Nervous system MCQ Quiz in తెలుగు - Objective Question with Answer for Nervous system - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Key Points

• The stretch reflex is an automatic response mechanism in the body where a muscle contraction occurs in response to its stretch.
• The process is orchestrated by the muscle spindle, a sensory receptor located within the muscle fiber, which senses changes in muscle length.
• When a muscle is stretched, the muscle spindle is activated and sends a signal via afferent neurons to the central nervous system (CNS), specifically to the spinal cord, informing it about the change in length.
• The CNS, in turn, responds by sending an impulse via efferent neurons to the muscle that has been stretched, triggering a muscle contraction that resists the stretch.
• This contraction will lead to increased muscle tone, which is the constant, slight tension present in the muscle at rest to maintain posture and response readiness.

• This response is part of a reflex mechanism known as the "stretch reflex" or "myotatic reflex" facilitated by muscle spindles, specialized sensory receptors within the muscle.
• Muscle spindles detect changes in muscle length and rate of change in length.
• When a muscle is stretched, the muscle spindle is activated, and it sends an afferent signal to the spinal cord.
• This in turn triggers an efferent signal causing the muscle to contract and resist the stretch, thereby increasing the muscle tone.
• This reflex helps maintain the muscle at a suitable length and contributes to postural control.

Hence the correct answer is option 3

Key Points

• Synaptic transmission is the process through which neurons communicate with each other.
• It involves transmitting an electrical signal (the action potential) from one neuron (the presynaptic neuron) to another (the postsynaptic neuron) via a synaptic cleft.
• At a chemical synapse, the electric signal of the presynaptic neuron is switched to a chemical signal and vice versa at the postsynaptic neuron.
• This chemical signal consists of neurotransmitters, which are released from vesicles in the presynaptic neuron into the synaptic cleft, where they can then act on the postsynaptic neuron by binding receptor proteins.
• SNARE complexes are a set of proteins that are critical for this process.
• Specifically, they enable the fusion of the neurotransmitter-filled vesicles with the cell membrane of the presynaptic neuron, allowing the release of the neurotransmitters into the synaptic cleft.
• Calcium ions play a crucial role in this process.
• When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open, allowing calcium ions to flow into the neuron.
• The influx of these calcium ions triggers the fusion of the vesicles with the neurotransmitter to the cell membrane via interactions with the SNARE proteins.
• Thus, the activation of voltage-gated calcium channels and the subsequent influx of calcium ions into the neuron are key factors that initiate the release of neurotransmitters from the presynaptic terminal into the synaptic cleft, facilitating neuronal communication.

• SNARE complexes are essential for guiding synaptic transmission.
• They play a crucial role in the process of neurotransmitter release from the presynaptic terminal.
• SNARE proteins facilitate the fusion of the vesicle membrane that contains the neurotransmitter with the cell membrane, allowing the release of the neurotransmitter into the synaptic cleft.
• When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open, and Ca+ ions flow into the cell.
• The influx of calcium triggers the SNARE-mediated fusion of the neurotransmitter-filled vesicles with the cell membrane, causing the neurotransmitters to be released.

Hence the correct answer is option 2

The correct answer is A, B and D only 

Concept:

• Spinal cord injury (SCI) often leads to an impairment of the respiratory system. The more rostral the level of injury, the more likely the injury will affect ventilation. In fact, respiratory insufficiency is the number one cause of mortality and morbidity after SCI. 
• Spinal cord injury (SCI) severely compromises both sensory and motor function . More than one half of all SCIs (56.4%) occur at the cervical level.
• Cervical SCI often leads to an interruption of the descending bulbospinal respiratory pathways, resulting in respiratory muscle paresis and/or paralysis; the more rostral the level of the injury, the greater the likelihood that a major respiratory impairment will occur. 

Explanation:

When the spinal cord is transected at the C1/C2 level:

A. The respiratory regulatory center is located in the medulla: This is true, as the primary respiratory centers that control breathing are located in the medulla oblongata, which is above the C1/C2 level. This means that cutting the spinal cord at C1/C2 disrupts the communication between the respiratory centers in the medulla and the respiratory muscles, stopping natural breathing.

