. Mechanoreceptors involved in touch sensation are activated by mechanical deformation of the cell membrane. This deformation directly affects ion channels, often leading to their opening, resulting in depolarization and initiation of an action potential.

2. Statement B: Correct. Olfactory receptors are G-protein-coupled receptors (GPCRs). When an odorant binds to these receptors, a cAMP-mediated pathway is activated. This results in the opening of cation channels, allowing an influx of Na⁺ and Ca²⁺ ions, leading to depolarization.

3. Statement C: Incorrect. Photoreceptors in the retina hyperpolarize, not depolarize, in response to light. Light exposure causes a reduction in cGMP levels, leading to the closure of Na⁺ channels, resulting in hyperpolarization.

4. Statement D: Incorrect. Thermoreceptors for cold sensation are not activated by voltage-gated Na⁺ channels. Instead, they rely on temperature-sensitive ion channels, such as TRP (Transient Receptor Potential) channels, which are specific to thermal changes.

Conclusion: The correct statements are A and B.

The correct answer is A, B, and C.

Explanation:

1. Statement A: Correct. During the absolute refractory period, voltage-gated sodium channels are inactivated, making it impossible to initiate another action potential, no matter how strong the stimulus.

2. Statement B: Correct. During the relative refractory period, some voltage-gated sodium channels have returned to a resting state, but the membrane is still hyperpolarized due to the activity of voltage-gated potassium channels. A stronger-than-normal stimulus is required to reach the threshold and initiate an action potential.

3. Statement C: Correct. The refractory periods (both absolute and relative) ensure unidirectional propagation of the action potential along the axon by preventing reactivation of the sodium channels in the region that has just undergone an action potential.

4. Statement D: Incorrect. The absolute refractory period is primarily determined by the inactivation of voltage-gated sodium channels, not the activity of potassium channels. Potassium channels play a role in the relative refractory period but are not the sole determinant of refractory periods.

Conclusion: The statements A, B, and C are correct.

The correct answer is A and D.

Explanation:

1. Statement A: Correct. During the depolarization phase of an action potential, voltage-gated sodium channels open, allowing a rapid influx of Na⁺ ions, which drives the membrane potential toward a more positive value.

2. Statement B: Incorrect. Voltage-gated potassium channels do not close immediately after the resting potential is reached during repolarization. Instead, they remain open briefly, which can result in hyperpolarization before they close.

3. Statement C: Incorrect. During the depolarization phase, only voltage-gated sodium channels are open. Voltage-gated potassium channels begin to open during the repolarization phase, not during depolarization.

4. Statement D: Correct. Voltage-gated sodium channels undergo inactivation after depolarization, which prevents further Na⁺ influx. This inactivation contributes to the refractory period, during which the neuron cannot generate another action potential.

Conclusion: The statements A and D correctly describe the properties of voltage-gated ion channels during an action potential.

The correct answer is B, C, and D.

Explanation:

1. Statement A: Incorrect. Depolarization occurs due to the rapid influx of Na⁺ ions through voltage-gated sodium channels, not the efflux of K⁺ ions. Efflux of K⁺ is associated with repolarization, not depolarization.

2. Statement B: Correct. The repolarization phase begins when voltage-gated sodium channels become inactivated and voltage-gated potassium channels open, allowing K⁺ ions to flow out of the cell.

3. Statement C: Correct. During the absolute refractory period, voltage-gated sodium channels are inactivated, which prevents the initiation of a second action potential, no matter the strength of the stimulus.

4. Statement D: Correct. Hyperpolarization occurs due to the delayed closing of voltage-gated potassium channels, causing the membrane potential to become more negative than the resting potential.

Conclusion: The statements B, C, and D are correct.