B. The respiratory regulatory center is located above the C1/C2 cut: This is also true. The medulla, which contains the respiratory center, is positioned above the C1/C2 level. Thus, although the respiratory center itself is intact, it cannot send signals to the respiratory muscles below the level of the cut, leading to a need for artificial respiration.

C. Heart regulatory center is above the C1/C2 cut: This is incorrect as it implies that a central regulatory center is directly controlling the heart rate at all times, whereas the heart primarily relies on its own pacemaker for rhythm. Neural input from the autonomic nervous system, particularly from centers above the C1/C2 level, can modulate the heart rate, but the heart itself can beat independently due to its pacemaker cells.

D. The heart has autoregulation: This is also correct. The heart has an intrinsic pacemaker (the sinoatrial node) that allows it to beat independently of neural input, so it continues to beat even though the spinal cord is transected. However, without modulation from higher centers, the heart rate may slow down.

Figure 1: Schematic drawing of the major respiratory neural centers and pathways in the rat. 

 

Key Points

Statement A - INCORRECT

• This statement suggests that the axon hillock, which is the initial segment of the axon closest to the cell body, has the highest threshold for generating an action potential.
• In other words, it requires a stronger depolarization stimulus compared to other regions of the neuron.
• This is because the axon hillock acts as a decision-making site for the initiation of an action potential.
• If the depolarization reaches a certain threshold at the axon hillock, an action potential is generated and conducted down the axon.
• However, this statement does not mention anything about direction-specific conduction.

Statement B - CORRECT

• This statement highlights that the axon hillock has a high voltage-gated sodium (Na⁺) channel density.
• These channels are responsible for the rapid depolarization phase of the action potential.
• When the membrane potential reaches the threshold, these channels open, allowing an influx of sodium ions and triggering the action potential.
• The presence of a large number of voltage-gated Na⁺ channels in the axon hillock makes this region more excitable and more likely to generate an action potential.

Statement C - CORRECT

• This statement explains why an action potential can only travel in one direction down the axon.
• Once an action potential is generated and travels down the axon, a fraction of the voltage-gated Na⁺ channels in the preceding portion becomes voltage-inactivated.
• This means that these channels are temporarily unable to open and participate in generating another action potential in the direction of the cell body.
• As a result, the action potential can only propagate in the forward direction towards the terminal end of the axon.

Statement D - INCORRECT

• This statement suggests that the number of voltage-gated Na+ channels is lower in the preceding portion of the axonal membrane, which prevents the generation of another action potential in the direction of the cell body.
• However, this statement does not provide an explanation for why the number of channels is lower or how it relates to the direction-specific conduction of action potentials.

Therefore, the correct answer is option 2 (B and C).

The correct answer is Option 3 i.e.Serotonin.

Key Points

• The numerous cells that make up the autonomic nervous system carry out a wide range of tasks.
• The lateral grey column of the spinal cord, which runs from T1 to L2, houses the cell bodies of the sympathetic nervous system.
• These neurons, called preganglionic neurons, move to the ganglia where they synapse and use acetylcholine to trigger nicotinic receptors on postganglionic neurons.
• Once at the designated location, the postganglionic neurons release norepinephrine to stimulate the adrenergic receptors.
• The parasympathetic nervous system is divided into a cranial and pelvic components.
• The cranial portion of the system is made up of the cranial nerves III, VII, IX, and X.
• Preganglionic fibers synapse on postganglionic fibers, which then innervate target locations, giving the parasympathetic nervous system a structure akin to that of the sympathetic nervous system.

Explanation:

Option 1: Neurotensin

• Neurotensin is a neuropeptide that functions as a neurotransmitter and neuromodulator in the central nervous system.
• It is involved in a variety of physiological processes, including the regulation of dopamine signaling, the modulation of pain perception, and the regulation of food intake and energy metabolism.
• It is released by sympathetic preganglionic neurons as part of the sympathetic nervous system response.

• Enkephalin is an endogenous opioid peptide that acts as an analgesic by binding to opioid receptors in the brain and spinal cord.
• It is involved in the modulation of pain perception and the regulation of mood.
• Enkephalin is released by sympathetic preganglionic neurons as part of the sympathetic nervous system response.

• Serotonin is a neurotransmitter that is involved in the regulation of mood, appetite, and other physiological processes in the central nervous system.
• It is mainly released by serotonergic neurons and is not typically released by sympathetic preganglionic neurons.

• Substance P is a neuropeptide that plays a role in pain transmission and inflammation.
• It is released by primary afferent neurons in the peripheral and central nervous systems and is involved in the transmission of pain signals from the periphery to the central nervous system.
• Substance P is released by sympathetic preganglionic neurons as part of the sympathetic nervous system response.

The correct answer is due to chemical synapse.

Explanation:

• A vast majority of synapses are chemical synapses. These involve the release of a chemical neurotransmitter by the presynaptic neuron, which packages into synaptic vesicle in neuron's synaptic terminal. When action potential reaches a synaptic terminal it depolarises the terminal membrane, opening voltage gated Ca²⁺ channals. The released neurotransmitter binds to specific receptors present on the post synaptic membrane.
• Chemical synapses contribute to the unidirectional propagation of signals in the nervous system. In a chemical synapse, the presynaptic neuron releases neurotransmitters into the synaptic cleft, which then bind to receptors on the postsynaptic neuron.
• This mechanism inherently supports unidirectional flow since neurotransmitters are released by the presynaptic neuron and received by the postsynaptic neuron, not in reverse.

Key PointsProportional to the length of axon:The unidirectional propagation of an electrical signal is not determined by the length of the axon. While the length of an axon can affect the speed of signal transmission (longer axons may have mechanisms like myelination to speed up signal propagation), it does not inherently dictate the directionality of the signal.

Due to electrical synapse:Electrical synapses involve the direct flow of electrical current from one neuron to another through gap junctions. While they do allow for the rapid transmission of signals, they do not inherently restrict the direction of signal propagation and can, in some contexts, support bidirectional flow.

Proportional to myelination: Myelination affects the speed of action potential propagation along an axon-the presence of a myelin sheath allows for faster signal transmission via saltatory conduction. However, myelination does not determine the directionality of signal propagation.

The correct answer is Option 1 i.e. Glutamate.

Concept:

• Eye is a photosensor that can even detect a single photon and transmit that signal to the brain.
• Cells of retina are the visual photoreceptors of the eyes.
• The visual cell contains two main parts: outer segment and inner segment
  • Outer segment - it consists of the light absorbing visual pigment.
  • Inner segment - it consists of nucleus, mitochondrial and other organelles that support the functions of the outer segment.
• Cilium or ciliary process connects the inner and outer segments of the retina. 
• Terminals present in the inner segment have synapses with the horizontal cells and bipolar cells which in turn have synapses with the ganglion and amacrine cells. 
• Visual cells are of two types- rod cells and cone cells.
  • Rod cells -  it consists of an elongated outer segment. It contains rhodopsin pigment which is responsible for dim-light vision also called scotopic vision.
  • Cone cells - it consists of a dome-shaped outer segment. It has photoreceptors for day-light vision also called photopic vision.

Important Points

• When the light strikes the retina, the photon is captured and 11-cis-retinal is converted to the all-trans-retinal. 
• Rhodopsin activates photoreceptor-specific G-protein transducin called G_T.
• Rhodopsin triggers the exchange of GDP to GTP on its α-subunit (Gα_T), which further activates the cGMP phosphodiesterase enzyme. 
• Activated cGMP phosphodiesterase decreases the concentration of cGMP which in turn leads to the closure of the cGMP-gated cation channels on the plasma membrane of the photoreceptors. 
• Closure of channels leads to hyperpolarization of the membrane which in turn decreases the release of neurotransmitter glutamate at the synaptic termini.

Hence, the correct answer is Option 1.

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 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.